13 Common Mistakes of Incorrect Pump Selection 

Correct pump selection is vital to ensure maximum process efficiency, low maintenance costs, and reliability.  

A correctly specified pump can prevent a range of issues from cavitation, a harmful process that causes damage to the pumps internal components, to avoiding unplanned downtime, unscheduled maintenance, and unexpected results.  In addition, choosing the right pump for your needs can increase energy efficiency by up to 20% which makes financial sense for the overall profitability of your business. 

There are a number of factors that should be considered when choosing a pump for your processes but, quite often many of these factors are ignored or not fully understood by the person making the final decision.   

Here are 13 common mistakes associated with incorrect pump selection. 

1. Under or oversizing 

One common mistake in pump selection is often a result of under or oversizing of pumps which leads to inefficient operation which will potentially compromise the system's performance.  

An undersized pump may result in the unit struggling to transfer the required volume of fluid in the time required due to pressure losses.  This leads to fluid recirculating as opposed to being transferred which limits operational output.    

An example could be a manufacturing facility handling high-viscosity fluids which become thicker at lower temperatures. An undersized pump would struggle to maintain the required flow rates to meet production targets as viscosity increases. Other issues which could be encountered include nuisance tripping or failure.  

On the other hand, an oversized pump can result in a number of issues which will reduce its life span.  These could be; 

• Greater flow and pressure than necessary leading to recirculation and dry running 

• Excess energy waste 

• Higher pressure losses if flow produced is greater than that for the recommended pipe size 

• Water hammer and potentially damage to the pipeline and associated system components

Therefore it is vital to consider all system parameters and operating conditions, including possible changes to capacity, diversification, or fluid properties before making your pump selection.  One solution to mitigate potential future changes could be to use a smaller pump to begin with and coupling it with an inverter drive to alter performance as and when it is required, and ensuring supply tanks are correctly sized at 7-10 times the required flow.  

2. Chemical Incompatibility 

Chemical compatibility is a key aspect of pump selection, which affects the lifespan and integrity of the components used within the unit. When components are incompatible with the pumped liquid, such as elastomers or casing materials, it can have a detrimental effect to the overall system leading to material failure which could be in the form of the swelling of components that results in damage, brittleness, or even dissolution.  Any incompatibility can reduce the life span of individual components, or even the whole system. 

Factors influencing chemical compatibility include; 

• The concentration of the chemical to be pumped 

• The temperature at which they're pumped 

• Whether other chemicals are used  

Other chemicals may be ones that the pump may potentially handle, but also chemicals used for cleaning such as in CIP, or solvents used for the dissolving of liquids which harden such as glues.  

Material compatibility ratings use a variety of scales which can range from 'A' for excellent compatibility to 'D' for severe effects, with 'X' representing untested or not enough information available. Despite a material's compatibility with a certain fluid, other characteristics such as flammability or abrasiveness and whether the liquid crystallizes upon contact with air should also be considered.  

The notion that a single pump solution can be compatible with all chemicals is a common misperception as varying liquid characteristics often require different material considerations. Also, with the advent of 3d printing of components, these can often be made from materials where there is a considerable lack of information and testing with chemicals - making their use difficult. 

3. Pump Speed is Too Fast for the Application 

Fluid dynamics is another area that can be impacted by an incorrect pump selection, especially where the pump speed is too fast for the application. Pump speed varies depending on the application, such as intermittent demand in bulk transfer or offloading applications.  It can become particularly problematic in continuous processing applications such as in equipment cooling, fuel feed to generators or engines, or in a Fast-moving consumer goods (FMCG) production facility.    

Viscosity and abrasivity of a fluid can also alter the pump speed required in a given application. Pumping abrasive materials at excessive speed can accelerate pump wear reducing efficiency and longevity as particles contain more force and energy as they pass through a system.  

This is apparent in sand, gravel and grout transfer operations, where excess pump speeds can rapidly erode internal components and shorten equipment's lifespan. Similarly, a pump speed which is too-high can negatively affect product consistency and quality; altering the consistency of substances like paint, yogurt, or creams which can thicken with agitation potentially leading to undesirable differences in finished product.  

A pump operating at excess speed in an application can also cause flow surging or even run dry if tanks are emptied quicker than expected, which could lead to unexpected shutdowns, inaccurate flow and cavitation.  

When handling viscous fluids such as sludge, molasses or heavy oils, a high pump speed may not allow sufficient time for the fluid to flow into the pump casing, reducing pump efficiency and putting the unit at risk of dry running.  

The operating hours of an application, fluid viscosity and abrasivity should always determine the final selection, ensuring the chosen speed and design is in alignment with the application requirement. 

4. Pump Design Not Suited to Abrasive Material 

When handling abrasive fluids, the incorrect pump selection can impede operations and greatly decrease the pumps lifespan. On the face of an application there are often multiple pump designs and variants which can handle a fluid, for example, a pump with internal valves such as an Air Operated Diaphragm design might be chosen for its efficiency and ability to transfer a fluid.  

However, efficiency is compromised when the valves clog or abrasive particles from the liquid being pumped causes damage to internal elastomers. When pumps clog, manual intervention is often required to disassemble units, remove the clog and replace components - which disrupts workflow and increases maintenance costs.  

Another example could be using a pump for mine dewatering where the fluid being transferred contains abrasive particles such as sand or rock fragments. An incorrect pump selection or lack of prefiltration may lead to premature pump failure due to excessive wear and tear, especially in designs of pumps with tight clearances. Similarly, if the pump's design speed is too fast for the application—such as a centrifugal pump running at high speed in a slurry transfer application, it can cause rapid erosion of the components and cause frequent breakdowns.  

Pump selection for abrasive materials requires careful consideration at enquiry stage. Particle type, concentration and size ultimately determine which pump is chosen for the application in order to achieve efficient operation, lowest lifetime cost, and prolong equipment life.  

5. Insufficient Cooling 

Another commonly overlooked factor during pump selection is the possibility of insufficient cooling when operating the pump via a Variable Speed Drive (VSD). A motor fan rotates at the same speed as the motor shaft providing effective cooling to the motor, however when at speeds less than 35Hz the fan rotates too slowly to provide effective cooling, which may lead to overheating.  

Therefore, when specifying a pump for a particular application, all duty points must be considered, especially those that require operation below 35Hz as below these speeds additional fan cooling will be required to ensure the motor is cooled. 

6. Heavy-Duty Design 

A costly mistake in unit selection is overlooking the necessity for heavy-duty design. Heavy-duty pump design is vital for operations that demand long hours of operation, where a process relies on a single unit or there are high discharge pressures, such as in mine dewatering, cooling applications, or in industries where processors operate 24/7 such as in the oil and gas industry.  

Distinctive features of a heavy-duty design are the use of; 

• Additional bearings in the pump housing that decrease the pump's dependency on motor bearings alone to extend its life and reliability 

• Thrust bearings designed to accommodate surges at the discharge end of the pump and keep the shaft in balance 

• Overhung bearing pump design to support the pump head and reduce forces on individual components 

• Oversized pump design to ensure the duty is handled comfortably and not working at maximum capacity at all times enabling operators to increase flow in the future as efficiency reduces.  

Despite these clear advantages, the mistake of choosing standard-duty pumps is often made due to cost considerations or a lack of understanding of real world operating conditions.  

Before making your final pump choice, decision makers should accurately determine the operating requirements and consult with an experienced pump manufacturer who can provide suitable pump design options to ensure the endurance and efficiency of your system. 

7. NPSH Required Is Too High for the Application 

Centrifugal pumps need a specific suction pressure known as NPSHR (Net Positive Suction Head Required), to ensure the desired flow rate is met. If it is not met, the pump can cavitate which is where fluid inside the pump casing begins to boil causing bubbles within the fluid to implode with vast amounts of energy.  This reaction and the vapor released will cause damage to internal components such as casings and impellers and will reduce flow and cause mechanical failure.  

To avoid cavitation, it is essential to ascertain the NPSH available to the pump, known as NPSHA. This should be at least 10% higher than the NPSH required by the pump to account for pump wear and tear, system losses and actual system losses between theoretical and real life installation.  

The NPSH Available can be increased by increase the size of suction tanks, lowering fluid temperature, reducing application altitude and increasing pipework size. The NPSH Required by a pump can be reduced through pump size, speed, by pump design, and through installation design.  

Cavitation can be triggered by high or low flows, low suction pressure, unexpected fluid heating, pump wear, and mismatched parallel flow pumps. Monitoring NPSHR in low NPSH conditions is important, and it is possible to reduce a pump's NPSH by 50-60% through the addition of an inducer. However, this only affects certain sections of the pump curve.  

8. Not Factoring in Changes in Fluid Viscosity 

Selecting a pump without considering changes in fluid viscosity is a common and potentially costly mistake which can easily occur in various industries.  An example in the food and beverage industry would be where a manufacturer may alter the ingredients of a mixture due to changing consumer tastes or ingredient shortages, which can inadvertently affect the viscosity of the mixture.  Alternatively, the oil and gas industry has seen fuels change from Heavy Fuel Oil at up to 1500cst to Low Sulphur Fuel Oil with a viscosity similar to water (1cst).  

A pump selected for a low-viscosity fluid will have insufficient motor power to transfer a thicker fluid at the same pressure and flow as that it was designed for. Furthermore, if fluid viscosity increases too much potentially the pump could operate at speeds too fast to allow fluid to flow into the casing of the pump.  
 
The viscosity of some liquids such as petroleum products – oils or animal fats can fluctuate due to temperature variations throughout the year, affecting pumping efficiency if not accounted for.  

Consequently, selecting the right pump requires a comprehensive understanding of the fluid's characteristics under all possible operating conditions. An application’s future raw material changes as well as storage temperatures of liquids throughout the year should also be evaluated.  

Not factoring in changes in viscosity can lead to inappropriate pump selection, causing potential operational problems like cavitation, increased energy consumption, premature wear, pump failure and insufficient flow or pressure. 

9. Improper Handling 

A common pitfall in selecting industrial pumps is improper solids handling, either by unintentional damage or failure to process them correctly. This is an especially important consideration in the food industry, where the texture and integrity during processing can directly impact the quality of the final product.  

For example, in fruit juice, soup, or sauce production, a pump that damages the solids might be acceptable and desirable to achieve a smoother texture helping to facilitate the next stages of processing. In contrast, incorrect pump selection in pie manufacturing could lead to unwanted damage of fruit fillings compromising the final product's consistency.  

Another issue can be the concept of shear sensitivity. Some fluids can experience shear-thinning behavior, meaning their viscosity decreases under shear stress. In these cases, a pump that generates high shear can drastically alter the material's properties and hence potentially ruin the end product. Others are shear thickening such as creams, and it is imperative that the fluid is handled without unintended changes being made. 

It is always important to understand the pump's minimum and maximum solid-handling capabilities to ensure it meets the specific requirements of the process. 

10. Incorrect Seal Selection 

Selecting the incorrect seal for a pump is a common mistake, which can drastically impact pump performance and often lead to premature failure. For instance, using an open spring seal when an encapsulated seal is needed is a common error.  

Open spring seals, often used for general fluid transfer are less suited for applications involving the handling of abrasive fibrous solids which may get trapped within the springs.   

Another issue can be opting for a single seal when a double seal is required especially in hazardous applications, or during the handling of high-temperature fluids where a double seal system provides extra safety and mitigates potential leakage.  

Similarly, a lack of attention to flushed systems can also result in pump failure. Flushed systems, where a compatible fluid is used to cool and lubricate the seal faces, are important for seal longevity in certain applications but are often overlooked.  

There can also be times when a seal-less pump is the best solution, but this is something only experience can recommend. 

Not consulting with a dedicated pump manufacturer often leads to improper pump-seal selection. Manufacturers possess in-depth knowledge and can provide invaluable assistance in choosing the most appropriate seal type for specific applications.  

Understanding the pitfalls of various mechanical seal design ensures informed seal selections extend pump service life, enhancing system reliability. 

11. Pump Selection based on Price, Not Lifetime Operation 

A common difficulty in pump selection is primarily focusing on the initial price, while ignoring the cost implications of the pump's lifetime operation or the ease in which it can be maintained. 

There are pumps which have a low initial purchase price, but they can be difficult to maintain or spare parts are expensive and need replacing regularly. 

The regularity of spare part replacement can considerably inflate a unit’s lifetime cost, especially when maintenance or down time is also considered.  

It is critical to align expectations with regards to ongoing maintenance and spare part consumption at enquiry stage. Consulting with an experienced pump manufacturer who can provide insights based on real-world applications providing a more holistic approach to the selection process helps align expectations with experience.  

12. Pipework Not Sized According to Pump 

In the design and installation of pump systems, a commonly encountered mistake involves specifying the pipework before selecting the appropriate pump—an improper sequence that can cause substantial performance issues and increased operational costs. The correct method should always be to match the pipework with the pump requirements and not vice versa.  

For example if a 4” pipe is installed within a process, but the most appropriate pump or subsequently selected pump, requires a 6” pipe, means the unit is operating in suboptimal conditions which could potentially cause cavitation, decreased flow, and even premature wear and tear. If outlet pipework is undersized then there can be large inefficiencies due to the amount of pressure required to deliver fluid down a pipe which is undersized causing the pump to work harder and consume higher amounts of energy.  

To achieve optimal harmony between a pump and the overall system is operates within it is fundamental to select the pump first, and then design the pipework to match.  Taking this approach reduces energy usage and prolongs the lifespan of the system. 

13. Temperature of Liquid 

Incorrect pump selection for high temperature fluids also features as a common mistake in industrial pump selection. The temperature of the liquid not only affects the pump’s internal parts, causing some parts such as elastomers at certain temperatures to deform or melt but it can directly influence the pump's priming and the NPSH Available for the pump to operate effectively.  

If a pump designed for high-temperature liquids at low viscosity encounters cooler liquids at high viscosity due a decision by a plant operator to reduce heating energy costs, it can cause the pump to struggle to transfer the high viscosity liquid causing the motor to trip, or insufficient flow. 

At the other end of the scale, should a pump designed for lower temperature liquids begin to transfer high temperature fluids that the pump is not designed for due to a decision to increase the fluids temperature to improve spraying it can cause pump slip or recirculation with some pump technologies. This was an issue we encountered, which you can read about in this case study, Additionally pump seals may not be suitable and could leak or the NPSH available could be lower than that required by the pump causing additional problems. 

In conclusion 

Correctly selected pumps ensure low energy use, extended component life and enhance the operational reliability of units to enable sustainable, cost-effective performance.  Consulting with an experienced pump manufacturer and supplier at the design stage of a new installation will ensure that every aspect of your fluid transfer requirements is taken into consideration and will help avoid any costly mistakes. 

To discuss your pump requirements, get in touch.