Pump up the savings

Where would you imagine the major costs – and therefore potential savings – associated with a pump would arise? The purchase price? The cost of maintenance? Or the running costs?

In fact, the purchase price of a pump represents less than 5% of the whole life cost, and even maintenance costs amount to only 8% on average. Which leaves the remaining 87% of the cost taken up by energy consumption. And in some applications, energy costs can actually rise to as much as 95% of the whole life cost – which means there are huge savings to be made through more efficient pump operation and more effective maintenance.

But to realise these potential savings, you first need to know what makes pumping so expensive, then how to select the right pump for the job, and finally how best to maintain the pump so it provides optimum performance and maximum energy efficiency.

As already identified, the major factor in the cost of pumping is energy, closely related to long running hours and pump efficiency: which can vary from as high as 90% to as low as 20%. As Fig 1. shows, the operating point (which should be at optimum efficiency) is at A, where the Head/Flow curve intersects the Resistance curve.

The Head/Flow curve tracks the relationship between head and flow, where maximum pressure is achieved with zero flow, and head gradually drops as flow is increased. The Resistance curve represents the actual head and flow potential produced by a given hydraulic system, which depends on the hydraulic characteristics of the pipework, and the distance and height to be pumped. Changes caused by, for example, valves closing or opening will steepen or lessen the resistance curve. However, where the line intersects the Head/Flow curve always represents actual performance of the pump on-site.

Power use is also charted in the graph above, and it can be seen that a centrifugal pump usually displays a rising rate power characteristic. Running a pump to the right of A on the graph risks overloading the motor.

Finally, the Efficiency curve shows that any pump operates at its most efficient (the Best Efficiency Point, or BEP) within a very narrow range. Where the vertical line A meets the Head/Flow curve is the duty point for which the pump is designed, and must be matched to the system characteristic of the site installation to ensure optimum pump operating efficiency. Failure to operate a pump at its BEP can lead to a shorter operating life as well as frequent failures. (See Fig 2.)

Other factors affecting pump performance include wear and tear, caused by abrasive particles in the pumping medium or poor water quality, both of which lead to erosion and corrosion.

Wear to the neck rings, leading to an increase in clearance, will result in leakage and recirculation from the high pressure area of the pump casing back to the suction side of the impeller, resulting in reduced head and flow. Similarly, reduced flow will result from corrosion and scale build-up in the pump casing. And finally, wear or damage to the impeller from abrasive particles, corrosion and cavitation will not only directly affect pump performance but will also cause mechanical imbalance, which will reduce the life of bearings and seals.

A more detailed understanding of how pumps function can be gained at one of the courses or workshop days organised by ERIKS in affiliation with the Pump Centre. Meanwhile, you can counter the effects of wear, reduce the costs of energy, and increase the efficiency of pumps through a clear action plan and scheduled maintenance regime – the cost of which will in most cases be quickly paid back through the resulting savings in energy costs. The action plan identifies steps to take – either yourself or in association with a trusted and experienced supplier – to ensure you achieve maximum life and minimum energy use for these critical assets, and pump up the savings to be made.

Contact your local ERIKS Service Centre on 0845 006 6000 to maximise the efficiency of your pumps.

A
• Estimate the cost of pumping as a proportion of your energy bill
• Target high energy users and known or suspected problem areas
• Use these costs to justify retrofitting of energy-saving features

B
• Develop routine checks and information logging of pump performance as part of the condition monitoring regime
• Consider alternatives to the use of valves for flow control
• Find and eliminate water leaks
• Minimise pumping during process interruptions
• If process requirements are intermittent consider on/off control

C
• If pumps are due for refurbishment consider the application of an efficiency enhancing/wear resistant coating
• Attend to any pump that is cavitating and investigate cause
• Repair leaking seals
• Use information from monitoring to identify problems and schedule maintenance
• Maintain pumps to ensure efficient operation
• Keep records of all pump maintenance
• When replacing a pump do not assume that the original duty was correct

D
• Ensure all pump operators have some basic knowledge of pumping principles
• Make information on any energy-saving initiative freely available to staff concerned
• Estimate savings, costs, and payback potential then data log to confirm