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Old 05-17-2018, 03:33 PM   #1
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Raw water pump - Sanity check

Iím troubleshooting the raw water system on a Next Gen 5.5kw and need a sanity check. For the pump pictured, which would be the inlet, and which is the outlet?

Thanks,
Brett
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Old 05-17-2018, 03:37 PM   #2
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Which hose goes to the through hull?
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Old 05-17-2018, 03:43 PM   #3
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That would be too easy.

The pump can be turned 180 degrees, putting the intake hose on either fitting. To clarify my question, based on the rotation of the impeller, should the inlet be connected to the top, or bottom?
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Old 05-17-2018, 03:44 PM   #4
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Top is inlet
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Old 05-17-2018, 03:49 PM   #5
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Quote:
Originally Posted by Tonic1 View Post
Iím troubleshooting the raw water system on a Next Gen 5.5kw and need a sanity check. For the pump pictured, which would be the inlet, and which is the outlet?

Thanks,
Brett
Out at the bottom of the picture.

L
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Old 05-17-2018, 03:51 PM   #6
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Top. looking at this end of the pump it is turning clockwise. The pumping chambers open at the top near the hose and close at the bottom near the bottom hose so the pump is pulling the water in the top and pushing it out the bottom. That is one way to tell. Also when you have 2 different size hoses as you do here, the largest hose will always be the inlet.
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Old 05-17-2018, 04:05 PM   #7
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Need to rotate engine and see which way impeller rotates. If CW, top is inlet.
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Old 05-17-2018, 04:15 PM   #8
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Thanks all, I thought top as well, and that was how it was connected. Since I’m getting no flow, and strainer is clear, time to pull hoses and check fittings in the supply side.
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Old 05-17-2018, 04:17 PM   #9
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Pump is designed to have water travel the long way around...and in this case the top would be the inlet.
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Old 05-17-2018, 04:44 PM   #10
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While you have the cover off, spin the engine to see if the impeller turns. The raw water pump on my Onan snapped the tap on the shaft where it mates to the engine.

Ted
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Old 05-17-2018, 05:30 PM   #11
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Good idea, O C Diver. I’ll check that as well.
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Old 05-17-2018, 05:55 PM   #12
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Worn pump won't want to prime. With pump all together, try to blow air through the pump, if air whistles through things are worn. Also bought a couple impellers that were like 0.020" shorter than normal and those would not prime.
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Old 05-17-2018, 06:17 PM   #13
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If you look at how the impeller fins are against the constricted side of the housing you see that the impeller rotates clockwise looking from this side.
The water is picked up at the top hose and, because of the constriction bending the fins closed, is forced out at the bottom.

How long has it been sitting - could the heat exchanger be clogged?
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Old 05-17-2018, 06:30 PM   #14
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Generator only started periodically to load check for past year. No extended run time in that period, but noticed minimal flow through exhaust the last few times. Checked strainer, all clear. Replaced impeller, no improvement. Cleared a bunch of impeller blades from the outlet hose. These must have been there a long time, because I replaced the impeller over a year ago and the one I removed was in good shape.

Planning to remove and check all hoses from strainer through heat exchanger and go from there. Just wanted to double check that the pump was oriented properly before I got too deep into it.

Thunderstorm chased me home today, and traveling all next week, so I’ll hit it after Memorial Day. Thanks again to all.
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Old 05-17-2018, 06:31 PM   #15
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While checking hoses, You might just as well change the inlet hose. Pumps work by creating a partial vacuum at the inlet then atmospheric pressure (14.7 psi at sea level) pushes the fluid into the pump. Its possible that you could have cut inside the hose that closes off the line when put under a vacuum. I've seen people pull off the hose and look through it and say its ok the reinstall and have it close as soon as the pump turns.
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Old 05-17-2018, 06:33 PM   #16
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Ok, my $1 is on a badly clogged exchanger. A boat sitting that long in Coral Gables warm water has got lots of little creatures up in there!

Waiting for what you find!
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Old 05-17-2018, 07:28 PM   #17
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So many answers and methods but the first was the most obvious and simple.
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Which hose goes to the through hull?
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Old 05-17-2018, 09:35 PM   #18
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So many answers and methods but the first was the most obvious and simple.
Simi, because he was getting no water throughput he was questioning whether or not the pump was put on correctly. Or whether it was 180 degrees off!
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Old 05-18-2018, 05:20 AM   #19
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Quote:
Originally Posted by menzies View Post
If you look at how the impeller fins are against the constricted side of the housing you see that the impeller rotates clockwise looking from this side.
The water is picked up at the top hose and, because of the constriction bending the fins closed, is forced out at the bottom.

How long has it been sitting - could the heat exchanger be clogged?
Send a diver down to check the hull inlet or pull the hose on the hull valve to see if it flows free.
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Old 05-18-2018, 11:46 AM   #20
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Quote:
Originally Posted by johnma View Post
While checking hoses, You might just as well change the inlet hose. Pumps work by creating a partial vacuum at the inlet then atmospheric pressure (14.7 psi at sea level) pushes the fluid into the pump. Its possible that you could have cut inside the hose that closes off the line when put under a vacuum. I've seen people pull off the hose and look through it and say its ok the reinstall and have it close as soon as the pump turns.
John
My genny intake hose delaminated on the inside and closed off flow. Great idea to change intake hose regardless. Boy did that one drive me crazy for a while.
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