Lately, we have provided several Variable Frequency Controllers for constant pressure water system and I have run into the same problem with a few of these. The problem is that there needs to be a means of holding pressure in the system and we are finding that this is not being installed or recommended prior to installing the drive.
The purpose of installing the drive is to maintain constant pressure in the system. This includes when there is no water being used and the drive is at rest or “asleep”. If we don’t have a means of check or holding pressure, the water just races back down the well when the drive stops thus causing pressure to drop and the drive to start right back up. At this point it once again builds pressure to the set point and when the systems is satisfied, shut down repeating this process again and again and again. This not only defeats the entire application but is very harsh on the drive, pump and motor.