Sewage air valves on trade effluent rising mains: what food and drink sites need to know
If your site pumps its own effluent, whether to a treatment plant or to the public sewer, that rising main needs air valves just like a water main. But it can’t use the same ones.
Food and drink factories, dairies, breweries and abattoirs often run their own effluent pumping stations and rising mains. They are easy to forget about, right up until one blocks, floods or starts to smell.
Why can’t I use a normal air valve on effluent?
Air valves for clean water have their working parts close to the liquid. Effluent carries solids, fats and fibres that can foul those parts, so the valve sticks open and leaks, or sticks shut and stops venting.
A sewage air valve is built differently. In the GA range, the float sits on an extended rod, so the valve closes before the liquid reaches the sealing faces. All the internal parts, including the float, seat and plug, are 316 stainless steel.
What do sewage air valves do?
The same three jobs as any air valve:
1. Let air out while the main fills, so it can run full bore.
2. Let air back in when pressure drops below atmospheric, to stop a vacuum damaging the main.
3. Bleed off air and gas that collect at high points while the main is running.
A small orifice valve (Fig 925 and 929) does job 3. A large orifice valve (Fig 935 and 939) does jobs 1 and 2. A double orifice valve (Fig 942 and 959) does all three, and is usually the best choice for a rising main.
Where should they go?
- Peaks of the main, and every 400–500 m on long runs: double orifice.
- Changes in gradient and vertical bends: small orifice.
- Close to pumps and at the top of vertical lifts: large orifice.
What options matter on an industrial site?
The GA range offers an odour control unit, worth considering if the valve chamber is near offices, neighbours or production areas. A flushing attachment makes it easier to clean out fats and solids during maintenance. An isolating gate valve lets the air valve be serviced without draining the main.
The Fig 942 double orifice valve comes in DN50–150, rated PN16, with a PN25 version and a low-pressure squat version for tight chambers. It seals at pressures as low as 0.2 bar.
The range is built under licence from GA Industries in the USA, where pumped sewage systems have been standard practice for many years.
Quick tip: if your effluent air valve chamber smells, the valve may be fouled or simply needs an odour control unit. Tell us what you’re seeing.
Before you enquire, have ready: main diameter, working pressure, what the effluent contains (fats, fibres, solids), the main’s profile, and whether odour is a concern.
Related reading: Which type of air valve do I need? · Air valves on pumped industrial mains
Contact us now to see how we can help you!
Contact us by email at sales@gavalves.co.uk or call us on 01484 711983
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