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Valve


Tim Maxwell
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That's a calibrated pressure relief valve that was very likely installed for thermal expansion control.

Expansion tanks (containment expansion control) are one method. Water release is the other method of thermal expansion control. There's also a toilet ball-cock fill valve with a relief valve, a ball valve with relief valve and a hose bib with relief valve, that can be used.

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Thank you Bill.

This one, and others I have seen have not had any type of drain.

My confusion yesterday was the location of this one. When I have seen them installed for thermal expansion they were installed above the water heater. This one was about 10 feet away on the wall.

The buyer brought up the fact that there was no expansion tank at the water heater and I showed him the valve but told him I would double check it on the best HI forum in the country.

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The buyer brought up the fact that there was no expansion tank at the water heater and I showed him the valve but told him I would double check it on the best HI forum in the country.

To expand on this a bit further: I see many older homes that do not have an expansion tank however the only time an expansion tank is required is when there is a device that prevents back-flow, into the city water distribution system, ie: black flow preventer - pressure reducing valve, in case of an over pressure condition. I think it was Jim Katen that pointed out that some pressure reducing valves will allow flow in the reverse direction (something I was not aware of).

Point is that just because there is no expansion tank does not necessarily make it wrong.

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. . . I think it was Jim Katen that pointed out that some pressure reducing valves will allow flow in the reverse direction (something I was not aware of). . .

True. These valves have a small spring-loaded bypass that will allow water from the house side of the valve to bleed back to the street side when the pressure at the house side exceeds that of the street side. The only way to identify these valves is by looking at the model number. With Watts, for instance, those valves with a B in the model number indicate that they include this feature (B = bypass). Here's an example: http://media.wattswater.com/es-25aub.pdf

Also, they'll only relieve pressure that's above the level of the street-side pressure, which might be too high to be of much use. Plus, like any mechanical device, they can fail.

- Jim Katen, Oregon

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