Is an Expansion Tank Necessary on a Fresh Hotwater System?

[Oliver L.]

Hey, this is fun!

My last post on this thread, as it seems that you will never satisfy everybody, so why bother...

No, a dripping relief valve isn't a major issue, except that on my boat I hate it when the bilge pump comes on at night, and I will get up and check just to make sure...

Yes, you can route the water from the relief valve into the bilge, since the worst that can happen is that your bilge pump is stuck, and then you would simply transfer the weight from the water tank to the bilge...

I would never route relief valve water back into the main tank - first, you simply should NOT restrict the flow of water out of the safety valve, and a hose back to the tank could get crimped or worse, and second, I see enough issues with keeping my fresh water fresh, and the warmer the faster stuff grows. Once it's in the hot water tank, it will go out via the shower pump or into a kettle (and thereafter...I'll leave that to your imagination).

In short, if you want to do it proper in my book, you put in an expansion tank, if you feel that that's a restriction of your personal freedom, you can leave it out - just as long as you are enjoying your boat...

Happy sailing!

Oliver

[sailorchic34]

Originally Posted by goboatingnow

Mins dribbles , yet I have a cold water accumulator on this boat !

Check valves on the hot water side are not common in British systems , thermostatic valves on the engine feed are as are the mixing valves on the cylinders.


My PRV empties into the bilge ! ( mind you so does my shower !)
Dave

I should note that the small quart (liter?) size accumulator Jabsco sells, is probably marginal to handle thermal expansion in a 6 gallon tank. For larger water heaters its just too small and you would get some relief valve popping.

While I agree that the relief valve popping is not of major concern, there is a chance that a bit of lime will clog the valve seat and allow all the water to drain into the bilge or overboard as the case may be.

[Deep6]

Well isn't this interesting, I am pretty much dizzy from all the debate. I've since consulted with some locals as well,their comments about saving electricity, peace and quiet and extending pump life, that coupled with this diagram:
http://www.surejust.co.uk/PDF/connections.pdf
And I've arrived at fitting 2 tanks.....1 is an
Amtrol Extrol 30 (4.4 Gallon capacity) Amtrol 30 EXTROL Expansion Tank, 4.4 Gallon (102-1) at PlumberSurplus.com

immediately after the Whale IC Freshwater pump on the cold water side,

and a Bell and Gosset HFT 15 (2 Gallon Capacity) 1BN326 - Bell & Gossett 1BN326 - HFT-15, 2 Gallon Hydronic Heating Expansion Tank

immediately after the hotwater tank hot water outlet, essentially following the diagram.

Now the only question remains is what pressure to set them at, anyone have a concise clear, answer given the label on the pump says static system pressure of 32 psi?

Thanks in advance....

[chala]

Originally Posted by jeremiason

ABYC Standards require a pressure relief valve on all Hot Water Heaters.

And so are other Standards. An accumulator is not a T&P relief valve.

Originally Posted by sailorchic34

Well the pump body test pressure may meet the T&P relief pressure setting, but the rubber diaphragm in the typical 12V pressure pump probably will have issues with the higher pressure….
However the standard T&P relief pressure in the US is 150 psig.

So it is for the OP to determine if his pump and the accumulator will withstand the pressure and if he feel that his system require a non-return valve.

Originally Posted by Oliver L.

I would never route relief valve water back into the main tank - first, you simply should NOT restrict the flow of water out of the safety valve,

To be safe a T&P relief valve cannot have its flow restricted. Safe T&P relief valves does not discharge into a pipe but discharge to open air, a funnel type water collector is part of the body of the valve onto which a drain pipe can be connected. The pipe is just a drain and is unable to discharge to a position higher than the T&P relief valve.