My Shur-Flo pump has started short-cycling......on/off in 3-5 second intervals. All valving is tight and no leaks detected in lines. Can these pumps fail internally with bad diaphram etc to cause this? Other things to look for?......Thanx.

Lee,
Maybe it can't keep it's prime? Water level very low in the fresh water tank? Only other thing I could think of is a leak in the water system somewhere...

If there is no leak then it sounds like the check valve is bleeding back...

Turn it on, let it run up to pressure and then rap it with a hammer. Does the short cycling stop now?

This kept my pump from short cycling when I was on vacation. When I got back home... I just replaced the pump.

From memory, these pumps have a check-valve which allows them to remain off until the next demand. Do you have a strainer prior to the pump? If not there could be something in the check valve preventing a good seal.
I use a small accumulator tank not so much to prevent short cycling but to eliminate pulsations and listening to the pump and plumbing, I have copper plumbing, in the middle of the night.

My pump did this also. About every 30 seconds it would run for a few seconds. It ended up being the auto-fill valve. For a temp fix I had a shut-off valve I installed right after the auto-fill valve.

An easy to test if it is this valve is unscrew the line off the tank and turn on your pump. If water starts coming out of the line with the auto-fill switch in the off position, the valve isn't closing all the way. Mine was just a dribble but enough to leak down every 30-45 seconds. Very annoying.

I'm assuming you have an auto-fill switch on your Barth. I don't know if all do. It is a nice feature when it works correctly.

quote:

Originally posted by Bones:

I'm assuming you have an auto-fill switch on your Barth. I don't know if all do. It is a nice feature when it works correctly.

I got tired of vinegar therapy and replaced it with a manual valve.

I installed a valve right after the pump on the outlet side. If my pump starts short-cycling, I turn off the valve to see if it is truly a leak or an internal leakdown. The pumps come apart easily, and a little cleanup often helps. The valves can be replaced as a kit. As we are often far, far away, I carry one.

What model of SHURflo pump do you have?

Is it hot to the touch?

Problem Solved!......(yet another one of those self-induced issues

After following thru on everyone's suggestions, I was still having a short-cycling problem. Final step was to replace pump (SHURflo 2088). This was one of those rare occasions when I actually took time to read the installation instructions...For short cycling, the troubleshooting section advised NOT to install restrictive elbows or valving within the first two feet after the pump......

To gain some under sofa storage space, I had recently re-routed some plumbing lines.
Sure enough, two elbows & a shut-off within the first couple feet. I re-did my re-do with a gentle curve of PEX & moved valve further downline...BINGO! Problem solved

Just wanted to pass it along to others...Apparantly, those SHURflo engineers do know more about their pumps than I do

Far be it from me to second-guess an engineer, but our Barth has had 90 deg elbows on both intake and outlet for a decade, and a shut off on the pressure side, as well.

I am running an elderly Shurflo whose 20-year warranty expired several years ago. Interestingly, it draws about half the current our spare does. The spare has been obsolete since '86, but still does fine with the elbows and shut off.

I have enough engineering classes to know that elbows do restrict flow, though. Max flow is not an objective for us, since dry camping requires water conservation. We boondock only, sometimes for months at a time, so it gets a lot of use. It is often a guest house, and the guests are really water-wasters, so that really works it, too.

Pascal's principle says that pressure on a confined fluid is transmitted equally and undiminished in all directions. That tells me that the pressure switch reads the pressure irrespective of flow. On a non-compressible fluid like water, the result would be instantaneous. Pascal also would not explain the distinction of how far away the elbow is from the pressure switch being a factor. Flow is at zero when the switch shuts off, so I would need an engineer to 'splain this to me.

I'm gonna take a WAG and bet that the new pump fixed the short cycling problem because the old pump had an internal leak.

BTW, what model was the old pump?

quote:

Originally posted by bill h:
Pascal's principle says that pressure on a confined fluid is transmitted equally... Flow is at zero when the switch shuts off, so I would need an engineer to 'splain this to me.

My guess, the fittings and the valve equaled out to a loop that wound up trapping air in it. You can compress air, and it would explain the short cycling condition.

quote:

I'm gonna take a WAG and bet that the new pump fixed the short cycling problem because the old pump had an internal leak.

...Can't argue with your physics Bill, that's why my original elbow/valve cobble-job close to the pump outlet didn't concern me. But the new pump is still in-the-box.....All I did was:

1. Turn old pump ON and confirm short cycling
2. Read trouble-shooting guide in new pump box
3. Eliminate some restrictions within 2' of pump
4. Turn old pump on, it ran for 5 seconds, shut off and then it ran only in response to faucet demands.

Don't know the rationale, only the results. Guess I paid $65.00+s&h for a one paragraph suggestion from SHURflo and got a "free" spare pump in the process

quote:

Originally posted by Bill N.Y.:

quote:

Originally posted by bill h:
Pascal's principle says that pressure on a confined fluid is transmitted equally... Flow is at zero when the switch shuts off, so I would need an engineer to 'splain this to me.

My guess, the fittings and the valve equaled out to a loop that wound up trapping air in it. You can compress air, and it would explain the short cycling condition.

You might be onto something with the air. another possibility is that a minuscule amount of air could have been previously sucked in on the suction side and formed enough of an air bubble or pocket to cause problems. A leak like this will be hard to detect, as no water will come out at the site, but suction will pull some air in. And, of course, changing things could have eliminated the leak. Perhaps just a bit of tightening could have done it, too.

My elderly Shurflo hates air. Since I use it to suck water up into the tank, there is a possibility of air getting into the system. I try very hard not to let it suck air, but sometimes it takes a day for the hammering to go away.

My newer (but still obsolete) spare plastic Shurflo doesn't care about air at all.