How much might your pump really cost?

19 December 2016

Steve Schofield explains how lifecycle costing can help to reveal the true cost of a pump.

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The need to cut costs wherever possible is a familiar requirement for food industry engineers. When it comes to pumping systems, choosing the lowest cost option may seem like the best short-term solution to achieving cost savings. However, it will almost always result in additional costs which could be avoided by spending a little more time and money at the specification and design stage.

Pumping systems can account for up to 50% of the total energy consumed by certain industrial processes. Add to this the need for ongoing service, repairs and maintenance throughout a typical service life of 20 years and pumps quickly begin to represent a substantial area of expense.

The expectations of some pump users can be unrealistic when it comes to the cost of ownership. In many cases they focus too much on initial outlay, opting for the least cost alternative, which is not always the best solution.

So what is the answer? The BPMA and many of its members are keen to emphasise the importance of life cycle costing (LCC) as a vital part of any pump purchasing and ownership strategy. Life cycle costing takes into account many factors, all of which impact on the total cost of owning and operating a pump, which includes much more than just the initial outlay.

A pump’s life cycle cost encompasses the total overall costs that accumulate throughout its life, from installation, energy consumption, operation, maintenance and down time, even environmental and through to the final decommissioning and disposal of the pump.

By carrying out an analysis of the costs that are likely to be incurred throughout the operational life of the pump, it is possible to objectively compare all the potential options at the outset.

Lifecycle costing can be useful for selecting new equipment and for justifying the upgrade of existing systems. Throughout the lifetime of a pumping system, it is unlikely that the same operating conditions will continue to prevail.

Factors such as the addition of new equipment upstream of the pump or changes in production techniques can all cause variations in pump duty away from the pumps ‘Best Efficiency Point’ (BEP) - the point where pump capacity and head pressure combine to provide the maximum efficiency performance. If the pump is incorrectly sized and is operating too far from its BEP, wear and tear can occur which can shorten its operational life.

An oversized pump will not only be inefficient, but will also cost more to maintain because operating too far to the left of its performance curve puts an extra strain on pump bearings and seals. A pump which is undersized for the duty may end up running too quickly, which may potentially ruin the product being pumped and prematurely wear out parts of the pump. Its efficiency will also be affected, resulting in excessive energy consumption.

Although a pump should be sized to an application, achieving this is not always straightforward. Involvement of third-parties and the need to meet possible changing future requirements can all affect the sizing of a pump. Over design on parameters is commonplace.

If every party involved in specifying a pump adds on even a small percentage to their sizing estimate, the end result can be a highly inefficient pump. The extra cost, both in terms of running and maintaining the pump can be very high over the life of the plant.

One survey of 4,000 installations showed that water pumps typically operate with a shortfall in efficiency of between 12.5 and 20% because they are incorrectly specified. The situation is worse for pumps that handle more unusual or complex media, such as chemicals or pharmaceuticals.

To help with changes in duty and assist with energy reduction many pump manufacturers are now promoting the use of variable speed driven pump systems, frequency drive being the most prominent system used.

By using variable speed drive’s in effect you are combining electrical and mechanical principles. The addition of the latest controls or ancillary equipment can help boost efficiency and enable pumps to meet changes in demand at a fraction of the cost of building a new system. In some cases, simply upgrading a pumping system can result in energy savings of up to 50%.

Good design

Maintenance and energy consumption represent the two most significant costs throughout the life of a pump. Minimising these costs requires a well-designed pumping system, where the pump is specified as correctly as possible to the demands of the application. The energy consumption and efficiency of a pump is closely linked to the way that a pumping system is designed and operated.

Every pump manufacturer should supply characteristic curves for their equipment illustrating pump performance under given conditions. These curves demonstrate the inter-relationship between discharge capacity, pump head, power and operating efficiency. Looking at the possible energy savings in a pumping system in 2010 the BPMA created the CPSA scheme (Certified Pump System Auditor), an industry specific professional qualification with the aim of creating a universally recognised and respected industry ‘standard' for individuals assessing the performance of a pumping system.

What to consider

Key factors that should be considered when specifying a pump include:

What sort of pump do you need? There are many different types of pump available, each suited to particular applications. The most popular types are centrifugal and positive displacement pumps. Centrifugal pumps are generally suited to fast flowing or low viscosity liquid applications where the pressure is relatively constant. They perform most efficiently and cost-effectively when operating at or near their Best Efficiency Point (BEP). Positive displacement pumps are suited to high viscosity applications, as they are better able to maintain a constant rate of flow.

It may also be necessary to consider what type of material the pump is manufactured from. Hygienic processes in the food and beverage industry, for example, are subject to the strict requirements of the Food and Drug Administration (FDA), which call for equipment to be manufactured from 316L stainless steel.

Is there sufficient pressure for the pump to work effectively? The efficiency and operation of centrifugal pumps, in particular, can be affected by the Net Positive Suction Head (NPSH) available. Basically, this is the amount of pressure that is required to prevent the liquid being pumped from vapourising inside the pump.

If the liquid vapourises, bubbles can be formed which will be carried into the pump. When these bubbles encounter zones of higher pressure in the pump, they will collapse violently, resulting in cavitation which can severely damage the pump. This problem can be designed out by ensuring that the available pressure on the pump inlet is greater than the pressure required within the pump.

Is the pump positioned in the correct place? Where a pump is positioned within a pipeline can affect its performance. As well as determining the amount of pressure available, the positioning of a pump can also affect the quality of the product being pumped. Too much or too little distance in the pipeline before the pump, for example, can lead to friction losses which can affect the flow rate of the substance being pumped, which in turn can affect the efficiency of the pump. The presence of pipe fittings, such as elbow joints, filters or other in-line equipment, can also affect the flow rate of a substance to the pump.

Don’t just purchase on cost alone. When it comes to selecting a pump, cheapest is not always best. Ultimately, the most cost-effective installation will be the one where the supplier can offer good technical back-up, an established track record and a reputation for high-reliability products based on sound research and development.

Always take the pump manufacturers’ advice! They do know best when it comes to ways of getting the best performance out of their pumps.

Steve Schofield is director and chief executive of the British Pump Manufacturer’s Association (BPMA).