Air Admittance Valves (AAVs): Durgo Valves, Studor Vents, and Soil Vent Pipe Alternatives for UK Plumbers

An air admittance valve (AAV) can protect water seals in traps by admitting air when negative pressure develops in sanitary pipework. For soil-stack work, the connection method, installation position and valve specification all matter. APM stocks 110mm options for both push-fit and solvent-weld systems, available online or from our Acton trade counter.

How an air admittance valve works

Discharge through a branch or stack can create negative pressure. If that pressure is not controlled, water can be drawn from a trap and its seal may be weakened. An AAV is normally closed, but opens under negative pressure to draw air into the pipework. It then closes again to help prevent foul air from escaping into the building.

An AAV admits air; it does not discharge air or relieve sustained positive pressure. It is therefore not automatically a like-for-like replacement for every open vent terminal. The drainage design may still require ventilation to outside air, depending on the system layout and applicable guidance.

Which APM valve should you choose?

Do not choose by colour alone. Confirm the pipe’s actual outside diameter and jointing system, the valve’s airflow classification and temperature range where relevant, and compatibility with the rest of the soil system. Do not confuse a soil-pipe AAV with an automatic air vent used on a sealed heating system: they perform different jobs and are not interchangeable.

Installation and design checks

• Check the drainage design. Consider the full stack and branch layout, not only the appliance nearest the valve. An AAV will not correct a blockage, poor gradient, undersized pipework or inadequate provision for positive pressure.
• Follow current guidance. The competent designer or installer should assess the work against the current edition of Approved Document H, relevant standards such as BS EN 12380, local requirements and the valve manufacturer’s instructions. A product standard does not by itself confirm that every proposed location is suitable.
• Use the specified orientation and level. AAVs are generally installed upright and above the relevant branch or appliance spillover level, but the required position depends on the valve classification, system and manufacturer’s instructions.
• Keep it accessible. Allow access for inspection, cleaning and replacement. Do not permanently box the valve in.
• Provide air and protection. The space around the valve must be able to supply air. Protect it from frost, excessive heat, dirt and damage, in line with its stated installation limits.
• Make the correct joint. Push-fit seals should be clean, correctly seated and lubricated only as directed. Solvent-weld joints need compatible cleaner or cement, suitable preparation and the stated curing time.
• Test before handover. Inspect joints and operate connected appliances to check discharge, trap seals and signs of leakage or abnormal pressure. Investigate repeated gurgling or odours rather than assuming a larger valve is the answer.

When to involve a drainage professional

Seek competent professional advice for shared stacks, multi-storey or complex drainage, recurring odours, uncertain vent provision, alterations that may need building-control input, or any design where positive pressure could occur. Existing defects should be diagnosed before a valve is added.

Order online or collect in Acton

Choose the FloPlast grey 110mm push-fit AAV or the Aquaflow black 110mm solvent AAV, then check the live product page for availability. For help matching an AAV to your soil-pipe system, call 020 8702 8080 or visit APM Plumbing & Electrical, 24 Western Avenue, Acton, W3 7TZ.

Visit us at APM Electricals, 31 Inglis Road, London, W5 3RL. Call 020 8819 5852.