- This topic has 7 replies, 3 voices, and was last updated 23 years, 4 months ago by
Harold Kestenholz.
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MasterPlumbers
I have a air type expansion tank(no bladder). I purged the tank but I still have rising water pressure that blows the pressure relief valve at the hot water heater. If something is waterlogged, how do I fix it?
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The pressure relief valve can weep at 25 psig and release at 30 psig. If the relief valve is off calibration, replace it.
Make sure the pressure reducing valve at the fill line is not creating the excess pressure. If you have a 2-story building or less, 12 psig is enough to automatically fill with. If the pressure has crept up by failure of the pressure relief valve, then replacing the pressure reducing valve will help. You can do this by shutting the hand valve befor the fill valve, then draining the water till the pressure reaches about 12 psig. Then open the hand valve and watch the pressure. If the burner is not on and the pressure creeps up, the valve is at fault.
If the system did not blow the pressure relief valve in the previous season and the pressure reducing valve is OK, the expansion tank was large enough. This means that the expansion tank must be evacuated of as much water as possible. If the draining sequence (purge) does not get rin of enough water, the tank can be disconnected, drained and then reconnected to make sure there is as much air there as possible, When you pressurize the system again, the tank will become about 1/4 full as the 12 psig pressure forces the water into the tank. You can tell by rapping on the tank and hearing the change in sound.
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Hey Harold please RE READ this question.
The person said the “pressure relief valve at the hot water heater.”
You Harold are thinking like a PROFESSIONAL who reads the ASME section IV regarding “Safety” & Pressure “Relief” valves.
We both know there is a big difference in not only operation BUT design and function.
This writer said “At the HOT WATER HEATER” and you kind sir took it as a boiler instead of a hot water tank.
If indeed this is a hot water tank (pressure vessel) with a proper T&P type of protection then this valve is most lightly “SET” at 150 PSI or 210 degree F
There are some valves that are rated for 125 PSI and in a closed system this kind of pressure is very possible.
Before the use of back flow preventers Or check valves hearing of a T&P operating was very rare.
What folks fail realize for ever action there is a reaction.
Installing a backflow for example without a properly designed expansion tank is one of the many dangerous conditions.
But the powers that be still allow anyone including stumble bum helpers to dabble in these installations and until a few folks get killed or maimed you will continue to read about valves seeping UNTIL metal fatigue causes the tank to rupture like we read about in engineering reports (NFPA ETC)
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You might be right about that, Sylvan. One reason I chose to talk about how to purge a non-diaphragm expansion tank for a hot water heating system is that I find it hard to believe that someone will fool with a system that has 125+psig. It is not usual for a water heater to have a guage on it to know if the pressure is in fact rising. Certainly if the water pressure coming into a water heater is over 125, then there will be some other problems in the house. Someone who is asking about how to do this task without knowing anything about it is looking for danger. I just feel safer talking about a lower-pressure vessel.
The procedures are pretty much the same, but it should be done by someone with the experience to know that a leak at 125+psig can blind and cut skin. It is cetainly not a job for someone with no knowledge or even a helper without years of experience.
If it is a weeping valve from temperature, then handling hot water is not safe either; though the post didn’t mention that, just the rising pressure problem.
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quote:
Originally posted by Harold Kestenholz:
You might be right about that, Sylvan. One reason I chose to talk about how to purge a non-diaphragm expansion tank for a hot water heating system is that I find it hard to believe that someone will fool with a system that has 125+psig. It is not usual for a water heater to have a guage on it to know if the pressure is in fact rising. Certainly if the water pressure coming into a water heater is over 125, then there will be some other problems in the house. Someone who is asking about how to do this task without knowing anything about it is looking for danger. I just feel safer talking about a lower-pressure vessel.The procedures are pretty much the same, but it should be done by someone with the experience to know that a leak at 125+psig can blind and cut skin. It is cetainly not a job for someone with no knowledge or even a helper without years of experience.
If it is a weeping valve from temperature, then handling hot water is not safe either; though the post didn’t mention that, just the rising pressure problem.
Harold REMEMBER the code officials and manufacturers DON’T CARE where the money comes from, other wise ALL gas fired appliances would be sold ONLY to a licensed person Qualified in the proper installation.
I have seen many “gagged” Safety valves Or improperly installed safety/relief valves being installed and being reduced to less then 1/2 of inch diameter OR completely plugged.
Go to a home center and look at the boilers being sold.
I just wrote an article for Loz last week regarding the home center menace and once it is put on the web YOU will be the 3rd person to see it.
Lawyers are going to have a feast attacking the GAMA and home centers in the next few years.
As an “expert witness” I nailed my big city a few times in court and laughing all the way to the bank with proving the incompetence Of the installer and product liability
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Absolutely right about that, Sylvan. I am still puzzled about this post. I was not aware of non-diaphragm expansion tanks being used on such installations. I have never used or sold one for this purpose.
Certainly ASME high-pressure vessels are used commercially, but I am still curious about this use on a residential system. Piped so the expansion tank is above the heater, air bubbles separating from the water as it is heated would collect any air and hydrogen produced in the process, so purging would not be necessary until hydrogen collects. The tank would have more than enough air; so the tank in this post must be too small. Then I would not encourage a smoker to purge the tank. If this is an old boiler expansion tank in use on a water heater, I expect to hear the report from a long distance at any time.
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Originally posted by Harold Kestenholz:
Absolutely right about that, Sylvan. I am still puzzled about this post. I was not aware of non-diaphragm expansion tanks being used on such installations. I have never used or sold one for this purpose.ANSWER
Harold HOW do you know this Person doesnt have a “bladder type” and thinks its a non bladder one he has?
REMEMBER a lot of folks call a boiler a furnace and a boiler a hot water tank so WE are at a total disadvantage not actually seeing what folks are talking about
Harold
Certainly ASME high-pressure vessels are used commercially, but I am still curious about this use on a residential system. Piped so the expansion tank is above the heater, air bubbles separating from the water as it is heated would collect any air and hydrogen produced in the process, so purging would not be necessary until hydrogen collects. The tank would have more than enough air; so the tank in this post must be too small. Then I would not encourage a smoker to purge the tank. If this is an old boiler expansion tank in use on a water heater, I expect to hear the report from a long distance at any time.
Answer Sylvan
Harold again thinking like US Heating guys we know any steam boiler GREATER then 15 pounds working pressure is considered HIGH PRESSURE
We also know any hot water boiler operating at 160 POUNDS and a temperature of 250 degrees is STILL considered low pressure according to ASME section IV and NBBI
Now lets take a pressure vessel like a hot water tank RATED to 300 pounds and a Normal working pressure of 125 and a pressure relief of 150 pounds.
If for some reason this tank does become slightly air bound ZOOM PRESSURE BUILDS very FAST even if you did have a an “expansion tank” to take up for the pressure temperature relationship,
I doubt very seriously it could handle all this excessive presure build up.
Remember even a hydronic system does NOT expand that much ( like a vapor system as water is hard to compress).
With the new devices to prevent back syphonage the need for any type of expansion tank is now needed more then ever before.
X TROL makes one for just hot water tanks for expansion during non peak hours when the city water preesure can increase by over 30 pounds PLUS compounded by heat here goes your pressure temperature relationship.
Your thinking like a heating guy looking for the stradification of air buddles in a closed system.
A domestic hot water system lets in FRESH water constantly hence MORE oxygen and more buddles so this is not really the problem in this system we are concerned about as every time a faucet is opened good bye bubbles ESPECIALLY on the upper floors.
On LARGE domestic hot water systems I have been known to install a automatic air vent like a Hoffman 78 rated for 150 PSI @ 250 degrees BUT I lower the T&P to a 125# model even though I know the Hoffman can with stand pressures up to 450 PSIG.
This is only for my very large commerical accounts would I need this kind of protection for possible air pockets as I hate having my bronze circulators cavitating as they can build up lots of heat and go BOOM.
ISNT PLUMMMMMMIN FUN Sylvan?
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Uh oh, Sylvan, now you are thinking like a heating guy. You see, in a residential heating system during the heating season, the circulators run for some time during an hour every hour to carry bubbles away. But a residential water heater’s load is ordinarily for two periods a day – during the morning at get up and cook time, and come home and cook time – about 5 hours per day. During the rest of the time and especially at night, the water sits there warm to let bubbles collect at the top. If there is a non-diaphragm tank piped above, the bubbles can go up there.
Now we have had some posts in the past asking about the clotheswasher appliance makers warning about hydrogen produced with possible release after collection in the washer. Collecting hydrogen, the lightest gas, in a tank can be something to worry about. Perhaps that is why I have never seen or sold a non-diphragm tank (not the Extrols, they have diaphragms) used in a domestic water system. The only open tanks sold in plumbing supplies were the thin-wall expansion tanks used for heating (not counting the heavy-duty ASME vessels sold for higher pressures.) So I worry about this post.
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