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HOUSE WATER TEMPERATURE ALERT
On another forum there was a post that really got my attention. The reason why follows.
On our coaches we have had Raritan (or comparable) hot water tanks which are set up so they can be heated with engine coolant. The tanks have a heat exchanger coil for engine coolant which heats the water.
It was apparent from our first coach that when we drew water after driving for a while the temperature was excessive and if we weren’t careful we could easily get scalded. So I started modifying the HW tanks by adding a thermostat and solenoid valve to control the coolant flow such that it shut off the flow of coolant when the water temperature reached the normal HW tank thermostat setting of 125 degrees.
My entire focus was on our safety and not wanting anyone to get scalded. This is especially true on later model engines whose temps run in excess of 200 degrees.
This morning I saw a post from an owner whose plumbing failed because the water from the HW tank exceeded the temperature rating of the plastic water lines used in his coach. I suspect our converters who use the type of water heater described above also use water lines appropriate to the temperatures and pressure. But my concern is if the water temperature / pressure relief valve on the HW tank has been changed. When new, the tanks are equipped with a 75 PSI / 210 degree pressure relief valve. But if someone were to go to a big box store and buy a pressure relief valve it might end up being a 175 PSI / 210 degree rated valve and there is the problem.
The valves look identical but the question is if the piping can handle both the higher temps and the higher pressures as the coolant brings the HW tank up to its operating temperature, and the water expands increasing the pressure. I would recommend looking closely at the valve data plate to insure you have the 75 PSI pressure relief valve. If not, be safe and change it to the proper valve. Also give consideration to modifying the system by adding a thermostat and solenoid valve to limit the hot water temperature.
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10 Replies
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That’s one reason I turn that coolant loop off and the other is almost getting scalded by 200+ water temps.
If you leave that engine coolant loop to the water heater open, do as Jon did and add a thermostat and solenoid. I changed out a Raritan water heater on a Liberty I had that had swelled in height making it a hard job to remove and the pressure relief valve had probably been changed to a home type water heater valve.
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If you turn off the coolant loop on a liberty in the winter or when driving in cold weather the heat exchanger in the water bay will not get hot coolant to heat bay , in summer ok not winter
Disregard Toms post if you have a liberty and are driving in cold weather and you want heat in water bay to keep from freezing the water pump and tank unless you have Gen running and breaker for bay heat on
Or if you have aqua hot and it’s not on you need the coolant loop open to get heat to water bay for heat exchanger -
I recall that Jon (The Genius) Wehrenberg has installed a solenoid to cut off hot coolant water from the Detroit Diesel when it gets above a reasonable temperature because he doesn’t like the extremely hot water in the water heater at the sinks after running down the highway.
We, like The Genius, have a Liberty and I presume that his Liberty like ours has a control valve for the shower that mixed hot and cold water to the precise temperature we desire so we don’t get scalded in the shower.
Has anyone put a mixing valve at the discharge of the water heater (say 120 or 125 degrees) so that the hot water to the coach never exceeds that temp. I like having all that really hot water in the water heater in reserve (no need to run the water heater for a long time after running down the road).
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Dick the problem with that is that the coolant will still over heat the water heater and cause the pop off valve to pop off over temp. The way Jon describes stops the coolant from coming in and over heating the water heater, thus maintaining a constant temp.
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Is the coolant loop turn off back in the engine bay?
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Assuming water lines do not fail as a result of excessive water temperature and pressures caused by the expanding water in the tank as it heats, the incorrect pressure temperature valve will cause the ends of the tank to expand.
The expansion of the water tank eventually causes it to become securely wedged between the top and bottom of the bay. It literally grows that much just because the wrong expansion valve was used. When that occurs it is cheaper to buy a new bus than to take a sawzall to a failed water tank so it can be cut apart and removed in pieces. There is a preventive measure that can be taken. In the cold water supply line to the HW tank there should be a check valve. The check valve is there presumably to prevent a sudden and unexpected back flow of hot water into the cold water side of the system. Drill a tiny hole in that check valve stop. A 1/32 inch diameter hole is enough. That will allow the expansion of the HW to be absorbed by the accumulator tank on the CW side and if there is a failure on the CW side there will be no sudden rush of scalding HW.
That of course presumes you maintain the correct pressure in the accumulator tank.
Bottom line…………use the correct expansion valve and you won’t have any mechanical failures such as the growth of the HW tank, and add a thermostatically controlled solenoid valve to limit HW temp.
As to freeze protection in the water bay, the coolant loop to the heat exchanger is separate from the loop for the HW tank so the solenoid valve does not create a secondary problem.
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Tim,
You can reach the cutoff valves above your fresh water pump in the plumbing bay compartment. I can reach mine without taking the panel off. Just follow the coolant hoses from your hot water heaters and you’ll see them.
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Tom, since our buses are very close build numbers I am curious if your relief valves are rated as Jon describes?
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Thx Tom!
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I’ll take a look Larry and report back, but they probably are..
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