Very strange short cycling

[Tab a]

Had to replace shallow well pump in a very small house. Old pump was half horsepower and burned up as resident didn’t pay attention to noises it was making (foot valve was bad ). New pump (rebuilt) is one HP. Pressure tank is 30 gallon and has an air pressure of 22.

With the system completely drained down, turning on power to pump causes the pressure switch to immediately rapidly turn on and off. Pressure on the gauge while this is happening is about 60 psi. When power is turned off that gauge pressure immediately drops to about 30 psi. By increasing the cut in pressure on the pressure switch I was able to get it to pump up without short cycling. However, after the few seconds it took to pump up, it again, began to short cycle. Turning off the power, then showed the pressure was about 55 psi and that did not fall over time. I checked the gauge and it’s OK., And I replaced the pressure switch with a new one 30/50. What none of us can figure out is why the pressure is immediately showing about 60 but when power is removed drops immediately to 30.
Thanks for your thoughts!

 

[Valveman]

Sorry for your problem. Sounds like you have a check valve between the pressure tank and the pressure switch?

 

[Sponsor]

 

[Tab a]

Sorry for your problem. Sounds like you have a check valve between the pressure tank and the pressure switch?

No, only the foot valve at bottom of well

 

[Reach4]

How about posting a photo (900 pixels, 200 kilobytes, max I think) that includes the pipe coming from the well, the pressure switch, and the pressure gauge , and the input to the pressure tank.

 

[Tab a]

Had to leave town for a day and won’t be back there until tomorrow afternoon. Don’t think it’s unusual—and has worked for the last 18 years. About a foot of 1 1/4 galv pipe from well to pump, 3/4” pex from pump, for about a foot, then 1/2” pex to tank/house piping. Pressure switch on the pump. Thanks

 

[WorthFlorida]

Does the pressure tank have a bladder? Did you completely drain the tank, set the pressure before turning on the pump? Is this one of those all in one pump and tank setup?

 

[Valveman]

As was said, next thing to check is the tank. Picture would help.

 

[WorthFlorida]

The rapid on/off indicates the bladder is broken causing the tank to completely be full without any air to hold a steady pressure. It probably what burned out the other motor. Did water spit out the Schrader valve? If yes the tank bladder is broken.

 

[Tab a]

Does the pressure tank have a bladder? Did you completely drain the tank, set the pressure before turning on the pump? Is this one of those all in one pump and tank setup?

Yes the tank has a bladder and yes the system was drained when the pressure was checked. Bled some air from the Schroeder and no water came out with air. Talked to the tank manufacturer people yesterday and they don’t think tank problems would cause these symptoms. Tank is separate from pump. Just talked to a pressure switch tech who suspects the pressure switch is being “ slammed” by the volume from the one horsepower pump, causing the short cycling. I can’t make it all fit, but it’s a better explanation than I’ve got so far.

 

[WorthFlorida]

Thanks for the update. In the first post you wrote the tank was 22psi. Was it a typo? For a 30/50 the tank empty it should be 28psi. You mention the cut in was increased but it didn't help.
Possibly the new foot valve is not closing and water is going back down the well shown by the pressure gauge, however, I don't think it would short cycle that fast.
This slamming effect could indicate it's a water hammer iis going on through out the home. Once short cycling starts does it ever stop without opening a faucet? During short cycling and opening a faucet is the water flow pulsing and slowly run steady as the pressure stabilizes? If yes I think the 1hp motor is too much. The pressure switch tech may be right. Going back to a 1/2hp motor maybe the solution. Did you up the hp because there wasn't a 1/2 rebuilt available?

The Valveman, Cary, has a company that manufactures a cyclic stop valve (CSV) https://cyclestopvalves.com/.

 

[Bannerman]

suspects the pressure switch is being “ slammed” by the volume from the one horsepower pump,

A properly functioning pressure tank should be acting to absorb the volume from the pump as fast as the pump can supply. Unfortunately, you have 1/2" PEX feeding the pressure tank, which will significantly reduce the supply rate to the pressure tank.

The pressure switch (PS) connected directly to the pump, would detect higher pressure while the pump is operating compared to when the PS is sensing tank pressure. When the pressure switch is sensing pressure at the tank tee, the pressure tank will also act to buffer pump pulsations.

Was the pressure switch for your old pump, also sensing pressure directly from the pump?

The usual recommended tank size, will require the pump to operate for 60-120 seconds to raise the pressure from the pressure switch Cut-In pressure (30), to the Cut-out pressure (50) while no further water is being consumed. Your 30 gallon pressure tank will only contain approx 8 gallons of water when the pump shuts off at the Cut-out pressure and so that tank would be appropriate for a pump that is capable of supplying 4-8 GPM.

 

[Valveman]

Like Bannerman says, small pipe between the pressure switch connection and the pressure tank can cause bouncing. Installing the pressure switch close to the tank usually fixes that problem.

 

[Tab a]

Thanks for the update. In the first post you wrote the tank was 22psi. Was it a typo? For a 30/50 the tank empty it should be 28psi. You mention the cut in was increased but it didn't help.
Possibly the new foot valve is not closing and water is going back down the well shown by the pressure gauge, however, I don't think it would short cycle that fast.
This slamming effect could indicate it's a water hammer iis going on through out the home. Once short cycling starts does it ever stop without opening a faucet? During short cycling and opening a faucet is the water flow pulsing and slowly run steady as the pressure stabilizes? If yes I think the 1hp motor is too much. The pressure switch tech may be right. Going back to a 1/2hp motor maybe the solution. Did you up the hp because there wasn't a 1/2 rebuilt available?

The Valveman, Cary, has a company that manufactures a cyclic stop valve (CSV) https://cyclestopvalves.com/.

I used a one horsepower pump because that’s what I had on the shelf, but will be going back to a half horsepower when I get one. As I recall, the original tank pressure was 26 to 28. Raising the cut in pressure of the original pressure switch did allow the pump to start without short cycling, but it still short cycled at the cut off range. Later, I tried lowering the tank pressure to 22 just to be sure it was below The cut in pressure of the switch.

I never tried opening a faucet while it was short cycling, but I did try leaving a faucet or two open prior to turning on the pump and that didn’t stop it from short cycling.

I have multiple rentals, all with shallow wells, and similar set ups. All are piped with half inch pex, and I think all have half horsepower pumps. Several 1/2 hp pumps have worked fine in this rental with the current pex set up. All had the pressure switch on the pump.

I did have some concern about the size of the pex with the one horsepower pump. I could fairly easily change pex to three-quarter inch from the pump to the tank, and then half inch off of that. Wonder if that might help?

As an aside, just to get water running temporarily, I installed a used one half horsepower pump that was reputed to work fine. Turns out it does work, but will not build pressure higher than 30 psi. It does not short cycle in the current set up.

Thanks again!

 

[Bannerman]

I could fairly easily change pex to three-quarter inch from the pump to the tank, and then half inch off of that.

Better yet, replace the 1/2" with 1" or larger. The 1/2" AFTER the pressure tank is not an issue.

Suggest also moving over the pressure switch to the tank tee. If you don't wish to relocate the actual pressure switch, which will involve extending the wiring, the PS may remain where it is currently located on the pump, but replace the sensing tube with a longer version to allow the sensing tube to be connected at the tank tee.

 

[Valveman]

I am surprised a 1/2HP doesn't bounce the switch. The smaller pump just isn't quite surging the pressure enough to bounce the switch. The pressure switch should always be close to the tank. Really the only way it works having the switch mounted on the pump case like they do, is if the tank is attached to a tee directly on the discharge of the pump.

If you have multiple rentals and 1/2" pex, you also have multiple problems with cycling and low pressure. Adding a CSV1A Cycle Stop Valve to the discharge of the pump still requires moving the pressure switch or sensing line to the tank or at least to the CSV1A. That needs to be done anyway. But then the CSV would stop all the bouncing (cycling), the strong constant pressure would push more water through the 1/2' pipes and make showers stronger, and the pumps would last longer.

 

[Tab a]

If you have multiple rentals and 1/2" pex, you also have multiple problems with cycling and low pressure.

Not sure exactly what you mean by this? I've never had short cycling problems prior to this, and have replaced the pump at least once in all properties, over the last 20 years. All the pumps I've ever seen around here have the pressure switch and sensing line mounted on the pump, not on the tank (which is not to say it's the right way to do it ). May have something to do with the fact that in all cases the pump is within a foot or so of the tank?
Thanks

 

[Bannerman]

Valveman said problems with cycling, not short cycling.

Pump's are designed to run continuously, 24/7. It is the repeated cycling On/Off that reduces the lifespan of the pump, pressure tank, foot valve, pressure switch etc.

A 1/2" connection before the pump pressure tank, will act as a bottleneck, reducing the flow rate from the pump. Due to the restriction and the fact that pump's boost pressure, the pressure switch at the pump will sense higher pressure while the pump is operating than is actually within the pressure tank, so the pressure switch will shut down the pump prematurely before the pressure tank has been fully filled to the shutoff pressure.

Although most pumps commonly cycle while water is being utilized, with the pressure tank filled to less than its maximum capacity, cycling will be more frequent than it would normally be. Increasing the supply line diameter to the PT will reduce/eliminate the bottleneck, permitting the PT to be filled more rapidly, and in moving the sensing connection to the pressure tank tee, the pressure switch will sense the actual pressure at the pressure tank instead of the boosted pressure directly from the pump while it is running.

To further extend the pump's and other components useable lifespan, while also supplying constant water pressure for your tenants, consider adding the CSV1A Cycle Stop Valve that Valveman recommended above. With a CSV, as long as 1 GPM or higher flow rate is being used, your existing pump will operate continuously without cycling.

 

[Tab a]

I see what you're saying--maybe it explains what I found:

My pump guy did unusually fast work (needed a replacement impeller) on the original pump, and I put it back in this morning. Pumps great, with no short cycling, at either end of the pressure range. So I can only assume the 1 HP size was just too much for the way I have it set up.

But, noticed that it will pump up to about 50 psi (30/50 switch), shut off, and gauge will immediately read about 40--and will hold fine if no open faucets. It may have always done this and I just didn't notice. Have learned through all this that it 'should' hold about where it shuts off (50). I also noticed that my memory was faulty: The pump is just a foot or so from the well, and the tank is just a couple feet from the pump, BUT there is probably about 8-10 feet of 1/2" pex between the pump/PS and the tank. So my set-up is probably causing this pressure 'drop'?

I can move the PS to near the tank but the largest Pex I have is 3/4". Maybe tank-->galv T for PS-->galv T for gauge-->T for 1/2 pex to house and 3/4 pex to pump?

Thanks again--progress has been made!

 

[Bannerman]

noticed that it will pump up to about 50 psi (30/50 switch), shut off, and gauge will immediately read about 40

Just as described above, the 40 psi pressure after the pump is shut off, signifies the pressure tank is only being filled to approx. 50% of its capacity.

The 1/2" bottleneck is restricting the flow rate to the pressure tank, causing the pressure directly at the pump to be rapidly increased, so the pressure switch is sensing 50 psi and is shutting off the pump even as insufficient water is passing through the bottleneck, resulting in the pressure tank to become only half filled. This will cause the pump to cycle at least 2X more frequently than should normally occur for that size pressure tank.

Because the 1 HP pump was capable of a significantly greater flow rate than the 1/2 HP pump, the bottleneck restriction resulted in the pressure at the pump to rise to 50+ psi almost immediately, so the pressure switch was shutting off the pump even as almost no water had yet passed through the bottleneck to the pressure tank. Since the pressure tank pressure continued to remain at 30 psi or less, without the pump running, the pressure in the entire system equalized, resulting in the pump to be reactivated, and so the cycle continued to be repeated ongoing.

Although 3/4" PEX between the pump and pressure tank will offer some improvement over the current 1/2" PEX, a larger diameter pipe would be better. Consider the diameters of the pump outlet and pressure tank fitting as the optimal size of pipe to utilize.

Galvanized fittings will corrode over time. Recommend using either brass or stainless steel fittings.

 

[Tab a]

Makes sense to me!

I'll try the 3/4 pex and see what happens.

Thanks for the advice!