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Old 18-05-2009, 19:25   #1
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Water Pressure Pump Diagnosis

Hello all,

We recently launched our new-to-us 1982 Hunter 33 and are having problems with the water pressure pump. If we turn on the breaker, the pump starts to run but doesn't seem to build up any pressure. We've tried opening one faucet, two, or all at the same time. No water comes out.

Other things we've tried:

- Disconnected the pump's intake and blew really hard into it. My wife confirmed that bubbles come out from the pick up pipe in the tank (which, BTW, is full). So we assumed there're no blockages in that line.

- Placed thumb in pump's intake while running. I expected to feel some suction on the thumb, but nothing at all. I'm not sure this is a valid test, though. Is it?

- Dissassembled the pump and made sure it was clean. I've never seen the insides of a diaphragm pump, so I can't really tell if everything is in good working order.

- After re-assembly, I blew into both ends of the pump and wasn't able to get any air through. Can I assume that means there's no leaks in the pump?

We're going to get a rebuild kit, but we're really not sure that's the problem. One thing we should've done is to make sure there's no air leaks downstream of the pump.

Another piece of information you may find useful is that the pump also feeds a water heater. The line coming out of the pump goes to the faucet in the head, the faucet in the galley, and the water heater.

For the extra curious, the pump is a SHURflo PRO Blaster, built in Sep/2000.

Can I get an education, please?



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Old 18-05-2009, 19:29   #2
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Does it have a strainer? When mine had that problem, the strainer was clogged with little crystals from the water tank.

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Old 18-05-2009, 19:33   #3
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I turned the boat upside down following the line from the tank to the pump, in hops of finding some kind of valve or strainer. Nothing! The lines goes uninterrupted and directly to the pump. The pump's intake doesn't even have a strainer. I would've thought they'd always have one.
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Old 18-05-2009, 19:34   #4
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try pouring some water into the intake side with the intake hose above the pump. It may need some help getting primed.
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Old 18-05-2009, 21:10   #5
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I had similar symptoms with mine. I called a friend who has lots of experience with boats, he told me it is very common to get air in the lines which keeps the pump from operating correctly, I primed it and it worked fine.
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Old 18-05-2009, 21:36   #6
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If you have the time, try reversing the lower unit where the valves are. Switch it around 180 degrees, so what is now the intake becomes the exhaust, and vice versa. These diaphragm-type pumps only pump in one direction. Possibly yours became reversed?
Re the "suction" test...yes, its good indicator. Perform this test again after reversing the housing.
Finally, sometimes the valves become "cupped", or have microscopic debris that prevents them from seating. A valve-rebuild kit will cure this.
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Old 18-05-2009, 21:46   #7
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I hate trouble with the fresh water pressure pump. After years of that I finally found the solution. The first signs of success I noticed after buying a spare pump. This seemed to help a lot. But the pump broke down anyway. I installed the spare and was angry enough to throw the old pump away. I bought a new spare pump. This was the moment I realized the real solution: I installed that spare pump too, using a 2nd breaker and plumbing it in parallel to the first pump. I never had a malfunction again after that (that's 4 years and counting).

There's a detail that might have to do with this, and I want to mention it although I am sure it's a minor factor. The new pumps I bought are these: West Marine: Sensor Max VSD Water Pumps Product Display

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Old 19-05-2009, 03:50   #8
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The SHURflo “Pro Blaster” 2088 Series is a 3 chamber diaphragm pump*, mostly utilized in Wash Down applications.

These pumps should be self-priming, up to about 6 Ft. of vertical lift.
Ensure that the supply (water tank to pump) piping is not collapsed, and/or leaking air.

These pumps will “stall” against a dead head.
An air-lock (dead head) in the discharge piping, from pump to fixtures can take a very long time to bleed, even with all fixture faucets opened. I installed a diverter valve, immediately after my D.W. Pressure Pump. The “divert” position discharges to open air, allowing the pump to self-prime. Once you get water flow out the divert port, re-set to normal plumbing supply, open all faucets, and be patient. It may take a few minutes to bleed the air out of the distribution piping, whereupon “solid” water (no air entrainment) will flow out the faucets.

* See “Cam Driven Diaphragm” Pump (page 10) ➥

See also SHURflo Instructions ➥
Gord May
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Old 19-05-2009, 07:10   #9
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Just a thought. The newer VSD pumps are a much better option. They are variable speed, and always seem to keep up with demand much better than the old style pumps did. Rather than throw any rebuild money at it, I'd certainly consider replacing it instead.
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Old 19-05-2009, 07:33   #10
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Thanks for all your ideas and comments. As usual with this forum, I received the education I was looking for. You've given me plenty of ideas to try.

Now if I could only put the kids in the freezer and retire, I'd have enough time...
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Old 19-05-2009, 17:41   #11
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Priming the pump fixed the problem. I read in Calder's book that diaphragm pumps are self-priming, so the thought of priming it didn't cross my mind on the boat.

Anyway, a quick prime and the pump runs like winter never happened.

Thanks for your help!

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