We have added a bypass to the tank from the volume pump outlet. This is part of a suggestion from the pump rep where he thinks that the cavitation in the case neck could be alleviated by more flow. Cavitation cause case neck erosion.

By design of the valve system, the pump operates at shut off for some seconds on a pressure up cycle.

We used a welded coupling on a pipe from the volume pump in the tank and connected a 3/8" pipe discharge to the tank bottom so that the pump never runs without flow. Production presses included this bypass pipe after January 2002. There is a slight increase in time to fill and evacuate the dome.

There is another possible remedy. If the configured time for the volume pump is too long and it runs at shut off when the high pressure pump overtakes the check valve in line with the volume pump then cavitation will result. If my memory serves me, the volume pump time was set at 20 seconds. You may be able to decrease this to 15 or less and still have a smooth transition to high pressure. Watch the gauges as the press pressurizes. If the pressure drops as the volume pump shuts off then increase the volume pump time, 1 second at a time until the decrease in pressure is minimal. This will be the optimized volume pump time.

Note that if a large load is followed by a small load then the pressure may decrease as the area above the dome is filled by the high pressure pump rather than the volume pump. However, the volume pump case should not be sacrificed in this scenario.