Raw water pump - Sanity check

[Tonic1]

I’m 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

 

[menzies]

Which hose goes to the through hull?

 

[Tonic1]

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?

 

[kchace]

Top is inlet

 

[Lou_tribal]

I’m 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

 

[johnma]

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.
John

 

[Ski in NC]

Need to rotate engine and see which way impeller rotates. If CW, top is inlet.

 

[Tonic1]

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.

 

[w8n4sun]

Pump is designed to have water travel the long way around...and in this case the top would be the inlet.

 

[O C Diver]

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

 

[Tonic1]

Good idea, O C Diver. I’ll check that as well.

 

[Ski in NC]

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.

 

[menzies]

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?

 

[Tonic1]

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.

 

[johnma]

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

 

[menzies]

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!

 

[Simi 60]

So many answers and methods but the first was the most obvious and simple.

Which hose goes to the through hull?

 

[menzies]

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!

 

[OldDan1943]

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.

 

[mike66]

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.

 

[Tonic1]

Great suggestions on replacing hoses. That, and cleaning heat exchanger are on the list for after Memorial Day.

 

[Simi 60]

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!

Oh, OK, I though he was asking what the inlet and outlet was .

 

[rbcooper]

My genset periodically gets a blockage in the intake flow due to jellyfish or seaweed blockage. A very simple real world testis to open the raw water seacock and verify that you get a flow of water to the open pump. If not disconnect hose at the seacock and verify good flow. If flow is good then any obstruction is between the pump and the raw water feed. If both are good then the possibility is a collapsed or other wise compromised hose or a blockage in the heat exchanger or....

RB Cooper

 

[Tonic1]

Thanks again to all who chimed in on this. Checked and/or replaced all hoses, still only minimal flow. Used Barnacle Buster to clean heat exchanger, using extra bilge pump hooked to discharge port of heat exchanger, back flowing through to pump discharge hose. Initially, barely a trickle, then within 15 minutes full flow and a lot of crud. Continued flushing for about an hour, flushed with fresh water and reconnected all hoses. Fired up generator and voila, full flow through exhaust.

Menzies and others who suggested clogged heat exchanger win the prize.