Pressure switches revisited

Q: The drawing of the pressure switch and Rex Cauldwell’s answer to Gregg Eads’s question (Second-floor water pressure) caught my eye. I have a similar-looking switch on my well system, and I’ve never been able to figure out why the switch shuts off if four or more water outlets are open at the same time. There is a small lever on the side of the switch that resets the switch and starts the pump after I’ve shut off all the faucets. But if I have a bunch of people in the house, it’s hard to control how many faucets might be open at one time. Does Rex have an answer for this one?

A: Rex Cauldwell, a master plumber and electrician from Copper Hill, Virginia, replies: The switch you have on your system is called a low-pressure cutoff switch. Like the switch I described in my original answer, a low-pressure cutoff switch is usually set to turn the pump on when the pressure drops to 20 lb. to 30 lb. and shut it off when the pressure rises to 40 lb. to 50 lb. But unlike a normal pressure switch, the low-pressure cutoff model also shuts off power to the pump if pressure drops to around 10 lb. When you draw a lot of water from the system at one time by opening four or more valves at once, the pressure drops below the cutoff level, which cuts the power to the pump until you reset the switch.

Low-pressure switches are designed for low-yield wells, which have a limited supply of water. If a well is low or runs dry, the switch is supposed to shut down the pump so that it doesn’t burn out from running continuously. But these switches are a royal pain, and I refuse to install them. The first thing you need to figure out is why a low-pressure cutoff switch was installed on your system.

I’m assuming that you have a submersible in-the-well pump. It’s possible that the installer put in an undersize pump to cut costs. For example, if a pump rated to 160 ft. is installed at 200 ft., the pump will work fine until the water level in the well is pulled way down. At this point the pressure will drop dramatically just as you’re describing. If you do have a low-yield well, there are expensive, involved ways of getting all the water you need. It’s also possible that you have a jet pump. In either of these cases, I’d recommend that you consult a reputable pump installer for the best solution to your particular problem.