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Old 11-20-2006, 12:48 PM   #1
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Do I need this "second" relief valve?

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
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Old 11-20-2006, 01:33 PM   #2
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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.
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Old 11-20-2006, 02:09 PM   #3
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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.
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Old 11-20-2006, 02:09 PM   #4
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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
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Old 11-20-2006, 02:12 PM   #5
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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
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Old 11-20-2006, 02:24 PM   #6
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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.
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Old 11-20-2006, 02:33 PM   #7
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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
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Old 11-20-2006, 03:30 PM   #8
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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.

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Old 11-20-2006, 03:37 PM   #9
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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
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Old 11-20-2006, 03:54 PM   #10
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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
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Old 11-20-2006, 04:07 PM   #11
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But do you want to know when the water heater is heating?

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.

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Old 11-20-2006, 04:35 PM   #12
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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.
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Old 11-20-2006, 05:17 PM   #13
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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...
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Old 11-20-2006, 05:41 PM   #14
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All OPRs are not created equal

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

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