Installing a pressure relief valve on Low Pressure Cylinder

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Kezza1992

2 posts

Wannabe Geek

#284208 7-Apr-2021 13:51

Howdy, I have a low pressure hot water cylinder which is rated to 7.6m, I have 7.6 valves on the HWC but no pressure relief valve which a plumber told me I need to install and can do myself. I have attached some pictures of the HWC setup but I'm thinking that I can install the valve at the top of the tee junction which leads up and through the roof, is this correct?

Any suggestions?

PS, not sure if the photos worked or not...

Bung

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#2687902 7-Apr-2021 15:23

Why do you "need" to install a 7.6 relief valve? The pressure will currently be governed by the height of the open vent above the pressure reducing valve. A relief valve gets away from needing a tall vent pipe but you still need to have somewhere for the water that comes out of the valve to drain. A 1986 tank is not far off its 40th birthday. If you are increasing the working pressure don't be surprised if it starts leaking.

elbrownos

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#2688208 8-Apr-2021 10:14

I'm surprised a plumber would tell you that you can install a relief valve yourself. That's definitely not something you can legally do yourself.

The benefit of having a relief valve is that you can get rid of the pipe on your roof, and you can often squeeze a bit more pressure out of your system by running it at it's rated pressure (76 kPa).

But I wouldn't waste the money and effort on such an old cylinder. Better to take the opportunity to upgrade to mains pressure. Or even put in a newer second hand low pressure cylinder. There are loads of LP cylinders less than 10 years old on Trademe for a couple of hundred dollars because people remove them to upgrade to mains pressure electric or instant gas.

Batman

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#2688238 8-Apr-2021 10:31

If you have a 1970 house and you want to convert to mains pressure do you need to replace all the pipes?

Bung

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#2689594 8-Apr-2021 20:53

The dodgy Dux Qest pipe was installed between 1977 & 1987 so a 1970 house should be OK. Sometimes showers and toilet cistern cold supplies were off the low pressure side of the reducing valve so a bit of reorganising is needed.

Kickinbac

468 posts

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#2692240 13-Apr-2021 19:39

Batman: If you have a 1970 house and you want to convert to mains pressure do you need to replace all the pipes?

If they are copper you should be fine. You may need to replace mixers if you have any.

davecla

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#2692412 14-Apr-2021 07:47

Why do you want to add a pressure relief valve? Unless you are reroofing and want to get rid of the penetration the open vent is doing the job.

Are you trying to stop a bit of water coming out of the open vent onto your roof during expansion?

If so, your plumber may be talking about a cold water expansion valve which is installed on the intake side after the pressure reducing valve.

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Kezza1992

2 posts

Wannabe Geek

#2693931 16-Apr-2021 18:13

elbrownos:

I'm surprised a plumber would tell you that you can install a relief valve yourself. That's definitely not something you can legally do yourself.

Well thats a little concerning then.....

I was just going off what the plumber suggested however from the responses here, his suggestion appears to be a little off so I'll be leaving it as is for the time being now.

Cheers for the responses team! Appreciate it!