DCV and Anti-Siphon WC inlet

[Diggory]

Hi there - I’m about to fit a new inlet valve to bottom entry cistern.
I’ll be using a FLUIDMASTER 400 Bottom Entry Fill Valve – 1/2″ Brass Shank.
I’ve used these before - this is third one I’ve fitted (for myself) and I quite like them.

It says ‘Anti-siphon design prevents contamination of water supply’.
Does that mean it won’t need a DCV on supply line ?

Thanks D

 

[CountryFan]

What do the instructions state? Probably best checking with WRAS if you’re unsure.

 

[Diggory]

Thank reply.
Instructions just refers to ‘supply pipe’.
Best D

 

[CountryFan]

Thank reply.
Instructions just refers to ‘supply pipe’.
Best D

Check this out

 

[Scally-Ho]

If my memory serves me well, the valve has been designed so that when not under positive pressure, the supply side is open to the atmosphere and therefore syphoning cannot occur. Once the pressure is applied, that route is closed. I have one in all three WWP's in my house and all function as they were designed to.

 

[Madrab]

Check this out

The last paragraph is the key part. Unless there is an air gap (AUK1) on a cisterns fill valve then a double check valve should always be used, when the supplied from the mains.

 

[Diggory]

Thank you for the link to helpful WRAS Certification Statement; that clearly states I should have a DCV (irrespective of the built in anti-siphon).

This is likely a silly question - an air gap / AUK1 on a cistern; I’m guessing with a bottom fill I don’t have one but how do I know ?

Thanks D

 

[Madrab]

I’m guessing with a bottom fill I don’t have one but how do I know

The clue's in the description, if it's a bottom fill it means it fills from the bottom of the valve, therefore there will always be a situation where the mains water could be in contact with the cistern water, hence the requirement for a DCV. Other fill valves, where there is a visible gap between where the water comes out of the valve and the finished fill level are valves that incorporates an air gap and a DCV isn't required. This should be at least 20mm above the finished fill level or twice the (edit) pipe size filling it - (15mm pipe x 2 = 30mm)

Some of the newer UK Fluidmaster valves provide that air gap, I have gone from the Black Pro bottom fill valves to these now, where space in the cistern allows

Fluidmaster AIRGAP 6000 Brass Shank Fill Valve

• BS 1212-4 compliant• No need for additional single/double check valve (no IRN 150 or IRN 160)• Eliminates backflow into the cistern• Fits virtually every cistern• Easy toolless installation• Height adjustable• Quiet refill owing to the spiral flow vortex generator• Optimum performance, even at...

www.toolstation.com

 

[Diggory]

Everyday is a school day - I’d no idea on that as an option. I just went for the type (400 series) I’d previously fitted. I’ll have a look at available space in cistern. Failing that, I’ll fit the DCV.

Thanks for clarifying the regs and the heads up to the Air-Gap variant.

Best D

 

[Madrab]

I’ll have a look at available space in cistern.

It doesn't actually take up that much more space, if you see what I mean, as the float is quite high up but if the cistern has a syphon flush valve then the wide shape of the syphon can get in the way, if the cistern doesn't have enough space to the right