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TPR Valve discharge tube questions


fyrmnk
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Hi all, couple things:

I've always recommended CPVC discharge tubes be secured to the tank to secure it to prevent flailing in the event of an activation to reduce risk of injury. However, I can't find that anywhere. Anyone else ever recommend that?

Also, just starting to see more CPVC used in this area for the tube. When it's regular water line rated at 180F at 100psi I flag it since the valve is set at 150psi and 210F. However read recently the 180F rated is okay. If it is, why since the discharge will be higher than the tube rating?

Thanks in advance for any input on these.

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Hi all, couple things:

I've always recommended CPVC discharge tubes be secured to the tank to secure it to prevent flailing in the event of an activation to reduce risk of injury. However, I can't find that anywhere. Anyone else ever recommend that?

Nope

Also, just starting to see more CPVC used in this area for the tube. When it's regular water line rated at 180F at 100psi I flag it since the valve is set at 150psi and 210F. However read recently the 180F rated is okay. If it is, why since the discharge will be higher than the tube rating?

Thanks in advance for any input on these.

The PVC discharge pipe I see in this neck of the woods always has "Rated for TPRV discharge piping" or something akin to it.

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This has come up from time to time on various inspector forums. Somewhere a few years back, someone had a comment and statement from the mfg. of plastic pipe that it was suitable for any use, including TPR discharge. Anyone got that, or am I imagining things?

Also, don't the big boxes carry that white plastic 3/4" x 5' pipe specifically for TPR discharge? I see boxes of the stuff every time I walk down the plumbing aisle.

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Take the worst case scenario with a functioning TPR valve...it discharges at 150 psi and 210°F. 210°F may soften the CPVC pipe a little, but it's not going to actually melt. The pipe has an open end (hopefully). I don't know what the pressure would be at any one posistion, but it will be a lot less than the 150psi. But, let's say some idiot did cap the termination. At 210°F and 150psi the pipe would probably burst, but that's a good thing. Remember, we are first and foremost trying to prevent the tank turning into a lethal bomb. Preventing scalding from discharge for anyone who, against all reasonable odds, just happened to be in the area at the time is very secondary.

The good folks that produce the various codes all say that CPVC is OK for TPR discharge piping. I'm sure they gave it some thought.

As for strapping down the discharge (talking about a termination at the floor...right?), I don't think that's a good recommendation. I suspect that around here most homeowners would loosen a seismic strap and then tighten it down over the discharge pipe. I could see the strap pressure flattening the pipe if it did become soft from discharge. If you are close enough to the water heater during a full discharge, you are likely to get hit with hot water "bouncing" off the floor, secured or not. I really don't see it "flailing" around like a garden hose.

BBBUUUTTTT...I do like copper!

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I see the plastic pipe that says its only for TPR valve use, but I was referring to when CPVC plumbing pipe is used.

Sorry, what I meant to say is I remember someone at an ASHI conference said that any pipe approved for supplies is suitable for TPR discharge, be it CPVC, copper, plastic TPR, or whatever.

Maybe I got that wrong. As far as flailing around, honestly, I think that's somewhere out there in the same odds as getting hit by a meteor. Or is that meteorite? (I know it's a meteoroid out in space.)

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Section P2803.6.1 #13 states that the discharge pipe "be constructed of those materials listed in section P2904.5 (water distribution pipe) or materials tested, rated and approved for such use in accordance with ASME A112.4.1" So no "regular" PVC allowed.

The IPC 2003 commentary says "The discharge pipe must have a rating of 100psi at 180 degrees F. Even with this rating, the pipe may be suitable for the even higher temperature of 210 degrees F because the discharge pipe is open to the atmosphere. Water heater temperature relief valves are generally set to open at 210 degrees F."

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