What is an air valve?

Why are air valves important?

Air valves play a critical role in maintaining pipeline performance and protecting infrastructure.

Key benefits of air valves

• Reduce internal corrosion caused by trapped air
• Lower energy use and operating costs
• Improve accuracy of flow meters and measuring devices
• Speed up filling of pipelines and improve pump efficiency
• Reduce the risk of water hammer and pressure surges
• Protect pipes during draining by preventing vacuum conditions
• Extend the service life of pipelines and equipment

By minimising air pockets, air valves prevent sudden air movement that can cause destructive pressure surges and system instability.

Types of air valves

Different operating conditions require different air valve solutions. The most common types used in water and wastewater systems are described below.

Air and vacuum valves

(Also known as kinetic valves, large orifice air valves, or vacuum breakers)

Air and vacuum valves are designed to handle large volumes of air.

Functions:

• Release large quantities of air during pipeline filling
• Admit large volumes of air during draining or sudden pressure drops
• Protect the pipeline from collapse due to vacuum conditions

Typical use:

Long pipelines | rising mains and systems with rapid filling or emptying cycles.

Automatic air release valves

(Also known as small orifice or pressure air valves)

These valves continuously remove small amounts of air that accumulate while the pipeline is under pressure.

Functions:

• Release air pockets during normal operation
• Improve flow efficiency and reduce energy losses
• Prevent gradual performance degradation

Typical use:

Pressurised pipelines where air builds up over time.

Combination air valves

(Also called double orifice or dual orifice air valves)

Combination air valves combine the functions of air & vacuum valves and automatic air release valves in a single unit.

Functions:

• Release and admit large volumes of air during filling and draining
• Continuously release small quantities of air during operation

Typical use:

Most modern pipeline systems where full air protection is required.

Rapid filling preventer valves

Allows for a 2-stage outlet functionality. The valve is fitted with a disc placed between the large float and the large orifice. The disc has several smaller holes that restricts the outlet capacity.

This restriction of the outlet will prevent excessive velocity of the outlet air stream and thereby also prevent the valve’s disc from slamming with the risk of creating a pressure surge.

The restriction on the outlet air flow is only engaged whenever the air velocity exceeds a pre-defined threshold, during low air flow the valve acts as a standard air valve with no restrictions. The inflow of air through the orifice of the air valve is not restricted, meaning that the valve prevents the forming of vacuum in the pipes during emptying or in the event of a pipe rupture.

Functions:

• Large air discharge at low pressure
• Controlled air release through a reduced opening at high velocity to reduce the risk of a pressure surge (rapid filling prevention)
• Small air release under pressure
• Large air intake during draining

Typical use:

Water column separation points (peak points) | High pressure surge locations.  

Vented non‑return air valves (VNR)

Vented non-return air valves work similarly to rapid filling preventer air valves; however, they differ in the fact that VNR air valves are equipped with a spring-loaded restriction disc. This means that the valve will have a restricted outflow regardless of the airflow velocity.

The restriction on the air outflow is always engaged, but the inflow of air is not restricted, meaning that the valve prevents the forming of vacuum in the pipes during emptying or in the event of a pipe rupture.

The VNR option is the preferred choice for applications where extraordinary protection of the pipeline against pressure surges is necessary.

Functions:

• Controlled air release during filling
• Small air release under pressure
• Large air intake during draining
• High discharge capacity
• Minimal splash / no splash during filling

Typical use:

Next to the common header check valve | Nearest to the pump house | High surge pressure locations.

Out‑only air valves

Allows for the valve to work as a standard valve in the filling stage of the pipeline. Once the pipeline is completely vented and free of air, the large orifice closes, and the automatic air valve function (small orifice) takes over and vents during pressurised state of the pipeline.

When pressure drops in the pipeline the non-return valve will prevent the valve from letting air into the pipeline. This function may be desired in pipelines where pumps start and stop frequently, and it is avoiding the external polluted media (water or air) entering the pipeline.

Functions:

• Large release during filling
• Small air released under pressure
• No air intake during draining

Typical use:

Suction of the pump | Submergible Chambers | Near industrial parks where polluted media (air) is emitted.

Where are air valves installed?

• Air valves are typically installed at locations where air is most likely to accumulate or where protection is critical:
• On rising mains from pumps
• At high points and local peaks in the pipeline
• Along long, uniform slopes (typically every 500 m)
• After pressure reducing devices
• At pipe diameter changes
• Upstream of flow meters
• Near filter and treatment installations
• At street underpasses and low points

Reliable air management for efficient pipelines

Correct selection and placement of air valves is essential for:

• Safe pipeline operation
• Long‑term asset protection
• Reduced maintenance costs
• Improved hydraulic efficiency

A well‑designed air valve system ensures that pipelines perform as intended—quietly, efficiently, and safely.