Plumbing help - air vent on waste to stop vacuum?
Plumbing help - air vent on waste to stop vacuum?
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Steve_W

Original Poster:

1,557 posts

195 months

Monday 1st March 2010
quotequote all
Morning all, bit of a long shot this one!

I recently bought a load of filtration equipment to enable us to drink the water from our borehole as the current filter system is knackered.

The chap who specced the system is on holiday at the mo or I'd phone him back to clear up my question, so I thought I'd drop a quick post here instead.

Once in a while the system runs a regeneration to clean the filter medium - the resultant backflush is then pumped to waste; because we're off-mains, this means to our existing drains which are some 30feet plus from the pump house.

The bit that I should have cleared up when the supplier was going through how to install it was "if you have to run the outfall pipe a long way (which I will), make sure you put an air vent in to prevent the water lying in the pipe"

His reason was that if you just leave the pipe unvented, when the backflush valve closes, the water in the outfall pipe won't drain due to causing a vacuum - hence the need for an air vent in to the pipe near the filter housing to stop the vacuum forming.

The only bit I need to know is what sort of pipe fitting would suffice as an air vent? The outfall pipe from the filter housing is 15mm.

Ta in advance!
Steve

Sam_68

9,939 posts

263 months

Monday 1st March 2010
quotequote all
Google 'Durgo Valve'

Trevelyan

727 posts

207 months

Monday 1st March 2010
quotequote all
Will the drain be pressurised (will the filter system pump the waste water away) or will it just be a gravity drain?

I'm no expert, but if it was my setup I'd probably just fit a tee into the drain pipe and fit a short section of vertical pipe with a normal non return valve at the top. This should allow air in, but prevent the water coming out if it's under any sort of pressure.

Steve_W

Original Poster:

1,557 posts

195 months

Monday 1st March 2010
quotequote all
Thanks gents.

The Durgo valve looks like the right idea - but I can't see one for the small pipe size I need - they seem to be a soil stack thing mostly.

Trevelyan, I thought about a non-return valve, but not sure if they open at a low enough pressure. The ones I found (Screwfix etc) seem set up to resist mains water pressure, which I guess is a lot more than a simple fall under gravity.

B17NNS

18,506 posts

265 months

Monday 1st March 2010
quotequote all
Sam_68 said:
Google 'Durgo Valve'
What he said, a Durgo or air admittance valve.

The smallest I'm aware of is 32mm. What is your pipe made of?

bimsb6

8,460 posts

239 months

Monday 1st March 2010
quotequote all
i seem to remember an air valve on a washing machine waste pipe to stop a vacuum forming that would be about the right size for what you need .

Steve_W

Original Poster:

1,557 posts

195 months

Monday 1st March 2010
quotequote all
B17NNS said:
Sam_68 said:
Google 'Durgo Valve'
What he said, a Durgo or air admittance valve.

The smallest I'm aware of is 32mm. What is your pipe made of?
I'll be plumbing the main system in using copper; however, the outfall pipe that I need the air valve for is effectively what looks like a white outer cover, black inner posh garden hose! biggrin In fact, that's what I was thinking of using to extend it to the drain!

It's a push fit over a plastic outlet spigot and is secured with a Jubilee clip. The supplier suggested heating the pipe in hot water to make it pliable to push onto the spigot.

Steve_W

Original Poster:

1,557 posts

195 months

Monday 1st March 2010
quotequote all
bimsb6 said:
i seem to remember an air valve on a washing machine waste pipe to stop a vacuum forming that would be about the right size for what you need .
Aha - that would be ideal - haven't got a link by any chance?

bimsb6

8,460 posts

239 months

Monday 1st March 2010
quotequote all
Steve_W said:
bimsb6 said:
i seem to remember an air valve on a washing machine waste pipe to stop a vacuum forming that would be about the right size for what you need .
Aha - that would be ideal - haven't got a link by any chance?
i'm trying to find one but failing ! it was a joining piece to fit 2 hoses together on the waste side of the washing machine ,i suspect it came from wickes but not 100% .

Steve_W

Original Poster:

1,557 posts

195 months

Monday 1st March 2010
quotequote all
bimsb6 said:
Steve_W said:
bimsb6 said:
i seem to remember an air valve on a washing machine waste pipe to stop a vacuum forming that would be about the right size for what you need .
Aha - that would be ideal - haven't got a link by any chance?
i'm trying to find one but failing ! it was a joining piece to fit 2 hoses together on the waste side of the washing machine ,i suspect it came from wickes but not 100% .
This one? anti-syphon kit

It looks like it could be what I need - thanks.

Edited by Steve_W on Monday 1st March 15:11

bimsb6

8,460 posts

239 months

Monday 1st March 2010
quotequote all
Steve_W said:
bimsb6 said:
Steve_W said:
bimsb6 said:
i seem to remember an air valve on a washing machine waste pipe to stop a vacuum forming that would be about the right size for what you need .
Aha - that would be ideal - haven't got a link by any chance?
i'm trying to find one but failing ! it was a joining piece to fit 2 hoses together on the waste side of the washing machine ,i suspect it came from wickes but not 100% .
This one? anti-syphon kit

It looks like it could be what I need - thanks.

Edited by Steve_W on Monday 1st March 15:11
that's it ,well found .

Ferg

15,242 posts

275 months

Monday 1st March 2010
quotequote all
For what it's worth, we used to fit those anti-syphon valves on water softener drain hoses and they were easily the least reliable water fitting I've come across in nearly 30 years of plumbing!! However, if a dribble from the valve isn't a worry they certainly do the job.

Steve_W

Original Poster:

1,557 posts

195 months

Tuesday 2nd March 2010
quotequote all
Ah, appreciate that Ferg - can you suggest a more robust solution?

Thanks,
Steve

Ferg

15,242 posts

275 months

Tuesday 2nd March 2010
quotequote all
Steve_W said:
Ah, appreciate that Ferg - can you suggest a more robust solution?

Thanks,
Steve
This sounds like a good idea.
Trevelyan said:
........just fit a tee into the drain pipe and fit a short section of vertical pipe with a normal non return valve at the top. This should allow air in, but prevent the water coming out if it's under any sort of pressure.
15mm tee and some jubilee clips + a 15mm non-return valve?

Steve_W

Original Poster:

1,557 posts

195 months

Wednesday 3rd March 2010
quotequote all
Ferg said:
This sounds like a good idea.
Trevelyan said:
........just fit a tee into the drain pipe and fit a short section of vertical pipe with a normal non return valve at the top. This should allow air in, but prevent the water coming out if it's under any sort of pressure.
15mm tee and some jubilee clips + a 15mm non-return valve?
It does - I just wasn't sure at what pressure the NRV opens - would the simple vacuum that water running down the waste pipe creates be enough to open it?

I guess a normal NRV is built to resist water pressure only one way - maybe I should get one & blow through it to see how easily the valve opens!

bimsb6

8,460 posts

239 months

Wednesday 3rd March 2010
quotequote all
Steve_W said:
Ferg said:
This sounds like a good idea.
Trevelyan said:
........just fit a tee into the drain pipe and fit a short section of vertical pipe with a normal non return valve at the top. This should allow air in, but prevent the water coming out if it's under any sort of pressure.
15mm tee and some jubilee clips + a 15mm non-return valve?
It does - I just wasn't sure at what pressure the NRV opens - would the simple vacuum that water running down the waste pipe creates be enough to open it?

I guess a normal NRV is built to resist water pressure only one way - maybe I should get one & blow through it to see how easily the valve opens!
thats how the one i mentioned works ,under pressure it seals and opens with very little vacuum .mine is under a kitchen unit with no leak issues ,it's been there for 2 + years now .