Water Pump / Pressure Switch won't turn off

Old 07-06-04, 03:20 PM
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Water Pump / Pressure Switch won't turn off


If anyone can help me with this question ... it would be greatly appreciated!!

I have installed a 1/3 hp McDougall jet pump onto a 82GAL bladder tank and this set-up is drawing water from a river. From footvalve to shoreline is approx. 20ft. From shoreline up an approx. 45 degree inclined hill is approx. 45ft. .... and from the top of the hill to the pump is a horizontal run of approx. 110ft. The total line from foot valve to pump is 175ft. The pressure switch on the system is 30 / 50.

The pump is a few years old but the rest of the system is brand new. The pressure switch and pressure guage are new as well. One note about the pump is that there is a plastic "adjustment screw" on the side of the pump which no longer is functional and I can only assume it is turned all the way closed as it cannot be adjusted in any way. My guess is that it may be an air volume control ??
The problem is this ..... With the pre-charge set at 28psi the pump will run but won't shut off. The system holds prime and water is available at the piping, ( It is set-up right now for lawn watering only ) but no water seems to be entering the tank. The pump will run constantly at 40psi but I have to manually stop the pump by pulling the plug to the outlet.

My first guess is that the pump is not strong enough to yield enough pressure to operate the pressure switch to the 50psi cut-off??

That being the case I probably would need to upgrade to a 3/4 h.p. pump.

Right now I have the system working but I have had to lower the pressure in the tank to 20psi.The pump will start at 28psi and run for approx. 10min before shutting off at about 38psi. With this set-up the tank does receive and accept water.

Again , despite my babbling .... my question is why can't I achieve a 50psi cut-off and would a larger ( 3/4 HP ) pump do the trick?

Any suggestions or recommendations would be appreciated.

Old 07-06-04, 03:44 PM
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Although there could be other issues, I think that you nailed it.
I would use a 3/4 hp pump with 30-50 psi for that set-up.
Good Luck!
Old 07-06-04, 04:41 PM
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You say no water is entering the tank. Yet you say it makes 40 PSI.
Is it pumping any water? It could be that it is just not primed.
I have also seen a small piece of debris like a stick or small pebble in the orifice of the jet keep a pump from building pressure even though it pumped water.
Old 07-06-04, 06:56 PM
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The pump is definitely pumping water. It just seems that with the 28psi in the tank, the pump can't offset the pressure of the tank to get to the cut-off point of 50psi. I can adjust the cut-in pressure up but I cannot adjust the cut-off pressure. Again the only way I can get the system to operate where the tank receives water and the switch will turn on and off on its own ... is by reducing the pre-charge of the tank to 20psi. By doing this the pump turns on at 28psi and shuts off at 38psi

This pump originally came from an older system which did have alot of iron build up and scaling. It is probably a good guess that the pump is nowhere near it's peak performance.
Old 07-06-04, 07:01 PM
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By the way guys .... thanks for the prompt replies. Again I appreciate any and all comments and / or suggestions.
Old 07-07-04, 06:19 PM
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A single line shallow well jet pump can only lift water 25' at sea level; you're 45 feet at 45 deg is how much vertical elevation? I see that as part of the problem and hp isn't going to improve that. But the usual cause of a jet pump not building pressure is a blocked inlet at the foot valve or blockage in the jet/nozzel. On many jet pumps there is a plug on the wet end under/above the suction line that you can take out that allows access to the nozzel but some don't have that feature.

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