If your pressure switch leaks air continuously, perform the following steps to find the source of the air leak. It may not be the pressure switch at all!
First, disconnect the small copper tube (unloader tube) from the side of the pressure switch at the brass elbow. If you feel air coming from this copper tube, then follow the tube to its other end where it connects to what appears to be a large nut.
This “nut” is the top of an internal tank check valve that threads into the tank (approximately 2 inches long).
The check valve is a one way valve that has a spring-loaded Teflon poppet which holds the air pressure in the tank and prevents it from leaking out.
However, if the unloader tube and check valve are not the source of the air leak, then the pressure switch may be faulty and should be replaced.