Deriving greater value through partnership

Brian Huxley, Director of the BPMA, explains how close liaison with manufacturers could help end users enjoy greatly improved levels of performance from their pumping equipment.

Pump manufacturers remain a largely untapped source of knowledge when it comes to the design of pumping systems, particularly from a whole-life-cost point of view.

Brian Huxley, Director of the British Pump Manufacturers Association (BPMA), explains how taking advantage of this knowledge could help end users enjoy greatly improved levels of performance from their pumping equipment.

Any pump manufacturer will tell you that designing a pumping system and specifying pump equipment is not a straightforward process.

Choosing the best pump equipment for an application is complicated by a whole raft of considerations that can greatly affect performance.

When it comes to the design of pumping systems, there are few bodies better equipped to advise what's best than a pump supplier or manufacturer.

Yet surprisingly, it is still comparatively rare for end users to take advantage of the expertise of pump suppliers when designing their pump systems.

Consequently, many users opt for systems that are ill-suited to the demands of their application and only call in the experts when problems start to occur, by which time they have often incurred prolonged downtime and impaired product quality.

There are several areas where errors can creep in when selecting a pump that can potentially trap the unwary.

One area where many problems occur is pump sizing.

Every engineer will be familiar with the process.

You make your calculations, then you add on a safety margin of a few per cent just in case.

First the plant designer does it, then the production engineer adds a little more in case of future expansion.

In the case of pump specification, the longer the supply chain, the bigger the margin becomes, and by the time pump suppliers recommend the nearest available size in their range you can end up with a pump that is going to be very inefficient indeed.

Every pump manufacturer can, or should, supply characteristic curves for their equipment illustrating pump performance under given conditions.

Simply put, these curves demonstrate the inter-relationship between discharge capacity, pump head, power and operating efficiency.

The ideal operating point for a pump is known as the "best efficiency point", or BEP.

This is the point where pump capacity and head pressure combine to provide the maximum efficiency performance from the pump.

If the pump operates too far to the left or right of the BEP, not only may its efficiency be compromised, but it can also be increasingly subjected to wear and tear which could 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.

On the other hand, a pump that is undersized for the duty may end up running too quickly, which may potentially ruin the product being pumped and also prematurely wear out parts of the pump.

Although a pump should be exactly 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.

"Overdesign on parameters is very commonplace", says Peter Staddon, Managing Director of JP Pumps part of Johnson Pump, which manufactures pumps for use in a host of industries including chemicals, petrochemicals, pharmaceuticals and food.

"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".

For pump manufacturers, another common problem is the lack of information with which they are provided by end users when specifying their requirements.

"All too often, we are just provided with information about flow rate and pressure and are expected to work everything else out from there", says Toby Frostwick, Projects Manager, Watson Marlow Bredel Pumps, which specialises in the supply of equipment for pumping difficult solids in a range of industries such as food, brewing and wastewater treatment.

"An ideal specification for us is one that gives information on everything from the type of substance to be pumped through to the materials that the pipeline is made of".

Agreement comes from Paul Mayoh, Technical Manager at steam system specialist Spirax Sarco, which supplies pumping equipment for condensate return systems: "A lot of the information we get is either inadequate or incorrect.

If we didn't go back and ask for further clarification, customers could easily end up with a pumping system that falls short of their expectations or which fails to help deliver maximum plant performance".

Unless the pump will be operating on clean water, arriving at the right specification is further complicated by the need to compensate for the properties of the fluid the pump is moving.

"Specifying a pump might be reasonably straightforward for a water pipeline or an application where the material being pumped behaves in a consistent way", says Frostwick.

"However, for applications such as pumping yeast in the brewing industry, factors like the viscosity or specific gravity of the material being pumped can have a big effect on efficiency".

When it comes to pump specification the same message keeps emerging: "Involving the pump manufacturer at the earliest opportunity is the best way for end users to ensure they get a system that gives optimum performance", says Staddon.

"Time spent early on getting the pump to work properly and eliminating the risk of future problems is time and money saved later on".

Steve Schofield is the Technical Director of the British Pump Manufacturer's Association (BPMA), the UK's primary trade association representing the interests of suppliers of liquid pumps and pumping equipment.

"For many years end users have stated that they will have open 'partnerships' with their suppliers", he says.

But the feedback from BPMA members is that reality does not often measure up to this vision of co-operation.

In spite of this it appears that pump suppliers are still willing to take the risk.

"I truly believe that many suppliers now wish to work more closely with end users on commercial and technical issues", says Schofield.

"To move forward there must be trust and commitment on both sides.

The rewards for the end user are many.

Some end users have true worldwide agreements with suppliers and have some of the most efficient plants running".

The following are just some of the key factors that pump manufacturers recommend considering when specifying the best pump for a given application.

First, what sort of pump do you need? There are many different types of pump available, each of which is suited to particular applications.

The two most popular types are centrifugal pumps 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, on the other hand, are particularly ideal for high viscosity applications, as they are better able to maintain a constant rate of flow.

With their low shear rate, these pumps can help to preserve the quality of certain substances, such as resins, yeast or inks.

It may also be necessary to consider what type of material the pump is manufactured from.

Hygienic processes in the pharmaceutical or food and beverage industries, 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.

Secondly, is there sufficient pressure for the pump to work effectively? The efficiency 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 transported from vaporising inside the pump.

If the liquid vaporises, 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 a phenomenon known as cavitation, which can severely damage the pump.

When designing a pump system, it is essential to ensure that the available pressure on the pump inlet is greater than the pressure required within the pump to avoid the occurrence of cavitation.

Thirdly, is the pump positioned in the correct place? Where a pump is positioned within a pipeline can also greatly affect its performance.

"We always tell people, pumps are designed to 'pump' not 'suck'", says Toby Frostwick.

"Always position the pump as close as practically possible to the fluid source".

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 inline equipment, can also affect the flow rate of a substance to the pump.

Fourthly, don't just purchase on cost alone.

When it comes to selecting a pump, cheapest is by no means best.

Although it might seem the best way to save money in the short term, opting for the lowest cost solution may potentially result in problems later down the line.

Be particularly careful where reductions in the purchase price have been achieved by cuts in supplier backup and expertise.

Ultimately, the most cost-effective installation will be the one where the supplier can offer good technical backup, an established track record and a reputation for high-reliability products based on sound research and development.

Finally, always take the pump manufacturer's advice.

It's surprising how many customers don't take advantage of the expertise available from the pump manufacturer when it comes to ways of getting the best performance from their pumps.

After all, nobody knows more about how to get the best out of a pump than the company that built it.

The British Pump Manufacturers Association (BPMA) will be one of the main bodies supporting Total Processing and Packaging, which will take place at the Birmingham NEC from 29th March to 1st April 2004.

Total Processing and Packaging 2004 will combine the traditional strengths of Eurochem, Interphex, Pakex, and the PPMA Machinery Only show, while placing an increasing emphasis on all elements of the packaging and processing value chain.

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