2002 310 catalina, 6 g water heater, the original pressure valve on it is set for 150 psi. If it ever got that high (for whatever reason) it would blow every fresh water hose fitting on the boat. Since this setting, at least to me, is too high what does the forum think about replacing it with a 50 psi (for example) which is 10 more psi than my fresh water pump output pressure?
Pressure/temperature valve and setting on water heater
- Thread starter east coaster
- Start date
The T and P valve on your tank is there to keep the tank from blowing up not the plumbing. There should be a check valve on the inlet that prevents the hot water from backing up into the CW plumbing. If the tank every reached 150 psi it would only blow out one fitting, then the pressure would be reduced.
When the tank is heated by the engine, the water temp will be about 160°F, the same as the engine's operating temperature. The pressure in the tank will likely be more than the 50 psi which will cause the valve to open, dumping water out until the pressure was reduced and then it would repeat until all the water in the system was drained.
When the tank is heated by the engine, the water temp will be about 160°F, the same as the engine's operating temperature. The pressure in the tank will likely be more than the 50 psi which will cause the valve to open, dumping water out until the pressure was reduced and then it would repeat until all the water in the system was drained.
Not exactly. The pressure relief valve must be set no greater than the maximum allowable working pressure (MAWP) of the pressure vessel OR can be chosen to protect the weakest pressure component in the system.
I must confess I don't know the rating of the relief valve on my water heater because very early in the game, I installed an accumulator to stop the periodic opening of the relief valve when starting out with a cold hot water tank.
IMO, without an accumulator, you would see repeated opening of the relief valve when starting out with a cold tank. This would eventually cause the valve to continuously leak. Where does the valve discharge to is always an interesting point ?
I would take a look at "what is the safe operating pressure for your tubing at 160°F" and go from there. One up from there would be to install an accumulator and not have to worry about ever getting to the higher pressures.
For reference the T&P valve on my boat is set at 75 lbs @210° F. At that level I have not had any difficulties with blowing the valve. One of you engineers can probably calculate what the pressure increase is when raising the water temp from say 50°F to 160°F.
Thank you both for your quick and thoughtful response. The TP valve has a short hose and when it goes off (it hasn't yet in the past 6 years) it goes to the bilge. I did have an accumulater tank but when my potable water pump went into permanent retirement, I purchased a new one that claims no accumulater is required. When I get to the boat tomorrow I will take a picture and post same. Have plastic hose for plumbing rated at 100psi when new. Will change over to pex this fall haulout. Thanks again.
Typical marketing yahoos. The newer pumps are what is called "proportional control" meaning that as the pressure gets higher the pump slows down rather than the complete ON/OFF operation of the pumps owned by us plebs which will experience rapid ON/OFF cycles when water is draw. Without an accumulator, these late model pumps will still experience the same overpressure that an ON/OFF pump would see when a cold tank is heated.
The volumetric increase as water rises from 50°F to 160°F is 2.31% .
Unfortunately, this tells us nothing about the pressure change as we further need to know the thermal expansion of both the hot water tank and the tubing which carries the hot water.
I would say that would satisfy all requirements of any boat's domestic hot water system.
FYI
I just installed a new Shurflo Aqua King II pump.
Even with the old pump I didn’t experience issues when the heater went from cold to hot. I do have a check valve that prevents the higher pressure in the heater from pushing hot water back into the cold water inlet side. So I don’t understand how pressure in the heater would affect the pump pressure.
Anyhow
The new one does not cycle on and off due to pressure build up during low flow rates.
The manual says it has a by pass valve that bleeds off the pressure under certain conditions that works with the on off pressure switch to prevent cycling on off while maintaining pressure.
It appears to eliminate the need for an accumulator to stop on off cycling.
Works very well for my use.
I just installed a new Shurflo Aqua King II pump.
Even with the old pump I didn’t experience issues when the heater went from cold to hot. I do have a check valve that prevents the higher pressure in the heater from pushing hot water back into the cold water inlet side. So I don’t understand how pressure in the heater would affect the pump pressure.
Anyhow
The new one does not cycle on and off due to pressure build up during low flow rates.
The manual says it has a by pass valve that bleeds off the pressure under certain conditions that works with the on off pressure switch to prevent cycling on off while maintaining pressure.
It appears to eliminate the need for an accumulator to stop on off cycling.
Works very well for my use.
I also have a Shuffle Aqua King, it one cycles when there is a leak in the plumbing system. Otherwise it comes on when a tap is opened and shuts when it is turned off.
A check valve in the HW inlet prevents back flow.
A check valve in the HW inlet prevents back flow.
Thank you all for your input, suggestions and what is on your boat and working for you. I now consider this thread closed.
160º is kinda low for a diesel. Typical thermostats that I've seen on boats are 170º or 180º; it's likely higher on trucks, more like 190 to 210º.
You don't know @jviss .
The actual temp of the engine is more like 170º but I doubt the DHW tank would ever get to 170º so hence the ballpark figure of 160º.
There you go again with the excessive affectation towards inanimate objects.I have a 2 gallon accumulator. I love it.
Ideal, outstanding, brilliant, top notch, exemplary, or consummate would suffice.