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Old 07-06-2019, 04:30 PM   #1
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Post Fresh water pump sometimes keeps running but only sucks air.

I have an intermittent problem I my Ď95 Roadtrek. The fresh water pump will sometimes run and run without pumping water. I suspect an air leak somewhere but itís hard to track down because it is intermittent. Sometimes after driving for a few hours we will hear the pump running when we turn the engine off. This canít be good for the pump. The pump has been replaced by one of the previous owners, perhaps in an attempt to fix this problem. I ran across another post addressing flooding which is actually a different problem, but which I have also experienced.
http://www.classbforum.com/forums/f5...html#post96061
The use of a timer as suggested in that post may just solve both problems for me. I am making this post with a different title for the benefit of anyone with the first problem I described above.
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Old 07-06-2019, 06:13 PM   #2
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The pump is pumping without you opening a tap or flushing, correct?

If you open a tap when you first hear it, do you get air or water?

I experience this when I'm getting ready to go out, have drained freshwater
tank completely after last trip, filled up for new trip. Takes a while for the system to get back up to pressure. But then I'm getting air out of the tap. So that seems normal. Once pressurized the only time I get the pump turning on by itself was when I had a leak somewhere causing the pressure in the system to drop and then it would only run for a second or so.
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Old 07-06-2019, 06:58 PM   #3
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Well it can be anytime. Sometimes it will pump water ok for a while when the faucet is open then suddenly pump air for a while. Maybe just a second or two or sometimes longer. Same for flushing the toilet. No consistency to it. I suspect the times it has been running for a long time is after the toilet has been used while I am driving. (Not to point any fingers at anyone of course)
I always open the faucet after filling the tank to bleed the air out before we start a trip. I have not seen any evidence of a water leak so far. It seems like when this happens it sucks air in but will not create enough pressure to trip the pressure switch. .
Sometimes I can stop it by opening the faucet to let the air come thru and allow water to get to the pump. It is almost like a vapor lock in a fuel system. Bleed it off to get the liquid in. Other times just turn the pump off and try again later.
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Old 07-06-2019, 07:18 PM   #4
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Originally Posted by blackbourn3704 View Post
Well it can be anytime. Sometimes it will pump water ok for a while when the faucet is open then suddenly pump air for a while. Maybe just a second or two or sometimes longer. Same for flushing the toilet. No consistency to it. I suspect the times it has been running for a long time is after the toilet has been used while I am driving. (Not to point any fingers at anyone of course)
I always open the faucet after filling the tank to bleed the air out before we start a trip. I have not seen any evidence of a water leak so far. It seems like when this happens it sucks air in but will not create enough pressure to trip the pressure switch. .
Sometimes I can stop it by opening the faucet to let the air come thru and allow water to get to the pump. It is almost like a vapor lock in a fuel system. Bleed it off to get the liquid in. Other times just turn the pump off and try again later.

We have found similar can happen when driving if a faucet or toilet is used but only if the tank is low on water so it sucks a bit of air. Never have seen an issue if the tank if more full so sloshing doesn't uncover the water outlet.
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Old 07-06-2019, 08:01 PM   #5
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Hmmm. Well I don't know pump mechanicals at all (i.e. can a faulty pump suck in air?) but it would seem that booster's comment about the fresh water tank is the logical place I can see air entering the system after it has been primed/pressurized. Either from a tank too low on water or perhaps the draw hose in the tank not actually down where it's supposed to be.

Any piping in the system could allow air in, but if it's on the pressurized side of the pump wouldn't water leak out there as well making the defect obvious? I suppose that it's possible on the feed side of the pump but I would guess there would be signs of water leaking there also.

Hopefully someone with more knowledge than me can help you troubleshoot it.
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Old 07-06-2019, 09:46 PM   #6
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I would check the suction side plumbing.
Especially, if it has one, a now 24 year old dome shaped supply strainer. My 18 year old strainer developed a broken tab a couple of years ago. I didn't recall hitting or running over anything that would have caused it, but could have without knowing it(small Áritter?).
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Old 07-06-2019, 10:39 PM   #7
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I would check the suction side plumbing.
Especially, if it has one, a now 24 year old dome shaped supply strainer. My 18 year old strainer developed a broken tab a couple of years ago. I didn't recall hitting or running over anything that would have caused it, but could have without knowing it(small Áritter?).
I agree.
Those clear plastic strainer covers that many pumps have are susceptible to freeze damage. Even if you blow them out thoroughly, residual water tends to seep back from the pump and freeze, sometimes causing cracks in the brittle plastic.

I have taken to removing them entirely as part of my winterization blow-out regimen.
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Old 07-06-2019, 11:18 PM   #8
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I have a '95 PleasureWay with a similar problem. I can pump water with no problem, but the pump sometimes likes to continue to run when all taps turned off (It doesn't hold sufficient discharge pressure to turn itself off) Problem was a suction leak at the pump intake filter. The filter is removable with a slight turn and pull and, after so many years, it doesn't like to seal completely when I put it back on. I wrap a little electrical tape around where the two plastic pieces(that hold the filter screen) fit together to ensure no air leak and have no further problems.
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Old 07-07-2019, 01:27 AM   #9
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Thanks all for the inputs. I assumed there was a filter somewhere, but don't know its location. I just looked at the pump and it is not there. Must be underneath some where. I'll have to drag out the "yoga mat" and slide under for a look see. Here is a pic of the pump.
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Old 07-07-2019, 03:55 AM   #10
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I have the same problem (to lesser degree) on my '2012 Airstream Avenue. Debris filter clear, even tried a new pump. Never a problem if I keep the fresh water above 2/3rds. So I just top it off more often and the problem stays away.

If I was to boondock for several days, then it would be a bigger problem that I'd have to address. Getting to the filler tube is not an easy matter.
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