Some kind of relief valve?

[John Arnold]

This is on the hot line at the water heater. The copper pipe at the top goes outside and is open, as if this is some kind of relief valve. Never seen this before. Water heater is typical with the usual TPR valve.

30392

[Dom D'Agostino]

Looks like it could be a Pressure Relief Valve.

530C Calibrated Pressure Relief Valves, Pressure-Only Relief Valves, Water Safety & Flow Control - Watts (http://www.watts.com/pages/_products_details.asp?pid=803)

[Mark Reinmiller]

This is on the hot line at the water heater. The copper pipe at the top goes outside and is open, as if this is some kind of relief valve. Never seen this before. Water heater is typical with the usual TPR valve.

30392

I have not seen one like that, but may be a pressure relief valve for thermal expansion. Could also be a vacuum break valve, but it does not look like the ones I have seen.

[JIM MURPHY]

I have not seen one like that, but may be a pressure relief valve for thermal expansion. Could also be a vacuum break valve, but it does not look like the ones I have seen.

That looks dangerous!

[Jerry Peck]

As Dom said, it's likely a pressure relief valve used for thermal expansion ...


Looks like it could be a Pressure Relief Valve.

530C Calibrated Pressure Relief Valves, Pressure-Only Relief Valves, Water Safety & Flow Control - Watts (http://www.watts.com/pages/_products_details.asp?pid=803)

However ... keep in mind that the maximum allowed pressure for the system is 85 psi - that pressure relief valve needs to be set no higher than 85 psi (most I find are set to 100 psi).

The T&P relief valve is set to 150 psi - that is allowed because that is a safety relief device for the tank, not a pressure limiting device for the system.

[Jack Foster]

Looks like a jerry-rigged pressure relief with a vacuum breaker to drain the line, except that the actual relief mechanism seems to be missing (plugged with something white?).

I can't quite read the information stamped into the side of the relief valve(?). You might be able to find more information from the manufacturer of that portion.

Is that a grub screw on the bottom of the rv portion?
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[John Arnold]

I don't even know what a grub screw is.

Did I mention that the homeowner is an engineer?

[Jack Foster]

I don't even know what a grub screw is.

A grub screw is a small screw that penetrates the side of a female pipe or fitting that bites into the male pipe and locks the fitting in place. They are commonly seen on the screw-on hose-bib anti-siphon devices. In that case the screw is turned in until the head breaks off. This prevents the removal of the device without damaging the male threads (in theory).

If the item in the photo is a grub screw, it would certainly indicate that this likely is a field assembled contraption, as it appears to be.

As for this thing being a temperature and/or pressure relief, it doesn't appear that there is enough room for the "tail" of the typical relief valve. It looks like someone just used a valve body to rig up whatever this thing is supposed to be.

[Jerry Peck]

If the item in the photo is a grub screw, it would certainly indicate that this likely is a field assembled contraption, as it appears to be.

As for this thing being a temperature and/or pressure relief, it doesn't appear that there is enough room for the "tail" of the typical relief valve. It looks like someone just used a valve body to rig up whatever this thing is supposed to be.

It's a pressure relief valve, not a temperature relief valve, no "tail" is needed for pressure relief valves.