Quick question on pressure valves

[Custom45]

Hi
Just installing a water heater for a boat that's fed from a 3 bar water pump (12v). It's a 30l tank with a 2kw immersion heater in. Fitting a pressure relief valve and expansion vessel but have a couple questions..

do these both go on the cold pipe that feeds the heater tank? I've seen examples of them on the outlet, but always thought they on cold feed?

does it matter which one goes first along the pipework? I was going to do expansion tank first, then relief valve nearest to tank.

Is this the correct way to fit the pressure relief valve? The top pipe will then just drain overboard.



Cheers

 

[Madrab]

It's usually to absorb the expansion back into the cold water supply. Follow the MI, it'll very clear about where everything is to be located.

That and I would also check whether plastic pipe is allowed as I would suspect it isn't given the temp range requirements (needs to withstand 90deg). Are they allowed on a pumped supply, I would again check the MI, failing that check with the manufacturer.

Given it is 30L vessel, is the installer qualified to work on unvented as a 30L vessel is covered by the Building Regs and normally needs to be notified. Not sure how the regs are covered on a boat though, I would guess if it is being used as a dwelling that it may fall under the buidling regs. Even if not It would be better to be safe than sorry.

These things can be really dangerous if not fitted properly.

 

[Custom45]

Thanks for reply Madrab. It's a private recreational boat (cabin cruiser), not residential in any way, so I believe it's only governed by Boat Safety Scheme, rather than building regs (but obviously want it done safely regardless).

I don't think plastic pipe & fittings are an issue. I've hired narrow boats from companies such as ABC that use plastic, they're bound by much tighter regulations. They also have hot water systems that produce much hotter water than mine will be capable of with more powerful freshwater pumps. I believe the PEX barrier pipe can withstand 92⁰c at 3 bar?

 

[Madrab]

As suggested @Custom45, I'm not up to scratch with regulations regarding boats. As long as you are happy that it complies then crack on.

If it's JG PEX barrier pipe then it's (82@ 3bar on CH) 95degC @ 6bar extended on HW, some other pipes have a lower temp/time tolerances, that's why I mentioned it. I only query these as it would be the things that would occur to me as an UV installer having installed a few of these and they usually prefer copper.

The pump aspect, again I'm not sure but always best to check.

 

[Custom45]

Thanks, yes it's JG pipe..



I'll check with local BSS inspector first, but pretty confident plastic is ok.