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Author Topic: Help with fresh water pumps not priming  (Read 2374 times)
belfert
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« on: October 22, 2007, 12:20:13 PM »

I have two model 2100 Flojet water pumps in my plumbing system.  They are rated as self priming up to 6 feet suction.  They primed fine with about 6 inches of water in the fresh water tank.  The problem is when I turned off the valves to the tank and tried to pump antifreeze the pumps would not prime. 

Any suggestions on this?  I might just remove the pumps and store inside for the winter as I need to redo all the pumbing anyhow.

Should I have a check valve near the pumps to help with losing prime?  The pumps always took a long time to start delivering water whenever they were turned on.  Part of the problem is due to leaks in my manifolds.

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Dallas
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« Reply #1 on: October 22, 2007, 12:30:49 PM »

Brian,

If the pumps are sucking air from anywhere at all other than the end of the pickup tube, they will not prime well. The more viscous the liquid, the less chance it will have of priming.

when I was using one 20 yr, old Shurflo pump, it would lift water 6' with no problem, until I developed a pinhole leak in the pickup tube. Then it wouldn't prime itself at all.

IHTH

Dallas
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maria-n-skip
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« Reply #2 on: October 22, 2007, 12:58:32 PM »

Brian,
 The only thing I would add is.

 If you have ever had a diaphram pump apart such things as calcium deposits etcetera can keep
 the rubber diaphrams from seating correctly. I just used rubbing alcohol to clean and the
 pumps worked better. The other thing to inspect is to make sure there is no rips or pin holes
 in the rubber.

  FWIW
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HB of CJ
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« Reply #3 on: October 22, 2007, 01:15:22 PM »

Some water pumps are better than others when it comes to pumping from a draft or suction condition rather than from a head or when under water.  Sometimes you have to "fool" the pump into "thinking" it is pumping from a head rather than from suction.

This can be done easily by establishing a condition where the pump always has water above it on the inlet side, rather than having the pump above the water source.  And naturally, even a tiny air leak on the suction side places all bets off.

Finally, some pumps do quite well on water, but for whatever reason (design?) do NOT do well at all pumping stuff that is thicker/heavier than water, such as oils, antifreeze, or thick stuff with trapped air mixed up in the liquid  Good luck.  Smiley Smiley Smiley
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bobofthenorth
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« Reply #4 on: October 22, 2007, 01:37:54 PM »

Something else that helps in the situation where you are trying to lift water with a poor self primer is to design the plumbing so that there is a natural head against the pump.  Nothing fancy, just run the line up as it exits the pump.  That way whatever water is in the system will stay against the pump.  When you have water & air the air will naturally rise through the water and help the pump hold its prime.  It doesn't take much - really all you need to do is make absolutly sure that there isn't a low spot immediately after the pump.  Ideally you would have a vertical riser coming out of the pump but that isn't always possible or necessary.



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« Reply #5 on: October 22, 2007, 07:19:59 PM »

Arrrggghh...

I use Shurflo 5.7 extreme pumps, They will just about pump wet air...

However.. They will gum up in the diaphram area due to dirty water like
what comes out of the city taps. It turns almost fuzzy in there after
about a year. Takes a serious chlorine zap and cleaning of the diaphrams
to solve..

Always Pre-filter anything that you put into the tank with a good carbon filter
system. It saves headaches later.

Pin hole air leaks in the suction line can lead to pump destruction too....

Sorry.. I know it didn't fix the problem...
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belfert
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« Reply #6 on: October 22, 2007, 07:38:31 PM »

My pumps are pretty much brand new.  I just turned them on for the first time maybe four weeks ago.  They have probably 150 gallons of water through them.  I can't see them as being dirty yet, but who knows.  I think I will just pull them and store them inside.

I bought a Flojet Sensor VSD pump to replace these two pumps.  I think I spent about $50 total (Ebay) on the two pumps I have now.

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JohnEd
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« Reply #7 on: October 22, 2007, 11:27:09 PM »

I have a Sureflo that has been going strong since 1990.  Actually only occupied the coach for three years of that time soooo....  I mounted my pump near the bottom outlet so it is forced to injest water and can't lose its prime.  Other than sweating the pump or line failing and letting all my fresh drain, I can't see why you would mount the pump above the tank. 

John
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belfert
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« Reply #8 on: October 23, 2007, 06:05:58 AM »

I have a Sureflo that has been going strong since 1990.  Actually only occupied the coach for three years of that time soooo....  I mounted my pump near the bottom outlet so it is forced to injest water and can't lose its prime.  Other than sweating the pump or line failing and letting all my fresh drain, I can't see why you would mount the pump above the tank. 

The pumps are not above the tank, but next to it.  They are mounted on the wall of the bay.  One is about 6 inches above the floor and the other about 15 to 18 inches above the floor.  When the tank is full the water level is higher than either pump.

This seemed like a good place for the pumps at the time since the manual says they are self priming and can be up to 6 feet above the liquid.  I might have room to remount the pumps below the tank when I redo all the plumbing.
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DrivingMissLazy
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« Reply #9 on: October 23, 2007, 06:25:51 AM »

Take the input connections off and check for debris. It many times happens with new installations.
Richard
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« Reply #10 on: October 23, 2007, 10:43:17 AM »

Belfert,

Hold on there Hoss.  You sound like you have solved your prime problem with a soundly designed installation.  You have a problem not related to height or prime.  The advice about checking for debret sounded really good.  Another post talked about small holes in the feed line.  The feed line can admitt air but not leak water....like a valve in the hole.  And, if you have a restriction along with that leak you have a lead pipe cinch (Sean, jump on that one, OK? Grin) of a problem.   That is something I have seen with fuel lines in the past and a dickens of a problem to isolate.

Just for grins Grin, do two things: 1)  Measure the voltage at the "across" the pump when it is "on".  Pump function falls off dramatically with a small reduction in volts.  2)  Take your pump apart.  4 phillips screws as I recall.  Check for stuff in the pump.

Good hunting,

John
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belfert
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« Reply #11 on: October 23, 2007, 12:56:25 PM »

Just to clarify, I bought the new pump not because of the priming issue, but because the pumps don't work well when they are working.  The pumps worked all throughout my trip and had no issues with priming from the water tank.  The priming issues started when I tired to pump antifreeze through the pumps.

Every time we turned on the pumps during our trip, it took up to two or three minutes to get water of any usable flow.  Even then, the flow was never very much.

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Dallas
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« Reply #12 on: October 23, 2007, 01:07:46 PM »

[q][/q]Every time we turned on the pumps during our trip, it took up to two or three minutes to get water of any usable flow.  Even then, the flow was never very much.[/b]

You may not believe it, and you may not want to hear it, but changing the water pumps out witha newer fancier model isn't gonna help if you don't fix the underlying cause of the problem in the first place.

That under lying cause is that you have an air leak on the suction side of the pumps and that's what allows them to lose prime.
The evidence of losing prime is the lack of instant water at the faucet and low flow.

Oh well, you aren't gonna listen anyway. Throw more money at it instead of fixing correctly in the first place.

Just my 50˘

Dallas
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HB of CJ
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« Reply #13 on: October 23, 2007, 01:21:27 PM »

Again...best quess here is...1) sucking air on suction side.  2) dirt in the works.  3) restrictive plumbing like too small dia. pipe or tight turns, expecially on inlet side.  4)  wrong type pump or mounted too high above water.  5)  no water in tank.  6) no power to pump.  7) no coach.  Smiley Smiley Smiley

We found that running "sweeps" rather than tight diameter turns made a difference on the suction side, along with using larger than necessary suction diameter pipe.  We also ended up using a water filled dedicated vertical "frost riser" pipe between the tank and the pump.  Good luck.
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belfert
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« Reply #14 on: October 23, 2007, 03:23:30 PM »

[q][/q]Every time we turned on the pumps during our trip, it took up to two or three minutes to get water of any usable flow.  Even then, the flow was never very much.[/b]

You may not believe it, and you may not want to hear it, but changing the water pumps out witha newer fancier model isn't gonna help if you don't fix the underlying cause of the problem in the first place.

I'm also going to replumb the entre freshwater system.  I have a number of leaks downstream from the pumps.  I had already replaced all the fittings on the suction side of the pumps the same day I first started up the pumps.  I'm fairly confident there are no leaks on the suction side right now.

The original pumps were a gamble anyhow.  They are only 2.3 GPM and that is why I had two of them installed.  I was just reading the specs again and I see they only go to 27 PSI.  I didn't realize that before and that is probably part of the reason they work so poorly.

Sometimes things don't work out on buses the way we thought they would.  My freshwater plumbing doesn't work the way I designed it so I have to redo all of it except the tank itself.  My plumbing had many leaks and I was only able to fix 50% of them before my trip.  We just turned the pumps on and off as necessary and minimized water use.
« Last Edit: October 23, 2007, 03:34:09 PM by belfert » Logged
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