Double Check Valve: position

[ToughButterCup]

I want to pipe water for the shower in our wetroom through a ceiling void and down the back of the shower stud wall. That means its really difficult to install a double check valve near the shower. - Just inside the ceiling space might be feasible  for me Ok, but wouldn't be convenient for many.

Is it OK to install a double check valve some distance away from the shower unit? I'm thinking in a small cupboard just downstream of our hot and cold water supply? The hot water tank will be bout 5 meters away.

[Jeremy Harris]

Probably worth checking the spec of the shower mixer, as some have built-in check valves (ours did).  The check valve is in the thermostatic cartridge on ours, with additional integral check valves on the inlet ports. 

 

Also, I believe the regs only require this if there is a risk that the shower head can contact contaminated water, so a flexible shower head being able to drop into a bath or shower tray.  There isn't a requirement (as far as I'm aware) for a check valve with a fixed shower head (unless the regs have changed recently). 

 

The standard (but unsatisfactory) way that some manufacturers get around the need to fit a check valve for a flexible shower hose, is to include a ring on the shower rail through which the hose is fed, so it cannot drop down into the tray/bath.  Given that many people probably unthread the hose from this ring, I've never been convinced it was a sensible way to get out of fitting a pretty simple check valve.

[ToughButterCup]

Hmmm, now ya tell me ( ? ) Just found out that the Hansgrohe iBox unit  that I have ordered has those check valves built in.

It was a bit wierd to watch a Hansgrohe video in which one of their  technicians  tested the valve by stabbing it with a screwdriver : but then, that's our Teutonic cousins for ya innit?

[Oz07]

Always wondered what those rings were for and in threaded them in previous houses. Every day a school day at buildhub uni 

[Mike]

20 hours ago, Jeremy Harris said:

Probably worth checking the spec of the shower mixer, as some have built-in check valves (ours did)

Do check the spec with care - non-return valves (a flap), singe check valves (spring-loaded), and double check valves (two singles in series) provide different levels of protection. I don't buy Hansgrohe, so those I've bought have only had non-return valves

 

If a shower hose is long enough for the head to reach the water in another fitting (other than a WC or bidet), then protection is required. That is either double check valves, or a means of preventing the hose reaching the water - shower screen, fixed shower heads, shorter hose, hose retainer or, if the shower if fed from a bath tap diverter, a self-cancelling diverter.

 

If a WC pan or bidet can be reached, then all of those means are acceptable except the double check valve, which doesn't offer enough protection (you can use a dedicated feed with a tank and an air gap, but nobody does). Which, as Jeremy notes, is somewhat strange as several of the alternatives can easily be bypassed. Seems sensible to me to always fit double check valves as a better-than-nothing backup, in addition to one of the other methods of protection.

Edited March 12, 2020 by Mike

[Jeremy Harris]

Ours had single check valves on both inlets (accessed from the rear) that looked like the same design of cone-type valve as used in an inline check valve (they were visible by looking down the inlet holes).  I didn't take it apart and check, but the guff that came with the mixer also mentioned another check valve built in to the thermostatic cartridge (accessed from the front).  My assumption (might be flawed) was that having two check valves in series met the requirement for a double check valve.  I wasn't really too bothered to check further, though, as the shower head can't physically reach anything like a WC.

[Mike]

2 minutes ago, Jeremy Harris said:

My assumption (might be flawed) was that having two check valves in series met the requirement for a double check valve

You're right; two single check valves in series = 1 double.