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Pressure relief valve


Mark P
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Page 14 of the Reliance Instruction Manual says: The discharge opening must not be blocked or reduced in size under any circumstances. Excessive length, over 30 feet (9.14 m), or use of more than four elbows can cause restriction and reduce the discharge capacity of the valve.

This would lead you to believe that four elbows are the max that you should use.

http://www.reliancewaterheaters.com/lit ... 53-002.pdf

Jeff Euriech

Peoria, Arizona

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Sort of, but not really; Reliance goes for the 4 elbow recommendation w/fuzzy language because of perceived corporate liability.

I don't think it's that fine tuned an issue; if it was, we'd see limitations on elbows in all supply pipe installations. And, elbows don't "back stuff up from the get go"; they're elbows, not restrictions.

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Originally posted by kurt

And, elbows don't "back stuff up from the get go"; they're elbows, not restrictions.

No Kurt, they are restrictions. One elbow is equal to X amount of feet of pipe. Anytime you design a piping system you need to calculate pressure drop. Elbows are much more restrictive to water flow than straight pipe. The point I was making is the water, discharging from the TP valve, must be asked to immediately change direction, this is a restriction. I still think it's bad pratice to pipe a 90° right after the TP outlet.

From A.O. Smith.

The temperature-pressure relief valve must be installed directly into the

fitting of the water heater designed for the relief valve. Position the

valve downward and provide tubing so that any discharge will exit only

within 6 inches (153 mm) above, or at any distance below the structural

floor. Be certain that no contact is made with any live electrical part. The

discharge opening must not be blocked or reduced in size under any

circumstances. Excessive length, over 30 feet (9.14 m), or use of more

than four elbows can cause restriction and reduce the discharge

capacity of the valve, see Figure 10.

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This is an example of taking a simple concept & complicating the heck out of it.

The restriction that an elbow puts on water flow, at the pressures & flow rates that occur in residential construction, is so miniscule & inconsequential that it almost doesn't exist.

These folks put stuff like that in their literature because they have to, not because it matters on a functional level.

This is another good example of home inspector's over complicating very simple things.

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Originally posted by Jim Baird

A plumber friend of mine says a local home inspector cited his use of CPVC to pipe discharge as being too low pressure/temp rated.

Plumber says open end negates pressure/temp rating as a performance factor. Neither side of the argument is budging.

I'm split on it. I buy the open cap negates the pressure rating but not the temp... but doesn't CPVC rate high enough to be used anyway?

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