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Another well pump question : pressure switch


allanb

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I have a well, with a pump that feeds a pressure tank from which the output leads to (a) a header tank for the swimming pool, and (b) a series of four taps in the garden for irrigation etc. The well pump is controlled by a pressure-sensitive switch on the pressure tank: the on/off range appears to be from about 2 to 4 bar.

The pool was installed about 25 years ago, and to judge by the corrosion on the pipe connections, the whole installation is probably quite old.

My question is provoked by the fact that when I open the valve to the pool header tank, or turn on one of the garden taps, the pressure switch starts to open and close very frequently : about twice a second. So quickly, in fact, that you can hardly see the pump ventilator blades stop before they start again. It makes quite a lot of noise while doing so, and it just doesn't sound to me as though it should be acting like that.

The operation of the switch corresponds exactly with the movement of the pressure gauge needle between the upper and lower limits. I think the gauge correctly reflects what's happening in the system, because if I'm using one of the garden taps I can see and feel the surges in the water flow.

I know almost nothing about these installations, but I wonder whether the problem (if it is a problem) could be caused by having too much water in the pressure tank, so that there isn't enough air to act as a pressure-absorbing buffer. The trouble with this theory is that if I let water out of the tank (there's a tap on the side of the tank. which I suppose is there for this purpose) it doesn't seem to make any difference.

If there was an instruction book, believe me, I would read it, but there isn't. Can anyone help?
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Don't use the pump when the pressure switch is doing this, it will burn the switch contacts, and possibly also damage the pump motor by starting and stopping the motor so rapidly, or burn out the motor if the switch contacts weld together.

It's quite easy to check/replace the rubber bladder in the tank. Switch off the pump, drain all the water pressure by opening a garden tap, and remove the circle of nuts and bolts from the plate holding the bladder in place. It looks a bit like a football bladder, and can be gently pulled out of the tank via the hole.

If the tank is wet inside the bladder has broken. Dry the inside of the tank well before replacing the bladder (to avoid it rusting). Tighten the bolts evenly. Before running the pump, pressurise the tank (around the bladder) with air to about 1 to 1.5 bar by means of the schrader valve in the end of the tank. I have had no problem finding bladders in bricolage or swimming pool shops.

The air pressure in the tank (around the bladder) should be a little less than half the cutout pressure of the switch with the tap open so the bladder can empty - it's no good trying to put air in the tank when the bladder is filled with water and cannot get out.

 

Edit. Correct description.

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Thank you for the replies.  I think the problem was simply that there was no air in the tank.

Apparently I have a different kind of tank : I believe mine has nothing inside it but air and water.  What you wrote about the bladder made me realize that maybe the tank itself could do the same job, by being partly filled with water and letting the air in the remaining space be compressed by the pump.

Following this inspired thought, I took the plug out of the top of the tank to allow air to enter, then opened the tap on the side of the tank (which is about a third of the way up).  Water drained for several minutes; the tank must have been practically full.  Then I closed the tap, put the top plug back in, and switched the pump on.  Bingo.   The pressure rose slowly to the cut-off pressure and everything now works as it should.

Thank you for the inspiration.  I hope this may be useful to anyone else who has no bladder.

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It's a long time since I saw a tank with no bladder. As you deduced, the tap on the side is for draining excess water.

The problems with this arrangement are :-

1) The tank rusts from the inside, not nice for drinking water, nor indeed for water going into a pool.

2) The air in the tank gradually dissolves in the water, and needs regular replenishment.

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[quote user="nomoss"]The problems with this arrangement are :-

1) The tank rusts from the inside, not nice for drinking water, nor indeed for water going into a pool.

2) The air in the tank gradually dissolves in the water, and needs regular replenishment.

[/quote]

Thanks for the warning.

I've heard that you can make water safe to drink by putting Scotch in it.

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