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(09-29-2017, 12:40 PM)geek2me Wrote: If the tank leaks, the water evaporates, or the tank otherwise runs low or runs out of water, the tank can explode or catch fire. In addition, water can be separated into component gases in small quantities, but if the quantities build up enough they can explode.
Risk is likely on the low side, but it does happen.
Isn't that what the pressure relief valve is for (not that I'd want it to be venting hydrogen gas)?
But maybe people are forgetting that I am not leaving the house unattended for weeks nor even days at a time. Whenever I am gone my neighbors come every day to feed my cats. So the water gets turned on when they enter the house (and will refill the piping, tanks, etc. if they lost more water than the expansion tank can refill) and then gets turned back off when they leave. If the HW tank leaks, they will see it. And normally I turn off the HW tank when I'm going to be gone for a week or more.
John
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You have a greater risk of being hit by two separate meteorites in the same day.
Blackhat
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(09-29-2017, 01:10 PM)jteneyck Wrote: Isn't that what the pressure relief valve is for (not that I'd want it to be venting hydrogen gas)?
But maybe people are forgetting that I am not leaving the house unattended for weeks nor even days at a time. Whenever I am gone my neighbors come every day to feed my cats. So the water gets turned on when they enter the house (and will refill the piping, tanks, etc. if they lost more water than the expansion tank can refill) and then gets turned back off when they leave. If the HW tank leaks, they will see it. And normally I turn off the HW tank when I'm going to be gone for a week or more.
John
The pressure relief valve is to vent excess water pressure. Steam and air may not activate the valve.
If people are still visiting the house daily, your risk should be very low.
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09-30-2017, 09:59 AM
(This post was last modified: 09-30-2017, 10:00 AM by geek2me.)
(09-29-2017, 01:28 PM)blackhat Wrote: You have a greater risk of being hit by two separate meteorites in the same day.
Please provide the data sources for your calculation of both meteorite risk and the risk of a fire or explosion caused by a water heater or boiler.
I said it was low risk, but obviously it happens, given news reports of at least a few cases each year.
The utilities think it is enough of a concern to warn customers to take precautions.
http://www.northeastgas.org/pdf/p_pirro_preventing.pdf
A more thorough and scientific analysis of the risk
http://www.nationalboard.org/Index.aspx?...164&ID=412
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(09-30-2017, 09:56 AM)geek2me Wrote: The pressure relief valve is to vent excess water pressure. Steam and air may not activate the valve.
If people are still visiting the house daily, your risk should be very low.
It's a temperature and pressure relief valve. It doesn't know what is on the loaded side. If any substance exerts a pressure greater than 125 psi, it opens. Air, water or fairy dust, if the pressure exceeds 125 psi, it opens. If the temperature of the sensing element exceeds 200 degrees, the valve opens. It doesn't matter if the sensing element is in air, water, steam or fairy dust. If it exceeds the valve rating, it opens.
Relief valves do fail, most commonly by leaking. Note the valve manufacturers instructions. They all state that the valve should be replaced after 5 years. A failure due to neglect is not the valve's fault. Perhaps your utility should mention that.
Blackhat
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09-30-2017, 02:59 PM
(This post was last modified: 10-01-2017, 09:32 AM by jteneyck.)
(09-30-2017, 09:59 AM)geek2me Wrote: Please provide the data sources for your calculation of both meteorite risk and the risk of a fire or explosion caused by a water heater or boiler.
I said it was low risk, but obviously it happens, given news reports of at least a few cases each year.
The utilities think it is enough of a concern to warn customers to take precautions.
http://www.northeastgas.org/pdf/p_pirro_preventing.pdf
A more thorough and scientific analysis of the risk
http://www.nationalboard.org/Index.aspx?...164&ID=412
Thanks. From the second article: " Of course, a properly functioning pressure and temperature relief valve would prevent such a failure."
Both documents you provided stated that an explosion required the failure of two safety controls, not a loss in supply water. Adding the ball valve will not compromise those safety controls.
John
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John, a minor point sort of, you should install a small expansion tank on the water line close to the heater. Normally any increase in pressure caused by heating the water simply goes back down the main. A backflow valve or shutoff will prevent that. You could set yourself up for the relief valve discharging and they are prone to not reseating 100%. Don't create a problem while solving another.
Blackhat
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(09-30-2017, 03:37 PM)blackhat Wrote: John, a minor point sort of, you should install a small expansion tank on the water line close to the heater. Normally any increase in pressure caused by heating the water simply goes back down the main. A backflow valve or shutoff will prevent that. You could set yourself up for the relief valve discharging and they are prone to not reseating 100%. Don't create a problem while solving another.
FYI in my area the new water meters contain a back flow device so they are requiring an expansion tank with a water heater install. I had to install a expansion tank as it would build too much pressure at times. Also our street pressure was above 80 psi normally. People started to have problems with the pressure relief valve dripping and replaced it. New one did the same, just doing it's job. Roly
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I bet your insurance company would entertain a discount on your homeowners insurance for having installed this. I think I read once that damage from flooding due to bursting pipes/hoses dwarfed their other claims.
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(09-30-2017, 03:59 PM)Roly Wrote: FYI in my area the new water meters contain a back flow device so they are requiring an expansion tank with a water heater install. I had to install a expansion tank as it would build too much pressure at times. Also our street pressure was above 80 psi normally. People started to have problems with the pressure relief valve dripping and replaced it. New one did the same, just doing it's job. Roly
Rest easy, BlackHat, I have an expansion tank just in front of my hot water heater. The situation Roly described is exactly what happened to me. The town installed new water meters that can be read from the street. When they did that they installed a check valve, too, I think to meet some new code. My HW heater's pressure relief valve didn't like that and blew water into the bucket I have below it. Fortunately, I saw the spray and figured out the cause, and solution. Got an expansion tank and that solved the problem.
About 6 months later I got a letter from the Town describing this exact problem and what to do about it. Turns out, several people had major problems when the pressure relief valve on their HW heater opened but didn't close, a few had several feet of water in their basement. Several of them sued the town because they were not made aware of what was almost certain to happen when the check valve was installed.
John
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