Water heater configuration......

[NYSail]

so my last thread I was speaking about my preasure release value releasing. So I replaced the valve and low and behold I had a trickle of water coming out after about a half hour of motoring hard. I replaced this tank about 4 years ago and just installed the new tank (raritan 1700 series 6 gallon) like the original tank was. So going through the manual this weekend I see they recommend an expansion tank located on the cold water line leading to the tank and a gate valve on the engine hot antifreeze leading to the hot water heaters heat exchanger. well guess I should have followed the instructions..... is this the way everyone installed the hot water tank?? I guess this could be my problem......
Thanks as always!!!

 

[Scott T-Bird]

I don't think it's the problem. First, you indicated that they are recommendations, not requirements. Second, I don't think a gate valve on the heat exchanger system is going to affect the pressure release valve on the water system. If you are suggesting that the engine-heated water builds to a pressure that causes leakage, I don't think a gate valve will regulate the heat. Aside from that issue, an expansion tank shouldn't be necessary to regulate pressure in the tank either. I believe the purpose of the expansion tank is to regulate pump operation, but I could be wrong. I just installed an isotemp heater, and neither of these 2 recommendations is offered in the manual. I installed a small accumulator tank in line between the pump and the faucets, but I have a cold water tee to the heater between the pump and the accumulator. The manual for the accumulator tank indicated that it doesn't need to be in line with all components of the system. The manual for the isotemp heater mentioned nothing about a need for expansion tank. It does have a pressure relief valve where the tank drains for winterization.

 

[Don S/V ILLusion]

Neither do I see any link between the relief valve and an expansion tank or gate valve.

Try the simple stuff first - is always a good plan.

Try exercising the relief valve. It may not be as "closed" as you think. This is a good mystery, not that is any consolation

 

[arf145]

And make sure it's the right valve. I believe they release on temperature and pressure, and I seem to remember from replacing the one on my previous boat's tank that several different temperature valves were available.

 

[Ken Cross]

Time out.
As water (or anything else) heats, it causes thermal expansion. Since you can't compress water it has to go somewhere. Either there is enough flex in the tank to absorb the volume or it will vent somewhere. The pressure relief valve keeps it from exploding the system. An accumulator (expansion tank) would certainly help with the increased volume. It's simple physics.
With an average thermal expansion (varies in water due to temperature) of .0006 per degree c
6 gallons of water would expand by about 0.118 gallons if the temperature is raised from 100F to 160F (a 33 degree c change.)
More expansion would be present if you started with cooler water in the tank.

As for the gate valve, it would add some utility if you for some reason didn't want the engine to heat the water, but I (like Scott said) don't think it would be an acceptable temperature control.


I hope this helps.
Ken

 

[jssailem]

NY Sail.I went online and checked the specs for the 1700 Raritan heater.

1. Temperature and Pressure Valve rated at 75 psi (517kPa) 210°F (99°C) is included for on-board nominal working system pressure of 50 psi (345kPa) maximum.

If you are producing 210F when running your engine then you have an over heating problem with the engine. If you are producing 75 psi then your pump is over sized and you are likely leaking in more places.

So lets look elsewhere for the leak. Did you use a sealant on the threads of the fittings? What did you use? If teflon tape did you get some beyond the threads so that it creates a gap to leak along the fitting? I prefer plumbers pipe sealant (like RectorSeal® T Plus2) that you paint on the threads. Designed for potable water, Seals the threads, remains pliable, fills the cracks and crevices. Only issue is it is a little messy. Only deal with it once.

 

[jlp0217]

I had the same problem when I replaced my hot water tank several years ago. The original gave out because the PO never hadn't replaced the anode for over 15 years. Anyway, the original had a failed check valve in the input line, which I also replaced. With the check valve in place, the expansion of the water as it is heated caused the pressure valve to release a little water. In short order, this caused the relief valve to fail, and always leak. If a check valve is in the line, an expansion tank is needed after the check valve. I just removed the check valve and let the accumulator tank do the job. If you have an on-demand pump and no accumulator, you may need the expansion tank, but I don't know why that would be different than your old tank.

As to the gate valve in the engine heat line, my engine (Perkins 4.236) runs at about 180 degrees. That's not enough to cause the release valve to open, but it is enough to trip the over temp breaker in the water heater. So I installed the gate valve, and while it slowed the temp rise, (I can motor longer before the breaker trips) it did not prevent trips. But I don't want the temp rise slowed, I want to be able to heat water quickly at anchor, so I keep the gate valve closed, leave the screws out of the panel covering the water heater, bored a hole in the cover and insolation over the breaker, and reset the breaker the next morning after shore power has been connected.

 

[Ron20324]

If you have the manual, does it tell you to service the internal air gap? My Attwood says to let the pressure valve SNAP closed. "A dripping TRV does NOT mean it is defective." Also, it specifies engine coolant heating for more than 2 hours will produce excessively hot water(and thus the gate valve idea, I suppose).