How to Choose the Actuator of Pneumatic Valves?
How to choose the actuator of pneumatic valves and protection methods？
I. Introduction to the selection basis
1. There are two main engine structures to operate the electric device of thrust valves: one is to directly output torque without the configuration of the thrust disc, and the other is to configure a thrust disc. The output torque is converted to the output thrust through the valve stem nut of the thrust disc.
2. Operation torque
The operation torque is the most important parameter in selecting the valve electric device. The output torque of the pneumatic actuator should be 1.2 to 1.5 times of the maximum operating torque of the valve.
3. The stem diameter to multi-turn type rising stem valves
If the maximum diameter of stems allowed by the electric device cannot pass through the stem of the valve supplied, it will not be assembled as an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the outer diameter of the stem of the rising stem valve. As for a part of the rotary valve and multi-rotary valve in the non-rising stem valve, although we do not consider the diameter of the valve stem through the problem, we should also fully consider the diameter of the valve stem and the size of the keyway in the matching so that it can work normally after the assembly.
4. According to the M = H/ZS calculation (M for electric devices should satisfy the total number of rotating rings. H is the height that the valve opens. S for stem drive screw pitch and Z for the stem thread).
5. The actuator of pneumatic valves has its special requirements, that is, it must be able to limit the torque or axial force. Usually, the valve electric device uses a torque-limiting coupling. When the specification of the electric device is determined, the control torque is also determined.
6. If the opening and closing speed of the output speed valve is too fast, it is easy to produce the water hammer phenomenon. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
II. Why is there a load situation?
Generally, the motor runs for a predetermined period, and the motor will not be overloaded. However, the overload may occur if the situation occurs as follows.
1. The power supply voltage is low. We can not get the required torque so the motor stops rotating.
2. The torque limiting mechanism is incorrectly set so that it is greater than the stopping torque, resulting in continuous excessive torque, then, the motor stops rotating.
3. It is intermittent use, and the heat accumulated exceeds the allowable temperature appreciation of the motor.
4. Due to some reason, the torque limiting mechanism circuit fails so that it is too large.
5. The use of the environment temperature is too high. It relatively makes the motor heat capacity decline.
III. The basic protection methods against overload are the following tips.
1. Thermal relay is used for the protection of motor blocking.
2. Thermostat is used for overload protection of continuous motor operation or point operation.
3. For short circuit accidents, a fuse or overcurrent relay is used.
The actuator of pneumatic valves is the indispensable equipment to realize valve program control, automatic control, and remote control. Its movement process can be controlled by stroke, torque, or axial thrust. The correct choice of valve pneumatic device is very vital to prevent the overload phenomenon (the working torque is higher than the control torque).
IV. The general combination methods
In the past, the way to protect the motor was to use fuses, overcurrent relays, thermal relays, thermostats, etc., however, these methods have advantages and disadvantages. There is no reliable way to protect pneumatic devices with variable loads. Therefore, various combinations must be adopted, which can be summed up in two ways as below.
1. Judge the increase or decrease of the input current of the motor.
2. It is to judge the heating of the motor itself. Either way, a given time allowance for the heat capacity of the motor should be considered.
I. Introduction to the selection basis
1. There are two main engine structures to operate the electric device of thrust valves: one is to directly output torque without the configuration of the thrust disc, and the other is to configure a thrust disc. The output torque is converted to the output thrust through the valve stem nut of the thrust disc.
2. Operation torque
The operation torque is the most important parameter in selecting the valve electric device. The output torque of the pneumatic actuator should be 1.2 to 1.5 times of the maximum operating torque of the valve.
3. The stem diameter to multi-turn type rising stem valves
If the maximum diameter of stems allowed by the electric device cannot pass through the stem of the valve supplied, it will not be assembled as an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the outer diameter of the stem of the rising stem valve. As for a part of the rotary valve and multi-rotary valve in the non-rising stem valve, although we do not consider the diameter of the valve stem through the problem, we should also fully consider the diameter of the valve stem and the size of the keyway in the matching so that it can work normally after the assembly.
4. According to the M = H/ZS calculation (M for electric devices should satisfy the total number of rotating rings. H is the height that the valve opens. S for stem drive screw pitch and Z for the stem thread).
5. The actuator of pneumatic valves has its special requirements, that is, it must be able to limit the torque or axial force. Usually, the valve electric device uses a torque-limiting coupling. When the specification of the electric device is determined, the control torque is also determined.
6. If the opening and closing speed of the output speed valve is too fast, it is easy to produce the water hammer phenomenon. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
II. Why is there a load situation?
Generally, the motor runs for a predetermined period, and the motor will not be overloaded. However, the overload may occur if the situation occurs as follows.
1. The power supply voltage is low. We can not get the required torque so the motor stops rotating.
2. The torque limiting mechanism is incorrectly set so that it is greater than the stopping torque, resulting in continuous excessive torque, then, the motor stops rotating.
3. It is intermittent use, and the heat accumulated exceeds the allowable temperature appreciation of the motor.
4. Due to some reason, the torque limiting mechanism circuit fails so that it is too large.
5. The use of the environment temperature is too high. It relatively makes the motor heat capacity decline.
III. The basic protection methods against overload are the following tips.
1. Thermal relay is used for the protection of motor blocking.
2. Thermostat is used for overload protection of continuous motor operation or point operation.
3. For short circuit accidents, a fuse or overcurrent relay is used.
The actuator of pneumatic valves is the indispensable equipment to realize valve program control, automatic control, and remote control. Its movement process can be controlled by stroke, torque, or axial thrust. The correct choice of valve pneumatic device is very vital to prevent the overload phenomenon (the working torque is higher than the control torque).
IV. The general combination methods
In the past, the way to protect the motor was to use fuses, overcurrent relays, thermal relays, thermostats, etc., however, these methods have advantages and disadvantages. There is no reliable way to protect pneumatic devices with variable loads. Therefore, various combinations must be adopted, which can be summed up in two ways as below.
1. Judge the increase or decrease of the input current of the motor.
2. It is to judge the heating of the motor itself. Either way, a given time allowance for the heat capacity of the motor should be considered.
