Do I need this "second" relief valve?

[peegreen]

From the Suburban website: http://www.rvcomfort.com/suburban/se...-37516Question 5Why does water drip from my water heater's pressure relief and temperature valve? Answer:You may experience water weeping or dripping from your water heater's pressure and temperature (P&T) relief valve when your water heater is operating. Water weeping or dripping does not mean that the P&T valve is defective. As water is heated, it expands. The water system in a recreational vehicle is a closed system and does not allow for the expansion of heated water. When the pressure of the water system exceeds the relieving point of the P&T valve, the vale will relieve the excess pressure.One way to reduce the frequency of this occurrence is to maintain an air pocket at the top of the water heater tank. This air pocket will form in the tank by design - however, it will be reduced over time by the everyday use of your water heater. To replenish this air pocket: Turn off the water heater.Turn off the cold water supply line.Open a faucet in the RV.Pull out the handle of the pressure relief (P&T) valve and allow water to flow from the valve until it stops.Release the handle on the P&T valve - it should snap closed. Close the faucet and turn on the cold water supply. As the tank fills, the air pocket will develop. Repeat this procedure as often as needed to reduce the frequency of the weeping P&T valve. If the weeping persists after following this procedure, you may elect to have your dealer install an expansion or accumulator tank in the cold water line between the tank and check valve to relieve the pressure caused by thermal expansion.

[Fyrzowt]

Thanks for all of the informative posts. I think I have a clearer idea of what is going on. I left the H2o heater on for a while today, and after the initial heat-up, I saw no more water discharge. It makes sense that if it only spits when heating the first time, that's when I would get the most expansion.
I'm probably OK, but I'll keep my eye on it. Thanks again, this is what makes this site so great.
Dave

[Phil Gobie]

The valve should not leak. If it is opening it is probably due to fatigue or it was opened manually and will not re seat. You only need one valve and it should be on the water heater. when you are on water hookup the hose alone will allow for normal expansion when you are running with the pump the pressure is not great enough to effect it. If you have a check valve and there is no provision for expansion it can cause the valve to open. If this is the case an accumulator or small bladder tank or even a shock arrestor will allow for expansion. The valve is for emergency relief only. If it is opened after sitting dormant it will likely leak when it attempts to close. As a plumbing contractor I would never open an existing one without expecting to replace it. As for soaking it in vinegar to clean it I would not recommend it. The springs are steel unless it was special ordered with stainless. The vinegar will encourage rust. The rusting spring can jeopardize the normal function. They should be replaced after they have leaked.
Phil

[jimmickle]

One of Atwood's reps recommended that when you hook up your water supply line at the campground, you NOT fill it with water first. By first attaching it and then turning on the CG faucet, you put some air into the system. Running a little water from the hot water faucet will get the needed air into the heater.

[Chuck]

Originally Posted by Phil Gobie

The valve should not leak.

well, who says its "leaking"? sounds like its just relieving excess pressure, which is exactly what its supposed to do.

Originally Posted by Phil Gobie

If you have a check valve and there is no provision for expansion it can cause the valve to open. If this is the case an accumulator or small bladder tank or even a shock arrestor will allow for expansion.

well, this is exactly the situation in a travel trailer: check valve between the internal plumbing and the hose-hookup to the city water supply...so the hose "can't" provide any relief.
the accumulators I've seen in houses are kind of big to fit in the limited confines of a camper. maybe they figured that this device was smaller/cheaper...also, you wouldn't want something "dribbling" on the floor in your house, but in the case of a camper, it can just dribble out onto the ground. I think I have a pic of the device in question from my trailer...I'll see if I can attach it.
the red arrow points to the relief valve.

[klattu]

Originally Posted by Tarheel

YES you do need it. I will prevent the heater from traveling throught the overhead and several blocks down the street. The relief valve will sometimes lift and allow small amounts of water to leak by, this is not unusual. If the leak becomes excessive it may need replacing. Before replacing the valve check the thermostat on the hot water heater it may be set too high and cause the valve to lift. By all means keep a relief valve in the system or don't use the heater. Heaters rarely ever fail but if they do and there is no way for the excessive pressure to excape it can be leathal.

Good visual answer...
I have had zero luck getting those valve to re-seat once they have opened.
Try and try, always end up replacing.
Adding a 'water hammer' helps absorb some of the pressure.
You rarely see on one a hot water line.

[Phil Gobie]

The valve should only be for a safety. It should not be used as a bleeder valve as it is not going to reseal consistency. If it is opened manually or automatically on a regular basis or occasionally it will get progressively worse and the spring is subject to corrosion. A devise to allow for expansion will work or allowing air into the system but using a relief valve as a bleeder is going likely to be problematic.