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Old 09-01-2013, 04:04   #1
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Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

Hello

A

I have a $70 Shurflo pump which is intermittently grunting as i type!! The system comes from the CW tank and splits to 4 different destinations -
1 galley tap/faucet
2 galley 3 stage filter system
3 head basin
4 head shower

as the pump grunts when #2 is used, I shall install an accumulator.

But... I have a 40L HW tank which will be heated off the engine. I assume I shall need HW piping to at least the head for the shower.

Will I need ano accumulator? (theres a pressure letoff valve on the tank)?

I guess a vsd pump might come into the total equation?

thnx
J
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Old 09-01-2013, 04:48   #2
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

Unless you have check valves installed, an accumulator ANYWHERE in the pressure side of the CW should suffice.
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Old 09-01-2013, 05:43   #3
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By "grunting" I assume you mean the pump periodically turns on for a short time. That suggests a leak either in the piping after the pump or one of the flappers in the pump itself. Fix the leak and it will stop grunting. An accumulator will not fix this problem. It will just extend the time between grunts and the pump will run longer each time. But the problem will remain.

Dan
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Old 09-01-2013, 05:56   #4
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

No, you shouldn’t require a second accumulator, when adding hot water.

Don Casey diagrams and explains a typical FW Plumbing system
Here ➥ BoatUS - BoatTech - Boat Plumbing by Don Casey
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Old 09-01-2013, 06:05   #5
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

Thanks both for your views.
GM ~ sounds good but .. why? Surely HW is on a different circuit and might need an accumulator?
ps can standard pumps and accs handle HW?
pps I clicked on the link but only got the home page. sounds a good link tho.
ppps I note that plastic hose/piping can function as a proxy accumulator with HW!!!

thnx again
J
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Old 09-01-2013, 06:17   #6
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

The HW "circuit" is fed from a "T" off the cold water side. The temperature of the water is irrelevant to pressure across the system. You will have friction loss from the pump end to the outlet which will correspond to the length and flow rate, BUT considering the flow volume in a typical marine potable water system that loss will not be significant.

Being non-compressible, water will have the same static pressure across the entire system. An accumulator anywhere on the system will reduce pump cycles, but to keep hot water from flowing to the cold side, the accumulator needs to be on the cold side before the heater.
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Old 09-01-2013, 08:08   #7
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

Quote:
Originally Posted by capngeo View Post
The HW "circuit" is fed from a "T" off the cold water side. The temperature of the water is irrelevant to pressure across the system. You will have friction loss from the pump end to the outlet which will correspond to the length and flow rate, BUT considering the flow volume in a typical marine potable water system that loss will not be significant.

Being non-compressible, water will have the same static pressure across the entire system. An accumulator anywhere on the system will reduce pump cycles, but to keep hot water from flowing to the cold side, the accumulator needs to be on the cold side before the heater.
Indeed.

Both the cold water supply(s) and the Hot Water tank are pressurised by the pump & accumulator that precedes them.
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Old 09-01-2013, 09:12   #8
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

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Originally Posted by GordMay View Post
Don Casey diagrams and explains a typical FW Plumbing system
Here ➥ BoatUS - BoatTech - Boat Plumbing by Don Casey
I have two objections to the diagram in this article, which is also attached to another post in this thread.

First, there should not be a check valve on the inlet to the hot water tank. The first reason is that as the tank heats up, the pressure inside the tank will increase and it will have nowhere to go except the relief valve. Better to let that pressure equalize across the entire system and the accumulator. Second reason is that when using the hot water, the mixer at the faucet will not be able to maintain a constant temperature. The pressures (and thus flow rates) of the hot and cold water will vary differently causing showers to alternate between scalding and freezing. Instead of a check valve, a vacuum relief valve should be used to prevent the backflow of hot water into the cold plumbing if pressure is lost.

Second objection is the lack of a thermostatic mixer on the outlet of the tank. Without such a mixer, dangerously hot water is available at the tap. Having a mixer at the tank is safer, and preserves your hot water in the insulated tank, not in the plumbing. The mixer should be protected with a heat trap to prevent it being constantly exposed to hot water, which over time will cause it to clog up with mineral deposits and fail.

I struggled with hot water on my boat for years with a system exactly as shown in the diagram. These alterations made a huge difference for me.
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Old 09-01-2013, 18:16   #9
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

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Originally Posted by JayH View Post
I have two objections to the diagram in this article, which is also attached to another post in this thread.

First, there should not be a check valve on the inlet to the hot water tank.
A check valve is very common in this location. If you are worried about HW pressure buildup causing a leak at the pressure relief valve put a few loops of flexible hose between the check valve and the hot water tank. This will provide the small amount of expansion needed. Water doesn't expand that much. Air however does expand a lot and this is usually the cause of drips from the pressure relief valve. Get the air out of the HW tank and the drips will probably stop.

Quote:
Originally Posted by JayH View Post
Second objection is the lack of a thermostatic mixer on the outlet of the tank. Without such a mixer, dangerously hot water is available at the tap.
You can also turn down the thermostat on the tank. Tanks with dangerously hot water inside are dangerous period. That is probably another reason your pressure safety valve leaked on the HW tank. These valves are sensitive to temperature and pressure. If the water is too hot the safety valve will leak.

Dan
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Old 09-01-2013, 18:24   #10
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

In the US, HW tanks have overflow valves to blow off excess pressure as needed, so the check valve is okay in most cases. You only need one accumulator and a T connection to the HW source. Your pump need to prevent water from back flowing from the pressure side back to the tanks. All the pressure water pumps I've seen have that feature.
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Old 09-01-2013, 21:35   #11
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Re: Accumulator for Existing Cold Water System - But Looking Ahead To HW System ...

Water when heated will expand. A 6 gallon volume (as in the typical water heater) will expand about a pint from 40 to 140 degrees F. An accumulator anywhere down stream of the pump will serve for thermal expansion and prevent pump short cycling.


If you use a VSD pump, THEN install a check valve before the water heater and add a accumulator down stream of the check valve. A VSD pump does not need an accumulator, but the Water heater will.

If you don't have a VSD pump then the check valve before the water heater serves no purpose.

While the T&P relief valve will burp the expanding water out, the pressure that it reliefs at will subject the hot and cold water system in a boat to excessive pressures and possible fitting failure in the long term. The typical relief valve reliefs at 100 psig or higher. While landside plumbing materials are designed for 80 psig, boat fittings/ hose clamps generally don't have that working pressure.

The 1 gallon-ish thermal expansion tanks at the big box stores will work better and cost less then the plastic marine accumulators.
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