My water pressure measures 80psi. When I shut off the water to the house, it drops to 20 psi. I have had a lot of air in the line since the water company dug up their main line and supposedly fixed some leaks. Would the air in my line explain why my pressure drops from 80 to 20 in about 10 minutes?
Plumbing – could air in the line cause drop in water pressure
plumbing
Related Solutions
Water pressure drops come from two sources:
1) A constriction in the line upstream, limiting the maximum inflow you can get.
2) More demand on the line, producing more outflow than the inflow can fully pressurize.
If a sprinkler zone is larger (serves too many heads), or if more zones are active at once, it will demand more water. Dividing the zone could be one solution.
If a sprinkler zone's pipe is kinked or otherwise obstructed, it may not be able to deliver as much water as is needed to fully pressurize the line.
If running the sprinklers reduces pressure at the sink, the point limiting that is going to be upstream of both, and you're probably also seeing pressure drops at the sink when you flush a toilet or run a bath. You can check for restrictions working back toward the source (valves not fully open, for example), but if the shared flow limit is what's coming into the foundation...
Pressure Switch
I've never seen a "safety cut-off" on a pressure system before, but typically the switching is done by a single box (known as a "pressure switch"). Pretty much all of them (at least from the last ~20 years) look something like this:
The large nut is used to control the pressure (both cut-in, and cut-out) and the small one controls the range between the two.
Finding on and off pressure
First of all, you need a working pressure gauge to be able to do anything, so replace that.
To find the current setpoints:
- Run the pump until it shuts off (this is the off pressure)
- Open a tap or two, and wait until the pump cuts in (this is the on pressure)
Btw, 95psi is really high. Most homes run 40/60 or 50/70. International Residental Code maximum is 80psi (IRC P2903.3.1). Beyond that, you'll potentially start having issues with leaking toilet valves in particular, but other failures are possible as well.
Bladder tank pre-charge
Normally the pre-charge should be set to 2psi below the on pressure, but if your tank recommends setting it the same it shouldn't make a huge difference.
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Best Answer
No, if the pressure is 80 when you turn it off then it would stay at 80 even with air in the line.
You have a leak. It could be as simple as a very slow drip at a garden hose faucet or as complicated as a main line leak.
By the way, this is a very common occurrence; faucets/valves generally leak a bit as they get old. If your piping and fittings are sound then there is no acute danger. If you are worried you should carry out an inspection of your piping system and fittings, looking for tell-tale signs like damp spots, water marks, stains, etc. Also, plumbers have leak detection equipment and procedures that may help.