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Fyrzowt · 11-20-2006, 11:48 AM

I just replaced the water heater in my '72 GT, upgrading it to an electric ignition model.
There is a relief valve marked 125# that is in the interior plumbing that dumps (relieves) down through the belly. I notice as the heater heats, that there is a small amount of water that occasionally exits the tube - approx 1/2 teaspoon every 15 - 30 seconds.

Do I need this valve? Is the water exiting normal upon heating the tank?

There is also the standard relief valve mounted directly to the upper part of the tank with a manual handle on it.

Thanks for any help,
Dave

Chuck · 11-20-2006, 12:33 PM

Well, the fact that its dribbling water out of it tells you either a: yes, you need it, and its doing exactly what it was designed to do, or b: its busted.

I'd have to guess that its "a:". Does it dribble continuously, or just until the water heater shuts off (when the temp is stable)? The short run of pipes in a trailer is going to be less able to absorb the pressure from expansion when the water heats up, than a full sized house system. and in houses, where this is an issue, they put in accumulator tanks to handle the expansion. The trailer is so small, and as you noted, its "teaspoons" of water coming out, the relief valve makes more sense.

Tarheel · 11-20-2006, 01:09 PM

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.

Fyrzowt · 11-20-2006, 01:09 PM

Chuck,
Thanks for the reply.
The tank was still heating when I made the original post, it is now done heating and the dribble has stopped. I suppose it could be normal, I never noticed it with the old heater but have only had this trailer out 2 times.
Dave

Fyrzowt · 11-20-2006, 01:12 PM

Quote:

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.

I understand the need for a relief valve. I was asking if I need both of them. It's my understanding that the valve on the tank is also a relief valve.
Dave

Tarheel · 11-20-2006, 01:24 PM

I know leaking valves are a pain but I don't want you getting hurt with a water tank that turnes into a steam tank. Many leak as they heat up and then seat. Try manually lifting the relief and letting some water flow then letting it reseat itself this might help. To be truthful I have always done all of the above just before going to the hardware store and buying a new relief valve.

Chuck · 11-20-2006, 01:33 PM

I wonder about the need for 2 of them, too. Without an expert opinion, I'd have to go with keeping it, because Airstream put it there, and they presumeably know more about it than I do...they thought it was needed; who am I to argue?

It might be that the one that is built into the heater itself is different...maybe less sensitive(?)...don't know, just guessing. could be that the possibility exists for the tank to be seperated from the pipes in the trailer by means of shutoff valves, so it needs its own non-bypass-able valve. (is that a word? ). also, excessive pressure could be coming in from the outside, too, having nothing to do with the water heater. So it backs up the on-board pressure regulator, too.

Tarheel says that failures are rare, but on my last house water heater, the device was utilized twice. Electric water heater: high-temp shutoff switch failed, so the water just got hotter and hotter and hotter, until the heating element got so hot that the built in circuit breaker tripped. But before this happened, the pop-off had to do its thing, and dribble water all over the basement floor. First symptom was excessively hot water in the shower one morning, (which I found but mildly curious, the first time), followed by NO hot water the next morning.

THAT problem caught my attention enough to make me go downstairs and actually look to see what was going on

TomW · 11-20-2006, 02:30 PM

Water heaters are required to have a relief valve, and it has to be able to relieve both high pressure and high temperature conditions.

At face value, it would appear that the other Over Pressure Relief (OPR) valve mounted on the cold water line is there in case the regulator fails to maintain low pressure & shore water pressure is excessive. I believe Airstream recommends a cracking pressure of 65 psig.

From experience, I have found that it is not a good idea for either the water heater's or the sytem's OPR valves to vent with any regularity as water deposits tend to build up on the sealing surfaces, and in time can crud the valve shut. When this happens, no OPR will occur.

With that said, I am still allowing my system OPR valve to dribble when the water heater is fired up. The proper solution is to mount a pressure accumulator on the line. I just have not got around to it.

Others have had luck with trapping an air bubble in the water heater to absorb pressure changes. Not me.

Tom

Fyrzowt · 11-20-2006, 02:37 PM

Thanks to all for their ideas. I will be using the trailer this weekend, and will watch it to see what it does. After the weekend I may pull it out and do a vinegar soak in case it does have deposits in it.
Dave

Tarheel · 11-20-2006, 02:54 PM

I have looked at my 94 water system pretty extensively as well as the piping diagram and to the best of my knowledge there is no relief on my cold water system. I have been in piping engineering for 25 years and do not see a need for it. Your piping system should not fail with external water hose connections. The system should have a working pressure of 125 psi. I have never seen city water or any external pressure that exceeds this limit. Your water regulator should take care of this before it enters the tailer. I didn't catch the fact that you were talking about the cold water side. Best of luck

TomW · 11-20-2006, 03:07 PM

Quote:

Originally Posted by Tarheel

...I have been in piping engineering for 25 years and do not see a need for it. Your piping system should not fail ...

Nothing wrong with Tarheel's post.

FWIW, I would rather have the cold water OPR because, if it is not present, the pressure gets high enough that water shoots out of the faucet rather forcefully if the faucet is opened during heating. While the splashing dies out quickly, I personally find it a little annoying.

Tom

Excella CM · 11-20-2006, 03:35 PM

It makes perfect sense that your relief valve would vent a small amount of water when the heater first comes on. The heated water expands, and without an accumulator, there is no room for the expanded fluid. The relief valve on the water heater should adequately protect the system. The way I perceive it, two valves double the opportunity for a leak. If it starts to leak, I would replace the second valve with a plug or, even better, a pressure guage so I could have one more piece of usless information to monitor! Also, a pressure accumulator mounted near the pump is a nice feature that cuts down on pump wear and noise-well worth the few bucks to put it in.

balrgn · 11-20-2006, 04:17 PM

A second relief set at the same setting would do you no good....

If the relief is lifting there is an issue causing something to over pressure...

TomW · 11-20-2006, 04:41 PM

Relief valves on water heaters are generally set at 150 psig & 210 degrees F.

Tom

peegreen · 11-20-2006, 05:05 PM

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 · 11-20-2006, 08:22 PM

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 · 11-22-2006, 04:42 AM

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 · 11-22-2006, 06:18 AM

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 · 11-22-2006, 07:50 AM

Quote:

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.

Quote:

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 · 11-22-2006, 08:46 AM

Quote:

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.