Control and Effect of Air in Irrigation Systems
Air in an irrigation system must be controlled because the presence of air bubbles and air pockets, or their absence (vacuum), can cause problems and damage to the system.
Problems and Damage Caused by the Presence of Air Pockets and Air Bubbles in Water Pipelines
- Uneven flow through the pipe – sometimes even stopping water flow altogether.
- High losses of water head and consequently, energy losses.
- Water hammer damage to the pipes, accessories and connectors.
- False readings of water meters and automatic metering devices (and consequent payment for water not supplied, virtual use of water above licensed pumping limits, under utilization of available water supplies, inadequate supply of water to crops because plants receive less water than the volume measured by the hydrometer or water meter).
- Inadequate supply of water to agricultural crops caused by throttling of flows and accumulated pressure losses at system ends.
- Extensive damage to impeller systems in water meters, hydrometers, sprinklers and sprayers.
- Corrosion damage.
- Physical risk - when large volumes of air are released at high velocity.
The Problems Exacerbated by the Presence of a Vacuum
- Mud and dirt are sucked into the system through drippers.
- Seals, drippers and other accessories are sucked into the main distribution lines.
- Uncontrolled entry of chemicals and fertilizers injected into agricultural and landscape irrigation systems.
- Vacuum-induced collapse of pipes and accessories (sub-atmospheric pressures).
- Increased risk of surge and slam conditions during the release of air pockets.
- Cavitation damages.
Control of Air in Irrigation Systems Using A.R.I. Air Valves
There are three main types of air valves installed in irrigation systems: air & vacuum, automatic air release and combination (double) valves.
Air & Vacuum valves discharge large quantities of air from non-pressurized pipes and are used mainly when filling a line. These valves also make it possible to admit large quantities of air when lines are drained and at water column separation. Air & Vacuum valves are also known as: kinetic valves; large orifice air valves, vacuum breakers, low-pressure air valves and air-relief valves.
Automatic air release valves continuously release relatively small quantities of air from a pressurized line. The automatic air valve is also known as an: air release valve; small orifice air valve and as a pressure air valve.
Combination air valves fulfill the tasks required of both types of valve – air & vacuum and automatic. In other words – they discharge or admit large volumes of air when filling or emptying a system and continuously release small volumes air when the line is pressurized.
Combination air valves are also known as double orifice air valves.
The Range of Advanced Air Valves from A.R.I. Flow Control Accessories
A.R.I. is one of the world’s leading manufacturers of air valves. A.R.I. engineers have developed a range of advanced composite material air valves, specially designed for use in agricultural and landscaping applications.
Technologically, the product range is based on the A.R.I. patented rolling seal mechanism, which replaces the old system that uses the valve float to seal air valve orifices. The rolling seal mechanism and the aerodynamically designed float, in this line of air valves, provide much greater efficiency (larger orifices) and have better resilience to withstand dynamic valve closure.
The new sealing mechanism enabled the development of small, lightweight air valves with a superior cost / benefit ratio. The width of the SG-10 automatic air valve from A.R.I. is a mere 87 millimeters; it stands no more than 140 mm high and weighs just 330 grams. Despite its small dimensions, the area of air orifice in this valve reaches 12 mm, which permits the release of 152 cubic meters of air per hour and can withstand pressures of up to 10 bar.
The valve's integral self-cleaning mechanism prevents blockages, leaks and particles from sticking to the sealing faces.
The DG-10 model valve is just 180 mm wide, (including the protruding drainage funnel) 209 mm tall and weighs only 1.1 kg. With 12mm of automatic orifice area and 804 mm of kinetic orifice area, intake and release of air is very efficient – even more efficient than much larger and much heavier air valves, which are overwhelmed and slam closed at lower differential pressures. The valve's integral self-cleaning mechanism prevents blockages and leaks and particles do not stick to the sealing faces.
The R&D team at A.R.I has also developed the AV-010 air & vacuum valve to provide solutions for agricultural and landscaping irrigation systems. The product is manufactured from composite materials and is available in 3”, 2”, 1” and 3/4” sizes. It is lightweight, compact and very competitively priced.