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.
A typical system should look similar to what is depicted
here:
This is a bit over-simplified but non-the-less shows the
correct placement for the check valve in the system. Without the check valve, there is no “system”
as it is an integral part of the plan.
Scott
