Air Release Valves in Irrigation

Air release valves in irrigation are essential for water pump powered irrigation systems. As the name suggests, they release air trapped in the irrigation pipeline. In this write up, we answer key questions on air release valves in irrigation

1. What is the purpose of air release valves in irrigation?

To remove air bubbles that build up at each high point of a water pump powered irrigation pipeline system. Trapped air causes;

• Pump failure
• Poor irrigation water flow
• High energy consumption by causing the pump to work much harder

Air release valves improve the efficiency of the irrigation system.

The other purpose of an air valve is to admit air into the system when the internal pressure of the pipeline drops below atmospheric pressures. By admitting air into the pipeline as the internal vacuum condition develops, the magnitude of the vacuum pressure can be reduced and as a result help prevent the pipeline from experiencing excessive deflection and/or collapse as well as help prevent the formation of a full vacuum condition in which vapor cavities may form from the fluid vaporizing

What is the origin of trapped air?

i. When irrigation pipes are laid, they are filled with air before water is pumped through them

ii. Irrigation water contains 2% air. When this air passes through the pipeline, it separates and builds up at the system’s high points

iii. Irrigation machinery and accessories such as water pumps, tees, elbows, saddle clamps, ball valves, connectors and so on allow in a certain amount of air

2. How does an air release valve work?

When air accumulates in the system, it creates diminution. This increases head loss which in turn causes higher energy consumption by the water pump. When the speed of water in the pipe increases due to the restricted pipe, the air bubble flows back to the pump. It causes a water hammer which can damage the pump.

If it is not carried by the speed of water, it accumulates in the system. This causes it to be air bound, which slows, then stops irrigation water flow

Air bubbles enter the air release valves located at the system’s high points then displace the water. The water level drops and when it no longer buoys the float, the float drops. This action opens the vent allowing accumulated air to escape

3. Where should an air release valve be placed?

At the high points (elevated sections) of your irrigation system. This is at the the hydrants, along the water pipe or at the end of the line. It is set in a vertical position with the inlet facing down. Pressured drip irrigation systems, sprinkler systems, centre pivot, and rain hose systems will have it in place

4. How do I choose an air release valve?

Determine the flow rate and pipe diameter, then match this with the appropriate air release valves for irrigation

5. How much do air release valves cost?

• 2″ Kes 8,000
• 1.5″ Kes 7,200
• 1″ Kes 5,500