Air relief valves are automatic valves that vent air during the filling of pipelines and vessels, and relieve pressure buildup caused by thermal expansion of trapped air. By releasing air pockets and compressible gases, these critical valves ensure efficient operation of piping systems and prevent damage from excessive pressure.
How DO Air Relief Valves Work?
Air relief valves contain a float, diaphragm or piston that rises when liquid enters the valve, sealing the air discharge orifice. As air accumulates above the liquid, the float, diaphragm or piston drops to open the valve and allow the air to vent. When the liquid level drops again, the float rises and closes the valve orifice.
Cast iron air valve is as designed to remain closed during normal system operation, and only open intermittently to vent accumulated air when required. They automatically reseal once the air has been discharged.
Various Types Of Air Relief Valves
There are several types of air relief valve:
• Float Valves – Contain a floating ball, lever or weight that rises and falls with liquid levels to open and close the valve orifice. Simple and reliable design.
• Diaphragm Valves – Utilize a flexible diaphragm that moves up and down with pressure changes to open the valve orifice. Often provide more precise control and higher capacities.
• Piston Valves – Feature a shaped poppet or piston that rises and lowers within a cylindrical bore based on pressure and liquid levels. Can handle high pressures and temperatures.
• Quick Release Air Valve – Designed to purge entrapped air quickly during pipeline filling operations. Often manually operated and opened until purging is complete.
Air Relief Valves Uses In Wide Range Of Industries
Air relief valves serve important functions within liquid and slurry handling systems, including:
• Pipeline filling – Allow automatic venting of air during pipeline commissioning to ensure lines are completely full of liquid before operation.
• Pressure relief – Prevent over-pressurization of pipelines, vessels and equipment during operation due to thermal expansion of trapped gases.
• Drain outlet – Provide an automatic air gap at water ends of drains to prevent backflow or back siphonage.
• Pumping systems – Vent air from casings and seal pots of pumps, devices and hydraulic systems during startup and operation.
• Level control – Allow air to escape from level sensors and instrumentation to provide accurate readings and control.
• Process systems – Maintain efficiency within industrial processes by releasing compressible gases that would otherwise impair proper operation.
Factors To Consider When Selecting Air Relief Valves
• Operating Pressure – Choose a valve with a pressure rating higher than the maximum system pressure. This ensures the valve can safely relieve excess pressure buildup.
• Temperature Range – Make sure the valve materials and seals can withstand the full range of temperatures the system may operate at. High temperatures can degrade valve components over time.
• Capacity – Select a valve with a flow rate greater than the maximum expected relief air volume. The valve needs to be able to relieve pressure buildup quickly enough to prevent system damage.
• Media Compatibility – Confirm the valve is constructed of materials and uses seals that are compatible with the specific liquid, gas or vapor in the system. Incompatible materials can fail prematurely.
• Enclosure – For outdoor applications, choose a valve with a weatherproof or explosion-proof housing as needed. The enclosure protects the valve from environmental conditions and safely contains any relief events.