We have two 6x4 Wemco Hidrostal pumps that have severe vibration problems. They vibrate suction piping, discharge piping and transmit back to each other when only one is running. They vibrate at all speeds, but get worse as the speed is increased. The specific gravity ranges from 1.3 to 1.5 and the temperature is around 46 deg F. There is plenty of NPSH, around 35 feet.

Does anybody have any experience with these pumps, specifically with this issue? I have seen suction piping vibrate and the pump, but never seen it transmitted to discharge piping like this.