TPRV, to test or not to test...

[SonOfSwamp]

Originally posted by Bain

"50 gallons of super-heated water suddenly exposed to the air and expanding to steam at a rate of at least 100 to 1 in a split second."

I don't understand. How does that occur? And why don't water heaters explode more often?

I realize that's the purpose of the TP valve, but very seldom have I heard of one actually tripping due to a problem.

Go to YouTube and search for "BLEVE."

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[hausdok]

Originally posted by Bain

"50 gallons of super-heated water suddenly exposed to the air and expanding to steam at a rate of at least 100 to 1 in a split second."

I don't understand. How does that occur? And why don't water heaters explode more often?

I realize that's the purpose of the TP valve, but very seldom have I heard of one actually tripping due to a problem.

They don't explode more often because the control valves are set to prevent them from reaching boiling temp and because of the TPR valve. If the thermostat controlling it goes bad and the water gets hotter the TPR holds steady until it reaches 150psi and then it releases. If I'm remembering my mechanics training correctly, every pound of pressure raises the boiling temperature of the water by 4 degrees (Of is it every 4 pounds raises it 1 degree); anyway, if the control valve goes bad and the water continues to get hotter and that TPR valve fails to relieve pressure the water will eventually reach boiling temperature. At that point the water continues to expand until it bursts the tank. That's when the super heated water, no longer constrained, strikes the colder air and flashes instantaneously to steam and expands, turning the tank into a rocket. How do you think fireworks rocket work? - gunpowder is ignited inside a tube and produces gas that expands rapidly in a micro-second and sends the rocket out of its launch tube. It's not that much different. It's also how steam engines use controlled steam expansion to move steam engine pistons.

Ever have one of those water powered rockets when you were a kid where you pumped pressure in above water and then suddently released it and watched it shoot up into the air? Imagine that on a massive scale sending a tank up through the roof.

About 5-6 years ago down in Burien, a video store owned by a Vietnamese family had a problem with their water heater; the TPR valve was spraying scalding water. They called a plumber who came out, looked at it and said that the tank was shot. He shut it down, unscrewed the TPR and screwed a metal plug in the hole so water wouldn't continue pouring out of the valve, and promised to return the next day to replace it.

The next morning, the employees came in to open up and discovered there wasn't any hot water to wash their hands so they turned on the water heater. About 45 minutes later, hot water began being forced out of faucets that were turned off and the plumbing began to vibrate. Just about the time they realized something was wrong and were about to shut the thing down, it exploded, destroying the store and blowing out the concrete block walls of the video store, shot up through the roof, crossed a 4 lane highway, and landed nearly 500 feet away. Nobody was killed but five people went to the hospital.

It's called a bleeve - a bi-level explosive event; for it to occur, you have to almost have the perfect storm of screwups and/or malfunctioning equipment. That's why it does't occur more often.

ONE TEAM - ONE FIGHT!!!

Mike

[Bain]

Thanks for the explanations.

Gotta go. This weekend's project involves the construction of a concrete bunker in my backyard in which I'm gonna relocate my water heater.

[charlieb]

Originally posted by hausdok

Originally posted by Bain

"50 gallons of super-heated water suddenly exposed to the air and expanding to steam at a rate of at least 100 to 1 in a split second."

I don't understand. How does that occur? And why don't water heaters explode more often?

I realize that's the purpose of the TP valve, but very seldom have I heard of one actually tripping due to a problem.

They don't explode more often because the control valves are set to prevent them from reaching boiling temp and because of the TPR valve. If the thermostat controlling it goes bad and the water gets hotter the TPR holds steady until it reaches 150psi and then it releases. If I'm remembering my mechanics training correctly, every pound of pressure raises the boiling temperature of the water by 4 degrees (Of is it every 4 pounds raises it 1 degree); anyway, if the control valve goes bad and the water continues to get hotter and that TPR valve fails to relieve pressure the water will eventually reach boiling temperature. At that point the water continues to expand until it bursts the tank. That's when the super heated water, no longer constrained, strikes the colder air and flashes instantaneously to steam and expands, turning the tank into a rocket. How do you think fireworks rocket work? - gunpowder is ignited inside a tube and produces gas that expands rapidly in a micro-second and sends the rocket out of its launch tube. It's not that much different. It's also how steam engines use controlled steam expansion to move steam engine pistons.

Ever have one of those water powered rockets when you were a kid where you pumped pressure in above water and then suddently released it and watched it shoot up into the air? Imagine that on a massive scale sending a tank up through the roof.

About 5-6 years ago down in Burien, a video store owned by a Vietnamese family had a problem with their water heater; the TPR valve was spraying scalding water. They called a plumber who came out, looked at it and said that the tank was shot. He shut it down, unscrewed the TPR and screwed a metal plug in the hole so water wouldn't continue pouring out of the valve, and promised to return the next day to replace it.

The next morning, the employees came in to open up and discovered there wasn't any hot water to wash their hands so they turned on the water heater. About 45 minutes later, hot water began being forced out of faucets that were turned off and the plumbing began to vibrate. Just about the time they realized something was wrong and were about to shut the thing down, it exploded, destroying the store and blowing out the concrete block walls of the video store, shot up through the roof, crossed a 4 lane highway, and landed nearly 500 feet away. Nobody was killed but five people went to the hospital.

It's called a bleeve - a bi-level explosive event; for it to occur, you have to almost have the perfect storm of screwups and/or malfunctioning equipment. That's why it does't occur more often.

ONE TEAM - ONE FIGHT!!!

Mike

Well gee Mike, if you want to go all technical!

That explanation does make it clear.

[Jim Katen]

Originally posted by hausdok

. . . It's called a bleeve - a bi-level explosive event; for it to occur, you have to almost have the perfect storm of screwups and/or malfunctioning equipment. That's why it does't occur more often.

ONE TEAM - ONE FIGHT!!!

Mike

I've heard it called "bleve," the letters standing for boiling-liquid, expanding-vapor explosion.

- Jim Katen, Oregon

[Bain]

Hey Mike,

I was in a rush this morning, but wanted to thank you for the detailed explanation. It makes sense to me now.

I realize it takes time to craft a long post, so please know I notice and appreciate all you do.

Oops, the concrete truck for the bunker's here. Gotta run and open the gate.

[hausdok]

Hi,

Thanks, but I wrote it last night when I was about to go to bed and when I woke up this morning I realized that I was probably way off in comparing it to a steam engine. If memory serves, the steam in a steam engine isn't flashed to expand it; it's constantly expanding and is meteredi in on both sides of a piston by a metered/switcing device. Still, the reason for the explosion is at least on the money; ....I think.

ONE TEAM - ONE FIGHT!!!

Mike

[Brandon Chew]

For your viewing pleasure -- Mythbusters water heater blast:

[utube]http://www.youtube.com/watch?v=P7DpfdQTHvY[/utube]

This is the site to which I send my clients: www.waterheaterblast.com

It is an easy URL to remember and the ninety second video that is available there is simple and gets right to the point.