Generator raw water pump losing its prime

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nocall
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Generator raw water pump losing its prime

Postby nocall » Fri Jul 10, 2015 9:56 pm

I have a 2005 MV34 (ELIXIR) with a Northern Lights genny. After replacing the raw water impeller for the second time in a matter of days I noted that as soon as the engine was stopped the water in the raw water strainer would drain back through the hose leading to the through hull fitting, leaving the strainer dry. So, as soon as the generator was started the impeller would run dry for the few seconds required before water was pumped up into the strainer. This has no doubt led to early impeller failures. My questions are: is this normal? The strainer is mounted well above the waterline and you can remove the top from the strainer with the shutoff valve open without water pouring out. Should there be any sort of check valve between the raw water pump and the heat exchanger? Has anyone converted to a 110 volt air conditioning pump to eliminate the use of fragile and expensive rubber impellers in the raw water pump? If so, some details on pumps, flow rates, and how it was engineered would be highly appreciated. Finally, how in the heck do you gain access to the actual generator through-hull fitting that is apparently below the generator? The Marelon shutoff valve is easy enough to get to but I cannot figure out the arrangement prior to that valve. As always, thanks for all the expertise and advice.

duetto
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Re: Generator raw water pump losing its prime

Postby duetto » Sat Jul 11, 2015 11:23 am

hi,

we converted to a 110V pump about 6 years ago for all the same reasons you're talking about and a few more. i will point out that we have an entec so i'm not sure about thruhull, etc on the later boats.

conversions was recommended by entec. it was easy. they sold me a march air conditioner (a/c) pump and a check valve. you can get pump for about $300 on inet. the check valve goes between the pump and the hose that would normally be the outlet of the belt driven raw water pump. you have to add hose from a/c pump to that place. NOTE: the a/c pump will not self prime so it needs to be mounted below the waterline. also you'll need to move a strainer into the bilge. you wire the pump to the output of the genset. this means no water gets to the genset until generator is producing 110V. a side effect of this is you can't fill the muffler and backfill the cyl from over cranking.

one last thing. we had to add a check valve between thruhull and a/c pump. when bow came out of water the pump would lose prime and get an air pocket which needed to be bled. we've used this for 6 years of icw/fl/bahamas and anchor out a lot. it's worked well for us.

feel free to email me if you decide to do.
john & diane cummings
duetto mv34 #23

James Power
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Re: Generator raw water pump losing its prime

Postby James Power » Sat Jul 11, 2015 9:25 pm

The genny raw water hose from the Marelon seacock to the Vetus strainer should have a good sized belly in it. This should stop the water from running back out. I have seen a few of the Marelon seacock bases that were not sealed properly, so they would suck air and not prime, as its on the suction side of the pump. There is no thru hull fitting below the genny. The fiberglass flange that the Marelon is mounted on is attached to a tube that runs straight down to the hull and is glassed in there. Also make sure the strainer lid and O ring is clean and tightened down properly.

Hope this helps
James

duetto
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Re: Generator raw water pump losing its prime

Postby duetto » Sun Jul 12, 2015 9:39 am

based on james' description, i think mounting an a/c pump below the water line on the newer boats will be difficult.
john & diane cummings

duetto mv34 #23

nocall
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Re: Generator raw water pump losing its prime

Postby nocall » Sun Jul 12, 2015 10:53 am

In the hazy past it seems I remember a mechanic remarking about a check valve in the raw water circuit between the raw water pump and the heat exchanger. He was of the opinion that such a check valve was a bad idea and we removed it. Now I think I know why it was there and why I should have left it alone. 20:20 hindsight works again. There was a loop between the strainer and the shutoff valve but for whatever reason it was not preventing the strainer from draining after the generator was shut down. Perhaps a bigger loop? It seems impossible to mount the strainer low enough to be below the waterline and the loop of connecting hose between strainer and shutoff valve loops up toward the deck and not down toward the bilge. For now, while we are in the Bahamas, we have devised a workaround where we start the generator while simultaneously opening the raw water shutoff valve. This keeps the strainer full and everything happy. As soon as we shut down, the reverse process occurs. It does take the coordinated efforts of two people but it does work, sort of.

Looking forward, if I do not want a check valve in the cooling circuit then I can see no other way than to add another through hull for the generator, perhaps in the hull below the galley sole next to the existing through hull for the air conditioning unit. There should be room to put an AC air conditioning pump and strainer there and then run the output to the heat exchanger, eliminating the engine mounted raw water pump entirely. I will probably have to move the fresh water pump to the area under the cabinet below the reefer but there should be room there. I am certainly open to better solutions.

duetto
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Re: Generator raw water pump losing its prime

Postby duetto » Mon Jul 13, 2015 8:57 am

hi,

if you're going to install check valve, i'd put it between strainer and seacock/thruhull and as low as possible. the downside of putting it before the strainer is that it can get clogged and in effect becomes the strainer.
john & diane cummings

duetto mv34 #23

nocall
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Re: Generator raw water pump losing its prime

Postby nocall » Mon Jul 13, 2015 9:30 am

I have heard that a check valve should be installed to open in response to pressure, not suction and thus be located downstream of the RW pump. If my memory is correct, that is where there was one before. I don't know if it came that way from the factory or if a previous owner installed it. There is a bewildering variety of check valves available and I am sure that something can be found.

If I decide the 110 volt A/C pump route, I wonder if replacing the existing thru hull for the forward air conditioning unit with a larger one and then creating a manifold to feed both the AC and the generator would be the way to go. Having the pump, seacock, shutoff valve, and strainer all below the water line and under the galley sole has some appeal. Ah, decisions, decisions...

jgonnerman
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Re: Generator raw water pump losing its prime

Postby jgonnerman » Wed Jul 22, 2015 4:12 pm

My boat has an entec genset which has/had the wonderful dual chamber water pump. After spending many hours and dollars I was advised that the now current solution to the pump problem is to install a 12 vdc electric coolant pump (johnson pump for MB turbochargers) and convert the belt driven pump to the raw water pump. This supposedly solves the problem of the 110 AC raw water centrifugal pumps getting air locked.

I made this change and began having raw water pump priming problems. The entec guru suggested a check valve as a surefire way to cure this problem .

I bought a swing valve check valve on ebay. the swing valve will open with suction and does not require a pressure to open. Works great.

My piping circuit is a thruhull under the refrigerator through the bulkhead up to a vetus strainer and then down to the raw water pump on the gen set.
I placed the check valve just inches from the thruhull.
John Gonnerman
San Diego Ca
"Westend Express"
2002 34 Hull 20

duetto
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Re: Generator raw water pump losing its prime

Postby duetto » Wed Jul 22, 2015 4:30 pm

hi john,

what are you using for 12V source (i.e. what is it wired to)? what makes it come on? what did the pump cost?
john & diane cummings

duetto mv34 #23

nocall
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Re: Generator raw water pump losing its prime

Postby nocall » Wed Jul 22, 2015 4:59 pm

There must have been a change in how the generator thru-hull is arranged on the 2005 34's vs. the earlier versions. In my boat I believe the generator water comes in to a inaccessible glassed-in tube which goes up to the shut-off valve, which is well above the water line. From there the intake hose makes an upward loop and then down, leading to the Vetus strainer. We have a Northern Lights generator so maybe things were built differently for other generators. It sounds like a check valve is the easiest solution. A swing gate check valve in the line between the shut-off valve and the strainer sounds. Is there any disadvantage to putting a check valve in the circuit between the RW pump and the heat exchanger? This one would open under pressure as opposed to one that operated by suction. Two check valves?

jgonnerman
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Re: Generator raw water pump losing its prime

Postby jgonnerman » Wed Jul 22, 2015 5:21 pm

First my source for all my entec solutions is doug jensen 386-872-1473. I believe he continues to consult for Mastery. Apparently the new entecs have this cooling circuitry using a 12vdc coolant pump

Doug set me on this path stating the new systems use the johnson cm 30 pump with a 5/8 outlet. this pump sells for over $300 at my local marine supplier. i bought the same pump on ebay for $145 but with a 3/4" outlet which i reduced down to 5/8. on the new units they have the pump on a bracket between the heat exchanger and the starter. on my unit i placed it on the front end of the genset and bolted it to the sound enclosure.

the pump draws about 2 amps until the thermostat opens and then the draw drops to about 1.2 amps. i provide that info because of the way i did my power was to use a relay which is connected to the control circuit which provides 12v when the circuit is switched on at the control panel inside the boat. I then used a lead from the starter for the source of the power for the pump motor. turn switch on the panel, relay closes, pump runs. in retrospect i believe I could have sourced power for the pump motor directly from the control circuit system and not bothered with the relay as the draw is quite low. the source of 12v for my relay or for the pump is the first sensor in the control circuit which is the coolant temp sensor, i just used a spade fitting which had one female and double male ends and plugged the existing control circuit lead and the new pump/relay lead on the other.
i bought a flat end cap for the johnson belt drive pump removed the second chamber and the front chamber became the raw water pump.
John Gonnerman
San Diego Ca
"Westend Express"
2002 34 Hull 20

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Re: Generator raw water pump losing its prime

Postby jgonnerman » Wed Jul 22, 2015 5:28 pm

2 check valves?

I don't think a check valve on the output side of a vane pump is going to do any good. the pump is a check valve in itself and its the input side of the pump that needs to have the check valve to prevent losing prime

the check valve i bought was off ebay and is clear plastic no metal parts so one can see if the line is primed and obvserve flow.

yes the northern lights setup on the later model boats is quite a bit different than the early entec installations. i considered converting to a northern lights and the entec's liquid cooled generator section versus the northern lights air cooled made me rethink that change out.
John Gonnerman
San Diego Ca
"Westend Express"
2002 34 Hull 20

Ortolan
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Re: Generator raw water pump losing its prime

Postby Ortolan » Thu May 12, 2016 6:59 pm

I had this same issue with the genset strainer "back-siphoning" to the seacock after shut-down. You could see it happen & hear the gurgling. I tried tightening fittings, sealing the strainer cover & even used sealant on all of the hose fittings to no avail.

I finally found a 2-part solution:

First I replaced the original Vetus strainer with a Vetus #FTR140 strainer. This model is a bit smaller than original, yet with an important design difference - the discharge port tube is raised up high within the strainer basket (the original had both ports low). This means that when the strainer tries to drain back to the seacock, you only lose about 1/4" - there is still a cup of water in the strainer, plus a cup or so in the hose to the water pump. When the genset starts it has that 2+ cups of water to the pump with only a second or two delay before it starts pulling water from the seacock - the water pump never runs dry.

That was a big improvement so I then tried installing a Jabsco #29295-1011 "non-return" valve immediately after the new strainer. These 2 have now prevented ALL "back-siphoning". There are on-line debates to having such a valve, but locating it after the strainer eliminates some concerns.

So far - so good!

Russ
Twin Sisters - Hull #100
Russ
Twin Sisters
2006 MV34 - Hull #100
www.esc-pod.com

duetto
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Re: Generator raw water pump losing its prime

Postby duetto » Fri May 13, 2016 7:24 am

hi russ,

could you clarify " immediately after the new strainer". do you mean between the pump and the strainer or between the strainer and thruhull?
john & diane cummings

duetto mv34 #23

Ortolan
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Re: Generator raw water pump losing its prime

Postby Ortolan » Fri May 13, 2016 10:43 am

John,

Between the strainer & water pump. Less likely to jam or clog with grass, etc.
Russ
Twin Sisters
2006 MV34 - Hull #100
www.esc-pod.com


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