Typical Applications Of Anti-blowout Valves In Pneumatic Actuator

By Author: Daniel Martyin
Total Articles: 5
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Pneumatic actuator is used to convert the energy of compressed air into some mechanical action. This action can be either rotary or linear motion, or supplying force at any particular point, depending on the type of actuator. A typical pneumatic actuator consists of a piston, a cylinder, and valves. The valves of a pneumatic actuator are also called ports. The piston is inserted in the cylinder and is sealed by a diaphragm, to restrict the air in upper portion of the cylinder. This allows air pressure to act downwards on the diaphragm, which moves the piston downwards causing movement in the valve stem attached to the internal parts of the actuator.

A Pneumatic actuator can have single or multiple openings for signal input. In single input actuators, there is one spot on the top or bottom of the cylinder. The spot is operated by a valve which require very less operating pressure, generally twice or thrice the input force. The larger is the size of the piston; more is the output pressure it can deliver. So, a large piston can be used to deliver very large output force, for a relatively small input force, like ...
... in the case of pneumatic lifts, a pressure of around 100kPa can be used to lift a car weighing over a thousand pound.

However care needs to be taken that the force multiplication does not cause any leakage of air. For this the blowout proof stem of the actuator should be extremely efficient, else the air would leak through the cylinder and cause improper functioning of the actuator. The output pressure developed by the actuator is transferred to the valve stem, which is attached to the valve plug. Greater force is required in high pressure pneumatic actuators to operate the valves and allow the flow of fluids in the cylinder.

Many pneumatic actuator manufacturers use a self adjusting stem housed in threaded and flanged valves. The valves are generally of sizes ranging from 1/2” to 10” , but even special size valves are produced by some manufacturers. The major concerns in designing a valve and determining is size are the force multiplication required and the anti blowout requirements of the valve to prevent any leakage.

Many advanced pneumatic actuators have a pressure transmitter to monitor the pressure in the cylinder and transmit a signal in the range of 20kPa to 100kPa. A pressure of 20kPa means that there is no pressure, while that of 100kPa means that the pressure is at its highest level. With the rise in pressure inside the cylinder, the output at the pressure transmitter rises. This rise in the transmitter pressure is sent to the valve, causing it to stroke down and block the flow of fluids. This reduces the fluid pressure in cylinder as excess pressure is released due to the out flow of fluids.