Sea water pump air locks

jimbay · #1 (**permalink**) 10-18-2011

I have a Bayfield 29'-re-powered her about 3 years ago with a Yanmar 3YM20.

I've had the following problem these past two summers-if I'm heeled more than about 10 degrees, I lose my prime on the sea water pump-I can hear the exhaust start to make a noise unlike the normal exhaust emission and turn the engine off to keep from overheating-then I either have to sail her or call TowBoatUS. For further information, the intake is on the starboard side of the boat. Since I single-handle or sail with my grandson whose only 7 and just learning, I have some concerns about this happening.

To bring her back I have to go downstairs and prime the hoses that lead from the strainer to the pump-sometimes I can't get this to work or it takes an inordinate amount of time to get her to come back up-had to do it once last summer when it was really kicked up and never did the pump to prime-sailed myself out of the situations.

I'm looking for suggestions for a solution-one idea that's been given to me is to relocate the intake for the pump lower-this is a full keel boat and the intake could be put on the side of the hull along the spot where the bilges are on the inside. Something makes me think that's not a good idea-just can't put my finger on what's wrong with it. Please feel free to email me with suggestions: him.jfrank@gmail.com

RichH · #2 (**permalink**) 10-18-2011

The Oberdorfer type pump on your YM 'should' be able to generate enough suction lift for it to be 'self priming for a 'few feet' height. Id check the pump impeller to side clearance (side plate) first before rearranging your 'plumbing'. Actually the impeller should be running with 'slight' friction & zero clearance to the pump body walls/plate. Your happy Yanmar dealer will have the actual fit (impeller to side walls) dimensions ... youll need an 'inside' and an 'outside' micrometer to check these distances (PLUS the pump's gasket thickness ... if the gasket is too thick the clearances between the impeller and the closure plate increases ... air leakage until primed !!!!).

jimbay · #3 (**permalink**) 10-18-2011

RichH

Thanks for replying-I'm not quite tracking on your suggestions.

I'm using the Globe run-dry impellers from Defenders-according to my understanding, this impeller actually has to bend at a certain point on the intake feed to the pump.

What I believe your telling me is that the rest of the way around I should check the clearances?

This pump doesn't have a gasket-it has an O-ring that is supposed to seal between the plate and pump body

There has not been a Yanmar impeller in this engine's pump since I replaced the original that came in the engine-I switched to the Globe impellers since I was told they were more tolerant to running dry

What strange to me about this whole thing is that I never has this problem with the old engine-2GM20F-and I know i sailed the boat heeled over more than 10 degrees a lot

mm2187 · #4 (**permalink**) 10-19-2011

It seems very odd that your having this problem because a fresh water pump pulls its own prime. I would thinkwhen the engine was installed that they would install a thru hull as close to centerline as possible. Do you think your intake is not underwater when heeling? Is you engine significantly higher then your waterline of the boat. I am guessing the 10° heel issue is only on one of the tacks? I would check your fresh water strainer to make sure you do not have a partial block that restricts flow as well as replace the impreller to the Yanmar OEM part.

olson34 · #5 (**permalink**) 10-19-2011

Those little raw water rubber-impeller pumps must have a decent end-plate seal -- on both sides of the impeller.
I had to have one outer end plate(cover plate) lapped to get some grooves out of it to restore some suction to our Oberdorfer pump. Later I had to replace the whole pump. Unlike the old pump design with its paper gasket, our newer one also has the O-ring on the plate, FWIW.

Our local water carries a higher load of fine abrasive silt due to the Columbia flowing thru hundreds of miles of basalt formations. That fine "sharp" silt will enlarge the cast pump chamber over time and reduce the suction.

Other waterways may put far less "wear" on their pumping systems. So "YMMV."
OTOH, it's one more factor to consider when planning for preventative maintenance on your engine.

So, how is the water composition where you operate your diesel?

Regards,
L

ps: Plus One on the comments from MM2187, also.

RichH · #6 (**permalink**) 10-19-2011

Quote:

Originally Posted by jimbay

RichH

Thanks for replying-I'm not quite tracking on your suggestions.

I'm using the Globe run-dry impellers from Defenders-according to my understanding, this impeller actually has to bend at a certain point on the intake feed to the pump.

What I believe your telling me is that the rest of the way around I should check the clearances?

This pump doesn't have a gasket-it has an O-ring that is supposed to seal between the plate and pump body

There has not been a Yanmar impeller in this engine's pump since I replaced the original that came in the engine-I switched to the Globe impellers since I was told they were more tolerant to running dry

What strange to me about this whole thing is that I never has this problem with the old engine-2GM20F-and I know i sailed the boat heeled over more than 10 degrees a lot

By clearances I mean the SIDE clearances that the impeller makes with the pump body and cover plate.
An Oring seal is best as it promotes a metal to metal restraint on the 'amount' of closure, gaskets vary in thickness thus may promote varying 'side clearances' that the impeller makes with the pump body, etc.

I'd go back to an OEM Yanmar impeller ... probably is a wee bit 'wider' ... and do a 'trial' with the OEM dimensioned impeller. It may be that Globe impeller is 'less wide' than the OEM Yanmar and is allowing air to leak past the ENDS of the vanes and impeller body. If the pump doesnt deveop enough 'dry' suction to prime the pump, the highest probability is that the air is passing across the SIDES of the impeller.

jimbay · #7 (**permalink**) 10-21-2011

Shock

Yes I'm pretty sure-as sure as you can be from the cockpit of the boat-that the intake to the pump is out of the water when I'm experiencing this problem-if I start to investigate below when I have heard the discriminating sound, the intake to the strainer is full-the hose that leaves the strainer that goes to the intake to the pump lots of times has to have water put into it.

By the way I haven't mentioned this before-the hose from the exit of the strainer to the intake to the pump is very long-this is because of space limitation for the placement of the strainer-by this I mean the sea water enters on the starboard side of the boat, travels to intake for the strainer on the port side, and then makes a return trip back to starboard to the intake for pump-think this means that the pump has a lot of head before it sees any water

RichH · #8 (**permalink**) 10-23-2011

Quote:

Originally Posted by jimbay

By the way I haven't mentioned this before-the hose from the exit of the strainer to the intake to the pump is very long-this is because of space limitation for the placement of the strainer-by this I mean the sea water enters on the starboard side of the boat, travels to intake for the strainer on the port side, and then makes a return trip back to starboard to the intake for pump-think this means that the pump has a lot of head before it sees any water

Hose diameter will greatly influence the 'friction' in a piping system. You might want to do a temporary 'bread board' trial using larger (& cheap) diameter hosing and temporary 'hose adapters', ditto too with 'SMOOTH' ID surface hose. This would also include eventual replacement of the seacock with a larger size ... and keeping the 'elbows' and other fittings to an absolute minimum and instead use 'long radiused' bends in the hose instead of 'keeping it neat' with unneeded/extraneous 'fittings'. Anything that do to remove 'friction' from a hydraulic system or piping/hose run will benefit the 'priming ability' of the pump .... less work to overcome the easier it is to 'prime' the pump.

Capt Len · #9 (**permalink**) 11-11-2011

Way I see it , make SURE thruhull is under water. Sucking air doesn't do it so move it. Other side and lower if that routes the hoses better. Make sure raw water pump is working. New impeller and proper end squeeze. I recommend an anti siphon vent first off the thru hull screen.but that's just me.

jimbay · #10 (**permalink**) 11-12-2011

Len
Thanks for input-boat is out of water now for winter-checked and that intake for pump ain't very far under boat! Gonna move it and then do all others suggestions-thanks to you-thanks to others for their interest also.