Why Air Valves Are Essential for Irrigation Systems: The Role of Ari Air Valves

Introduction

Ask most growers to list the critical components of their irrigation system and they will mention pumps, filters, drippers, and control valves. Very few will mention air valves. Yet air valves are one of the most important protective devices in any pressurised pipeline — and their absence is responsible for some of the most damaging and costly failures in irrigation infrastructure.

This guide explains what air valves do, why they are essential, the different types available, and where they should be installed in your system. We also cover the Ari range of air and check valves, which are trusted by irrigation engineers across the UK and internationally.

What Is an Air Valve?

An air valve (also known as an air release valve, air vent valve, or combination air valve) is a device installed on a pressurised pipeline that automatically manages air within the system. It performs this function without any manual intervention — opening and closing in response to the presence of air or water at the valve seat.

Despite their small size, air valves perform a critical role that affects the safety, efficiency, and longevity of the entire irrigation system.

The Three Jobs of an Air Valve

1. Releasing Air During System Fill

When you first pressurise an irrigation system, large volumes of air are trapped in the pipework. If this air cannot escape, it forms pockets that block water flow, cause uneven pressure distribution, and prevent drippers and sprinklers from operating correctly.

An air release valve opens fully when the system is empty or filling, allowing trapped air to escape rapidly. As water reaches the valve, the float rises and seals the orifice, preventing water from escaping once the pipe is full.

Without air release valves, filling a system can be a slow, frustrating process — and air pockets may persist in high points of the pipeline, causing ongoing performance problems.

2. Releasing Small Air Pockets During Operation

Even during normal operation, dissolved gases come out of solution and small air pockets accumulate at high points in the pipeline. Over time, these pockets grow and restrict flow, increase energy consumption, and cause pressure fluctuations.

A small orifice air release valve (sometimes called an automatic air release valve) continuously vents these small air pockets during pressurised operation. The small orifice remains open under pressure, allowing air to escape while the hydraulic pressure prevents water loss.

3. Admitting Air During System Drainage or Vacuum Conditions

This is perhaps the most critical — and least understood — function of an air valve. When a pump stops suddenly, or when a pipeline drains rapidly, a vacuum can form inside the pipe. If air cannot enter the pipeline quickly enough to fill the void, the resulting negative pressure can cause catastrophic pipe collapse, particularly in thin-walled pipes such as HDPE and PVC.

This phenomenon, known as column separation or negative pressure transient, can destroy pipework in seconds. A vacuum breaker or combination air valve admits air rapidly when negative pressure is detected, preventing pipe collapse and protecting the entire system.

Water Hammer: The Hidden Threat

Water hammer is the pressure surge that occurs when flowing water is suddenly stopped — typically by a rapidly closing valve or a pump trip. The kinetic energy of the moving water column is converted into a pressure wave that travels back through the pipeline at the speed of sound in water (approximately 1,200 metres per second).

These pressure spikes can be many times higher than normal operating pressure and can cause:

• Burst pipes and blown joints
• Damaged pump seals and impellers
• Failed solenoid valves and control valves
• Cracked filter housings
• Dislodged drippers and fittings

Air valves play an important role in water hammer mitigation by preventing the vacuum conditions that allow column separation — one of the primary causes of severe water hammer events. They are often used alongside pressure vessels and slow-closing valves as part of a comprehensive surge protection strategy.

Types of Air Valves

Single Orifice Air Release Valves

Designed to release small air pockets during pressurised operation. The small orifice remains open under pressure, continuously venting accumulated air. Used at high points along pipelines where air naturally collects.

Double Orifice (Kinetic) Air Valves

Feature a large orifice for rapid air release during filling and vacuum breaking during drainage, plus a small orifice for continuous air release during operation. The large orifice closes when water reaches the valve during filling, and reopens when negative pressure is detected.

Combination Air Valves

Combine all three functions — large orifice air release, vacuum breaking, and small orifice continuous release — in a single unit. The most versatile and widely used type in irrigation systems. A single combination valve at each high point replaces the need for multiple separate devices.

Anti-Shock Air Valves

A specialised version of the combination valve that incorporates a controlled closing mechanism on the large orifice. When air is being expelled during system fill, the large orifice closes slowly as water approaches, preventing the sudden valve closure that can itself cause a pressure surge. Recommended on systems with long pipelines, significant elevation changes, or high flow velocities.

Check Valves

While not strictly air valves, check valves are closely related and often installed alongside them. A check valve allows flow in one direction only, preventing backflow when the pump stops. This protects the pump from reverse rotation and prevents contamination of the water source from backflow in the irrigation system.

The Ari Range of Air and Check Valves

Ari is one of the world's leading manufacturers of air valves for water and irrigation applications. Their products are engineered to handle the demanding conditions of agricultural and horticultural irrigation, including exposure to UV, fertilisers, and varying water quality.

The Ari range includes single orifice, double orifice, combination, and anti-shock air valves in a wide range of sizes and pressure ratings, as well as check valves for pump protection and backflow prevention.

Browse our full range of Ari Air and Check Valves to find the right valve for your system.

Where to Install Air Valves

Correct placement is as important as selecting the right valve type. Air valves should be installed at:

• All high points in the pipeline — air naturally migrates to the highest points in a system
• The pump outlet — to release air on startup and protect against vacuum on pump trip
• Long horizontal runs — at intervals of 400 to 800 metres to prevent air accumulation
• Downstream of control valves — where vacuum conditions can develop on valve closure
• At the end of mainlines — before the transition to lateral pipework

As a general rule, it is better to install more air valves than you think you need. The cost of an additional valve is trivial compared to the cost of repairing a collapsed pipe or a water hammer-damaged pump.

Maintenance

Air valves are largely maintenance-free, but should be inspected at the start of each season:

• Check that the valve moves freely and is not seized or corroded
• Inspect the float and seat for wear or debris
• Verify that the valve is not continuously weeping water — this indicates a worn seat or damaged float
• On anti-shock valves, check that the throttling mechanism operates correctly

Conclusion

Air valves are small, inexpensive components that perform an outsized role in protecting your irrigation system. Installing the right air valves in the right locations is one of the most cost-effective investments you can make in system reliability and longevity.

At IrriSmart, we stock the full Ari range of air and check valves, backed by 20+ years of irrigation expertise. Browse our Ari Air and Check Valves collection online, or contact our team for advice on specifying the right valves for your system.