Water heater valve

[Gregg Austensen]

THis is the first time I have found thi stype of valve discharging at the outlet end. I know they are sometimes used in place of expansion tanks. What are they called? Thanks!

[Jerry Peck]

That's a pressure relief valve.

The knob turns and adjust (within limits) the setting of the valve.

[Gregg Austensen]

Jerry, What's the difference between this and the TPR valve on all water heaters?

[Jerry Peck]

Gregg,

A T&P relief valve has two modes of operation: Temperature and Pressure. The typical T&P for water heaters is set to release at either 210 degrees (temperature) OR 150 psi (pressure).

A pressure relief valve as in your photo is only set to relieve as a set pressure setting, maybe 80 psi. All depends on the setting of the valve.

All a pressure relief valve does is relieve the thermal build up of pressure, or the over pressure of a high pressure system, it offers no safety measure for a water heater, it just protects the plumbing system from failure (leaks) due to over pressure.

[Gregg Austensen]

So having water discharge is not always an issue? The house had 90psi and a constant drip at the discharge along with a very green plant. If the valve is set lower than this (90psi) then it will discharge? I would think that this constant discharge would not be normal. Also there was an old T&P on top of the tank. Any thoughts?

[dick whitfield]

That valve does not appear to be in the relief valve portion of the piping. I would think the valve in the picture is a not-so-normal shut-off valve.

[Gregg Austensen]

Jerry, I just noticed you are in Ormand Beach. My sister lives there as did my father until he passed in January. Next time I make it down there I'll have to look you up and maybe ride with you if your open to that.

[Jerry Peck]

So having water discharge is not always an issue? The house had 90psi and a constant drip at the discharge along with a very green plant. If the valve is set lower than this (90psi) then it will discharge? I would think that this constant discharge would not be normal. Also there was an old T&P on top of the tank. Any thoughts?

If the pressure was at 90 psi, you want it to drip continuously, because 90 psi is too high.

What is needed, then, is a pressure regulator valve to reduce the pressure to less than 80 psi.

Then, because there is a pressure regular installed, making the system basically a closed system, you will want to install an expansion tank to take up the thermal expansion.

Typically, an expansion tank is installed right at the water heater on the cold water inlet. As the water heats up, the increased water pressure causes water to back up toward its source (all valves are closed, so the water cannot flow anywhere to reduce the pressure). Being as water is a liquid, the pressure is basically the same throughout the entire system and you need to have a place where the excess pressure (from the thermally expanding water) to go, and that is where the expansion tank comes in. There is a bladder in the tank with pressurized air on the top of it and the water is pressing on the bottom of it, water is incompressible and air is not, so the air compresses even more, taking up the expanding water, creating 'more room' in the water system, thereby reducing the pressure in the water system.

I forgot who here had that problem, but they installed an expansion tank and their problem went away. Because that is what those expansion tanks are for.

I *would not* leave the pressure relief valve in the system knowing the pressure is too high, I would (my house - install an expansion tank) (house I was inspecting - recommend an expansion tank be installed).

[Jerry Peck]

Jerry, I just noticed you are in Ormand Beach. My sister lives there as did my father until he passed in January. Next time I make it down there I'll have to look you up and maybe ride with you if your open to that.

You are welcome to stop by, but I retired and moved to Ormond Beach from South Florida, so we could ride out to ... one of the Big Box stores? :)

[Jerry Peck]

I forgot to include this from the IRC. (bold and underlining are mine)
- P2903.4 Thermal expansion. In addition to the required pressure relief valve, an approved device for thermal expansion control shall be installed on any water supply system utilizing storage water heating equipment whenever the building supply pressure exceeds the pressure-reducing valve setting or when any device, such as a pressure-reducing valve, backflow preventer or check valve, is installed that prevents pressure relief through the building supply. The thermal expansion control device shall be sized in accordance with the manufacturer's installation instructions.

I have a difficult time getting plumbing inspectors and building officials to "understand" what "In addition to" and "the required pressure relief valve" means.

It means: 1) You shall have the pressure relief valve, and, 2) you shall have a means to control thermal expansion (i.e., an expansion tank).