Generator water intake obstruction

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John&Ria
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Re: Generator water intake obstruction

Post by John&Ria »

For those of you who may still be interested, the saga continues.

Today I ran the generator for a short period and observed very little water entering the screening bowl, and very little discharge at the underwater hull outlet. I then shut down to install a new impeller. A relatively small portion of one vane was missing on the 'old' one (7 hours use), so pulled the end cap off the heat exchanger to look in the hoses for remnants of the vane. No sign of anything. Started the generator again with the new impeller in place but no change in the conditions. Next I pulled the discharge hose from the muffler as well as the hose that exhausts water from the Vetus down through the hull. No evidence of blockages that I could see in any of those components. To be sure I inserted my dingy pump hose as far down the water discharge outlet as I could. Pumping produced plenty of air bubbles from the hull outlet.

That was enough trouble shooting for now so I headed to my boat yard to speak with the experts there. After discussing the problem and various options my next step will be to use a garden hose to feed the system via the screening bowl (top off and water flowing in there). I'm told that if the pump is working and there is no downstream blockage the system will handle all the water the hose can provide. If that works it likely means there is still an upstream blockage somewhere, which I will try and dislodge using the pressure of the water hose and/or by inserting a coathanger up through the intake screen on the bottom of the hull (fortunately the water in our marina basin has now warmed up, so a swim shouldn't be too bad 8)).

Another piece of advice I received that may be useful to others is to squeeze the hoses leading from the water pump to heat exchanger. Apparently the pressure in the system when it is working is only 1-2 psi, however it can rise to 50 times that if there is a downstream blockage in the system. These 'soft' hoses can easily be squeezed by hand when the pressure in the system is low, but become very hard when the flow is restricted and the pressure is high. This seems a simple way to determine if a blockage exists before or after the water pump.

If none of these efforts produce a solution then His Idea will be taking a trip to see the experts.

Cheers,

John
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Re: Generator water intake obstruction

Post by duetto »

this may or may not apply. friends of ours had a 34 that had trouble holding a prime. we debugged it down to the joint where the builtin tube providing the water from the thruhull mates to hose going to pump.

could you have a small air leak which is preventing pump from exerting max suction?

we have the old genset setup, so i'm not very familiar with your physical installation.
john & diane cummings
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John&Ria
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Re: Generator water intake obstruction

Post by John&Ria »

John, yes an air leak could be part of the problem. I’ll be checking for leaks on the intake hoses as part of my next steps.

Thanks for your interest.
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Re: Generator water intake obstruction

Post by John&Ria »

Today I fed the strainer bowl using a garden hose. The pump performed as it should, sucking up all the water I could provide with the hose at maximum flow. Bubbles were evident at the discharge outlet. This would seem to confirm that the issue is not with the pump or any part of the system downstream of the strainer bowl.

I also tried using water from the garden hose to provide backforce to the inlet portion of the system, however it was not very effective because I could not get a tight seal (water was spraying everywhere). As an alternative I again used my dinghy pump to use air as the backforce. This method once more provided plenty of bubble activity around the hull inlet.

Unfortunately, when the bowl was resealed and the generator started again the original flow issue returned, i.e. little to no water flowing into the bowl from the intake hose from the secock. I should mention that during these tests I've always filled the strainer bowl with water to ensure the pump has an initial prime.

I decided it was time to visually check the hull intake opening (a swim was required). I discovered no obstructions at the opening, and also when I used a piece of plastic coat hanger to probe up inside the intake about 15 inches.

At this point I thought the pump must not be keeping its prime due to an air leak of some kind. I checked to ensure all the intake hose connections were secure and discovered that of the two clamps attaching the hose to the seacock, one was somewhat loose and the other was entirely loose. Both were made secure.

Given the promising results from the other steps I'd taken I had hoped this final action would resolve the issue. Unfortunately it was not to be - when the generator was started again the water flow to the strainer bowl had not improved and there was no evidence of normal discharge at the hull outlet.

If anyone has other suggestions to diagnose the problem I would welcome them. Thanks.
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Re: Generator water intake obstruction

Post by duetto »

just for my information, is the pump new with genset or original? and while i'm at it why do you have a new genset?

baring any revelation from my previous question, my assumption is you have an air leak between the pump intake and the "tube", which is bonded into the hull. again i assume that would include a couple of pieces of hose, the strainer, and the seacock. the most obvious possibility is the sea strainer cover. have you inspected the seacock to hull connection. i would try taking saran-wrap and covering the seacock to "hull" joint as tightly as possible, trying to cutoff any air intrusion. if this helps you know where the problem lies. another test would be to mix up some palmolive dish washing detergent and water and covering the joint with the liquid and then pressurizing gently with your pump into the hose from the seacock to the strainer. if you see bubbles you have a leak.

don't give up, good luck
john & diane cummings
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Re: Generator water intake obstruction

Post by John&Ria »

Hi John,

Unfortunately my original generator packed it in this year after less than 700 hours of use. We don't know the cause for sure, but the failure was likely the result of a frozen/cracked manifold caused by unseasonably cold temperatures that overwhlemed the modest heating element we used. Live and learn!

So yes, we are now talking about a brand new generator and brand new impellers (7 hours only on the first one). Needless to say, having this latest problem show up so soon after purchase is somewhat annoying :x !

Thanks for the further thoughts of what to do next. I especially liked your idea of using soapy water and the dinghy pump to see if we can produce bubbles somewhere. Unfortunately, getting around the generator to get access to the seacock is going to be an SOB. I have to make a decision whether I want to take on the hassle or just pay a much younger and more athletic mechanic to do the job for me. If this happens it won't be until late July, however this is not a big burden because our expected summer cruises will not require the use of the generator if we plan properly.

By the way, I have inspected the sea strainer cover very closely a number of times - now wouldn't that be a simple one to solve! - but I can see no evidence of any cracks and the rubber seal looks fine.

I will be taking another swim with a longer metal coat hanger to see if I can inspect the inside of the tube all the way up to the seacock. My mechanic still believes there is an obstruction somewhere in there. We shall see.

Thanks again for you interest and encouragement.

Cheers,

John
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Re: Generator water intake obstruction

Post by duetto »

one last suggestion. smear some marine grease on the strainer seal. it will make sure there is a good seal.
john & diane cummings
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James Power
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Re: Generator water intake obstruction

Post by James Power »

Good idea on looking at the seal between the seacocks and tube flange Duetto. Came across this a few times years ago. Might also look at a possible collapsed hose inner liner on the suction side.

James
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Re: Generator water intake obstruction

Post by John&Ria »

James, thanks for the additional information that you have also seen this before. I'll be having a closer look at the intake hose, seacock and flange.
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Re: Generator water intake obstruction

Post by Nick »

There’s a dinghy trip you can take from Great Harbor on a “river” to other side of island. Ask at marina for directions, but basically take a left out the harbor cut and follow the coast until you see the outlet.
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Re: Generator water intake obstruction

Post by John&Ria »

Problem solved. The restriction turned out to be a stubborn mass of eelgrass that eventually arrived (not sure how exactly) at the intake port for the strainer bowl, where I was able to remove it. No air leaks evident anywhere, and the system is now working as it should.

Thanks to all who offered their suggestions.

Cheers,

John
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