These cause excess heat and noise to be generated as the armature moves, reducing efficiency and increasing the levels of power that need to be generated to operate the solenoid. Foremost among these is the disruption in the magnetic field, produced by air gaps within the solenoid core, around the iron circuit and the non-magnetic tube. Energising the solenoid lifts the armature against the spring, allowing the supply air through to an outlet port.Īlthough the Skinner system is relatively simple and is still widely used in solenoid valves, it suffers from a number of inherent problems.
The Skinner design incorporates a spring loaded armature, enclosed in a tube of non-magnetic material and held against the air inlet port by the force of the spring, with the port being effectively sealed by a rubber pad inserted into the bottom of the armature. This was developed by an American called Skinner and was first used in the 1930s. Instead a small solenoid pilot valve is used to control the flow of air to a pneumatically driven spool.Įarly solenoid pilot valves were based on similar design to that used in directly operated valves. These cannot, however, be operated directly, due to their longer stroke and higher levels of internal friction. In Europe, poppet and elastomer sealed spool valves are far more common.
Although these devices offer relatively fast response times and can be switched at any air pressure, they are relatively large, expensive to manufacture and require additional electronic control equipment before they can function. Solenoid valves use electro-magnets to operate valve spools either directly or, more commonly, indirectly, by means of a pilot valve.ĭirect operation can only be achieved in valves incorporating almost frictionless, short stroke, steel spools without seals typically these include directional control valves, which are widely used in America. Solenoid valves are used widely throughout the pneumatics industry, as an effective and reliable method of controlling actuators and similar pneumatically operated devices.
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