Priming raw water pump

[zrod]

Hi.

I have a hunter 340 1999 with yanmar engine.
I am looking for a solution for my raw water pump that refuses to pump unless it is primed.
Have anyone faced such a problem and could solve it?
Untill now, i have changed the impeller, cleaned the cover, by still , the pump does not start unless it is primed.
Thank you.

 

[Don S/V ILLusion]

What's the condition of the O ring seal one the face?

 

[zrod]

It is in good condition. I have tested whether there is an air leak by blowing into the pump, and no bulb were seen.

 

[Ralph Johnstone]

Priming raw water pump

by blowing into the pump, and no bulb were seen.

Any chance of disconnecting the hose right at the thru hull and doing a soap test from there up to the pump ? Make sure all the water is out of the pump and hoses for the air test (water won't make bubbles) to work.

 

[zrod]

Any chance of disconnecting the hose right at the thru hull and doing a soap test from there up to the pump ? Make sure all the water is out of the pump and hoses for the air test (water won't make bubbles) to work.

I did not get you.
What do you mean by soap test?
I have isolated the pump, and installed a direct connection from a water gallon, the pump does not work before priming.

 

[Warren Milberg]

What is the condition of the cam on the top inside of the pump? It may be worn and in need of replacement.

 

[zrod]

What is the condition of the cam on the top inside of the pump? It may be worn and in need of replacement.

there is a small circular stripe of 1mm at the place the impeller Is turning.

 

[seadaddler]

Water

If you disconnect the hose that goes into the pump from the thru hull water should pour out if not that could be the problem.
Nick

 

[Ralph Johnstone]

Priming raw water pump

I did not get you.
What do you mean by soap test?
I have isolated the pump, and installed a direct connection from a water gallon, the pump does not work before priming.

A soap test is for checking small leaks.

Disconnect the hose from the thru hull, drain the water from it, get someone with big lungs to blow into the hose, then spray the hose joints with a soap solution. A good soap solution would be 10% dish soap in water.

The fact that the pump DOES pump after it's primed certainly does lead me to believe it's an air problem.

One more kick at the cat here ................ what happens if you shut the engine down and then immediately start it again ? Does it pump ? What if you shut it down for five minutes and repeat ? Fifteen minutes ?

Maybe do this under cover of darkness at night lest the neighbours start to wonder.

 

[zrod]

A soap test is for checking small leaks. Disconnect the hose from the thru hull, drain the water from it, get someone with big lungs to blow into the hose, then spray the hose joints with a soap solution. A good soap solution would be 10% dish soap in water. The fact that the pump DOES pump after it's primed certainly does lead me to believe it's an air problem. One more kick at the cat here ................ what happens if you shut the engine down and then immediately start it again ? Does it pump ? What if you shut it down for five minutes and repeat ? Fifteen minutes ? Maybe do this under cover of darkness at night lest the neighbours start to wonder.

I've tried all this without sucess.
I think i'll end up buying a new pump.
Thanks for all who've tried to help

 

[kloudie1]

Right on, Ralph.. HAd the same problem with pump not pumping until primed on a friend's boat.. ended up being two problems.. The blue "run dry" impeller was just a smidge too small in OD and the hose going from the strainer to the pump had a couple of cracks in it .. The cracks would leak air with engine running, but water did not come out when sitting still..Pump would stay primed for about 15 minutes but any longer and we had to re-prime.. changed hose and put in a real impeller and everything got OK.. Not blasting the blue impeller folks it is just that this impeller which they'd recommended for this pump was just enough "off" to give heartburn. I am sure there are folks who've had good experience with those..