Water pressure switch to protect well pump?

[Pooh_Bear]

There is a type of pressure switch that will cut the pump off if the pressure falls below a pre-set level. The pump cuts on at about 35psi and off at about 65psi and the pressure tank holds pressure on the output lines. If the pressure drops below a pre-set level (20psi usually) it will cut the pump off completely. The pressure should only drop that low if the well goes dry. Otherwise the pump and pressure tank keeps the pressure high enough to keep the switch from tripping. It's a safety mechanism to prevent burning up the pump motor if it runs out of water. Where I live in Chattanooga Tennessee area you can get one of those pressure switches for under $30.

Here's one on Ebay:
WATER WELL PRESSURE SWITCH WITH PUMP PROTECTION

Pooh Bear

[dubman]

The thing is at the moment I just use a gravity storage tank in the attic, with float switch and overflow pipe. This system works well, though I suppose it's not compatible for using with a pressure switch. I was hoping to find some simple solution if possible. I don't suppose there are special float or magnet type switches which could operate at a depth of 20 meters in a narrow bore well? Thanks.

[speedbump]

The B/W floatless liquid level control will do what you need. It's not cheap though. Your probably looking at $250.00 plus.

[Pat]

20 metersof water is roughly two atmospheres or about 30PSI and not likely to squeeze a Styrofoam or cork float. A hollow plastic float small enough to fit in your bore might be small enough to take the pressure but checking with the MFG might be wise.

I have signed my name on the side of a large Styrofoam cup before and then attached it to an oceanographic instrument package that was lowered into the La Jolla trench to a great depth. When retrieved the cup was some distorted and not really symmetrical and was about the size of a sewing thimble with a itsy bitsy signature on it.

I thing 20 meters is a pretty mild depth for any float that is of a slightly robust design.

Alternatively you can run a small diameter plastic tube (such as the tube used for hooking up refrigerators to a water supply) along the wire leading to the pump. This tube would be open at the bottom and attached to either an aneroid switch at the top (in air) or to a pressure sensor. I haven't stayed current wth this product line but Signetics used to make a chip that gave an analog voltage output dependent on the pressure in a tube connected to it. A little signal conditioning would be required. You would need to compare the voltage from the pressure sensor chip to a reference voltage such that when the voltage representing the water depth passed the threshold a relay would open and remove power from the pump.

This circuit should be designed with some hysteresis such that the water depth that would cause the pump to be shut off would have to be less than the water depth required to re-enable the pump to run by some margin. This would keep the pump from cycling on and off over and over as the water level rose a tiny bit and shutting off as soon as the pump started up again. That would cause a premature pump failure.

Pat

[dubman]

oh? I never heard of a water supply for a refrigerator...I did lower a float switch before , don't remember but maybe 50 meters, and it got squashed by the pressure. I suppose float switches are designed to be no more than a few feet under water....

That pipe system sounds a bit complicated - though I was wondering about that..maybe lowering a 2 cm pipe to 20 meters, and when the water level falls below 20 meters, the pressure at the top of the pipe would change, and trip a switch...maybe by suction ???? But then there's the problem of turning the pump back on again, or maybe the best system is just to turn it on manually, because the pump being out of water should be, in theory, a rare event, but obviously a dry run protection system is vital, just in case...

[speedbump]

I'm a firm believer in the KISS method. Especially in water systems controls.

Keep it simple stupid; has worked for me time and time again.

[CJDave]

My extensive background in water supply usually leads me away from threads like this because of all the do-it-yerselfers and the massive amounts of misinformation that seems to swirl around those "experts"; but I'll break my rule and post to this one. The B/W liquid level control is your best bet, and be sure to drop in a third electrode that is connected to the secondary side, ground leg of the B/W control. The third electrode will make it possible to use a B/W in a well and pump system that is all plastic; or otherwise constucted of non-conductive materials. You have a choice as to the secondary voltage on that B/W. If your water is exceptionally pure, I suggest a 440V secondary. There IS an air-aneroid setup as someone mentioned, but those are generally used where massive amounts of floating or entrained crud render a hanging electrode system useless.

[Pat]

Dave, My aneroid unit was to control a sewage lift pump to empty a holding tank for a septic tank output. That pump/motor unit froze up and was replaced with a unit that uses a float switch.

I notice that no one mentioned acoustic ranging or LIDAR. A little fussing and an IR "tape measure" would git 'er done.

Pat

[dubman]

Yea, I like the simplicity of float switches - I use one in the attic tank to get the water from the well. BUT is there a float switch (or something similar) that could be lowered to about 20 meters that could survive the water pressure at that depth? Or are float switches intended for near surface use?

[Pat]

I have seen commercially available float switches based on a varnished cork which should survive the approximate 30 PSI pressure.

If you are handy at all you should be able to make a float switch using a mercury switch or similar.

Pat