It is almost impossible to keep a pump system completely drip tight. Those constant pressure pumps do not have any pressure differential between on and off. This means the water in a pressure tank is not doing any good. When the system is always at 50 PSI, you never put any water in a pressure tank, and never get any out. A leak of only a few thimbles of water will make the pump come right back on.
A system with a 40/60 pressure switch is able to use all the water from a pressure tank, as the pressure drops from 60 to 40, before the pump starts. This way even with a little tank that only holds one gallon of water, you get to use the whole gallon before the pump starts.
The leak could be at any connection but, Iíll bet it is the check valves. Even though you have multiple check valves, they will leak back. Sometimes multiple check valves leak back worse than a single check valve. A single check has the entire pressure keeping it closed. Multiple checks split the pressure up where each check only holds a part of the pressure, and doesnít stay closed as well.
If this is a Franklin Sub Drive or Mono Drive, the problem is most likely the check valves. This is because the Franklin units use a pressure switch with only 1 PSI between on and off. That means the switch can open and close up to 2 million times per month. That also means your check valves are opening and closing 2 million times per month. The switch and the check valves donít last very long that way.
If it is a Grundfos or Goulds they use a transducer instead of a switch and is not quite as bad on the check valves. If you have a leaky toilet or dripping faucet, they can also start cycling millions of times, and then the check valves go bad as well.
These are just a few reasons why a Cycle Stop Valve (CSV) makes a much better constant pressure system than any of the variable speed type. You can even use a CSV with the variable speed systems, to take the cycling out of the switches and check valves.