我们首先来看什么是拨叉式气动执行器：拨叉式气动执行器是气源驱动拨叉盘进行阀门的启闭的执行机构，在结构上与齿轮齿条式气动执行器有区别。
Fork type pneumatic actuator with high torque
At present, there are mainly two types of angular stroke pneumatic actuators: rack and pinion type and fork type. In terms of internal structural design, there are significant differences between fork type pneumatic actuators and rack and pinion type actuators. The gear internal rack actuator is a meshing parallel structure, which transmits power through the meshing of a circular gear on the output shaft and a straight rack. The position of the meshing remains constant, resulting in a constant reciprocating output torque.
The fork type pneumatic actuator is an embedded rotating structure, which generates torque by pushing the "fork plate on the rotating shaft" through the rotating pin of the fork type active cold arm. The rotating pin slides relatively without resistance in the rolling groove of the core fork plate, and the effective force arm changes accordingly. Ultimately, the output torque changes with the angle of the shaft, and reaches the limit value at the valve opening and closing points, thereby obtaining the optimal output torque to meet the needs of the butterfly valve The control of ball valves is required.
The fork embedded structure increases the effective length of the arm, without wasting or reducing the arm length due to the thickness of the rack. In practical applications, it has been found that fork type pneumatic actuators can generate a 50% greater opening and closing torque than rack and pinion actuators.
(The above is the output torque of the gear rack type, and the following figure is the output torque of the fork type)
From the above figure, we can conclude that the output torque of the fork type pneumatic actuator is a curve that reaches its limit when the valve is opened and closed, and the output curve of the fork type is very suitable for the working conditions of ball valves and butterfly valves.
Price issues with fork actuators
So, let's return to the question, why do large diameter butterfly valves use fork type pneumatic actuators? Because large diameter butterfly valves require greater output torque to drive the valve's switch, then the owner needs to purchase actuators with greater torque, and actuators with greater torque require more expensive prices. If a fork type pneumatic actuator is used, a slightly smaller torque actuator can be used to drive a large diameter butterfly valve.
Fork type actuators have smaller volume and weight
The question is' large diameter butterfly valve ', so large diameter butterfly valves have a large volume and heavy weight. Generally, a crane is used for installation, which is very inconvenient for installation and maintenance.Taking the inlet valve with a diameter of DN700mm as an example, the actuator needs to be at least 3600NM. If a rack and pinion actuator is used, the weight is 80kg-120kg. If a fork type pneumatic actuator is used, the weight is only 48kg, which will be 48.1% less in volume and more convenient for installation and maintenance.
So it would be better to use a fork type pneumatic actuator for large-diameter butterfly valves!
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