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Old 14-04-2015, 17:56   #16
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Re: Air lock in raw water pump

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Originally Posted by Rik-lu View Post
Next what I will try when I go back to my boat in April is to lower the Vetus cooling water strainer which is maybe mounted to high.
( D2-55 Volvo not md55 as I wrote above by error.)

I checked this, the Vetus cooling water strainer was 30 cm above waterline and I lowered it to 15 cm ( the minimum Vetus recommends ).

see vetus screenshot:



Still it is not able to suck the water without filling the strainer first. (my impellor is new)

After filling the strainer - with some chance it starts pumping the cooling water without draining the water pump.

But doing some tests it works not always and I have to drain the pump.
The intake and outtake of the pump are both from below to the pump, so the pump itselves makes the airlock.

As I also mounted a " Speedseal " with knurled thumb bolts now, it is much easyer and quicker to drain the system.

http://www.speedseal.com/speedseal.html
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Old 14-04-2015, 19:43   #17
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Re: Air lock in raw water pump

Rubber impeller pumps that are typically used as raw water supply pumps for marine engines should easily move air through the system. If it doesn't, there is a problem with the pump. Often it's just a worn cover plate. Remove the cover plate and look for wear on the inside where the impeller rides against it. If you see wear, flip the cover over and put it back on with the smooth side in. This should greatly improve the self priming. Look for wear in other parts of the pump, typically the cam and rear wear plate.

If the pump isn't worn, look for an air leak on the intake side of the pump.
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Old 14-04-2015, 21:31   #18
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Re: Air lock in raw water pump

Hopcar, my boat has the same problem - heeling while motoring sucks air into the system and the pump won't self prime until I remove and reinstall the cover plate. Does this suggest a worn cover plate?

Removing the cover plate I think drains the outflow hose from the pump. Could there be a problem with the outflow side, like clogged exhaust or something to do with the anti-siphon loop?
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Old 14-04-2015, 21:52   #19
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Re: Air lock in raw water pump

Sun/Moon, if the cover plate is worn enough to cause a problem, you'll be able to see scratches on the inside. I don't know why removing and reinstalling the cover would temporally fix the problem.

If you've got enough wind to heel that much, turn off the damn motor. You're a sailor!
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Old 14-04-2015, 22:21   #20
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Re: Air lock in raw water pump

Unfortunately I'm 2000 miles away from the boat, so I can't go look at the cover plate. I hope to rectify that soon, but please don't tell my boss just yet!

And I agree that if you've got enough wind to heel that much you don't need the engine. But sometimes the heel is caused by the wake of a monster boat that is oblivious to his impact on others.
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Old 15-04-2015, 20:12   #21
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Re: Air lock in raw water pump

Worn pump or not I had this problem after moving my strainer to a higher more convenient location removing it from the mount back lower solved the problem until it went back to the original location which was a none stop rise to the pump. This only happened offshore in larger waves
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Old 21-04-2015, 00:28   #22
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Re: Air lock in raw water pump

I am having this issue on my Crown 34 and I'm getting pretty fed up. Attached I is a result of one of the times this happened while caught in 30+kts under the Narrows Bridge in Tacoma WA. Ended up having to sail in with no engine while it got dark. but still had a great time once we were at the dock and learned A LOT as a skipper that day. :thumbup:

Evening Tide, do you have any photos of your air bleed set-up? I have been fixing my issue by priming the system from the hose where it connects to the mixing elbow. I'm planning on adding a Tee with a ball valve and a hose adapter so I can do it without disconnecting anything on the fly. (or maybe bleeding off air. I'm going to have to look into that)

Great info so far. Thanks everyone. I love these forums!

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Old 21-04-2015, 04:08   #23
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Re: Air lock in raw water pump

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Hi James- I tried to attach some photos (don't know if it worked). I drilled a small hole in the top of the raw water strainer and then epoxied on a piece of aluminum to add some thickness so I could tap some threads. The plastic fittings are from hardware store. One photo shows the plastic tube with another fitting. I was trying to make a check valve to let the air out but it didn't work so I am using a valve that I must open when I want to release air.

My strainer is two inches below the water line and it is the high point where air collects. The plastic tube comes from the strainer top to a location just inside the companionway where I can easily reach it while I am in the cockpit. The whole setup is a little crude but works reliably. I can hear air gurgling out when the valve is openned. The valve must be closed when the motor is running because even a small air leak will air-lock the pump.
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Old 21-04-2015, 11:24   #24
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Re: Air lock in raw water pump

I wonder whether your problem might be on the discharge side of the raw water pump. The impeller pump can self-prime but probably not against any significant back pressure, or, perhaps, if there is air in the discharge.
Could you have a block in the cooling bundle? Have you tried draining the muffler? Might there be a sag on the discharge side? Air must rise up out of the discharge, I imagine.
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Old 21-04-2015, 12:02   #25
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Re: Air lock in raw water pump

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Originally Posted by James Alberding View Post
I have been fixing my issue by priming the system from the hose where it connects to the mixing elbow. I'm planning on adding a Tee with a ball valve and a hose adapter so I can do it without disconnecting anything on the fly. (or maybe bleeding off air. I'm going to have to look into that)

Great info so far. Thanks everyone. I love these forums!

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Be careful doing that as you can easily water lock the engine. Best to figure out what the problem is and fix that instead of risking ruining your engine.
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Old 21-04-2015, 15:23   #26
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Re: Air lock in raw water pump

At some point you have to ask yourself why yours is the only boat in the marina needing an air bleed valve on the engine cooling system.
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Old 21-04-2015, 17:06   #27
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Re: Air lock in raw water pump

Yes, Terra Nova- I wondered if I was the only one (in the marina) to have this problem and that's why I started this thread. If I count correctly about six others have said they have similar problems. That's amazing to me. I conclude that my crappy little pump won't pump air if it is even slightly worn. It's not a rebuildable pump so I have solved the problem for my boat and the air bleed sounds stupid but works very well.
I think I have read that some "blue water" sailors close the thru-hull whenever the motor is not in use and this was one solution that worked well for me but for a day-sailor it seems like a lot of bother.
To more directly answer your question, most boats in the marina don't have this problem because they stay in the marina in their slips. (Ha!)
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Old 21-04-2015, 17:32   #28
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Re: Air lock in raw water pump

If the 6 others who have the same problem were all in your marina, I think you'd have an argument.

If the sea water intake line rises continuously, through a strainer, then to the pump, there should be no air lock. It sounds like your pump is bad.
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Old 22-04-2015, 10:11   #29
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Re: Air lock in raw water pump

When the engine is shut down, the water level in the intake piping will drop to sea level, about 15cm below the strainer unless a vacuum forms downstream. When starting up, the raw water pump must remove enough air from the intake hose and strainer to reduce the pressure at the pump inlet sufficiently to establish water flow to the pump (self priming the pump). Apparently the pump could do this when it was new but now that it has aged, it's capacity has been diminished and it doesn't always self prime. I'd check for obstructions and air leaks from the hull to the strainer to the pump. Then I'd look at the discharge hoses and eliminate any sags that might hold water that could limit the discharge of air from the raw water pump upon start up. Then I'd make sure the anti-siphon valve is working and not sticking closed. This could also hold water in the system, blocking start up air flow. Finally I'd consider relocating the strainer to at or below sea level to reduce the amount of air removal needed for self priming. If keeping the strainer above sea level is a priority, I'd begin to look at replacing the raw water pump with a different model known to self prime in this configuration. That may be an expensive trial and error route to go down though.
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Old 22-04-2015, 20:53   #30
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Re: Air lock in raw water pump

If you are going to close the intake each time you should put your key on the valve to prevent starting the engine with the valve closed !
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