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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 09-01-2008
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water pumps..

I have a 2 cylinder volvo diesel. It has a mechanical water pump.
I think it's a very common type. It has the rubber impeller rotating inside the brass cylindrical cavity. Raised area on the side of the cavity to create pumping action.

What is the failure mode for these types of pumps? They seem so simple.

The reason I ask is that my pump seems very weak. I discovered this when I tried to install a groco raw water strainer. Just this bit of extra resistance caused NO water to flow. When I put the old hose back on, it worked. There is no blockage in the new strainer or the two new pieces of hose.

Maybe the metal inside the pump cavity is worn to the point that water is getting around the rubber flaps?

Help!
gh
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Old 09-02-2008
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Have you changed the impeller? Should be changed annually IMHO. When you installed the strainer, did you open the seacock and fill the filter? There should be no resistance in a strainer, something else must be going on.

John
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Old 09-02-2008
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Hi John,
The impeller is new.
On the two new hoses and the raw water strainer, I can easily blow into one end and shoot water out the other side.
The seacock was open.

I admit it is weird. I put the old ratty hose in.. water comes out the back.
I put the new hose and strainer in.. no water.

The strainer filled up just by the pressure of the water outside of the boat.

gh
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Old 09-02-2008
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Most raw water pumps are made by Jabsco or Johnson. The smaller ones are pretty critical on the fitting of the impeller, particularly from front to back. If it isn't snug, there's no seal, and no water gets pumped. If you can blow through the pump, I'd say you have the wrong impeller installed.

Take the cover off the pump and lay a good straight-edge across the opening. The rubber on the impeller should be touching, just barely. (Too tight and it won't work, either.)
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Old 09-02-2008
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Is the all of the new strainer and all the new hose below the waterline as it should be?
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I was able to blow thru it, but now I cant remember if I was cycling the motor at the time. I'll have to try it again.

Not sure if it's mounted below the water line, but the clear plastic cup will fill up based on the water pressure alone. Why does it need to be below the water line?

gh
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Old 09-02-2008
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Check for air leaks in the intake hose to the pump from the strainer or maybe loose clamps.

Remember rule one--

The last thing you mucked with is the first thing to mess up.

Rick
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Quote:
Originally Posted by groundhog View Post

Not sure if it's mounted below the water line, but the clear plastic cup will fill up based on the water pressure alone. Why does it need to be below the water line?

gh
If not mounted below the waterline entirely...the cup may fill but the full filter up to the outlet may not fill and the air gap may be why the impeller can't pull the water through with the filter attached.
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Old 09-03-2008
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Ok. Disconnected the hose attached to the seacock and tried to blow through the water pump and impeller. Couldn't do it. So it seems there is a seal with the impeller.

No strainer in line. Just the old hose to the water pump and on through the engine...... hmm.

I know what ur going to say. I should have just tried to blow through the pump only with out the engine and exhaust still attached...

gh
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