Monthly: March 2015

 I. Introduction.

The safety of fans operating in underground mining plants can be considered in three aspects:

1. Operational safety.

The fan, like any machine, cannot pose a threat to the operator or employees who may be in its vicinity. Typical hazards include the risk of injury from rotating elements, the risk of burns from elements at elevated temperatures, the risk of crushing in the event of loss of stability, etc. General requirements in this regard are included in the Machinery Directive (EU 2006/42/EC),

2. Work safety in explosion hazard conditions.

Fans intended for operation in potentially explosive atmospheres, such as underground mine workings, in addition to general safety requirements, must also meet the requirements of the Atex Directive, which include that the fan cannot become a source of ignition causing an explosion of methane or coal dust, due to sparking or high temperature of one of the construction elements.

3. Ventilation effectiveness as a condition for crew safety.

Not only must the fan itself not pose a threat, but above all, it must fulfill its function of ventilating mining workings, which is important for the safety of the mining plant, as it is to ensure an atmosphere free of substances harmful to employees and substances posing an explosion hazard.

In practice, three basic factors determine the safety of fans:

• Construction quality
• The right selection for a given application
• Method of operation

These factors will be discussed below, with particular emphasis on design issues.

II. The impact of fan design on its safety.

The requirements that the construction of mining fans must meet are the subject of numerous legal acts. The most important of them are:

• Geological and Mining Law Act of February 1994 (Journal of Laws No. 27, item 96, as amended),
• Act on the conformity assessment system of August 2002 (Journal of Laws No. 166, item 1360, as amended),
• Regulation of the Minister of Economy of December 22, 2005 on essential requirements for equipment and protective systems intended for use in potentially explosive atmospheres (Journal of Laws No. 265, item 2203, 2005) Directive (EU 94/9/EC Atex),
• Regulation of the Minister of Economy of October 21, 2008 on essential requirements for machines (Journal of Laws No. 19, item 1228, 2008) EU Directive 2006/42/EC,
• Harmonized standards (level of detail A, B, C).

For main ventilation fans, the following are important: the following standards:

• PN-EN 14968: 2007. Design of fans used in potentially explosive atmospheres.
• PN-G 50080: 1996. Mining fans for the main ventilation of mines.
• PN-EN 13643-1 2003. Non-electrical devices in potentially explosive atmospheres, part 1. Basic assumptions and requirements.
• PN-EN 13643-5: 2005. Non-electrical devices in potentially explosive atmospheres. Protected by structural safety 'c'.
• PN-G-04161: 2003. Mining fans for main ventilation. Tests of basic operating parameters.
• PN-EN 1127-1: 2009. Explosion prevention and protection.
• PN-EN 60529: 2003. Degrees of protection provided by enclosures (IP code).
• PN-G-50000: 2002. Labor protection in mining. Mining machinery. General safety and ergonomic requirements.
• PN-93/N-01359. Balancing rigid rotors.
• PN-N-01358: 1990. Methods of measurement and evaluation of vibrations.
• PN-N-01307: 1994. Permissible noise values ​​in the work environment.

According to the Atex directive, machines intended for use in potentially explosive atmospheres are classified as follows:

1. Group I – includes machines used in underground mining plants. They are divided into two categories:

a) Category M1 – machines capable of operating in explosive atmospheres

b) Category M2 - machines that must be turned off in the event of an explosive atmosphere.

It should be noted that fans with an electric drive are M1 category machines, because constructing them in the M1 category, i.e. in a way that would prevent safe operation in an explosive atmosphere, is practically impossible due to the impossible to eliminate the threats posed by the electric motor.

2. Group II – devices intended for work on the surface, which are divided into 3 categories. They will not be discussed here as they are beyond the scope of this paper.

Moreover, the regulations distinguish between electrical and non-electrical devices. fans are classified as non-electric devices (except for structures permanently integrated with an electric motor), because from the point of view of regulations, they are treated separately from the electric drive motor.

The regulations also distinguish between:

a) Explosion-proof machines, i.e. those that are resistant to explosions and can continue working after an explosion occurs,

b) Machines that do not have an explosion-proof structure, i.e. cannot survive an explosion.

Explosion-proof construction is sometimes confused with the so-called intrinsically safe construction, which means that the machine cannot survive an explosion, but is not the cause of an explosion due to the generation of an electric spark.

In practice, the fans are not explosion-proof, because providing them with the required explosion resistance would mean complication and strengthening of the structure, which would be incompatible with economical construction and operation.

It should be emphasized that with the adoption of the EU machinery safety assessment system, there was a significant change in approach. Before entering the EU, the documentation of machines intended for use in mine undergrounds was subject to examination before approval was granted, i.e. the safety of the fan was examined and verified by an entity independent of the manufacturer.

In accordance with EU regulations, in the case of non-electric machines of group I category M2, the manufacturer confirms compliance with the requirements by issuing an EC declaration of conformity. It means meeting the requirements of the standards by directly applying them or by demonstrating that the requirements are met in another way. The manufacturer is obliged to submit the machine documentation to the notified body. This documentation is not examined by a third party, but only serves to determine the manufacturer's fault if a problem occurs. This means that users should verify the manufacturer's reputation. It cannot be ruled out that some manufacturers may assess the safety of the machines they produce in an unreliable manner. The intervention of third parties, e.g. Mining Offices, consisting in the verification of declarations submitted by the manufacturer in accordance with applicable rules, takes place only after the occurrence of serious failures requiring the identification of those responsible.

The fact that there are numerous standards (including those mentioned above) does not mean that the fan design results directly from these regulations. The standards vary in their level of detail, with some containing only general guidelines. However, even standards containing detailed guidelines do not currently have to be compulsorily applied. As mentioned, the manufacturer may not apply these standards unless he or she demonstrates that the safety objective set out in the standard has been achieved in another way.

It follows from the above that the safety of the fan does not result directly from the applicable regulations, which contain requirements rather than recommendations on how to meet these requirements. Safety depends crucially on the design of the fan, which in turn depends mainly on the experience and design potential of the manufacturer. The safety of the fan (mainly eliminating the risk of explosion) is determined, among others, by: the following factors:

– Material design (non-sparking material vapors, no risk of electrostatic charge accumulation, corrosion resistance)

– Limited temperature of external elements

– Appropriate dimensions of gaps between fixed and rotating elements

– Stiffness and balance of rotating elements

– Correct vibration level

– Resistance of the structure to unexpected loads

– Guards for rotating parts

III. The influence of the method of operation on the safety of fans.

As with any other machine, its safe operation requires the operator to follow the recommendations provided by the manufacturer in the operating manual, including: method of installation, start-up and operation. The issue of technical culture of operation is even more important in this case than in the case of other mining machines, because fans belonging to the group of rotating machines are less resistant to improper operation than simpler machines.

Of particular importance is the method of carrying out overhauls, which must be periodically carried out by all machines operating in difficult conditions found in mine undergrounds. As mentioned at the end of the previous point, the safety of fan operation is determined by numerous design factors that must be observed during renovation. Due to the complexity of the fan, which is a complex rotating machine, meeting them requires appropriate equipment and access to technical documentation. For this reason, from the point of view of work safety, the best way to carry out a fan overhaul is to commission it to the manufacturer.

From a legal point of view, the issue of repairs of mining fans is regulated by par. 428 of the regulation dated June 9.06.2006, XNUMX, which says:

"Machines, devices and installations are operated, maintained and repaired in the manner specified in the technical and operational documentation."

Moreover, it should be borne in mind that fans put into operation before Poland's accession to the EU operate until their technical death based on the approval decisions of the President of the WUG. In this case, par. also applies. 428. Additionally, approval decisions generally contain lists of documentation on the basis of which they were issued and an order that, after renovation, the machine should be restored to a state of compliance with the documentation that was the basis for approval.

IV. Proper fan selection is the basis for work safety.

Each fan has certain nominal parameters for which it was designed. Operation with parameters close to the nominal ones is beneficial both in terms of energy, because then the highest energy efficiency is achieved, and in terms of movement, because then the work is stable and takes place with the lowest level of vibration and noise.

The fan's parameters are described by its flow characteristics, which are the dependence of the increase in pressure generated by the fan (so-called pressure) on the efficiency. Theoretically, the fan can operate with any combination of parameters resulting from the characteristics. In practice, the fan's operating point is determined by its cooperation with the system in which it is installed. This system is the route through which air is forced. It may be a ventilation duct as in the case of duct fans, or the entire cross-section of the working as in the case of main ventilation fans. Such a system also has its own characteristics, which show the dependence of pressure losses on flow, i.e. it shows what pressure difference is needed to pump a specific capacity through the system. The operating point of the fan in the system is determined by the intersection of its characteristics with the system characteristics. The selection of a fan for the system is optimal if, with an efficiency close to the nominal efficiency of the fan, its coupling equals the pressure losses in the system. In practice, the fan does not always operate at its nominal point, but close to it. There are two criteria for assessing the extent to which operating parameters may differ from the nominal ones:

a) Energy criterion

b) Criterion of stable operation

The first condition is met when the fan has high efficiency at the operating point, not much different from the maximum efficiency at the nominal point. In such a case, energy losses occurring during the conversion of power supplied to the fan from the engine into energy transferred to the pumped gas are insignificant. The permissible range of fan parameters in terms of energy should be marked on its characteristics, and the size of this area depends on the fan's regulation capabilities.

The second condition for the correct selection of a fan to the network (requirement of stable operation) results from the fact that most fans do not have accumulation characteristics Ap (Q) that decrease monotonously with increasing efficiency. In particular, axial fans and centrifugal fans with forward-curved blades have characteristics of the so-called saddle or with a point of discontinuity. The monotonic part of such a characteristic is located to the right of the vertex of the characteristic (i.e. for higher efficiency) and this is the range of stable fan operation. If the fan characteristic intersects with the network characteristic to the left of the characteristic peak, there may be a situation where there is more than one point of intersection of the characteristics, which means that the fan can operate with different combinations of parameters, changing them stepwise. This is the so-called "pumping" characterized by the fact that the fan operates at variable efficiency and power consumption, which is accompanied by increased noise and vibration. This results in an increased load on some structural nodes of the fan, which may lead to its failure. In practice, this phenomenon occurs when the fan is incorrectly selected for the network and, due to too low pressure, it operates in the area of ​​too low efficiency. This situation threatens the safety of the mining plant, firstly because the ventilation is ineffective, and secondly, due to unstable operation, the probability of fan failure increases. To avoid this, it is assumed that the fan pressure at the operating point should not exceed 90% of the maximum pressure.

V. Summary.

Fans affect both the safety of the staff and the safety of the entire mining plant through the potential risk of explosion and lack of effective ventilation.

In order to eliminate these threats, the construction of fans must comply with applicable regulations, which is a necessary but not sufficient condition, as these regulations are not detailed enough. The experience and reputation of the fan manufacturer play an important role.

The correct selection of a fan for the system, as well as the method of its operation, especially the quality of renovations, have a very important impact on safety.

engineer Roman Pawlik

Mine categories.

Mines where operations have been suspended can be divided into two categories:

• mines where mining was interrupted but retained the possibility of resuming it in the future,
• mines liquidated irreversibly.

The first group includes plants where exploitation is currently economically unprofitable, but which have significant raw material resources at their disposal, access to which is maintained in the event of a change in economic conditions. In such a situation, dewatering should be carried out using the same method as for a working mine, i.e. using stationary pumps installed in a traditional pumping station.

This does not require any investment, apart from the possible replacement of the pumps themselves in order to adapt them to work with optimal efficiency in terms of capacity reduced by technological inflows.

The decision to irreversibly close down the mine does not raise any doubts when resources are depleted, but in other situations it requires caution. Once such a decision is made, it can be technically implemented in several ways:

• backfilling the shaft without any drainage (the case is not considered in the article),

• backfilling the shaft while treating it as a water intake. This means leaving a small diameter well and using deep well pumps,

• flooding of the shaft, with the water level fluctuating significantly. In this case, it is easiest to use submersible pumps. However, in practice, a situation where the water level in the shaft changes quickly and to a significant extent is unlikely due to the significant capacity of the flooded workings. Apart from that. if a decision is made to drain the shaft, it is in order to control the water level in it for some reasons and to prevent its significant fluctuations,

• flooding of the shaft, and the maximum permissible level is established.

The need to control the water level may result from maintaining higher mining levels, or from the need to prevent water from penetrating neighboring active workings through connections located above a certain level, or from flooding areas that have degraded as a result of many years of mining. This situation will probably occur most often in practice. It is then possible to apply several technical solutions discussed in the article.

Factors determining the choice of drainage system:

Economic and legal conditions.
There are many factors that determine the choice of a specific solution. Here are some of them:
• cost of decommissioning works and the value of the surface area,
• hydrogeological situation, in particular the safety of neighboring active mines and the threat of flooding
areas on the surface, degraded as a result of many years of mining,
• the possibility and need to use mine water for municipal purposes
and the impact of mine closure on their quality (possibility of contamination with toxic substances found in flooded workings),
• the possibility and need to use inactive mine workings as a waste dump,
• legal issues, including the question of how a flooded shaft is treated from the point of view of mining regulations.

The decision on the selection of a drainage system for a closed mine should be preceded by a discussion covering at least the above aspects, and not limited to fragments of the problem.

Conditions in the field of pump technology.
Mine drainage is usually carried out using centrifugal pumps. Theoretically, it is possible to use positive displacement pumps, e.g. diaphragm pumps, which achieve high energy efficiency. However, positive displacement pumps are large and heavy, which calls into question the possibility of installing and operating them in a closed mine shaft. Moreover, the price of positive displacement pumps and the costs of their installation are much higher than for centrifugal pumps. Given the relatively low lifting heights that occur in closed mines, the possible energy benefits do not justify such a significant increase in investment outlays.

For these reasons, in practice only the use of centrifugal pumps should be considered. In pump theory, the concept of speed factor is used, which captures the relationship between rotational speed, efficiency and lifting height from the centrifugal pump stage. A lower discriminant means a lower rotational speed, lower efficiency or a higher lifting height from the step.

Design experience shows that the value of the discriminant determines the optimal proportions and shape of the pump impeller, as well as the efficiency that can be achieved. Optimum occurs for the so-called medium-speed pumps, while both for lower and higher values ​​of the discriminant, the achieved efficiencies are worse.

If there are solids in the pumped liquid, lower speed ratings are used for durability reasons, because at higher rotational speeds, the pump elements (especially the inlet edges of the blades and sealing rings) wear out more quickly. Therefore, and in order to obtain better suction properties, traditional main drainage pumps, adapted to pump contaminated water, are designed as slow-running ones, which means a reduction in efficiency compared to the possible optimum. In turn, submersible pumps are designed to obtain a minimum external diameter, as this allows for minimizing the costs of drilling a well. This means adopting a higher than optimal speed factor, with the resulting reduction in efficiency. Moreover, "wet" motors are used to drive submersible pumps, which have lower efficiencies than traditional electric motors, which results, among other things, from the resistance encountered by the impeller in the liquid.

It follows from this that, from the energy point of view, for dewatering closed mines, where there are no solid particles in the water and where there is no limit to the pump diameter, pumps with optimal speed characteristics should be used, characterized by better efficiencies than both traditional mining pumps and from deep well pumps.

Furthermore, energy losses in the pipelines must be taken into account. The use of submersible pumps lowered on the pipeline from the surface makes it necessary to limit the diameter of the pipeline due to weight and cost. This results in increased flow losses in the pipelines, compared to other drainage methods that allow the use of existing pipelines with larger diameters.

In order to minimize operating costs, pumps used to drain a decommissioned mine should enable automated operation without supervision. This basically excludes the use of solutions such as stuffing box seals, relief discs or oil-lubricated plain bearings, as they require relatively frequent adjustment and maintenance.

Photo 1. High-performance submersible feed pump.

 Other technical conditions.

The pumped underground water will be water with a minimum content of solid pollutants and with a chemical composition appropriate to the water of the mine in question. The inflow values ​​in relation to the working mine will decrease not only by the amount of process water, but also according to the increase in the water level in the shaft.

Due to the regulations on the safe operation of a shaft (well), it should be assumed that inspections will have to be carried out in the shaft and that explosive and toxic gases will not be allowed to collect in the shaft in concentrations that threaten human life or may cause an explosion. Therefore, the shaft will have to be equipped with ventilation and gas concentration control systems.

The need to conduct an inspection of the shaft requires the installation of a permanent or portable device for people to move. On each dewatered shaft it will also be necessary to install a permanent or portable device for lowering pumping systems (pump sets, pipelines, etc.). The type and therefore the price of these devices will depend on the solution adopted.

Comparative analysis of possible drainage methods for liquidated mines.
In practice, water level fluctuations will most often be insignificant. It will therefore be possible to use both submersible pumps and stationary pumps driven by "dry" engines.

Dewatering with deep well pumps.
The advantages of deep-well pumps include insensitivity to uncontrolled changes in water level and maintenance-free operation. However, the disadvantages include:
• not the highest efficiency of submersible pumps and engines,
• high investment outlays (pumps, engines and pipelines),
• expensive spare parts and high costs of inspections and renovations of machines imported in sets,
• complicated construction of some submersible pump structures
and engines, which extends the time of inspections and renovations,
• difficult access to the website.

The installation of submersible pumps involves hanging them on a pressure pipeline, usually lowered into the shaft from the surface - figure 1.

Additional disadvantages of this solution are:
• heavy weights of lowered and lifted pump systems,
• difficult access to lifting equipment for lowering and lifting pumping systems and power cables and high costs associated with it,
• high energy losses in pipelines, which, due to cost and weight, have smaller diameters than stationary pipelines in the shaft,
• all, even the smallest, maintenance works require lifting the pump and the engine to the surface, which involves the need to dismantle the entire discharge pipeline, expected difficulties in dismantling the pipelines, in the presence of dissolved chemicals in the water, making the operation of lifting the pumps for inspection difficult,
• lack of mounting of the pipeline in the shaft, which favors the occurrence of vibrations.

Disadvantages from this group can be eliminated by suspending submersible pumps on shorter pipelines under the platform deep in the shaft and using existing pressure pipelines - figure 2.

Figure 1. Figure 2.

Dewatering with stationary pumps.

Since in a mine where mining operations have been suspended, mechanical impurities will not be present in large amounts in water, stationary pumps with optimal speed characteristics and a modern design allowing for maintenance-free operation can be used for dewatering.

The advantages of stationary pumps are:
• highest energy efficiency,
• maintenance-free operation,
• low weight of the pump unit allowing the use of transport devices with medium load capacities,
• affordable price of pumps and engines (especially in the case of domestic pumps and engines),
• simple and reliable design,
• available and not too expensive, national service,
• small energy losses in pipelines,
• easy assembly and disassembly of pump units.

Stationary pumps can come in several variants, but the above-mentioned advantages are common to each of them.
The basic variants of the installation of stationary pumps are discussed below, paying attention to the associated disadvantages.

Shaft pumps.

A vertical pumping unit can be installed on the shaft platform, in which the engine is built above the platform and the pump is immersed in water - figure 3. The whole thing is connected to the pressure pipeline existing in the shaft.

The disadvantages of shaft pumps are higher purchase costs than for horizontal stationary pumps (especially for longer pump shaft lengths), more complicated and expensive inspections and renovations, as well as a small range of permissible water level fluctuations, limited by the shaft length.

On the platform built in the shaft, a pump can be installed in a vertical arrangement - Figure 4, with optimal speed characteristics, allowing for high energy efficiency. The pumping unit operating on the platform is powered by a submersible pump, which eliminates the need to prime the unit before starting and allows for significant fluctuations in the water level. The pump pumps water through the existing pipeline.

The disadvantages of this solution include the cost of a flange motor, which is higher than for a horizontal motor, and the slightly lower efficiency of the feed pump, which also constitutes one more device in the reliability chain.

Stationary horizontal pumps built on a platform in the shaft with a feed pump (submersible). If there is enough space in the shaft, a horizontal pump can be installed on the platform - Figure 5, with optimal speed, powered by a submersible pump and connected to the existing discharge pipeline.

The disadvantage is that the horizontal arrangement of pumps requires more space for installation on the platform (limited by the dimensions of the shaft). The use of a feed pump has advantages and disadvantages as in the previous case.

Figure 3. Figure 4. Figure 5. Figure 6.

Stationary horizontal pumps built in a recess near the shaft with a feed pump (submersible).

A variation of the last option may be to install a horizontal stationary pump in a recess next to the glass - Figure 6, instead of on the platform. This is particularly advantageous if such a cavity exists. Otherwise, the disadvantage is the cost of implementation.

In the last three variants, the use of a feed pump can be omitted. However, this limits the range of water level fluctuations to a few meters and makes it difficult to start the pump due to the need to prime it in the event of a leak in the foot valve.

Drainage from the existing main pumping station with submersible pumps supplying water galleries.

If there is a pumping station above the expected water level in the flooded shaft, it can be used by feeding water to the water galleries with a submersible pump. Alternatively, the pump from the existing pump room can be moved to a recess near the shaft, located near the expected water level - Figure 7.

The advantage of this solution is low investment cost and the use of pumps adapted to work in difficult mining conditions. The disadvantage of using existing pumps is that they have lower energy efficiencies than pumps designed for pumping clean water, and that they require maintenance during operation and more frequent inspections.

Figure 7.

Technical and economic analysis.

The above-mentioned variants do not exhaust all possibilities of solving the problem of drainage of closed mines. Each individual case will vary, due to pumping parameters (inflow and head) and the condition of existing infrastructure. However, this will always be a qualitatively different situation than for a new investment. For obvious reasons, efforts should be made to use existing equipment, for example pipelines or entire pumping stations, which, on the one hand, limits investment outlays and, on the other hand, reduces the cost of decommissioning works.

Each case requires a technical and economic analysis before deciding on the drainage method. The starting point should be to determine the pumping parameters, which is not a simple issue, because it is not always easy to predict how the water inflows will change after the cessation of operation. Also, choosing the water level to be maintained in the shaft requires analyzing many factors. It should be emphasized that maintaining drainage capacity with wide variability of parameters is not always advisable. Any short-term changes in inflows, resulting, for example, from increased precipitation, can be compensated by changing the number of pumping hours per day. However, if it is expected that the parameters will change within a few years, it is economically justified to modernize the system in good time instead of long-term pumping with sub-optimal parameters.

Economic analysis should take into account three main components:

• investment cost,
• cost of electricity,
• other operating costs, mainly maintenance and renovation costs.

Costs incurred in subsequent years should be discounted, which means that the costs incurred in the first few years have the greatest impact on the analysis result. Techno-economic analysis may give different results for individual cases. However, conclusions that apply in every situation can be formulated:

• the investment cost for deep-well units is always higher than for pumps with "dry" engines, which is due to their more complex structure. In the case of imported deep well pumps, investment outlays are particularly high compared to stationary domestic pumps,

• deep well pumps have lower energy efficiency than stationary pumps, which are the optimal speed indicators and are driven by "dry" engines. Therefore, increased investment outlays for the purchase of submersible pumps will not be recovered due to lower electricity costs, but on the contrary, these costs for submersible pumps will be higher,

• in terms of other operating costs, submersible pumps also have no advantage over stationary pumps. Modern stationary pumps can achieve maintenance and overhaul intervals as long as deep well pumps, but the cost of overhauling a submersible pump and its drive motor is always higher than the cost of overhauling a pump with a "dry" engine,

• for submersible pumps lowered on the pipeline from the shaft framework, a major inconvenience is that all, even the smallest, maintenance work requires lifting the pump to the surface, which involves the need for expensive dismantling of the entire pressure pipeline and power cables, the costs associated with maintaining the shaft infrastructure do not differ much for deep well and stationary pumps. In both cases, ventilation of the shaft is required. Stationary pumps do not require the maintenance of hoisting machines, which can be replaced with simpler devices for people to drive. Such devices should also be used when submersible pumps are used to enable inspection of the condition of the shaft,

• the use of main drainage pumps existing in mines for drainage of closed mines should not be ruled out. This solution is characterized by very low investment costs. The operating costs of existing main drainage pumps will, of course, be higher than the operating costs of modern clean water pumps due to the required maintenance and lower efficiencies. However, it may turn out that in some cases this will be the cheapest solution.

Summary and Conclusions.

How to deal with mines where mining has been suspended is a problem with serious financial consequences. Since the funds for mining restructuring come largely from the state budget, it is also a problem of national importance. Technically, it is a multidisciplinary problem involving many mining-related specialties. It is regrettable that attempts to solve it ignore the institutions and companies with the greatest experience in the field of mine drainage.

As shown above, there are many technical methods of dewatering closed mines. It is unreasonable to prefer some of them based on unclear criteria. A deep analysis should be carried out to enable the development of assumptions for appropriate practice. Only on this basis should tender specifications be formulated for individual installations, and not certain solutions be imposed in advance without proper technical and economic justification.

If, as a result of the above-mentioned analysis, transparent rules for selecting optimal solutions for the drainage of closed mines are created and announced, both POWEN and other domestic producers will be able to offer specific pumps either from those currently in the production offer or in during design, or specially constructed taking into account the formulated requirements.

MSc. Stanisław Perchał

Dr. Eng. Grzegorz Pakula

The article was published in issue 3 of the "Pompy-Pompownie" magazine in 2000.

Construction assumptions.

In the past, the POWEN Pump Factory mainly produced pumps intended for difficult applications, such as pumping mine water and hydrotransporting mixtures containing significant amounts of solids.

In the case of pumps for this purpose, the most important design criterion is usually resistance to unfavorable operating conditions, and other considerations, such as dimensions or even to some extent efficiency, play a less important role. For this reason, the scope of use of this type of pumps outside heavy industry is limited.

As the demand for pumps for heavy industry shows declining trends, the POWEN Pump Factory began work a few years ago on constructing a series of pumps intended for easier applications, such as pumping clean, cold water. Potential applications of such pumps are primarily water supply installations and industrial cooling water circuits.

Before starting the construction works, market research was carried out to determine, in addition to determining the required operating parameters, what features of the pumps are most important to users. Thanks to the kindness of our potential recipients, primarily employees of water supply companies who found time to respond to the survey we prepared, we managed to specify detailed user requirements. The results contain virtually no surprises. Of course, every experienced designer is able to predict in advance what the user can expect from the pump. Market research allowed us to establish a hierarchy of these expectations. As the answers obtained show, three criteria are definitely the most important in the case of water supply pumps:

• operational reliability and the ability of the pump to operate without maintenance,
• high energy efficiency,
• moderate price.

In the second group, among the less frequently mentioned but also important criteria, there were:

• availability of service and spare parts,
• noise generated by the pump.

Research shows that users pay relatively little attention to the dimensions of pumps and the overall aesthetics of their appearance.

First, a series of monoblock single-stage pumps was developed because, according to market research, pumps of this type are able to handle the majority of the required parameters.

During the construction works, all of the above user requirements were taken into account. The pump element that required the most frequent maintenance was usually the stuffing box. The new series assumes that only mechanical seals will be used, and there is no space for installing a stuffing box. This provided the added benefit of a compact design and minimal shaft overhang, eliminating potential pump vibration problems.

Another issue that can cause reliability problems is the transmission of axial force. For example, the use of traditional relief ports is only effective as long as there is adequate throttling at the gaps restricting flow through the ports. If, due to wear, the dimensions of the choking gaps increase, not only do hydraulic losses increase, but the effectiveness of the unloading also decreases due to the increase in pressure behind the impeller. For this reason, after tests, in the new series it was decided to transfer the axial force entirely on the engine's rolling bearings.

It is worth emphasizing the cooperation of the engine manufacturer - Celma Cieszyn, which made appropriate modifications to the bearings. Transferring the axial force through rolling bearings not only eliminates reliability problems, but also does not cause the deterioration of efficiency that accompanies other methods of load relief.

Monoblock pumps of the new series, thanks to their design, do not require any maintenance between periodic inspections, apart from the inevitable start-up activities, such as filling and bleeding.

In order to achieve high efficiency, the pump parameters were selected so that they were close to the optimal value of the speed factor. Initially, it was assumed that, in cooperation with specialists from the Silesian and Wrocław Universities of Technology, a whole range of new flow systems would be developed.

This program was partially implemented, but the situation changed after the creation of a capital group that included, in addition to the POWEN Pump Factory, also the Warsaw Pump and Fittings Factory and the Świdnicka Pump Factory. WFPiA and ŚFP already had flow systems with appropriate parameters and high efficiency (e.g. A and CH series pumps). However, these types are intended for use in more difficult applications (hot water, chemicals) and therefore have their own bearings and a more extensive shaft sealing system. As a result, when used for clean, cold water, they are less price competitive. The use of existing hydraulic systems for monoblock pumps allowed for the acceleration of work on the series of types and made it easier to meet another user demand - obtaining a moderate price. The new series was marked ON. The full name of the pump also includes the diameter of the discharge port in millimeters and two additional letters. The last letter B means a monoblock pump, and the penultimate one means a type of flow system with different parameters (e.g. ON-200BB, ON-200CB, ON-150BB). Since it is possible to use virtually all flow systems existing in the capital group to build monoblock pumps, the type series covers at least the scope of work of the Warsaw type series A, expanded with additional type sizes from Świdnica and Zabrze.

ON-200BB pump parameters.

As an example, the parameters of the ON-200BB pump will be discussed (Fig. 1), which has a new flow system developed from scratch. It has been subjected to a very extensive research program. The nominal parameters are: efficiency 550 m³/h, lifting height 38 m, rotational speed 1480 rpm, which gives a speed factor of approximately 38, close to optimal.

The maximum efficiency of the pump in the standard version is 84%. Research has shown that by coating standard castings with preparations that increase smoothness, a further increase in efficiency of 2-3% can be achieved. The ON-200BB pump is characterized by favorable, flat efficiency characteristics, thanks to which it has a very wide effective operating range. Fig. 2 shows the area in which the pump operates with efficiency above 80%. The chart was created as a result of testing rotors with external diameters ranging from 300 to 369 mm. Variability of parameters can, of course, also be successfully implemented by adjusting the rotational speed.

The basic version of the pump is combined with a 75 kW motor. For external rotor diameters reduced below 340 mm, it is possible and even advisable to use a 55 kW motor, which only requires a change in the frame structure.

The ON200BB pump has very good suction properties. The required NPSH is on the order of 4 meters. Thanks to properly designed hydraulics, the pump operates quietly - the measured noise level at the workplace does not exceed 53 dB and is lower than the noise caused by the electric motor.

Development versions.

The successful flow system of the ON-200BB pump has already been used in other designs. A submersible pump with the same parameters has been developed (efficiency 550 mXNUMX).³/h, lifting height 38 m, rotational speed 1480 rpm, engine power 75 kW) and a multi-stage pump, which with this capacity reaches lifting heights of up to 230 meters. These new, interesting structures will be presented to the readers of "Pomp-Pompownia" in a separate article.

At the customer's request, the ON-200BB pump can be equipped with a monitoring and diagnostic system that records operating parameters and automatically reacts in the event of operating irregularities.

After passing stand tests at the factory testing station, the ON-200BB pump has already been used in real workplaces. One of the first was the drainage of the pool that forms during heavy rainfall at the bottom of an open-cast lignite mine. This floodwater is difficult to pump out using the main, stationary drainage system. Specialists from KWB "Bełchatów" developed a concept of pumps floating on pontoons, connected to flexible pipelines (photos 1 and 2). The pump inlet is located below the surface of the mirror, which eliminates problems with priming and bleeding during start-up. ON-200 pumps turned out to be suitable for this application, both in terms of parameters and dimensions, and have been in operation since spring 2001.

Two types of pump were used (ON-200BB and ON-200FB), differing in lifting height (40-70 m) and, as a result, also in engine power.

The pumps proved to be resistant to contaminants found in rainwater. This original method of installing the pump (shown in the photo during tests in the swimming pool) deserves wider popularization, because it seems possible to use it, for example, to drain floodplains during flood operations.

Dr. Eng. Grzegorz Pakula.

The article was published in issue 3 of the "Pompy-Pompownie" magazine in 2002.

Author's comment:

“The article was written in 2002, when work on the development of the ON series was ongoing. Since then, the series has been significantly expanded and currently includes 10 types covering the working area shown in the figure below. Engine powers range from 11 to 160 kW. ON pumps are used mainly in surface drainage of open-pit mines. The most popular are pumps from the ON-200 group with a nominal capacity of 500 mXNUMX³/h and lifting height (depending on the type) 30-80 m. ON pumps are used in other industries. This series has the potential for further, significant expansion of applications because it combines reliability with a moderate price.”

Fig. 1. Operating area of ​​ON series pumps.

Pumping highly contaminated and aggressive media

The pumping technique using submersible pumps was pioneered by Scandinavian companies. In 1948, the first fully submersible pumps were manufactured. The history of submersible pumps in the Polish pumping industry was initiated by the Zabrzańska Fabryka Maszyn Górniczej, currently POWEN SA. In 1952, the production of submersible pumps type EW-50 (Fig. 1) was launched in the former Zabrzańska Fabryka Maszyn Górnicze (Fig. XNUMX), intended for mining and meeting the requirements of the mining regulations in force at that time. .

Figure 1. EW-50 pump.

Submersible pumps were originally used only for drainage purposes. Then the scope of their applications expanded to include sewage management, and then they were also used in technological processes in industry. This became possible thanks to the expansion of the production of submersible pumps, the use of various flow systems and construction materials, and the use of technical progress in many areas, including: in the mechanical seals and electric motors industry. All this influenced the design of submersible pumps to such an extent that they began to replace the previously used stationary pumps.

POWEN SA, using its several decades of experience in the construction, production and operation of submersible pumps (in mining and outside mining), stationary pumps for highly contaminated (sludge) liquids, has developed and implemented a series of submersible pumps intended for difficult operating conditions.

Working conditions considered difficult include, among others: when pumping:

• mixtures of solids and liquids with high specific density (up to 1700 kg/m³ ) and high (up to 50%) solids content in the liquid,
• untreated (raw) sewage,
• highly saline liquids,
• liquids with petroleum contamination.

The processes of pumping these media occur in particular in industries such as:

• Energy – in hydrotransport of slag and ash,
• Municipal management - when pumping untreated sewage, heavy sludge, sludge and removing sludge from sand traps,
• Mining - in hydrotransport in processing plants, hydrotransport of backfill, transport of mixtures for waste placement, pumping of saline waters and cleaning of water passages,
• Metallurgy – when pumping water with scale,
• Chemistry – when pumping water with petroleum contamination,
• Aggregate mines – in hydrotransport of sand, gravel, stones, etc.,
• Sugar industry – in hydrotransport of beets, etc.

Submersible pumps are used instead of stationary pumps due to lower assembly and installation costs and operational advantages.

The rest of the article describes the possibilities of use and applications of submersible pumps produced by POWEN SA intended for difficult operating conditions in sewage treatment plants, power plants, heating plants, underground mining, aggregate mines, metallurgy, sugar industry, etc.

Submersible pumps for untreated municipal sewage.

Submersible pumps intended for untreated municipal sewage must be adapted to pump liquids containing, among others:

• solid bodies such as sand, gravel, stones, bricks, etc.,
• metal elements, i.e. short rods, screws, etc.,
• fibrous materials, i.e. rags, bandages, fibers woven into the so-called braids or tight balls.

The reason for this state of affairs is still inadequate management of commercial and industrial waste. This means that pumps used to transport untreated (raw) sewage operate in difficult operating conditions. Submersible sewage pumps are equipped with various flow systems commonly used in stationary pumps. To choose the right flow system, in addition to the basic parameters (Q, H, n, n), the properties of the pumped medium are also important, which determine its design and material solution.`

The most frequently offered submersible pumps for untreated sewage include:

• pumps with grinders or cutting knives,
• pumps with open, free-flow impellers,
• pumps with single-channel or two-channel closed impellers, pumps with closed multi-vane impellers.

Figure 2. Figure 3. Figure 4. Figure 5. Figure 6. Pump P-15-V80/4A Pump P110-S125/4A Pump P55-K100/4A Pump P75-Z100R/4A PumpP75-Z100T/4A

It is known that none of the solutions is a universal solution for all cases of sewage pumping. Pumps with grinding devices for raw sewage should only be used where waste segregation is properly managed. Untreated sewage often contains metal elements that damage the cutting knives in shredding devices.

Multi-blade impellers with small diameters often become clogged with long-fibrous materials contained in the sewage and cause the pump to operate improperly. The operation of an open rotor, thanks to its symmetry and balance, is much more advantageous in terms of movement than that of a single-channel rotor. Single-channel impellers achieve higher efficiencies than open, free-flow impellers. Each impeller has its advantages, the decision which impeller to use also depends on the size of the pump. At low powers up to 15 kW, where efficiency does not play such a big role and the criterion of movement reliability is decisive, open rotors with free flow have found wide application.

For high pump power, single- or double-channel impellers are used.

POWEN SA offers new P series pumps intended for untreated (raw) sewage. The new series of pumps enables solving various problems related to pumping untreated sewage and other highly contaminated liquids.

For pumping untreated raw sewage containing solids, metal and fibrous elements, POWEN SA offers open-impeller, free-flow pumps of hydraulic type V (Fig. 2), S (Fig. 3) and K (Fig. 4) pumps. The free passages of these pumps, depending on the pump size, range from 54-100 mm. For wastewater grinding, pumps with grinding devices of the R hydraulic type (Fig. 5) or with a cutting knife of the T hydraulic type (Fig. 6) are offered. Flow systems and housings of submersible pumps are made of ductile cast iron, depending on the need. acid-resistant cast steel or special cast steel with a hardness of 60HRC.

One of the indispensable elements of every sewage treatment plant are sand traps. Granular impurities such as ash, coal and, above all, sand are removed in sand traps. For the process of pumping sludge from flat bars, POWEN SA offers submersible pumps with free-flow rotors with a system to prevent the sedimentation of pollutants. A prototype submersible sewage pump type P15-V80/4A with a sludge washing system (Fig. 7) was subjected to operational tests at the sewage treatment plant in Piekary Śl. The operation of this pump and the sludge washing system received very positive user reviews.

Submersible pumps for liquids with petroleum contamination.

P-1BA/I pumps are offered by POWEN SA for pumping liquids with petroleum contamination coming from sewage tanks at gas stations (Fig. 8). This pump is made of materials resistant to chemically aggressive liquids and is approved for operation in rooms and zones at risk of explosion of media classified to subgroup IIA according to PN-84/E-08119.

Submersible pumps for liquids heavily contaminated with solids.

Hydraulic transport of liquids contaminated with strongly abrasive solids is commonly used in hard coal mines, iron ores and non-ferrous metals, mineral raw materials, power plants and heating plants, large farms, etc.

The useful effect of a hydraulic system is mainly to move solids, and water is the ONLY necessary carrying medium. Hydraulically transported solids (coal, ore concentrates, mineral aggregates, sand, fly ash and energy slags, clay, etc.) differ significantly from each other, both in density from 1400 to 3000 kg/m³, hardness and grain size of the mixture with water, they are characterized by very diverse composition and must be transported with different parameters. For pumping the above-mentioned media, mainly stationary pumps are used, specially designed for highly contaminated liquids, which are commonly called slurry pumps.

The design features of slurry pumps and the conditions related to their selection are presented in detail in the article published in PP 6/2000 from June this year. If you want to use submersible pumps to solve the problems of transporting contaminated liquids, where only stationary pumps have been used so far, you need to adopt all their distinctive features.

POWEN SA based on many years of experience in the construction, production and operation of PH type stationary slurry pumps. PH-S and PHP developed and implemented into production a submersible slurry pump type P370-V175/6A (Fig. 9) with a power of 37 kW and a rotational speed of n = 960 rpm. The pump is designed for medium with a density of up to 1700 kg/m³ granulation of solids up to 100 mm and solids content in liquid up to 50%. The P370-V175/6A pump is equipped with an innovative design of the impeller with double blades. This ensures reliable pumping of contaminated liquids with high efficiency throughout the entire operating period, significantly increasing pumping economy and reducing its total operating cost. In the P370-V175/6A pump, the mechanical seal is exposed only to the pressure resulting from the immersion depth, and not to the discharge pressure, as in most pumps. A special sealing system installed directly next to the bearings made it possible to shorten the shaft overhang, which affects the reliability of movement. The pump housing and impeller are made of wear-resistant cast steel with a hardness above 60HRC. The motor body with a special design for heat dissipation allows the pump to operate in partially submerged conditions. The pump motor is protected against overheating by switches built in the stator windings on each phase and by a controller built under the engine cover. The controller turns off the pump drive during long-term dry operation. All pump fasteners are made of stainless steel. P370-V175/6A pumps have proven operational reliability in installations for pumping water and slag mixtures in power plants and heating plants.

Figure 7. P15-V80/4A pump – scavenging system.

Figure 8. P-1BA/I pump at the CPN gas station.

Figure 9. P370-V175/6A pump.

Summary.

The article discusses the issues of submersible pumps for pumping highly contaminated and highly abrasive liquids. Submersible pumps produced in Poland and abroad, thanks to the dynamic development of design and material engineering, have achieved high reliability in recent years.

Due to the unquestionable benefits, especially lower assembly and installation costs, submersible pumps are gaining more and more areas of application.

Roman Pawlik.

The article was published in issue 8 of the "Pompy-Pompownie" magazine in 2000.

Author's comment after 15 years:

"The article 'Submersible pumps for operation in difficult conditions' is no longer valid for the production of submersible pumps of the types P15-V80/4A, P110-S125/4A, P55-K100/4A, P75-Z100R/4A and P75-Z100T/ 4A (figs. 2 to 6), the production of which has not been undertaken.
Currently, the validity of the above-mentioned article may only apply to the submersible pump intended for pumping liquids with petroleum contamination, the P-1A/I type pump (Fig. 8) and the P-370 type submersible pump (Fig. 9) intended for pumping liquids heavily contaminated with solids (medium with a density of up to 1700kg/m3, solids granulation up to 100mm and solids content in the liquid up to 50%). If the above-mentioned pumps have valid certificates, they can be offered on the market.”

Reasons for using multistage pumps.

The operation of a centrifugal pump is based on the fact that the mechanical energy absorbed from the drive motor is converted in the rotor mainly into the kinetic energy of the pumped liquid. In subsequent elements of the flow system (blades, spiral channels, diffusers), kinetic energy is transformed into an increase in pressure. Analyzing the mechanism of energy transfer in the pump, we come to the conclusion that the lifting height obtained (approximately proportional to the pressure) depends on the maximum speed achieved by the liquid in the flow system, while the maximum speed depends on the speed of the end of the impeller blade. Therefore, if we want to increase the lifting height of the pump, we must strive to increase the speed of the impeller blade at the outlet, which can be achieved by increasing the impeller diameter or increasing the rotational speed. However, the lifting height that can be obtained from one rotor is limited because the speed of the blade end cannot be increased indefinitely for strength reasons. At too high speeds, the rotor would have to be too massive to withstand the stresses from the centrifugal force. The second reason that limits the lifting height that can be obtained from one stage is the so-called wading losses, i.e. energy losses resulting from the friction of the rotating impeller with the liquid surrounding it. Since these losses increase with the fifth power of the rotor diameter, when the diameter increases, the wading loss quickly causes a deterioration of efficiency to an extent that disqualifies such a rotor design. What is important is not the absolute value of the wading loss, but its ratio to the total energy transferred to the liquid by the impeller. Figuratively speaking, a "narrow" impeller, i.e. having a large diameter in relation to its width, has a higher ratio of wading losses to the total energy transferred to the liquid than a "wide" impeller, because a larger impeller width means a higher flow rate and, therefore, a greater energy transferred to the liquid by the impeller. Strictly speaking, the relationship between the rotor lifting height H [m], flow rate Q [m3/s] and rotational speed n [rpm] is captured by the speed factor: nsq = n-Q1/2-H-3/4.

Increasing the lifting height at a given rotational speed and capacity causes a decrease in the differentiator. Optimum efficiency can be obtained in the range of 30-55, but below this range the efficiency decreases, primarily due to the increase in the share of wading losses. Design experience shows that the value of the speed factor determines the optimal proportions and shape of the rotor, which is schematically shown in Fig. 1.

In practice, the lowest values ​​of speed factors used in pumps are at the level of a dozen or so.

Figure 1. Dependence of the achievable efficiency and the optimal shape of the rotor on the speed factor.

With a discriminant value below ten, it is impossible to obtain satisfactory pump efficiency, which is why designs with such low values ​​are rarely encountered, only in specific applications where the need to obtain a combination of low efficiency with high lifting height is more important than energy efficiency. However, in basic applications, the speed factor must be within the correct range. This is the reason for building multistage pumps, because if we want to build a pump with good efficiency at a given efficiency and rotational speed, we cannot exceed a certain lifting height from one impeller. However, if a lifting height exceeding this value is needed, the only way is to use several stages in the pump, thanks to which the speed rating for one stage is within the appropriate range.

Energy transfer mechanism.

In a multi-stage pump, the mechanism of energy transfer is as follows: in the impeller, the flowing liquid absorbs mechanical energy, which, at the outflow from the impeller, largely exists in the form of kinetic energy related to the peripheral velocity of the liquid (a certain part of the mechanical energy is converted into pressure energy already in the impeller, depending on the so-called degree of rotor reactivity). The liquid at the outlet of the impeller therefore has a higher pressure than at the inlet and a much higher velocity. The next element of the flow system is the interstage guide, whose task is to slow down the swirling motion of the liquid and transform the associated kinetic energy into pressure.

The interstage guide often consists of two parts: a centrifugal guide, where the basic transformation of kinetic energy into pressure takes place, and a centripetal guide, whose task is mainly to supply the liquid in the axial direction to the next rotor, and the pressure increase here is much smaller than in the centrifugal guide. As a result, after flowing through the entire pump stage consisting of the impeller and guide vanes, the liquid has the same velocity as at the inlet to the stage, but a higher pressure.

Figure 2. Changes in kinetic energy and liquid pressure in individual elements of the pump stage.

In the next stage, the cycle of energy transformations is repeated. An example of changes in kinetic energy and pressure in individual elements of the pump stage is shown schematically in Fig. 2.

It should be taken into account that the drawing is intended only as a simplified illustration of the energy transformations taking place, while the proportions between the values ​​of kinetic energy and pressure increases as well as the exact course of the line depend on the specific design solution.

Design issues.

Single-stage centrifugal pumps are offered by many manufacturers because their construction is relatively simple. However, the design of multistage pumps and their manufacturing technology are so complex that they have been successfully mastered by a much smaller number of manufacturers.

Rotational speed and number of stages.

Obtaining the assumed lifting height and efficiency when designing a pump is a relatively simple task, but achieving high efficiency is much more difficult.

While the efficiency of a small single-stage pump is often treated as a secondary issue, provided that other parameters are met, in the case of multi-stage pumps, due to their usually high power consumption, efficiency is one of the important elements. For this reason, plants that undertake the design of multistage pumps must use more sophisticated hydraulic calculation techniques than are sufficient for single-stage pumps.

One of the first decisions to be made at the design stage of a multistage pump is the selection of rotational speed. In most cases, the synchronous speed of the electric motor is used, because in multistage pumps, due to the significant power consumption, belt transmissions are almost not used, and devices for regulating the rotational speed (so-called inverters) are rarely used. Only some pumps feeding power boilers use gears to increase the rotational speed above 3000 rpm. The pump is usually designed for a given capacity, and then the rotational speed and lifting height from the stage are selected so that the speed factor is within the appropriate range.

In practice, two synchronous speeds are mainly used for multistage pumps: 1500 and 3000 rpm. Each of them has its advantages and disadvantages.

A lower rotational speed increases the pump's dimensions, but on the other hand it facilitates obtaining good suction properties. Moreover, it increases the durability of the pump, especially when pumping contaminated liquids, and reduces problems related to the dynamics of the rotating unit.

Conversely, a higher rotational speed generally makes it easier to obtain the optimal speed ratio, reduces the size and weight of the pump, but worsens the suction properties, limits durability and increases the difficulty of controlling vibrations.

Determining the maximum allowable number of steps is also an important decision. This results in the shaft diameter, which must allow the transfer of the torque that increases with the number of steps and ensure the required shaft stiffness.

Of course, due to the unification of elements, the shaft diameter calculated for the maximum expected number of stages is also used in pumps with a smaller number of stages. This is unfavorable because the increased diameter of the rotor hub makes it difficult to achieve high efficiency.

To partially eliminate this contradiction, in some solutions, when the number of stages is close to the maximum, a double-sided drive from two motors is used, which allows the shaft diameter to be reduced. The maximum number of stages also dictates the pressure that the pressure casing and stage casings must withstand and therefore their wall thickness.

All this means that the number of pump stages can only vary within a certain range, otherwise the dimensions resulting from the requirements for the maximum number of stages differ too significantly from those optimal for the minimum number of stages. For this reason, high- and medium-pressure multistage pumps are designed separately.

Transfer of axial force.

In multistage pumps, a difficult problem is the transfer of axial force. The pressure acting on the rear wall of the rotor is higher than the pressure at the inlet to the rotor. This pressure difference, multiplied by the area of ​​the inlet ring contained between the impeller neck and the hub, gives the force acting on the rotating assembly in the direction opposite to the liquid flow. The forces from individual stages add up, as a result of which the total axial force in large multistage pumps can reach several dozen tons.

One of the methods of balancing the axial force is the construction of multistage pumps consisting of two rotor sections set in opposite directions, which cancel the axial forces. This requires the use of an overflow through which the liquid, after leaving one section of the rotors, is fed to the inlet to the other. The disadvantage of this pump system is the complexity of the structure, because instead of two there are four stubs, two of which are connected with each other by a shaft. In such a solution, the internal seal between the sections may cause construction and operational difficulties. There is also a risk that in certain dynamic states the forces from both sections are not completely balanced. This situation may occur, for example, during start-up, when one section is thoroughly vented and the other is not. A momentary power imbalance can cause a crash.

Another method of balancing the axial force is a relief disc which, under the influence of axial force, is pressed against the counter ring mounted in the pump casing. The liquid flows from the last stage of the pump between the disc and the counter ring, i.e. the disc works similarly to a sliding bearing lubricated by the pumped liquid, transmitting axial force. However, what is crucial here is the difference in pressure acting on the disc from both sides. There is the ability to self-regulate the gap between the disc and the counter ring.

As the gap increases, the pressure drop in it decreases, as a result of which the pressure difference acting on the disc decreases and the axial force closes the gap. Similarly, when the gap is closed too much, the pressure drop increases, causing a pressure difference that pushes the disc away. Due to this effect, the relief disc is stable in movement. An additional advantage is a significant reduction in the pressure acting on the shaft seal on the discharge side. Its disadvantage, however, is the reduction in pump efficiency and sensitivity to the content of mechanical impurities in the liquid, which results in a decrease in durability. There is also a risk of accelerated wear if a pump that is not fully vented is started. A similar solution is the so-called relief piston, but it is less reliable in movement.

The axial force can also be removed by using relief holes in the rotor, accompanied by a choke ring on the rear wall of the rotor, as a result of which the pressures acting on the rotor wall are balanced. However, the use of relief holes causes some return flow and disruption of the flow structure in the impeller, which reduces the efficiency of the pump. In medium-pressure pumps, rolling bearings of an appropriate design are generally sufficient to transfer the axial force. Another solution is to install an axial bearing lubricated with oil supplied by a separate displacement pump.

Dynamics.

Due to the length of the shaft, an important issue in multistage pumps is the dynamics of the rotating system. When designing the shaft and bearing, critical speeds and natural frequencies must be calculated to avoid resonance and excessive vibrations during pump operation.

These calculations are difficult because the methods known from solid mechanics are not fully accurate in this case, because the interaction of the rotating unit and the flowing fluid is the source of both hydrodynamic excitations and damping, for which there are no fully accurate methods. computational. In this context, it should be noted that traditional stuffing boxes with string filling provide additional support for the shaft with a certain ability to dampen vibrations. Modifications sometimes used to replace the traditional stuffing box with a mechanical seal may, in some cases, increase vibrations.

Technological requirements.

In the construction of multistage pumps, the requirements for manufacturing accuracy are much stricter compared to single-stage pumps. Since there are significant pressure increases between successive stages (and both sides of the guide and impeller), internal seals should be used to limit the flows. Seals between rotating and stationary elements take the form of gaps that choke the flow. For them to be effective, the gap cross-section must be as small as possible. On the other hand, since the relatively long shaft of the multistage pump may have some dynamic deflection, the gaps must not be too tight to avoid seizure. Obtaining optimal gap dimensions is made more difficult by the fact that the elements of subsequent stages are fitted together to form a dimensional chain, which in unfavorable cases may lead to the addition of deviations and exceeding the permissible gap dimensions tolerances.

A similar problem concerns the axial dimensions. Typically, the elements mounted on the shaft (impellers, spacer sleeves) create a dimensional chain independent of the dimensional chain created by the vanes and casings, which may result in the fact that in the event of an unfavorable addition of deviations, the corresponding impellers and vanes will not be in the correct position relative to each other after the pump is assembled. myself. To avoid this, appropriate construction measures should be used, tighter tolerances for the dimensions of individual elements should be observed, and assembly should be carried out according to special technology. During assembly, the issue of seals between elements that do not move relative to each other is also very important. For example, there is a significant pressure difference on both sides of the impeller. If the contact surface between the rotor and the sleeves located on both sides is not properly sealed, return flow will occur under the rotor along the shaft, leading to its damage. A flow of a similar nature may also occur along the junction of the centrifugal and centripetal guide vanes and at several other locations in the multistage pump. Avoiding such effects, which reduce efficiency and cause damage, requires the use of appropriate design solutions and careful installation.

The manufacturing technology also affects the dynamics of the rotating assembly. Its individual elements must be made precisely enough to avoid unbalance. After processing, each rotating element is additionally static balanced to eliminate the remaining unbalance, but even this does not guarantee smooth operation of the pump, because after assembly, due to assembly stresses, deformations may occur (e.g. slight skewing of the rotors), causing dynamic unbalance. For this reason, the rotating assembly should be test-assembled and dynamically balanced in this condition.

Multistage pumps manufactured by Powen.

Powen is one of the few Polish pump companies that has mastered the problems related to the design and implementation of multistage pumps. He has been building this type of pumps for several decades. The traditional area in which multistage pumps are used is the main drainage of mines, where the required lifting heights exceed even 1000 m and the capacities are in the range of 80-800 m3/h (most often 300-500 m3/h).

Currently, there are two types of main drainage pumps in production. The OW series, including pumps in the OW-AM and OW-B versions with discharge port diameters of 100, 150, 200, 250 and 300 mm, covers the capacity range from 80 to 800 m3/h and provides lifting heights of up to approximately 800 m.

Higher lifting heights, up to 1050 m, are available in the OWH series pumps, with discharge port diameters of 200 and 250 mm, which corresponds to a nominal capacity range of 300-500 m³/h. OWH pumps are designed to operate in series, which allows lifting heights of up to 1400 m to be achieved. Both series of types are based on similar design assumptions: they operate at a rotational speed of 1500 rpm (except for OW-100B and OW-150AM pumps). designed for 3000 rpm), which provides them with very good suction properties and durability when pumping chemically and mechanically polluted water. Relieving discs were used to transfer the axial force due to the certainty of movement in extremely difficult operating conditions.

OS series pumps, used, among others, as auxiliary drainage pumps, are medium-pressure pumps providing lifting heights of up to 250 m.

They are produced in OS-AM, OS-B and OS-C versions with discharge port diameters of 80, 100, 125, 150, 200 and 250 mm, which covers the capacity range of 30-550 m³/h. They are designed for 1450 rpm, which ensures their durability in difficult operating conditions. The transfer of axial force is ensured by rolling bearings, supported in some pump sizes by relief holes in the rotors. Due to the diversity of the chemical composition of mine water, several material solutions are used in OS, OW and OWH pumps, from gray cast iron to chrome cast steel ensuring resistance to aggressive brines.

In addition, Powen produces medium-pressure ZW-50 pumps, designed for 2950 rpm, characterized by low efficiency (18-22 m³/h) at a relatively high lifting height (190-325 m), which combination of parameters is required, for example, when powering hydraulic systems.

All multi-stage pumps manufactured by Powenu meet the strict occupational safety requirements set by the State Mining Office and are certified for operation in mine undergrounds.

The reliability of Powenu pumps is proven by the fact that drainage of all Polish mines has been based on them for over fifty years, and throughout this period there has been no case of a serious water hazard resulting from poor quality of the pump.

Multistage pumps manufactured by Powenu, especially OW and OS pumps, although designed mainly for mining, have found wide application in many other fields, especially where difficult operating conditions occur, and have gained recognition thanks to their solid construction and reliable operation.

Powen is currently conducting construction work on a new series of medium-pressure pumps intended for lighter applications, and primarily for pumping clean water. The creation of design assumptions was preceded by extensive consultations with potential users. As a result, the features of the pumps most desired by users were determined and the design assumptions were formulated so that the new product would be able to provide them. The leading features of the new series include high energy efficiency, reliability and the ability to operate without maintenance. Soon, Powen will present its new range to users in "Pomp-Pompownia", showing how the above technical requirements have been met and, what is equally important, how it has been reconciled with a reasonable price. The authors are convinced that the new product will become a standard in the Polish industry, as was the case with other types of product lines produced by Powen.

MSc. Władysław Tywoniak Ph.D. Eng. Grzegorz Pakula

The article was published in issue 12 of the "Pompy-Pompownie" magazine in 2000.

Author's comment after 15 years:

"Over the 15 years that have passed since the text was written, the physical basis of operation of multistage pumps has not changed, but there have been some changes in design solutions related to progress in similar fields of technology. In 2000, as stated in the text, the regulation of multistage pump parameters by changing the rotational speed was rare due to the high price of high-power frequency converters. Since then, due to the decline in their prices, these devices have found widespread use even for high-power multi-stage pumps. Progress has also been made in the field of rolling bearings. Currently available bearings transfer, among others: higher axial loads, as a result of which in some multistage pumps it was possible to do without relief holes, which contributes to increased pump efficiency.

As a result of the consolidation of the Polish pump industry, POWEN SA has built the POWEN-WAFAPOMP SA Group, which offers a much wider range of multistage pumps than those discussed in the article. New multistage mining pumps have been developed to replace the types mentioned in the text. High-pressure pumps of the OW-AM and OW-B series will be gradually replaced by pumps of the H series, and medium-pressure pumps of the OS-B, OS-AM and OS-C series by pumps of the M series. Pumps of the M and H series are completely new designs that functionally replace their predecessors, but with completely new technical solutions.”