You may have heard the term “air admittance valve” or AAV, but what is it and how do you use it? Well, that’s what this guide will explore. As an essential component of the soil drainage system, you must understand its role and how to use it.
Table of contents
- What is an air admittance valve?
- Where should an air admittance valve be installed?
- Potential issues with air admittance valves
What is an air admittance valve?
Air admittance valves are essential for the performance of soil drainage systems. Also known as AAVs or durgo valves, they help re-balance the pressure within a soil pipe to normal levels.
How does an air admittance valve work?
Air admittance valves are designed to activate in response to negative pressure. As negative pressure occurs, the valve opens to allow air into the pipe. The valve keeps undesirable odours out of the house by closing when the pressure is balanced and opening only when necessary to allow air to enter.
Air admittance valves often feature rubber seals to help create a complete seal and increase the effectiveness of the valve, preventing any odours from escaping through small gaps.
Typically, air admittance valves are fitted using a push-fit joint. This allows pipes and sockets to be fitted together without the use of tools. Push-fit joints incorporate a rubber seal to create a completely watertight and airtight fitting. They can, however, also be bought with solvent-weld joints. These use a chemical reaction during the application of a solvent to create a watertight and airtight permanent bond.
Why pressure changes within soil pipes matter
Due to air being carried along the pipe, pressure changes happen when a toilet is flushed or any water flows through the waste pipe. This, in turn, creates negative pressure. To restore balance, air is drawn into the pipe from wherever possible. Particularly from plug holes in bathtubs, sinks, and showers. This can cause a number of issues, including unpleasant odours being released into the home, wastewater coming up from the trap into the sink or basin, poor drainage of water, and gargling sounds when drainage occurs.
Traditionally, this pressure change issue is addressed with an open pipe outlet installed on the roof. This allows air to be drawn into the pipe from the external environment, preventing it from being drawn from sinks, basins, and other sources within the home, thus removing the issues associated with it.
The other alternative is to use an air admittance valve in situations where an open pipe outlet isn’t possible. This can be in situations where there isn’t a pipe outlet that is more than 3 metres from a window or in situations where the building has roof windows – the pipe can let out bad odours, so situating this near a window can be a bad idea!
Where should an air admittance valve be installed?
Air admittance valves are typically installed on soil pipes that are at least 200mm above the highest water entry point, i.e. the highest point at which wastewater will travel through a soil pipe. They are usually installed at the end of a soil pipe, but they can also be installed inline via a branch.
Air admittance valves are usually installed in lofts or cupboards to avoid becoming an eyesore. However, they do require a level of ventilation. As such, it’s important to ensure that they are in a space that receives a flow of air. Additionally, try to place the air admittance valve in an accessible area in case it needs access when a blockage occurs.
Can air admittance valves be used outside?
Air admittance valves can be installed externally, but this is uncommon and is usually done only when the soil pipe is too close to an open window. Open pipe outlets must be installed more than 3 metres away from a window that opens, but air admittance valves can be closer than this. If you are installing an air admittance valve externally, you’ll need to purchase a valve that is frost-resistant and unaffected by extreme weather conditions.
Potential issues with air admittance valves
Keep an eye out for these problems to make sure they are resolved as quickly as possible because AAVs are not flawless.
Bad smells and loud gargling noises
Unwanted odours may be emitted, gargling sounds may be heard, or wastewater may enter the sink from the soil pipes. All of these indicate that there may be an obstruction in the waste pipe causing issues with the air admittance valve that needs to be cleared. If not fixed, this would prevent gases from being pushed down into the sewer, preventing water from draining away.
To resolve this, take a look at our guide on how to unblock a drain.
The valve is stuck in a certain position
Occasionally the valve may get stuck. In this case, a simple spray of lubricant should help to loosen the valve and ensure it is back in working order.
The valve was installed incorrectly
The air admittance valve may have been installed too low, which could be another problem. To reduce the risk of this issue occurring, ensure that the valve is higher than the highest point of any shower, bath, sink, or toilet.
