Industrial Pumps Blog

Check out any recent engineering survey and you find many, if not most, installations are fitted with oversized and underutilized pumps. Underutilization is inefficient: it costs the same to operate irrespective of whether the utilization rate is 50-per cent or 100-percent.

It comes down to built-in operational margins that increase between the original design requirements and ultimate pump installation. Designers know the required flow rate, but instead of recommending a pump that fits the flow rate they build in an extra percentage. The engineering team looks at the design recommendations but consider it sensible to allow for a greater flow rate – a safety margin. Already the pump is bigger than required so, there’s added running costs and under utilization: possibly 10-percent or more. Once the pump size has been reviewed and discussed by the various parties in the chain there’s every chance that a pump may be 15 to 20-percent bigger than required resulting in unnecessary initial expenditure and ongoing running costs.

A 20-percent oversized pump is likely to consume around 20-percent more energy, but aside from the extra running costs and under utilization, other factors are involved in fitting oversize pumps. Pumps are designed to operate at full capacity. If the flow rate is 20-percent less than the pump was designed for then it needs to be adjusted to compensate for less fluid to pass through it. Pumps operating at less than full capacity are more likely to need extra maintenance during their lifetime. Underutilized pumps suffer from extra wear. Bearings go out of alignment then the pump starts to vibrate and this makes for further wear. The pump has to shut down for costly repairs and so the flow rate ceases while the pump is being repaired.

The more times this occurs the less efficient the installation becomes and efficiency and costs are interlinked.

Designers and engineers should treat with caution the idea that installing a larger pump will lead to better and more efficient operation.  The reverse is true in many instances, yet review any of the major engineering surveys conducted from time to time and you will quickly learn that the majority of installations are fitted with oversized pumps.

Installing larger industrial pumps than is required, is leading to inefficiencies and increased costs.

So why does this happen?

First of all, everyone involved in the design and selection chain are adding in their own safety margin.  The original design team comes up with a required fluid flow of 100gpm but decides to factor in a 5% safety margin and specifies 105 gpm.  The plant owner takes the 105 gpm and decides they want a 10% safety margin and rounds up the figure, so now we have a pump specification for 116 gpm.  The procurement team tries to source a pump to meet the specification, but one is not available so they go to the next highest capacity, and so the pump installed has 130 gpm.

Without really knowing it, you have fitted a pump with a 30% excess capacity in the mistaken belief that this will improve plant uptime and be cost effective.

Or an oversize pump can simply be fitted because it is what was held in stock at the time.

In any event, why does fitting oversized pumps increase costs and reduce efficiencies?

Larger pumps use more energy all else being equal.  A pump with a 30% increased capacity will consume around the same proportion more in energy than the original design specification.  Energy is not cheap and a 30% hike in usage translates to a materially higher operating cost but the story does not end there.

Additionally, the larger pump needs to be throttled back to achieve the design desired flow of 100 gpm which leads to a directly proportional increase in the pump head.  It is not uncommon when all of this is factored into an efficiency calculation, that an efficiency rating of 50% or less is achieved or put another way, incurs double the energy cost.

Throttling the larger pump back means the installation is operating at a higher discharge pressure which is likely to lead to erosion, wear, misalignment and excessive vibration.  All common sources of non-routine maintenance and sudden failure necessitating increased plant downtime and more frequent maintenance checks.