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Thread: Under Pressure!

  1. #1
    Join Date
    Apr 2009
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    Question Under Pressure!

    I recently installed a new electric 40 gallon hot water tank at my mother’s house last week only to find that is soon began discharging water from the factory default 150 PSI pressure relief valve. The water pressure within the area is extremely high which requires a switch to a 175 PSI pressure relief valve to remedy the problem. However, I was not able to locate a long shank (2 ½”) 175 PSI pressure relief valve anywhere to fit the new hot water tank. (Only short shank 175 PSI valves). As a result, I purchased several brass couplings and extensions to modify the short shank 175 PSI valve just enough to fit the new hot water tank. This was initially just a temporary fix until I was able to find the time to plumb a new pressure reducer to curb the beastly water pressure with in my mother’s house… which I have already installed and completed. However, my question to you is NOT… will this modification work and whether it is SAFE… but why isn’t this a SAFE long-term modification? Every local-yokel plumbing “expert” stated “I wouldn’t do that if it were up to me!” However, after some further thought, I began thinking that there wouldn’t several fail-safe’s have to break for this to be a hazardous condition?
    1. If the 175 PSI pressure relief valve’s settings were increased to even double the PSI settings (350 PSI) wouldn’t it still blow the relief valve before blowing the tank?
    2. For the above to occur… wouldn’t the hot water tank’s thermostat have completely stick/fail? (This is a brand new high end “energy smart” hot water tank).
    3. If the hot water tank’s thermostat did fail… would the 30 amp breaker do it’s safety turn off role due to electrical over heating and surge?
    By no means… do I propose to sound like a plumbing expert whatsoever. However, common sense tells me that my modified 175 PSI pressure relief valve is a safe long term solution and that it seems highly unlikely that the above fail-safe could occur resulting in a hazardous condition. However, I am taking the time to “Ask TOH” in regards to this matter!

  2. #2
    Join Date
    Dec 2007
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    Default Re: Under Pressure!

    The reason why you had difficulty finding a 175 psi valve to fit is probably due to residential hot water tanks only have 150 psi valves.

    Personally I think you're hedging your bet on something that's dangerous, never mind voiding the warranty on the tank.


    3. If the hot water tank’s thermostat did fail… would the 30 amp breaker do it’s safety turn off role due to electrical over heating and surge?
    No , not if it doesn't overdraw on the current.

  3. #3
    Join Date
    May 2009
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    Default Re: Under Pressure!

    donobk -

    Not a plumber; but do have some expertise...

    I don't believe a Hot Water heater is rated for 350psi at all. Not anything close.

    Your thinking they put this huge safety shield margin in - and they haven't. That would take a lot more steel, and wall thickness. Hot Water Heaters are mostly made up of foam. The actual tank steel walls are very thin, and glass lined.

    Couple of years ago - here in Seattle (Burien actually) - a Hot water Boiler had a pressure relief valve which failed to relieve, or they had removed it and plugged it because it was weeping (some such dumb thing.) Anyway - it blew the entire side out of a building; and went thru the roof of the building across the street... It made the National News...

    Point of fact: A 5,000psi pressure gas bottle (I know, WAY more pressure) will go 5 miles - and then travel thru a 1 foot thick concrete wall...

    You DON'T want to be playing around with the design characteristics of the hot water heater. It has HOT water in it. And the walls are thin for weight.

    You could probably get away with the 175. But why chance it? In a few years the thing starts leaking when it never gets to 150psi. They are not supposed to be close to that pressure relief value. Operating it close to those pressures - weakens the tank; and brings you more likely to have a severe problem...

    BTW: Rheems makes a 'Marathon'/ hot water heater. Electric. No metal tank. Totally composite. No rusting. No anodes. And those GE "Energy Smart" hot water heaters - with the little green LED light - go hinky all the time. I have one, and the circuit board died less than 6 months into operation from new... I also have the same at a different house - and it has had no problems for the last 4 years... So go figure. But I'm no longer convinced of their long lasting quality. And I purchased the 'lifetime' warranty models...

    DS.

  4. #4
    Join Date
    Apr 2009
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    Default Re: Under Pressure!

    there was an episode on myth busters where they actually closed up the release valve to see if it would do what you said....go thru the building. And it did!

    Of course they fudged with the thermostat as well, but they were proving a point.
    Last edited by peterbouchard; 05-09-2009 at 06:22 AM.

  5. #5
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    Apr 2009
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    Cool Re: Under Pressure!

    Quote Originally Posted by bsum1 View Post
    The reason why you had difficulty finding a 175 psi valve to fit is probably due to residential hot water tanks only have 150 psi valves.

    Personally I think you're hedging your bet on something that's dangerous, never mind voiding the warranty on the tank.



    No , not if it doesn't overdraw on the current.
    Thank you for you comments... but I am not worried about voiding my warranty whatsoever. Also, I can easy find 175 psi PRV's at my local hardware store... The problem is finding a long shang 2 1/2" 175 psi PRV which will fit the tank properly?

  6. #6
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    Apr 2009
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    Default Re: Under Pressure!

    Quote Originally Posted by peterbouchard View Post
    there was an episode on myth busters where they actually closed up the release valve to see if it would do what you said....go thru the building. And it did!

    Of course they fudged with the thermostat as well, but they were proving a point.
    Yes, I have seen that episode... but they had to fuge it in order to blow...

  7. #7
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    Apr 2009
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    Wink Re: Under Pressure!

    Quote Originally Posted by spammed3@sky View Post
    donobk -

    Not a plumber; but do have some expertise...

    I don't believe a Hot Water heater is rated for 350psi at all. Not anything close.

    Your thinking they put this huge safety shield margin in - and they haven't. That would take a lot more steel, and wall thickness. Hot Water Heaters are mostly made up of foam. The actual tank steel walls are very thin, and glass lined.

    Couple of years ago - here in Seattle (Burien actually) - a Hot water Boiler had a pressure relief valve which failed to relieve, or they had removed it and plugged it because it was weeping (some such dumb thing.) Anyway - it blew the entire side out of a building; and went thru the roof of the building across the street... It made the National News...

    Point of fact: A 5,000psi pressure gas bottle (I know, WAY more pressure) will go 5 miles - and then travel thru a 1 foot thick concrete wall...

    You DON'T want to be playing around with the design characteristics of the hot water heater. It has HOT water in it. And the walls are thin for weight.

    You could probably get away with the 175. But why chance it? In a few years the thing starts leaking when it never gets to 150psi. They are not supposed to be close to that pressure relief value. Operating it close to those pressures - weakens the tank; and brings you more likely to have a severe problem...

    BTW: Rheems makes a 'Marathon'/ hot water heater. Electric. No metal tank. Totally composite. No rusting. No anodes. And those GE "Energy Smart" hot water heaters - with the little green LED light - go hinky all the time. I have one, and the circuit board died less than 6 months into operation from new... I also have the same at a different house - and it has had no problems for the last 4 years... So go figure. But I'm no longer convinced of their long lasting quality. And I purchased the 'lifetime' warranty models...

    DS.
    Thank you for taking the time to respond. Also, i completely agree with you in regards to the potential bomb-like properities of this matter. However, it isnt like i removed and/or plugged up the tank. It still has a brand new functioning PRV... just rated 25psi higher. The valve would still pop if the pressue would reach that level. I was just making a point in regards to the 350 psi comment. Everyone states that it is a dangerous modification... but completely do NOT agree b/c nobody has explained - PROVED to me exactly why it is dangerous!!! The only possibly way that it could be potentially MORE dangerous than a regular 150 psi or 175 psi PRV installation is if the brass coupling extenstions somehow would increase the 175 psi discharge level higher than 175 psi and/or cause it to fail??? This is my real concern and/or question?

  8. #8

    Default Re: Under Pressure!

    I think it has to do with the flash point temperature of steam is reduced when the pressure is increased. Relief valves function within a margin not precisely at a particular point certain of pressure or temperature (plus/minus). I remember something about steam flash having expansion and power something like 10,000 times the volume of water and more powerful energy than any bomb.

    Water heater storage tanks are manufactured with tolerances but could have a defect or weak point they aren't all tested.

    Follow the listed instructions and labeling on the water heater and tank & boiler plumbing rules and using the required standard temperature and pressure reducing valve and maintaining it.

    Household plumbing and fixtures aren't designed to withstand such high operating water pressures.

    A pressure reducing valve at the main of the type that doesn't completely close the system and an expansion tank or a dump valve in the toilet tank for the excess pressure from the expansion from heating the water should solve the problems you mentioned and is the usual way to address overly high main water pressure.

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