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Old 20-04-2016, 07:29   #16
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Re: Generator Water Pump

Rubber impeller pumps trap water in the housing when they shut down. That water is there to lubricate the impeller on start up.
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Old 20-04-2016, 08:06   #17
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Re: Generator Water Pump

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Rubber impeller pumps trap water in the housing when they shut down. That water is there to lubricate the impeller on start up.
Yes but does it trap enough? there are only a few oz and if so why so many pump failures on above water level installs. As we all know a check valve is pron to failure
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Old 20-04-2016, 08:39   #18
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Re: Generator Water Pump

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Just to point out the obvious. An engine driven pump doesn't deliver water when the engine isn't running, neither should the independently driven pump. You don't want to fill the water lift muffler and then back water up to the cylinders. Time the start of the electric pump AFTER the engine starts and stop it at the same time the engine stops.

I'll use a 115V March Air Conditioner pump, it will run whenever the generator is producing 115 VAC power by connecting it directly to the generator output
So there is no way the pump could get power without the generator producing power, meaning of course engine running.

My Gen / shorepower switch is one or the other, it's not physically possible for the generator to be connected to shorepower, so shorepower can't power the pump either.

I called Nexgen, they said basically no problem, knock yourself out, recommended me to not use a 12V pump as it's possible a relay could stick and cause the pump to run with motor off. According to them, I need 4 GPM min. March pump I have is rated I think for eight GPM, but that may be a rating with no losses, so I'm going to give it a shot and see if I'm overloading the exhaust with water or not.
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Old 20-04-2016, 08:41   #19
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Re: Generator Water Pump

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I'm currently installing a generator and I noticed that nothing in the manual addresses this. The manual has a lot of info related to not getting siphons etc. that would flood the engine.

My generator is above the water line so I shouldn't need an anti-siphon in the line. But I installed one anyway as both a safety measure and as a way to know that the water pump at least always has water available in the discharge leg that would be able to lubricate the pump on start-up.

Mine is above water line also, and I was advised to install the anti-siphon loop for heeling and just it's cheap insurance, no compelling reason not to have it.
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Old 20-04-2016, 08:54   #20
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Re: Generator Water Pump

Yes it does trap enough. You only need a few drops to lubricate the impeller for the second or two that it takes for the pump to prime.

All pumps fail eventually wether they are above the waterline or not. There are so many factors that affect pump life that it's hard to pin point any one thing.

In your example where the pump has to lift water there is additional strain on the impeller the higher it has to lift the water.

If you want to go to the effort of trapping more water in or near the pump, I don't see any problem with that, I just don't think it's worth the effort.
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Old 20-04-2016, 09:23   #21
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Re: Generator Water Pump

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Originally Posted by a64pilot View Post
I'll use a 115V March Air Conditioner pump, it will run whenever the generator is producing 115 VAC power by connecting it directly to the generator output
So there is no way the pump could get power without the generator producing power, meaning of course engine running.

My Gen / shorepower switch is one or the other, it's not physically possible for the generator to be connected to shorepower, so shorepower can't power the pump either.

I called Nexgen, they said basically no problem, knock yourself out, recommended me to not use a 12V pump as it's possible a relay could stick and cause the pump to run with motor off. According to them, I need 4 GPM min. March pump I have is rated I think for eight GPM, but that may be a rating with no losses, so I'm going to give it a shot and see if I'm overloading the exhaust with water or not.
sounds good but think of the following....

what happens if you are connected to shore power... will your AC pump fill the generator with water if you don't somehow remember to switch it off.

What happens when your generator flicks the breaker and the AC stops... will your generator overheat.

You then might have to install some additional controls that start to make the simple impeller pump look good again.
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Old 20-04-2016, 09:34   #22
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Re: Generator Water Pump

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Originally Posted by HopCar View Post
Rubber impeller pumps trap water in the housing when they shut down. That water is there to lubricate the impeller on start up.
You have to find a way to trap some water so that even when worn, the pump gets water when it first turns.
Installing the strainer slightly above the pump can achieve this.
This will greatly increase the life of the pump.

I think that this subject is not often discussed as the installation has to be done so that there is absolutely no chance of water syphoning into the engine.

An impeller that sits in seawater will last significantly longer than one that runs dry till it sucks up some seawater. and the pump will last longer too.
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Old 20-04-2016, 10:00   #23
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Re: Generator Water Pump

My genset & pump sit 21" above the waterline. I installed a check valve just above the thru-hull shutoff. Impellers average probably 250-300 hours.
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Old 20-04-2016, 10:21   #24
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Re: Generator Water Pump

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sounds good but think of the following....

what happens if you are connected to shore power... will your AC pump fill the generator with water if you don't somehow remember to switch it off.

What happens when your generator flicks the breaker and the AC stops... will your generator overheat.

You then might have to install some additional controls that start to make the simple impeller pump look good again.
You can't parallel the generator and Shorepower, it's physically impossible, it would be a safety issue and could destroy a generator if you could.

AC pump is solely connected to the generator, nothing else, pump will be connected to the generator prior to the 30 amp Gen CB, but will have it's own circuit protection, in the event of pump failure, it will be the exact same as the mechanical pump failure, if you do nothing eventually the cooling system of the generator will overheat and the generator overheat switch will shut it down, possibly damaging the water lift muffler too though, but same failure mode either electric or mechanical pump. I want to do this for three reasons.

1. Premature failure, I'm not the first that has had the cooling pump fail, lifespan seems to be about a year, regardless of hours of operation, I got 200 out of mine. Seems average Airconditioner pumps run for thousands of hours and years before failure. How often do people run the AC on average when at the slip? More than I will run this generator I assure you.
2. Mechanical pump prior to seizure, leaks salt water, being mounted in the same enclosure as the generator head itself, it spray salt water in and around the generator, that will lead to bigger problems I believe than a failed pump.
3. Ease of repair, due to where it's located in the Lazarette, it's a bear to get to the pump, Nexgen makes it very simple to remove and replace, but access is limited in my boat, a March pump I can locate in an easily accessed location so that it is simple to R&R.

I've ordered a Jabsco pump, will be in in two weeks, I will put it in spares so going back to mechanical will be as easy as two hoses and two bolts if I chose to.
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Old 20-04-2016, 12:24   #25
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Re: Generator Water Pump

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Originally Posted by a64pilot View Post
So why can't I plumb in a March Air conditioner electric pump that runs whenever the generator in making AC power?
I did exactly that, and used it for a season and a half so far. No complaints, works great.

I had ongoing problems with the belt-driven pump on my Onan 7.5KW genset. It always seemed to work OK at the dock, or when I was just testing, but fail when I actually needed the genset.

I went through pretty much the same thought process spelled out above. The pump takes its power directly from the generator side. It took a while to find the right wires to tap into, but it only runs when the generator is producing power. I have two other identical March pumps on board for the air conditioners, so in a pinch I have spares.

I consider this one of the better modifications I've made. I still check on the coolant flow out the exhaust, but now I enjoy seeing good, full pulses every time, instead of the anemic spittle it would occasionally produce before.
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Old 20-04-2016, 12:58   #26
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Re: Generator Water Pump

I have two AC's also, one 16K and one 5K, and have two March pumps in spares, one is for when the cheapo pump that came with the little AC dies although it's still chugging along, perhaps I have misjudged it, and the other was a spare, so now I'm going to use the spare for the generator.
If it works and I think it will then I will have three identical pumps so one spare will cover all three.
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Old 20-04-2016, 13:13   #27
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Re: Generator Water Pump

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Originally Posted by wayne.b View Post
===

I had similar repeated raw water pump failures with a Kohler generator that I bought new. Kohler eventually acknowledged that the original pump had been under spec'd by their engineers and replaced it with a much larger pump under warranty. There was no repayment for the aggravation however. I would keep after Nexgen and try to make a case for something similar. As a point on interest, which Nexgen model do you have?
Really, which Kohler model do you have. My new Kohler 9Kva came with the exact same water pump that the old one had even though the engine was a lombardini instead of a Yanmar.

I gave the old one away and the first thing in the rebuild was to replace existing Jabsco water pump with an AC pump. They just took a lead off the output circuit to the water pump and everything worked fine. As you know these are not self priming pumps so have to ensure plumbed properly and below water line.
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Old 20-04-2016, 13:14   #28
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Re: Generator Water Pump

I just spoke to an old generator guy. He confirmed my memory that there was a model of Onan that had a gear driven pump that would leak water into the engine if the seal failed. The common fix was to use an electric pump just as A64 suggested.


He said it's still pretty common with people who are just tired of changing impellers.
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Old 20-04-2016, 13:36   #29
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Re: Generator Water Pump

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My genset & pump sit 21" above the waterline. I installed a check valve just above the thru-hull shutoff. Impellers average probably 250-300 hours.
250-300hrs is ridiculous. What? Change the oil, change the impeller? The impeller should be changed annually as a preventative measure and should last much longer than this.

Your pump is shot, or the guts are anyway. Change the pump!!!! What are they worth? Couple Hundred bucks. Well worth the aggravation.
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Old 20-04-2016, 13:56   #30
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Re: Generator Water Pump

Most owner installs I have seen try to install a generator with the least effort and the most convenient spot. The closer to the keel the pump is and the straighter the intake plumbing is, along with a good strainer, the longer the impellers last. It's better if the thru hull is deep, too. My 2 generators have the same impellers I put in when I bought this boat in 2011. My mains have the same impellers I put in then, too. 500 hours a year roughly on the mains, and about half of that on the generators. One Onan and one Perkins. If they have been sitting several months, I put a small amount of water proof grease in the housing before running. I don't do any special winterizing unless I know I will be shutdown for many months. And then it's engine prep.
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