Plumbing help - air vent on waste to stop vacuum?
Discussion
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
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
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.
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.
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.
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 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?

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 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?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?It looks like it could be what I need - thanks.
Edited by Steve_W on Monday 1st March 15:11
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?It looks like it could be what I need - thanks.
Edited by Steve_W on Monday 1st March 15:11
Steve_W said:
Ah, appreciate that Ferg - can you suggest a more robust solution?
Thanks,
Steve
This sounds like a good idea.Thanks,
Steve
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?Ferg said:
This sounds like a good idea.
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?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?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!
Steve_W said:
Ferg said:
This sounds like a good idea.
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?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?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!
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