Plumbing in the Home/Water pressure on well system
Bit of a conundrum here. Our well has never gone dry in the 20 years we've lived here, and the previous owner / builder stated the same. The kids are gone, so there is only normal use for two people. The submersible pump was changed probably 18 years ago.
In the past few weeks, the pressure has been dropping to zero. The 40-gallon pressure tank is only a few years old and in good shape. If we go down and hold the lever on the pressure switch, the pressure will come up to the point where we can let the lever go and the tank will continue to fill to around 56lbs before the pump kicks off. When we manually do that, the pressure may be fine for days or just until we use up the current tank (like a shower and laundry).
I put a new pressure switch at the pressure tank a couple weeks ago as a first measure; the problem is still pretty much unchanged. The old switch and new were both rated / preset for 40 - 60. The air pressure in the tank was at 18 psi, and I increased it to 24 psi. I'm hesitant to increase the cut-in adjustment since both switches are basically doing the same thing.
When we manually restart the pump, air can be heard moving through the lines until it purges itself. I don't have any reason to believe the foot valve is the culprit.
Our water is clear as always (although there have been times over the years when dirt / sediment can be seen for a couple days, usually after an intense rainy season or melt). The well is about 30 feet deep and, I suspect, the chamber at the bottom is probably big by this time (this property used to be a gravel pit).
Anyway, I'm thinking two possibilities: (a) the pump is going (but the fact that it is responsive to manual restart and that it generates good pressure makes me doubt it), or (b) our water table is changing. I can view at least a mile 'upstream' of my well and there is no construction or other disruptive activity that I can see. I'm discounting the pressure switch(es) as the cause, but that doesn't make it so.
Any thoughts or experiences jump to mind?
It sounds like you have a low pressure cut off switch. It has a lever on the side that has to be raised up for a few seconds/minutes to keep the pump running. When this happens, it's because the pump couldn't keep up with the demand. It's a protection device built into the switch. This tells me that either your pump is not keep up or your water level may be dropping below the pumps inlet.
Eighteen years is a long time for any submersible pump to last. So if it's going, it's to be expected.
The switch is doing what it's supposed to do, so don't blame it. Also, your tank (if it's a bladder tank) should be set to two pounds less than your cut on of 40. So with all water pressure out of the system, set the tank to 38 psi.
You also said you could hear air moving through the lines, that suggests that the water level dropped allowing the pump to get a slug of air.