The size of a vacuum pump is dictated by the demand of the washing process. This means that during the milking process there is the potential for the vacuum release valve to be open for long periods, which in turn adds to the running costs of the system.
Vacuum pumps with variable speed drives (VSD) are now being promoted by manufacturers. They automatically reduce the speed of the vacuum pump so that the right vacuum level is provided without the vacuum release valve opening. Energy savings of 30-60% are claimed but they cannot be retro-fitted to all types of vacuum pump.