Liquid piping systems are prone to collecting air from incoming fluids, pumps and connections. This air can cause inefficiencies and serious operating problems. Air release valves, familiar to most people, can expel trapped air in a pipeline.
Air release valves are probably the most widely used type of air valve and are characterized by small orifices, weighted floats and leverage mechanisms. The combination of these three features allow air release valves to expel air or gas at full operating pressure. Since air release valves have orifices that range in diameter from 1/16 of an inch to 1 inch, they have a limited capacity for admitting and exhausting air. In other words, a typical piping system will not be filled or drained using just an air release valve; such an action would take weeks. Air release valves automatically vent small pockets of accumulated air or gases as those pockets accumulate in a liquid piping system. For example, an air release valve mounted on the top of the pipe could automatically release trapped air that accumulates in the top of the piping system.
When installed, air release valves are “normally open” and expel air. It is only when liquid enters the valve that the float rises because of its buoyancy and seals off the valve’s orifice. Conversely, as air accumulates in the valve body, the float will drop because of its weight and reopen the valve. To reopen an air release valve under operating pressure requires a mechanical linkage for magnifying the weight of the float and breaking the pressurized seal on the orifice. Because of this, mechanical linkage is needed to multiply the weight of the float, and the orifice diameter on air release valves is limited in size to reduce the breaking force needed.
When air is allowed to accumulate in pressurized pipelines, efficiency is sacrificed, and serious system damage can occur. By having an understanding of air valves, system designers can better select and install air valves to protect liquid piping systems.