Short cycling of well pump when no water is running

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JRehme

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I have a Flotec jet pump that's maybe 7 years old that I'm using to pump water from a rain tank into an RV. It has started short cycling. The weird thing is that it doesn't happen when water is running -- then it runs full-out. But when the water isn't running at all, it short cycles, very fast. I can't understand the principle of what would cause that.

Now, confession time: I don't have a pressure tank in this system. It's running the water for an RV, and I replaced an RV pump with this one 7 years ago and didn't know that this kind of pump is supposed to run with a pressure tank. So, yes, I know the advice is to put in a pressure tank, and in fact I've got one on the way. But it's going to be a pretty big nuisance, because I don't have a great place to put it, so I'd much prefer not to install it. Plus, I don't see how the pressure tank would solve this problem, given that it's happening when no water is running. And -- the system worked fine for 7 years. Yes, there was a bit of short cycling when the water was running, but the water usage in the RV is so low that I wasn't too worried about it.

I already tried replacing the pressure switch, and that didn't change the behavior.

So, my questions are:
1. What would cause short cycling when no taps are open and no water is running?

2. Why do RV pumps not require a pressure tank when jet pumps do?

3. Is there any way of solving this problem without putting in a pressure tank?
 

JRehme

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I hosed out the inside of the pump and that solved it. So apparently the problem was some bit of crud affecting the little hose going to the pressure switch.

So now it does short cycle some while running into the trailer, but it doesn't short cycle when the water is off. Which is what the behavior has been for years. Perhaps I'll get ambitious and install that pressure tank someday, but for now, I've got what I wanted. Hooray.
 

JRehme

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OK, so it's no longer short cycling when there's no water running. BUT -- when I run the water for a while, eventually the pump turns off, and then it takes it a while for it to wake up and turn back on. The water stops completely in the meantime. What could the problem be now?
 

Valveman

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That short cycling that is happening while you are using water is tripping the thermal overload in the motor. It takes a few minutes to cool off before it resets itself and starts the pump again. A pump running a full amps needs to run for at least 1 minute, 2 minutes is better, and running continuous while using water is best. You can get a large enough pressure tank to make the pump run for a minute. Double the size of tank and you can make it run for 2 minutes. But if you have a Cycle Stop Valve the pump will run continuously while using water, and it will still do this even if you only have a little 4.5 gallon size pressure tank. Rapid cycling while using water is just as bad for the pump as rapid cycling while not using water.
 

JRehme

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Yep, I just added a small pressure tank and it seems to have solved the problem. It's a bit mysterious to me why it worked fine in the past without it, but hey, this will make things better all around. Thanks for your help.
 

Valveman

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Yep, I just added a small pressure tank and it seems to have solved the problem. It's a bit mysterious to me why it worked fine in the past without it, but hey, this will make things better all around. Thanks for your help.

You must have had some air in the water lines somewhere, and it was working like a small tank. When all the air gets out of the lines the pump will cycle like crazy. But the pump will probably still cycle while you are using water, unless you use as much water as the pump can produce. The tank will just make it cycle a little slower.
 

Reach4

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Could it be that the pump had a little built-in pressure tank that failed?
 
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