WH pressure relief valve & wall thickness
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URL: http://www.rpod-owners.com/forum_posts.asp?TID=3659
Printed Date: 21 Jun 2025 at 2:22pm
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Topic: WH pressure relief valve & wall thickness
Posted By: ontheroadagain2
Subject: WH pressure relief valve & wall thickness
Date Posted: 26 Jun 2013 at 10:44am
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On 3-11-12 Techntreck commented on "NO, don't release the pressure relief valve of your water heater to get water into the heater's tank (which someone earlier had mentioned doing)" Well, I made the mistake of doing that when first trying to get water into the heater on our 2012 172. I don't know how much of the 'require cushion' I let out; but having done it (and there are probably others as well). What should you do to replace it? Drain the whole system as if you're winterizing it and start over? ...or? I've been using it and we're heading out to the Black Hills in a day or so for our first major trip. I'm doing a batch of mods right now and will probably post pics when we get back. I was just checking on the exterior wall thickness issue, screw anchors and that kind of thing (when I ran into the above WH comment). Is there anywhere on the forum where all this valuable info is 'gleaned' and put together in some kind of list of basic"facts for all" to work from? What also would be helpful is some shots of R-Pods under construction where the 'skeleton'; if there is one could be seen before all the foam and sheet plywood gets laminated in place. Forest River could probably contribute such fotos and they would be a great help to the many that ask about 'studs', etc. Shots of where the wiring is all being routed would be of greater help. Sorry in advance of this info is somewhere already...I always just google the question and it takes you to posts that pertain...and maybe that's missing already accumulated info. ------------- '04 Americamp M 270RKS 5er @ seasonal site |
Replies:
Posted By: techntrek
Date Posted: 26 Jun 2013 at 9:26pm
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Personally I would drain the water heater - either open both low-point drains and the WH pressure relief valve (ironically), or take the anode out. Then let it refill normally. Several of us have commented on the interior walls when we've done mods, but you would have to search around to find that info. I'm not sure anyone has had to put a hole through the exterior wall. Or do you mean the interior of an exterior wall? Do a search here for "factory tour" and you'll find the pics of the half-built pods. ------------- Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ http://www.rpod-owners.com/forum_posts.asp?TID=1723 - Pod instruction manual 
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Posted By: ontheroadagain2
Date Posted: 27 Jun 2013 at 9:35am
 thanks techntrek, I'll be doing just that this morning. By the way, what is the negative impact of not restoring the 'cushion of pressure'? I think I'll take the anode out...in all the years of camping with travel trailers, pop-ups, etc.; it has always been a pain to deal with the rusty anode when winterizing and worse...not finding the correct size socket that fits them and using some make-shift set-up of crescent, etc. So #1-get the socket. #2-drain the WH and all the old "left over" fresh water and #3-refill. I noticed the huge response to a maintenance manual; which I'll start checking into when I get back from Custerville. Thanks again. ------------- '04 Americamp M 270RKS 5er @ seasonal site |
Posted By: Keith-N-Dar
Date Posted: 27 Jun 2013 at 12:22pm
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I may not drain the system, just isolate the water heater like one does to winterize. Then remove the anode, drain, put it back and refill. ------------- Keith-N-Dar Boris & Betty (Boston Terriers) 2011 R-Pod 177 2010 Ford F-150 |
Posted By: furpod
Date Posted: 27 Jun 2013 at 1:02pm
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I am not totally understang the WH issue.. BUT.. If I understand it, you had an empty hot water heater. You hooked up to city water or filled your FW holding tank and turned on the pump, either way, a wet pressurized system. Then, in order to get water into the WH, you opened the blow off valve and vented the air there. Instead of just opening a hot water handle in the trailer. If that is what you are saying, and are worried, no need. Unless the safety valve is leaking now, you didn't hurt a thing. ------------- |
Posted By: techntrek
Date Posted: 27 Jun 2013 at 1:46pm
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The problem is by opening the pressure relief valve the cushion of air that normally rests at the top, was removed. That cushion is needed as the water temperature increases. Water doesn't compress as the water heats up and camper water systems are too small to absorb the extra pressure. Even homes must now have a separate air bladder installed to help with this even though those systems are much larger.
------------- Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ http://www.rpod-owners.com/forum_posts.asp?TID=1723 - Pod instruction manual
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Posted By: furpod
Date Posted: 27 Jun 2013 at 3:41pm
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I don't think that is how they work.. if you open that valve (which you are supposed to do periodically), you instantly get water out... even on my house water heater, where the valve is at the very top of the WH.. there is literally no way to keep "air" in the WH. The fact that water doesn't compress is WHY we need a safety valve, so it can open and allow the pressure out if the WH malfunctions. The bladder and expansion tank are separate from the WH itself, and it's purpose is to reduce and/or eliminate both water hammer, and pressure lag, when opening a faucet. You can in fact buy small ones for your RV, to help with the surging of water that can happen when on the pump.. http://www.campingworld.com/shopping/item/shurflo-accumulator-tank/2290 ------------- |
Posted By: ontheroadagain2
Date Posted: 27 Jun 2013 at 11:12pm
 I'm truly amazed at the various thoughts. My very first home was an 1860's farmhouse with a jet pump hooked up to a sand point. The pump eventually went south and I replaced it with one of the bladder types and had to pump air into the bladder. It was vaguely explained 'how much air pressure' and I ended up guessing at the pressure and living with it for the next fifteen years with nary a problem. So I thought this would be fairly simple. I drained all the water from the fresh water tank (no city water hook-up was ever involved). I opened all the hot water valves thinking they are somehow involved in the system (after thinking more later I realized the water pump is in between so that was a moot effort). O.K. Water is gone. I opened the pressure relief valve just a crack and it spit an almighty blast of spray all over the work area, me and anything else within three feet. That was nuthin'. I then decided it would be better to loosen the anode and let all the water out the bottom end. I used the 1-1/16" socket I'd found and ratchet the anode out....once it got close to the last few threads it started spitting and I ratcheted faster. "POW" the anode said as it shot across my driveway hitting a brick stair trim wall...along with that 'bullet' came all six gallons...maybe only 5-1/2 who can measure it; but it covered a Lot Of Driveway with white bits of crud and all that water pretty much instantly.....another gallon trickled out and there I stood in total amazement. I had opened a 'bomb' without knowing it. I hope anyone reading this will learn from my mistake...what was it? I should have gotten a large rag or similar and covered the work area and released the pressure valve into a old bucket or waste basket....even the garbage can. There is obviously quite a bit of static pressure left in these tiny water heaters. Needless to say the mess of spray was everywhere and I broke out the garden hose and set it on "jet spray". I then examined the slightly bent anode...straightened it...it was missing a bit of the porous material; but plenty was left for the rest of the season...and reinstalled it, closed the pressure relief valve and refilled about 18 gallons into the fresh water tank and went inside and turned on the pump and got everything up to snuff. I welcome all your hilarious comments; but I'm sure there are a few out there that will definitely treat there WH with a bit of respect about this pressure issue. Thanks for all your comments and we're heading for the Black Hills tomorrow night. ------------- '04 Americamp M 270RKS 5er @ seasonal site |
Posted By: techntrek
Date Posted: 28 Jun 2013 at 9:05am
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Interesting furpod. I've just eyeballed the height of the upper water line and the pressure relief valve and from what I could see, the valve was higher. That might still be true, but the air pocket that is left gets compressed so much that the water line is above the pressure relief valve.
ontheroad - actually the water pump is between the fresh water tank and the rest of the system. It is before the water heater so opening the hot water valves should have removed any pressure in the system. Even opening the cold water valves should do that - as far as I know there are no backpressure-prevention valves in the system which would prevent the pressure in the water heater from pushing backwards through the cold water system. Then opening the pressure relief valve should have definitely removed any pressure, if you left it open. ------------- Doug ~ '10 171 (2009-2015) ~ 2008 Salem ~ http://www.rpod-owners.com/forum_posts.asp?TID=1723 - Pod instruction manual
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Posted By: furpod
Date Posted: 28 Jun 2013 at 10:08am
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Yes, it's easy to think that it must have something to do with air at the top, but it's not actually. If you go look at water heaters at the hardware store of your choice.. if that was how they worked, some water heaters have the safety valve halfway down their body.. lot of air.. As stated, opening the pressurized system is.. entertaining. it's best to turn off pump or disconnect from city water, then open the sink faucets to relieve the static pressure before removing the anode.. or.. make sure to have someone videoing the pressurized opening..lol Here is a link to what they do and how they work.. If the system is working properly, while there is a slight pressure rise based on the WH expanding the water in the tank, your plumbing system is designed to hold that pressure, it's when it malfunctions, and heats to high, that bad things can happen. MythBusters did a pretty good episode on it. I think they shot the core of a standard residential WH 400 feet into the air, after it went through a ceiling and roof structure.. Took well above 300psi in the system if I remember right, and they achieved that pressure by removing/bypassing all the safety devices.. http://www.watts.com/pages/support/tp.asp?catId=64 - Watts I was forced to learn a whole lot more about plumbing in homes then most people need to know because of the reef tank, I have all kinds of "extra" pluming, pressure gauges etc. Then I got to learn all about RV plumbing by not using a pressure reducing valve when hooking up the 'stream in a campground that had "spotty" pressure.  ------------- |
Posted By: furpod
Date Posted: 28 Jun 2013 at 10:16am
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Just for fun.. http://dsc.discovery.com/tv-shows/mythbusters/videos/exploding-water-heater.htm - Kaboom ------------- |
Posted By: TrinityTurret
Date Posted: 13 Oct 2013 at 10:20pm
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Anode rod shoots out like an arrow? I'm investigating draining the water heater, but came across videos & posts about people who simply unscrewed the anode rod and WHOOSH, the rod shot out like an arrow. Do NOT want that to happen to me. So, to remove that built-up pressure, if I simply open the hot water knob on the sink, will that be enough to avoid this happening? ------------- There's only one way... |
Posted By: Bill-GA
Date Posted: 13 Oct 2013 at 10:31pm
Make sure the heater tank T-values are in the Heater position (normal) so the pressure will bleed out thru the sink faucet. ------------- Bill & Bev 13 yr old dachshund 'Elsa' 2010 RP-176T (tent & slide-out) 2011 Toyota Tundra 2WD TV |
Posted By: Keith-N-Dar
Date Posted: 14 Oct 2013 at 5:35am
Yes, what he said. but you do need to open the tap to drain the pressure. Mine didn't shoot out like an arrow, but I did get a face full of water the first couple of times I removed it. Now I open the tap and remove the pressure. ------------- Keith-N-Dar Boris & Betty (Boston Terriers) 2011 R-Pod 177 2010 Ford F-150 |
Posted By: kymooses
Date Posted: 14 Oct 2013 at 10:46am
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I always drain mine through the low point drains. No pressure and then very little water splashing me when I remove my anode rod. ------------- https://calendar.google.com/calendar?cid=cnBvZC5zcG90dGVyQGdtYWlsLmNvbQ - RPod Rallies https://www.google.com/maps/d/embed?mid=1W1foQXGtrjf8aYly1uh0b-bHPfI&hl=en_US - RPod Owner Map |
Posted By: asreichler
Date Posted: 14 Oct 2013 at 6:09pm
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An interesting fact The change in volume is not a constant. The density of water changes with temperature. You should be able to calculate the change in volume using data on the specific volume of water at 60° F (0.01603 cubic feet per pound) and 90° F (0.01610 cubic feet per pound). The percent increase is 0.01610/0.01603 = 1.0044. This would be a 0.44 percent increase in volume. Source: http://www.engineeringtoolbox.com/water-specific-volume-weight-d_661.html - 10 ------------- 2014 178 TV 2004 Dodge 2500 deisel |
Posted By: Jdub
Date Posted: 14 Oct 2013 at 7:02pm
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How does the rod vanish? Is there a core that doesn't dissolve? I took the rod out to empty the tank and it is very thin at the base but still fat in the middle and end. Is it going to just fall off, or it there a core that remains no matter what? This is after only one summer.
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