Originally Posted by
jlisenbe
If the gauge is located between the tank and filter, and knowing that the switch is on the pump, then the gauge is "seeing" the same pressure as the switch. That being the case, then the switch should respond at 20#. But it sure seems that cleaning the filter solved the problem, so good for you.
Your thinking on the filter is flawed. Water will flow through the filter unless it is completely clogged, which is unlikely. There will only be a pressure drop from one side of the filter to the other when water is being used. It might be 35# before the filter, and only 30# after the filter. Once you turn the water off, the pressure will equalize on both sides. It's not a situation where water will not flow through the filter until the pressure gets up to some level of pressure.
If you keep watching the gauge as pressure falls, at what point does the switch cutin on its own? It might be that you are expecting it to cutin at 20 when in fact it won't do so until 17. You can adjust that cutin point rather easily if you want to.