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Old 23-08-2019, 06:51   #1
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Water pressure - short cycling

I'm sure I'm missing something here - my fresh water system has been acting up. I've cleaned the mesh filter upstream of the pump. I've checked the air pressure in the expansion tank (~50psi).

When running cold water, the pump cycles on and off (faster than 1 per sec). On hot water, even when the hot water tank is not on, it runs normally. Does anyone recommend any resources for me to educate myself to diagnose this problem before I burn out my pump?
Thanks!
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Old 23-08-2019, 09:13   #2
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Re: Water pressure - short cycling

Sounds like the pressure tank diaphragm has split and water is inside the normally dry section. Small air volume inside the tank goes to 50psi and to zero quickly as taps opened.

Turn off the pump, open a cold water tap and drain to zero psi. Then hook up an air pump to the valve on the pressure tank. If (after any more water stops coming out the tap) you get the sound of air leaking, or if the pressure never stabilizes at 50psi then diaphragm has a split.
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Old 23-08-2019, 12:37   #3
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Re: Water pressure - short cycling

50 psi is probably too much pressure. My recollection of most pressure pumps is that they kick off at about 30 psi. The pressure setting is usually marked on the pump and you need to pressure the accumulator to about 1/2 the shut of pressure, which on a 30 psi shut of pump is 15 psi.

If you set the accumulator pressure higher than the pump shut off pressure the pump will shut off before it introduces any water into the accumulator and consequently it cannot "accumulate" any volume of water to feed back into the system to prevent short cycling.
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Old 23-08-2019, 15:17   #4
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Re: Water pressure - short cycling

Quote:
Originally Posted by barold View Post
I'm sure I'm missing something here - my fresh water system has been acting up. I've cleaned the mesh filter upstream of the pump. I've checked the air pressure in the expansion tank (~50psi).

When running cold water, the pump cycles on and off (faster than 1 per sec). On hot water, even when the hot water tank is not on, it runs normally. Does anyone recommend any resources for me to educate myself to diagnose this problem before I burn out my pump?
Thanks!
Can you expand on your comment about the hot water side?
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Old 23-08-2019, 19:47   #5
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Re: Water pressure - short cycling

Mine does this, but I dont have an accumulator. I think the hot water tank acts an expansion tank and holds the pressure better. The cold water side will chatter a lot unless the faucet is opened wide open to keep the pressure low. I assumed it was the older style cheap pump, supposedly the newer ones are much smoother and have a variable pressure sensor or something ?
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Old 23-08-2019, 19:54   #6
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Re: Water pressure - short cycling

There could be some deposits stuck in the orifice of the pressure switch or the switch has gone bad.
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Old 23-08-2019, 20:04   #7
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Re: Water pressure - short cycling

I think Dymaxion is on the right track. The accumulator tank is not doing its job of preventing short cycling. The hot water heater is probably functioning as an accumulator tank on the hot water side, so the hot water doesn’t short cycle.
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Old 23-08-2019, 20:10   #8
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Re: Water pressure - short cycling

Zemurray you need to add an accumulator tank or switch to a pump designed to work without one.

Jabsco makes a variable speed pump that doesn’t need an accumulator tank.
ShurFlo makes a pump that has a bypass that returns excess water back to the intake side. It runs full speed anytime a faucet is open. It doesn’t need an accumulator tank either.
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Old 23-08-2019, 22:40   #9
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Re: Water pressure - short cycling

Quote:
Originally Posted by zemurray View Post
Mine does this, but I dont have an accumulator. I think the hot water tank acts an expansion tank and holds the pressure better. The cold water side will chatter a lot unless the faucet is opened wide open to keep the pressure low. I assumed it was the older style cheap pump, supposedly the newer ones are much smoother and have a variable pressure sensor or something ?
The problem with using the hot water tank as an accumulator is that air gets back into the piping and causes the taps to spit. It'tl blow your tooth paste clear off the brush.
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