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Old 13-03-2016, 11:33   #1
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Loss of prime in fw pump

Sorry, this is my third post today! Having a bad plumbing day I quess. Anyways, my other problem (the last one I hope) is that after draining my freshwater system to replace a 35 gallon water bladder that leaked, I can't get the system to pressure up. It worked fine before I drained it, but now is just a trickle. The pump is a jabsco belt driven diaphram pump that is supposed to be self priming. The motor works fine and the belt is tight. There is an accumulator after the pump. I've run the pump for at least a minute or two with no result. Is their a way to syphon the water through or is the pump toast?
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Old 13-03-2016, 12:38   #2
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Re: Loss of prime in fw pump

Two questions, did the new bladder have a "cap plug" to keep dust out etc. and is the faucet open when you are trying to prime. I am reluctant to believe the pump failed simultaneously with replacement...stout little pumps


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Old 13-03-2016, 12:43   #3
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Re: Loss of prime in fw pump

Is the bladder tank vented?
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Old 14-03-2016, 13:34   #4
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Re: Loss of prime in fw pump

When my freshwater system is pumped dry it will not prime itself until I take the boat out.
For some reason it needs a good shake and rattle to break an airlock that forms someplace...
After it is fine unless run dry.
One of those mysteries I gave up trying to solve, I'm fine with a problem that is actually fixed by going sailing!
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Old 14-03-2016, 14:01   #5
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Re: Loss of prime in fw pump

As Captjcook suggests, open your water faucet about 1/2 way.
Worse case, find the intake line and pour some water directly into it if your tank level is low and you can access the intake.
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Old 15-03-2016, 23:16   #6
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Re: Loss of prime in fw pump

Thanks for the help. I've tried it again with both the filler cap and the faucet open but still just getting a trickle. Will check for an air leak somewhere.
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Old 16-03-2016, 06:21   #7
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Re: Loss of prime in fw pump

One more suggestion...remove the supply line to the pump, see if gravity feed is working, might clear airlock.

On my a/c system (which is on the list to rework, I know why, it is under my head vanity...not much room) I have an airlock that when I clean my strainer...I disconnect discharge, blow back till I hear bubbles at thru hull and suck prime...real pita!

I was thinking your pump would self prime.

Best of luck!


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Old 16-03-2016, 06:54   #8
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Re: Loss of prime in fw pump

Captjcook, I have the same setup. I have a short hose about 4 feet long. I put it on the discharge with a funnel on the other end and pour about a quart of water into the funnel which is held high. That primes the pump. If I am at a marina I use the fresh water hose that I use to fill my tanks or wash the deck. I just stick the garden nozzle into the hose and pull the trigger. If not at a marina I use a jug of seawater and the funnel. Hope that give you an idea!
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Old 16-03-2016, 07:22   #9
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Re: Loss of prime in fw pump

IIRC my dinghy pump sucked in through the same kind of port it blew through.

If you can cobble together an adapter maybe you could use it to suck the water up through your sink tap/faucet.

Not hard to suck an air bubble through with your mouth actually but I might be less squeamish than some.

I have to do it almost every time my tank runs out unexpectedly - which is usually when I'm in the shower, obviously.

Maybe check pipes to pump weren't accidentally reversed?
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Old 16-03-2016, 08:41   #10
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Re: Loss of prime in fw pump

I need to move my pump down an inch, footpump needs to move...which will be replaced this weekend while I replace fw supply and mount my new sw deck washdown pump...might as well have one miserable day on my knees and butt and get it all done...not meaning to hijack this thread...sorry...

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Old 16-03-2016, 16:02   #11
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Re: Loss of prime in fw pump

You probably have a check valve problem. Air is less dense than water so once primed everything seals and holds. We use a shuflo pump for our hydro and when new works great but overtime if you loose prime it won't self-prime. Once primed it holds and works just great until we let the water level run out. It could also be a little piece of fluff or what not stuck in the check valves. Easy to fix.
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