XF1604C-2.00 Continuous Air Release Valve
Continuous Air Vent Vacuum Relief Valve allows continuous release of any air that remains in or enters into the system to escape during operation. This eliminates trapped air from blocking the flow of water through the system.
Why You Need Air Vent/Vacuum Relief in Your Irrigation System
We do not generally think about air when we are planning an irrigation system, however, it is something to be concerned about. The three main concerns are:
- When your pipelines are not full of water, they are full of air. This air must be expelled as water fills the lines.
- During normal operation of your irrigation system, dissolved air is released from the water in the form of bubbles.
- At system shutdown, vacuum conditions may arise as water drains out of the pipelines if sufficient air is not introduced into the lines.
Any of these issues can be resolved with proper installation of air vent and vacuum relief valves. This can prevent damage to important components in your irrigation system.
We will do our best to describe the issues involved with air and vacuum in an irrigation pipeline; the different types of valves: Automatic (Continuous) Air Release Valves, Air/Vacuum Relief Valves and Combination Air/Vacuum Relief and Air Release Valves; and proper placement of these relief valves.
Trapped Air in a Pressurized Pipeline
How does air get into the pipelines?
In most irrigation systems, the pipelines are full of air when the system is not in use. When your irrigation system shuts down most of the water drains out through the emitters or any auto drain valves you might have installed and is replaced by air. Additionally, pumps can introduce air into the system. Lastly, water itself contains approximately 2% air by volume. The dissolved air comes out with temperature or pressure changes in the system in the form of small bubbles. Turbulence and water velocity increase dissolved air.
How does the trapped air affect the system?
Water can be 800 times more dense than air, so trapped air is compressed when the system fills, it will accumulate at high points and form air pockets that may cause damage. If an accumulation of air is suddenly dislodged it can cause a surge of water, called water hammer, which has a damaging effect on pipes, fittings and components. Deadheading of the pump is another problem. This occurs when the fluid flow is stopped and the pump impeller continues to turn causing the fluid temperature to rise to a level that can damage the pump. Corrosion from cavitation is also a concern. Cavitation is the forming of bubbles or voids in a liquid that when they implode can cause tiny shock waves which in turn can damage pipe walls and components. Trapped air is especially common in very low pressure systems or in long piping situations where air pockets may restrict or even stop flow if not released.
What are the solutions for preventing entrapped air?
First and foremost is installing air relief or release valves at specific points in your system. These can be automatic relief valves or even hydrants or manually operated valves. Next, minimize the high points or peaks in your layout as much as possible. Keep in mind that water velocity will push air bubbles to the high points so plan your system accordingly especially in low pressure designs. If using a pump, keep suction intake well below water level to prevent siphoning air with the water.