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Old 18-03-2009, 04:34   #16
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Nick
Do you have an accumulator tank?
Does your water heaters pressure relief valve blow when you heat her up?
If no...where does the pressure go?
Are your supply lines flexible/expandable?
Thanks
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Old 18-03-2009, 05:06   #17
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Another vote for the Jabsco. My accumulator failed, so I bought the variable speed Jabsco and retired the original pump to "spare" status, instead of replacing the accumulator. Love it. No complaints at all. I can hear it run, but it's not overly loud. It's mounted under the saloon setee with rubber isolation pads around the screws.
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Old 18-03-2009, 05:17   #18
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I've had two different accumulators which have failed. I believe the second has an air bladder to maintain pressure (not sure) but the take away is that it has no effect whatsoever on 'performance' except that whenever there is demand for water - open valve - the pump come on duty and forces the water out of the faucet at a perfectly acceptable rate. I experience no pulsing. I am using a surflo pump. The pump noise is perhaps a down side and maybe accumulators lengthen pump life by having fewer cycles. But performance wise we have no pressure water problems with a non functioning accumulator.
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Old 18-03-2009, 05:30   #19
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Check valve at the water heater?
Any blow off from the water heaters safety valve?
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Old 18-03-2009, 05:35   #20
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No check valve, and no w/h safety valve operations in my setup, James.
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Old 18-03-2009, 05:46   #21
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I have the Jabsco VSD 17. It works great! Volume and pressure is wonderful. There was an issue with some of the earlier models, under voltage conditions would cause them to fail. Mine was replaced under warranty and has not been a problem.
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Old 18-03-2009, 05:47   #22
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Thanks Hud
So what happens to the pressure when after the pump has brought the system to full pressure, then the heater kicks in and adds expansion?
Is it just absorbed through flexible connections in the system??
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Old 18-03-2009, 06:00   #23
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James I don't get where you are going here. The heater over pressure from expanded hot water is hardly enough to create a problem. In my system the water is usually maintained hot since it is created by a heat exchanger off the engine cooling. It would be unusually for me to come aboard, run the engine and not use the water system "releasing" built up pressure which is not very significant to begin with. No pressure relief valve necessary.
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Old 18-03-2009, 06:07   #24
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Isn't it required that hot water heaters have an overpressure relief valve? If the pressure gets too high the valve releases excess pressure. I thought the accumulator was to mitigate water hammer and its primary intent is to increase the longevity of the pump.
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Old 18-03-2009, 06:29   #25
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My concern came after reading what Randal wrote that his safety valve used to blow often until he installed an accumulator.

I have a check valve at the WH and all by lines are rigid....so I'd have very little room for the system to absorb expansion from excess pressure.

I thought I'd install my new Jab$co accumulator in the hot water side.....then I thought it may not be such a good idea since the heat may be tough on its bladder.

So now I'm wondering if the check valve should come out, and the accumulator installed as the instructions show...in the cold water side, right after the pump.

Just a note, that their instructions do show a check valve at the WH.

That’s why I'm confused and keep hammering away at this.

I don’t want to be blowing off the safety valve as part of the norm.
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Old 18-03-2009, 10:18   #26
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James,

I understand your concern and you should move the checkvalve because it is there to prevent backflow when cold lines are opened.

We never have the overpressure valve activate. We have rubber hose like exhaust hose but for hot water service. I'm not sure if these would expand...

You don't need to have an expansion tank on hot water for some reason I don't grasp yet. It's the same for shore-installations: they do have them in central heating but not on water-heaters... but ashore there's no pressure-pump with checkvalves so it's different.

I assume that maybe it also matters which waterheater is used? We have a 40 liter s/s Isotherm and it's all I wish for.

cheers,
Nick.
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Old 18-03-2009, 10:19   #27
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I think people are getting a little confused about the purpose of the pressure relief valve - it is to protect the hot water cylinder (not the pipework) which has a very low pressure rating, compared with the pipework which has no problem handling the slight increase in pressure from hot water.
All HW cylinders need to have a relief valve, especially those that use the cooling water">engine cooling water circuit to provide heat
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Old 18-03-2009, 10:49   #28
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Quote:
Originally Posted by Randal Johnson View Post
John
My boat was built with a Jabsco pump that was promoted as not needing an expansion/accumulator tank so the builder didn't install one. The problem was the system has a hotwater heater in it. The pressure relief valve would discharge occasionally and I traced it to the fact that the heated water had no place to expand to. I installed a tank and now have no problem.
Randal
I'm starting to think the key in this puzzle is in the use of no check valve and flexible line on the cold side....the hot water must expand.

I'm still waiting to hear from Randal if he had a check valve, and if so then where did he install the expansion tank.

I appreciate you patience with me...but again my system is rigid.
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Old 18-03-2009, 13:26   #29
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James,

As far as I know, the only purpose the accumulator serves is to keep a standard pressure pump from rapidly cycling when a faucet is opened. It should be installed just downstream from the pump and before the distribution manifold.

All my lines are clear flexible tubing, and there's no check valve at the water heater. I've never experienced a pressure relief valve operation. I can't imagine it being a problem unless there was a problem with the w/h temperature sensor, and the heating element stayed on until the water began to boil.
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