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How much do you know about the structure and principle of pneumatic actuator?

Time: 2020-11-16 08:45:50Copyfrom: Wuxi shengernuo Control System Co., Ltd

How much do you know about the structure and principle of pneumatic actuator?

There are two kinds of pneumatic actuator:diaphragm type and piston type.It can be used as the pushing device of general control valve to form pneumatic diaphragm control valve.The piston type actuator has large thrust,which is mainly suitable for large diameter and high pressure drop.The long stroke actuator can output angular stroke,which has large output displacement and torque.It is suitable for the valve with angle control such as butterfly valve and damper.There are two forms of membrane actuator:positive action and reaction.When the signal pressure from the regulator or valve positioner increases,the valve stem moving downward is called the positive action actuator,while the valve stem moving upward is called the reaction actuator.Specifically,in the figure,when the pressure signal passes into the diaphragm chamber from the top of the corrugated diaphragm,it is a positive acting actuator,and when the pressure signal passes from the bottom of the corrugated diaphragm into the diaphragm chamber,it is a reaction actuator.By replacing individual parts,the two can be modified to each other.

The static characteristics of pneumatic diaphragm actuator indicate the relationship between signal pressure and stem displacement in equilibrium state.According to the force balance relation under the equilibrium state,p*a=k*l can be obtained

Where:P is the output pressure signal of the regulator;a is the effective area of the diaphragm;K is the elastic coefficient of the spring;and l is the displacement of the actuator push rod.

It can be seen that the actuator push rod displacement L is proportional to the input air pressure signal.

The pneumatic diaphragm actuator is mainly composed of elastic film balance spring and push rod,and its structure is shown in Fig.3-28.The actuator is the pushing device of the actuator,that is,after receiving the standard air pressure signal,it converts into thrust force through the diaphragm,which makes the push rod move and drives the valve core to move accordingly,thus changing the opening of the valve.

The dynamic characteristics of the actuator can be regarded as a first-order inertial link,and its time constant depends on the size of the membrane head and the length and diameter of the pipeline.

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