Sending chilled water from heat-exchangers, the five pumps, which rack up annual energy costs of £181,400, were found to be showing significant signs of wear, failing to achieve manufacturer performance levels.
With an average load of 45% - equivalent to 2.2 pumps running at any one time - the pumps had even more demands on them during warmer weather, dragging down their Best Efficiency Point.
Pump optimiser Riventa evaluated the horizontal end-suction pumps, which are driven by a motor with an inverter drive to allow control of the flow rate, using its specialist FREEFLOW technology for thermodynamic measurement. This included suction and discharge pressures either side of the pump, differential temperature, and motor input power.
The measurements enabled the calculation of differential head across the pump, hydraulic efficiency and volumetric flow.
Pumps were altered gradually. After each change, a test point was taken, while allowing enough time to obtain the best statistical average. Performance was tested at an incumbent set point, followed by throttling each pump to reduce its flow rate. That allowed other pumps running in parallel to increase in speed to compensate, with a final test point taken at this moment.
By throttling, Riventa carefully observed the maximum possible flow through each pump, without altering the overall flow to the plant. Relative to the manufacturer’s typical performance, data showed the shape of the pump curves indicated severe internal recirculation due to high wear.
“While pumps 1-3 achieved a good relationship between power and flow, pumps 4 & 5 were not performing when at lower flows," Steve Barrett, managing director of Riventa, said. "This indicated a high likelihood of internal recirculation – from high to low pressure parts of the impeller – being caused by high wear.
“Our measurements provided the food processor with a very strong case for robust savings: basic refurbishment with internal coating plus replacement of wear-rings, bearings and seals - or a comprehensive refurbishment, which would also include a new, tailored impeller.
"As energy costs become more of a concern than ever before, food processors can make big savings on equipment such as pumps by having them tested properly. As well as reducing energy bills, companies can maximise reliability and minimise whole life costs."