It is a well-known fact that each pump operating at a constant rotational speed achieves parameters resulting from its characteristics, i.e. with a specific efficiency, it produces a specific lifting height and achieves a specific efficiency, from which parameters the power consumption results. Although the pump can operate with any combination of parameters resulting from the characteristic curve, it works properly only near the so-called nominal parameters, i.e. those for which it was designed. In this range, the pump achieves its highest efficiency. The more the actual operating point of the pump moves away from the nominal point, the more the efficiency differs unfavorably from the maximum, and other unfavorable phenomena appear in the form of increased vibration and noise levels. The point at which the pump operates in its characteristic curve depends on its cooperation with the system in which it is installed - the pump operating point is the efficiency at which the pump characteristics intersect with those of the pumping system. The correct selection of a pump therefore involves carefully calculating and drawing the characteristics of the pump system, and then finding a pump whose characteristics intersect with those of the system in terms of optimal efficiency.

Although the above statements should be obvious to every mechanical engineer, in practice many pumps are incorrectly selected, as a result of which they operate with efficiency much lower than achievable. This fact results not only from the author's own observations, but is confirmed by research of such recognized institutions as the American Hydraulic Institute or the European association of pump manufacturers Europump. Their estimates show that as a result of improving the quality of pump selection for pumping systems, up to 40% energy savings can be achieved, which is much more than by increasing the efficiency of the pumps themselves. In the latter area, the possibilities of progress are limited, because currently pump designs are so refined that, as a result of further development of pump design methods and pump manufacturing technologies, an increase in efficiency greater than a few percent should not be expected. (This statement applies to properly designed pumps produced by serious manufacturers, which does not exclude the existence of poor quality pumps on the market which, for energy reasons, should be replaced by products of an appropriate technical standard).

When selecting pumps for a system, two qualitatively different situations should be distinguished:

1. Fixed operating point, i.e. a situation in which the parameters required by the system do not change. In this case, there is no technical reason for the pump to operate outside its optimal range, and if so, it is an engineering error that requires correction by one of the methods discussed later in the text.

2. Parameters periodically change due to the changing demand of the system (during the daily period, depending on the seasons, etc.). If this situation occurs, it is technically not possible for the pump to operate optimally at constant speed in every situation. At most, you can minimize losses by selecting the pump for the most common combination of parameters. To improve the selection quality, a certain method of adjusting the pump parameters is needed. The above-mentioned data regarding the potential for energy savings of up to 40% in pump systems primarily concern the use of better control methods, because the possibility of achieving savings of this order in the case of a fixed operating point occurs only in rare cases of grossly incorrect selection.

There are four most well-known methods of parameter regulation, each of which has strengths and weaknesses (only methods applicable to various types of pumps are listed here, methods applicable only to specific design solutions are omitted, such as regulation by changing the angle of blades in pumps propellers or by pre-rotation steering wheel):

a) Regulation by throttling a valve on the discharge side – it does not require high investment outlays but does not bring good energy results. It is best suited for pumps and pumping systems with flat characteristics and for pumps with increasing power characteristics.

b) Regulation by discount – suitable only for pumps with power consumption decreasing with efficiency (e.g. propeller pumps and some diagonal pumps).

c) Regulation by changing the rotational speed – requires significant investment outlays, but creates the potential for significant energy savings compared to, for example, throttling control. It gives the best results in pumping systems where the amount of losses dominates over the static head (e.g. in circulation systems), but is less suitable for situations where the static head dominates (e.g. change in efficiency while maintaining a constant, high discharge pressure).

d) Regulation by changing the number of pumps operating in parallel (this is not a method of regulating a single pump, but the entire pumping station) – the advantage of this method is low cost, but the disadvantage is that pumps with lower capacities usually have lower efficiency than one larger pump replacing them. This method is best suited to situations in which it is necessary to obtain pumping station capacity that varies significantly while maintaining approximately constant pressure in the discharge manifold.

Although, as mentioned, optimization of the control method has the greatest potential for energy savings, this issue will not be discussed here, as it requires much more space than the scope of this article allows. We will summarize the regulation issues by saying that this is a very important issue from the energy point of view and in each case it requires the selection of an individual, optimal solution (generally from among the above-mentioned four possibilities).

In the following, we will focus on the simpler issue of selecting pumps for a fixed operating point. First of all, it is important to understand where the cases of incorrect selection come from in such a theoretically relatively simple and well-known situation.

The following main reasons can be distinguished:

1. Simple selection error. – In the case of large investments, pumps are often treated as secondary auxiliary machines and therefore their selection does not receive as much attention as the most important devices. Designers of large installations are usually specialists in a given technological process, who do not always sufficiently understand pumping issues and do not always consult specialists in this field. If a large investment is implemented on a turnkey basis, the pump manufacturer is rarely the general contractor (tender participant) and therefore has limited opportunities to make arrangements with the user.

2. Excessive caution. – Although the methods for calculating system characteristics are theoretically known, there is a range of uncertainty in estimating flow resistance. For this reason, in order to avoid a situation where the pump does not provide the expected performance, designers usually select it with a certain excess of lifting height. If this reserve is excessive, the pump "escapes" to higher capacities, leaving the optimal operating range.

3. Change in demand – Over the years, the required parameters may change in relation to the design assumptions. For example, such a situation is typical for water supply and heating networks, where, due to the development of cities and changes in technology, there are significant changes in the parameters required from pumps.

4. Layout optimization – It should be emphasized that one of the basic possibilities of saving energy for pumping is the optimization of pumping systems involving the reduction of losses. This may involve eliminating elements causing unnecessary choking (pipe sections with too small a diameter, incorrect fittings) or introducing new technologies (e.g. filters or heat exchangers with lower pressure losses). Paradoxically, introducing such changes leading to energy savings means that the pumps in the installation may find themselves outside the optimal operating range because they have excess lifting height. In order to take full advantage of the energy saving opportunities resulting from the reduction of resistance, the pump parameters must be modified.

If, for any reason, the pump parameters do not meet the system requirements, their parameters should be adjusted to improve pumping efficiency.

The methods used for this purpose will be presented in the second part of the article.

Dr. Eng. Grzegorz Pakula

Advice regarding the current operation of pumps could basically be reduced to the recommendation to read User Manual specific copy and to emphasize the need to comply with it. Without diminishing the importance of following the Instructions, we can attempt to formulate a few general comments applicable to the current operation of pumps, regardless of their design.

Modern pumps are built in such a way that the requirements for ongoing maintenance are minimal. Ongoing maintenance practically comes down to monitoring operating parameters in order to detect deviations from the nominal level. In fact, the only structural node that requires relatively frequent maintenance is the string gland, which requires adjustment of the leakage, which is achieved by tightening or loosening the screws securing the gland that presses the packing. A properly adjusted stuffing box should have a drip leak (of the order of a few drops per minute), which is required to ensure lubrication and cooling of the surface of the sleeve cooperating with the packing material. Pressing the gland too hard to completely stop the leak will result in overheating and damage to the gland. Care should be taken to properly capture and drain the leak (usually through a hose connected to the lower part of the stuffing box body), as water spilling around the pump promotes corrosion. If excessive leakage cannot be reduced by further tightening the gland, the packing cords must be replaced. This is usually possible without dismantling the pump, although it can be troublesome. First, remove the used sealant. Pulling out the deepest cords can be done using special tools in the form of flexible rods with a thread at the end that can be screwed into the packing. New sealing cords should be installed in the form of sections with a length corresponding to the shaft circumference. Spiral winding of packing material onto the shaft is unacceptable. The places where the ends of subsequent sections are joined should be located on opposite sides of the embankment. After replacing the packing, the stuffing box should not be tightened too much, but the leakage should be initially increased and then gradually reduced. Replacing the packing will not bring the expected effect if the sleeve surface is too damaged (unevenly worn, corroded, etc.). In such a case, the sleeve must be replaced, which usually requires partial disassembly of the pump.

 Unlike traditional rope stuffing boxes, the increasingly used mechanical sliding shaft seals usually do not require any ongoing maintenance. Their use is limited to observing the leak, which should be invisible. When it appears, it is necessary to repair the seal, which, due to the precision of this device, is best entrusted to the manufacturer's service. However, compared to cable glands, mechanical seals are more sensitive to unfavorable operating conditions. Increased shaft vibrations increase the likelihood of mechanical seal failure, therefore, when operating pumps equipped with such seals, the vibration level should be controlled and limited. In addition, mechanical seals fail easily when running dry, so the pump requires careful bleeding before starting.

Bearing maintenance comes down to maintaining the proper level of the lubricating agent (solid grease or oil) and replacing it at the frequency recommended by the manufacturer. Both too low and too high a level of lubricant leads to improper operation of the bearings, resulting in an increase in temperature. It is also important to maintain the cleanliness of the lubricant, which requires checking the seals of the bearing chamber installed in the place where the shaft exits from it. It is unacceptable to operate the pump with water pouring on it or in excessively dusty conditions, as this may result in damage to the seals of the bearing chamber and, consequently, to the bearings themselves over time.

During operation, it is important to check the condition of the pump installation, including checking the tightening of the screws and checking the alignment with the engine. This last procedure should be performed periodically because the initial, correct alignment of the pump and motor may deteriorate during operation. Loosening the screws securing the pump to the foundation leads to an increase in vibration levels, and loosening the screws securing the suction pipeline to the pump flange may cause air to enter the pump.

During operation, the patency of the piping supplying the required media should be checked (e.g., bearing cooling water, barrier liquid for sealing, water drainage from under the relief disc) and ensure that these media are supplied at the required flow rate

During operation, it is important to monitor the pump's operating parameters. An increase in power consumption (or motor current), unless it is related to a change in efficiency, is always a signal of irregularities; it may, for example, be a sign of rubbing of the internal elements of the pump. Similarly, an increase in bearing temperature is an alarm signal. The most common cause in this case is an incorrect amount of lubricant, but the increase in temperature may also result from excessive load on the bearings (e.g. due to misalignment of the pump and motor or due to operation with parameters significantly different from the nominal ones) or may indicate a deteriorating condition. technical bearings.

The hydraulic parameters of the pump, i.e. efficiency and lifting height, should also be monitored. If they change and it is not due to a change in the pump system (e.g. an increase in flow resistance caused by closing the valves), this is a disturbing symptom and usually indicates a technical problem. The pump should operate as close to its nominal parameters as possible, because operation away from them increases vibrations and noise, which accelerates the wear of structural nodes, especially bearings. It is also important to observe the suction pressure because its excessive drop indicates the risk of cavitation. The causes may be too low a liquid level in the suction tank, a clogged suction strainer or suction pipeline, or too high pump efficiency.

Dr. Eng. Grzegorz Pakula

I. Introduction.

Planning pump renovations requires finding answers to two basic questions:
1. When should the pump be sent for overhaul?
2. What parameters should the pump achieve after renovation?

In finding answers to the above questions, an energy analysis of the pump system based on testing the operational efficiency of the pumps is helpful. The level of this efficiency depends not only on the design and quality of the pump, but also on the quality of the pump selection for the pumping system. The energy efficiency of the pump is also a function of time due to the deterioration of its technical condition during operation.

II. Planning pump renovations based on energy consumption monitoring.
Preventive planning of pump overhauls is aimed at carrying out the overhaul before a serious failure occurs, which helps reduce the overhaul costs and prevents emergency downtime of the installation. Such planning is usually based on one of the two most commonly used methods:

1. Planning based on the number of working hours
2. Planning based on monitoring technical parameters

The first method involves using intervals between renovations determined on the basis of the manufacturer's recommendations or the user's own experience. In some cases, the pump renovation period may result from the renovation period of the installation in which the pump operates. Such a situation may occur, among others: for pumps operating in power units, when the renovation of the pump is carried out during the renovation of the entire unit, planned not for the technical condition of the pump, but for the remaining machines and devices
This is a simple method in principle and does not require incurring costs for monitoring systems, but it is usually conservative, i.e. it usually leads to repairs being carried out more frequently than indicated by the actual technical condition of the pump.
In order to precisely determine the moment when renovation is required, planning methods based on monitoring the pump's operating parameters are used. In the energy industry, this usually includes monitoring the vibration level and/or temperatures of specific pump structural nodes.
However, it is possible and even probable that the pump is in good operating condition, i.e. it shows an acceptable level of vibrations and temperatures, but has reduced energy efficiency. Such manifestations of technical wear of the pump, such as increased roughness of the flow channels due to corrosion, enlargement of sealing gaps, and changes in the outlet angles of the blades resulting from wear, do not often result in unfavorable operational symptoms in the form of vibrations, but they do cause a significant reduction in efficiency. In such a situation, it is advisable to carry out renovation despite the pump's operational efficiency, due to the reduction in the cost of energy consumed.

The Powen-Wafapomp SA Group carried out energy measurements of feed pumps scheduled for renovation before it was carried out, which was aimed at determining the extent to which the efficiency may decrease during operation. Some units of feed pumps, for which the efficiency of new pumps should exceed 80%, were to be overhauled with an efficiency of 70%. This was due to significant wear and tear or improper previous renovation.
For example, for a pump operating at the parameters Q = 450 m3/h, H = 1800 m, and at a water temperature for which the specific gravity is 9400 N/m3, such a ten percent reduction in efficiency means an increase in power consumption by approximately 380 kW. Assuming the cost of a kilowatt hour is PLN 30 and assuming 8000 operating hours per year, it can be calculated that the cost of increased energy consumption is PLN 900. PLN per year. This amount significantly exceeds the cost of a major overhaul of this type of pump.
This example indicates that it is worth sending the pump for renovation when its efficiency has deteriorated, even if mobility is maintained, because the cost of renovation will be returned in the form of reduced energy consumption for the drive.

In practice, to determine the optimal moment when the pump should be sent for renovation, it is enough to record the number of cubic meters pumped and the number of kilowatt-hours used to drive the pump. It can be assumed that the cost of operating the pump consists of two main components: the cost of renovations and the cost of energy consumed (other costs, such as maintenance costs, are of a lower order). During operation, it is necessary to monitor how both of these components affect the cost of pumping a cubic meter. If we divide the renovation cost (which can be treated approximately as constant) by the number of cubic meters pumped since the previous renovation, we will obtain the renovation cost per cubic meter. This value decreases during operation as the amount of pumped liquid increases. If the amount of energy used to drive the pump is monitored, multiplying it by the price of an energy unit and dividing it by the number of cubic meters pumped will give us the average energy cost per cubic meter pumped. This value increases during operation due to the deterioration of efficiency due to the progressive deterioration of the pump's technical condition. Adding the renovation cost and the energy cost gives the total cost of pumping a cubic meter. This value initially decreases during operation due to the decreasing renovation component, but at some point it begins to increase due to the increasing energy costs. From an economic point of view, it is advantageous to send the pump for overhaul when such an increase is detected, even if the pump is still functional.

The above method of determining the optimal moment to send the pump for renovation is appropriate under two assumptions. Firstly, the pump operates at approximately constant parameters, otherwise the change in energy consumption may result not from a deterioration in efficiency but from a change in parameters. Secondly, the renovation will restore the initial efficiency of the pump, because otherwise the expenses incurred for the renovation will not be recovered in the form of savings on energy costs.
The example relationship shown above between the cost of renovation and the costs of additional energy consumption due to reduced efficiency indicates that the basic criterion for accepting the renovation should be the efficiency of the pump unit obtained after the renovation. This efficiency should also be the basic criterion for selecting a renovation contractor, because the quoted numbers indicate that the differences in the cost of energy consumed significantly exceed the differences in renovation costs. Each time after renovation, the pump should be subjected to acceptance tests at a testing station in order to check not only its operational efficiency but, above all, its energy efficiency.

III. Assessment of the pump system in terms of energy as a basis for renovation planning.
The purpose of a major overhaul of the pump is not only to restore it to full operational efficiency, but also, and even above all, to obtain the required hydraulic parameters by the pump. This means that the renovated pump should provide a specific performance at a specific lifting height, and operation at such a specific point should be performed with appropriately high energy efficiency. These parameters should be specified in the renovation order, and the client should hold the renovation contractor accountable for obtaining them. For this purpose, after renovation, acceptance tests should be carried out to check whether the specified operating point is met within the specified tolerances.
In practice, renovation is most often carried out as the so-called reconstruction overhaul, during which the initial parameters of the pump are expected to be achieved. Very often, the parameters specified on the nameplate are specified as the parameters required after renovation. This is a simple solution that does not raise any formal doubts, but it does not always give optimal results because in many cases the rated parameters differ from the optimal ones.

This may be due to several reasons such as, but not limited to:
a) A past mistake in determining the required parameters or in selecting the pump
b) Change in required parameters since the initial pump selection
c) Reduction of flow resistance in the system as a result of replacing the fittings (valves, filters, etc.) with devices of a more modern design.

These or similar reasons may prevent the pump from operating at optimal efficiency, causing pumping energy consumption to exceed necessary levels.
For this reason, before ordering renovation, it is advisable to perform an energy assessment of the system in which the pump to be renovated operates. The purpose of this assessment should be to determine at what point in its characteristic curve the pump operates and how this point relates to the point of optimal efficiency. This task is relatively simple to accomplish if the pump characteristic H(Q) is known (change in lifting height with change in efficiency). In such a case, a simple measurement of the pressure increase generated by the pump is sufficient, which allows the estimation of the lifting height. On this basis, you can determine at what point in the characteristic curve the pump is operating. This situation occurs for relatively new pumps, which do not show significant wear, and for which the characteristics measured at the factory test station are known. In this way, you can assess whether the pump is properly selected for the system, i.e. whether it operates at its highest efficiency level.

For pumps that have been in operation for a long time, the situation becomes more complicated because it must be taken into account that the pump characteristics may have changed due to wear. The measured pressure increase no longer clearly corresponds to the performance resulting from the characteristics of the new pump. In such a case, the measurement of the pressure increase can only serve as an indicative indicator of the quality of the selection, allowing for the detection of significant irregularities. In such a case, efficiency should be measured to precisely assess the selection of the pump for the system. In principle, it is also a simple measurement, but its implementation in some cases encounters problems in industrial installations. These problems may result, among other things, from the fact that for precise measurement, a straight section of pipeline of a certain length is required on which the flow meter must be installed. It is not always possible to meet this requirement in an industrial installation. If possible, it is recommended to precisely measure the pump characteristics at the factory test station before the renovation, which allows for a clear assessment of its condition and the operating point at which it was located before the renovation.

The second element that should be taken into account when assessing the quality of pump selection is the system characteristics, without knowledge of which correct selection is impossible. Determining the characteristics of the system requires determining the static lifting head (lifting height at zero efficiency) and the relationship between losses resulting from flow resistance and the efficiency, which is theoretically parabolic. At the design stage, the characteristics of the system can be estimated by calculation, which, however, is always subject to certain errors or deviations related to the adopted safety margin. For this reason, the selection of pumps may be subject to errors, as the pump is often selected with an unnecessary excess of lifting height due to the assumption of a safety margin when estimating flow resistance. The planned renovation of the pump may be an opportunity to verify the computational characteristics of the system. The actual characteristics can be obtained by measuring pressures at several capacities.
The characteristics of the pump system during operation change to a lesser extent than the characteristics of the pump. Therefore, with known system characteristics, measuring the pressure drop in a specific section allows for estimating the efficiency with better accuracy than measuring the pressure increase generated by the pump, and thus for a more precise estimate of the position of the operating point in relation to the optimal point.
By analyzing the characteristics of the pump and the characteristics of the system, it is possible to assess the quality of the selection and, on this basis, decide whether the pump should be restored to its rated parameters after renovation or whether it is advisable to correct its parameters due to the improvement of energy consumption. Such an assessment requires knowledge and experience in pumping system audits.

It should be emphasized that pump operation beyond the optimal point causes negative consequences beyond the increase in energy consumption. There is also an adverse effect on the durability of the pump. Energy losses occurring in a pump operating near the optimal efficiency point are mainly volume losses (return flows through hydraulic gaps) that cannot be completely eliminated, as well as impeller wading losses and friction losses in the flow through relatively narrow channels of the hydraulic system. However, when operating away from the optimal point, losses occur due to internal turbulence in the pump. Unlike the previously mentioned ones, these losses are a serious source of vibration forcing, which has a devastating impact on the technical condition of the pump. Therefore, by operating the pump beyond the optimal operating point, we not only lose energy, but also use it to activate the mechanism that destroys the pump.

IV. Methods for correcting pump parameters during renovation.
If, as a result of the analysis of the pump parameters, it is found that it is not properly selected for the system, it is advisable to make appropriate corrections during the renovation. There are ways that do not require significant expenditure and can be performed within the scope of a basic renovation. This includes selecting the appropriate rotor diameter. By rolling the impeller, the pump lifting height can generally be reduced by approximately 20% without significant deterioration in efficiency, which results in a significant reduction in power consumption. Therefore, it is an easy-to-implement method of reducing the parameters of a pump selected with an unnecessary excess of lifting head. The range of optimal efficiencies shifts towards lower efficiencies when the rotor diameter is reduced. Determining the optimal impeller diameter requires experience. It is also possible to increase the pump parameters by using an impeller with an above-standard diameter, which is possible to some extent by using the machining allowances present on the casting. Please note that changes to the impeller diameter should be made in consultation with the pump manufacturer. A significant change in the dimensions of the rotor leads to a change in the critical rotational speeds of the rotating assembly. Moreover, due to the inevitable inaccuracies of casting technologies and the resulting uneven distribution of casting weight, each rotor after machining to its final diameter must be dynamically balanced, preferably together with the entire pump rotating assembly. For this reason, corrections to the impeller diameter should only be undertaken by plants with the appropriate equipment.
It should be emphasized that changing the rotor diameter during renovation does not generally affect its cost, and may allow for a significant improvement in energy consumption. Therefore, it is an almost investment-free opportunity to achieve energy savings, because the only expenditure in this case is the expenditure on system analysis.
In addition to the commonly known method of correcting parameters by changing the outer diameter of the impeller, there are also more sophisticated methods of rotor machining that allow for changing the pump characteristics.

Belong to them:
a) Changing the outlet angles of the blades by the so-called their "undercut"
b) Changing the angle of the blade outlet edge in the meridional section by oblique rolling
c) Sharpening the edges of the blades
d) Flattening of the impeller inlet
e) Correction of the geometry of the inlet part of the blades

These procedures, performed together or separately, allow not only to change the nominal parameters, but also to some extent change the slope of the characteristic and change the anti-cavitation properties of the pump. Developing a design for a rotor machined in a special way requires significant construction knowledge, and if it is to bring the desired results, it should not be undertaken by people without experience in this field. As with simple diameter turning, or even more so, it requires appropriate plant equipment.
If the correction of pump parameters should go beyond the scope possible by changing the method of rotor machining, further modifications should be made. For multi-stage pumps, a natural solution may be to change the number of stages, which allows the pump's lifting height to be changed without changing its optimal efficiency. For some pumps, manufacturers have different versions of flow systems (impeller or impeller-director) that can be installed in the same pump. It is therefore possible to change the version of the flow system during renovation, thus achieving a better adaptation to the requirements of a given pump system.
An even more far-reaching method is a general modernization of the pump, which involves redesigning its elements to new parameters. This usually involves retaining the existing bodies and replacing the internal components. However, the economic sense of this type of treatment should be carefully analyzed. The cost of developing a good hydraulic design and modeling for new castings is significant and difficult to justify in the case of individual modernization. (it is different if, as described above, an alternative flow system is created with multiple uses in mind). It should also be borne in mind that the scope of changes in parameters that can be achieved by maintaining the pump bodies and replacing its internal elements is limited because the bodies, and especially their connectors, are designed for specific capacities and pressures. Deviating too far from the initial parameters may result in deterioration of efficiency (too high flow losses) and even a serious failure if the strength limits of the structure are exceeded.
If we are dealing with a case of a drastic failure to adapt the pump parameters to the requirements, the optimal solution is often to replace it with a different type, despite the costs involved. An analysis of the costs of excessive energy consumption often shows that it is profitable.

V. Formal and legal aspects of renovation.
The pump is legally in operation on the basis of documents issued by the manufacturer when the product is placed on the market. Since the implementation of the EU product safety assessment system, the documents formally required for the operation of the pump unit are the manufacturer's declaration of compliance with standards and the CE marking. The manufacturer has the right to stipulate, and generally does, that in the event of significant interference in the structure of the pump, for example during an overhaul involving the replacement of essential elements, these documents become invalid and the manufacturer is not responsible for further safe operation. Therefore, if the renovation contractor went beyond the scope allowed by the manufacturer in the operation and use manual, the renovation contractor should re-analyze the safety of the pump unit and issue its own EC declaration of conformity.

VI. Checking the pump parameters after renovation.
As shown in the example above, differences in pump efficiency can lead to higher energy costs than the renovation cost. Even a seemingly slight deviation of the efficiency of the pump unit from the expected value has a serious impact on the cost of energy consumed. It should be noted that the differences in pump efficiencies obtained after renovations carried out by companies at different technical levels may be significant. Moreover, what is important is not the maximum efficiency value at the optimal point of the characteristic curve, but the efficiency value at the operating point. It is worth emphasizing that the decrease in operational efficiency may result not only from poor quality of renovation leading to reduced maximum efficiency, but also from poor selection of the system. For typical pumps, a drop in efficiency of 3% usually occurs when operating with an efficiency that differs from the optimal one by 10-15%.
This means that in order to avoid unnecessary electricity costs, the acceptance of the pump after renovation should include energy measurements to check whether the pump reaches the specified rating point and whether it has the required efficiency at this point.

VII. Summary.
Planning pump renovations should be based not only on the monitoring of operational parameters, but also, and even primarily, on the basis of monitoring energy parameters.
Before ordering renovation, it is advisable to carry out an analysis of the pump selection for the system in order to determine whether the pump's rated parameters are optimal. Pump renovation is an opportunity to correct its parameters, which in many cases can be done using methods that do not require significant expenditure.
Acceptance tests of the pump characteristics after renovation are necessary to determine whether it reaches the rated point and whether it has the required efficiency at this point, because the economic consequences of even relatively small deviations are serious.

Dr. Eng. Grzegorz Pakula