What Is the Role of Springs in Single-acting Pneumatic Actuators?

Pneumatic actuators are actuators that use air pressure to drive open and close or adjust valves. The commonly used air powered actuators are mainly valve positioners and handwheel mechanisms. The function of the valve positioner is to use the feedback principle to improve the performance of the actuator, so that the actuator can realize accurate positioning according to the control signal of the controller. The function of the handwheel mechanism is to use it to directly control the control valve to maintain the normal production process when the control system is out of power or gas, the controller has no output or the actuator fails.

 

Actuators are divided into three categories: pneumatic, electric and hydraulic according to their energy form. Pneumatic actuators can also be pneumatic diaphragm actuators and pneumatic piston actuators. Pneumatic actuators can also be divided into single acting pneumatic actuator and double acting pneumatic actuator. The switching action of the actuator is driven and executed by the air source. Below we mainly introduce single-acting pneumatic actuators.

 

Working Principle of Single Acting Pneumatic Actuator

 

When compressed air enters the middle cavity of the pneumatic cylinder piston from port 2, the two pistons move toward the ends of the cylinder, forcing the springs at both ends to compress. The air in the cavities at both ends is discharged through the air port 4, and the two pistons simultaneously drive the gear shaft to rotate counterclockwise. After the compressed air is switched by the air actuated solenoid valve, the two pistons in the cylinder move to the middle under the action of the spring itself. The air in the middle cavity is discharged from the air port 2, and the two pistons simultaneously drive the gear shaft to rotate in a clockwise direction. By rotating clockwise and counterclockwise, the purpose of opening and closing the actuator pneumatic valve is achieved.

 

The opening and closing of a double acting rotary actuator requires the thrust of compressed air to perform. In other words, this type of pneumatic actuator will be fixed in a certain position when it loses air.

 

Spring in Single-acting Pneumatic Actuator

 

Single-acting pneumatic actuators belong to the automatic reset type. After losing the air source pressure, the actuator will drive the valve back to the initial set position under the action of the spring force. Relatively speaking, it is safer and more reliable.

 

In a single-acting pneumatic actuator, the role of the spring is so important, so how to ensure that the spring is safe at critical moments?

 

First of all, the material of the spring is very critical. The spring is made of coiled spring steel wire. Various grades of spring steel have different properties, strengths, and prices. Imported wire and domestic wire are even more different. Correspondingly, the fatigue life and strength of the final spring are also quite different. The precision-made spring can easily exceed 1 million times during the entire service cycle, and the attenuation of the force value is only 10%-12% (compared with the original force value before the fatigue test).

 

Secondly, the single-acting pneumatic actuator spring is composed of a spring seat and a copper pipe connection. The quality of the connection directly affects the quality of the actuator. Will the spring bend sideways? Will the spring make abnormal noise during operation? Does the spring have a 5° adjustment margin?