The valve actuator is one of the devices used to operate the valve and connect it to the valve. The device is driven by electricity and its movement can be controlled by stroke, torque or axial thrust. Due to the operating characteristics and utilization of the valve electric device depends on the type of valve, the working specification of the device and the position of the valve on the pipeline or equipment. Therefore, it is crucial to master the correct selection of the valve electric device; taking into account the prevention of overload (the working torque is higher than the control torque) has become a crucial part.
The correct choice of valve electric device should be based on: 1. Operating torque: Operating torque is the most important parameter for selecting the valve electric device. The output torque of the electric device should be 1.2~1.5 times the maximum torque of the valve. 2. Operational thrust: The main structure of the valve electric device has two kinds. One is that the thrust plate is not configured. In this case, the torque is directly output. The other type is configured with a thrust plate. At this time, the output torque passes through the stem nut in the thrust plate. Convert to output thrust. 3. Rotation number of output shaft: The number of revolutions of the output shaft of the valve electric device is related to the nominal diameter of the valve, the pitch of the stem, and the number of threads. It is calculated according to M=H/ZS (where M is the electric device should satisfy The total number of turns; H is the opening height of the valve, mm; S is the thread pitch of the stem transmission thread, mm; Z is the number of threads of the stem.) 4. Stem diameter: For multi-turn type stem valves, electric valves cannot be assembled if the maximum stem diameter allowed by the motorized device cannot pass through the stem of the valve with which it is fitted. 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 stem valve. For the partial rotary valve and the multi-rotary valve, although the stem diameter does not have to be taken into consideration, the diameter of the stem and the size of the key groove should be fully taken into account in the selection so that the assembly can work normally. 5. Output speed: The valve's opening and closing speed is quick, easy to produce water hammer phenomenon. Therefore, appropriate opening and closing speeds should be selected according to different conditions of use. 6. Installation and connection method: The installation method of the electric device includes vertical installation, horizontal installation, and floor installation; the connection mode is:
There is a thrust disk stem pass (Ming rod multi-turn valve)
The multi-turn non-thrust disk stem of the dark rod does not pass a part of the rotary electric device. It is an indispensable device for realizing valve program control, automatic control and remote control. It is mainly used in closed-circuit valves. However, the special requirements of valve actuators cannot be ignored—it must be possible to limit the torque or axial force. Usually the valve electric device uses a torque limiting coupling.
When the specifications of the electric device are determined, its control torque is also determined. When it is running for a predetermined period of time, the motor is generally not overloaded. However, overload can occur if:
1. The power supply voltage is low and the required torque cannot be obtained, causing the motor to stop rotating.
2. The torque limit mechanism is erroneously set so that it is larger than the stopped torque, causing continuous generation of excessive torque and stopping the motor.
3. When used intermittently as a jog, the heat generated accumulates and exceeds the allowable temperature rise of the motor.
4. For some reason, the torque limiting mechanism circuit malfunctions, causing excessive torque.
5. If the ambient temperature is too high, the heat capacity of the motor is relatively reduced.
The above are some of the reasons for the occurrence of overload. The motor overheating caused by these causes should be considered in advance and measures should be taken to prevent overheating.
In the past, the method of protecting the motor was the use of fuses, over-current relays, thermal relays, thermostats, etc. However, these methods also have their own advantages and disadvantages. For electric devices that are load-changing, absolute protection is not available. of. Therefore, a combination of methods must be adopted. However, due to the different load conditions of each electric device, it is difficult to propose a unified approach. But to summarize most of the situations, you can also find common ground.
The overload protection methods adopted can be classified into two types:
1. Determine the increase or decrease of the motor input current;
2. Judging on the heat of the motor itself.
The above two methods, regardless of the kind, must take into consideration the time margin given by the motor thermal capacity. It is difficult to make it consistent with the heat capacity characteristics of the motor in a single manner. Therefore, we should choose a method based on the cause of overloading--combination and compound method, in order to achieve a full-scale overload protection.
The motors of Rotork's electric devices are embedded in the windings with a thermostat with the same insulation level as the motor. When the rated temperature is reached, the motor control circuit will be cut off. The heat capacity of the thermostat itself is small, and its time-limited characteristics are determined by the heat capacity characteristics of the motor, so this is a viable method.
The basic method of overload protection is:
1. Thermal load protection for continuous operation or jog operation of the motor;
2. Protection against motor stall using thermal relay 3. Use fuses or overcurrent relays for short circuit accidents.
The correct choice of valve electric device and the prevention of overload are closely related. Should pay attention to.
The correct choice of valve electric device should be based on: 1. Operating torque: Operating torque is the most important parameter for selecting the valve electric device. The output torque of the electric device should be 1.2~1.5 times the maximum torque of the valve. 2. Operational thrust: The main structure of the valve electric device has two kinds. One is that the thrust plate is not configured. In this case, the torque is directly output. The other type is configured with a thrust plate. At this time, the output torque passes through the stem nut in the thrust plate. Convert to output thrust. 3. Rotation number of output shaft: The number of revolutions of the output shaft of the valve electric device is related to the nominal diameter of the valve, the pitch of the stem, and the number of threads. It is calculated according to M=H/ZS (where M is the electric device should satisfy The total number of turns; H is the opening height of the valve, mm; S is the thread pitch of the stem transmission thread, mm; Z is the number of threads of the stem.) 4. Stem diameter: For multi-turn type stem valves, electric valves cannot be assembled if the maximum stem diameter allowed by the motorized device cannot pass through the stem of the valve with which it is fitted. 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 stem valve. For the partial rotary valve and the multi-rotary valve, although the stem diameter does not have to be taken into consideration, the diameter of the stem and the size of the key groove should be fully taken into account in the selection so that the assembly can work normally. 5. Output speed: The valve's opening and closing speed is quick, easy to produce water hammer phenomenon. Therefore, appropriate opening and closing speeds should be selected according to different conditions of use. 6. Installation and connection method: The installation method of the electric device includes vertical installation, horizontal installation, and floor installation; the connection mode is:
There is a thrust disk stem pass (Ming rod multi-turn valve)
The multi-turn non-thrust disk stem of the dark rod does not pass a part of the rotary electric device. It is an indispensable device for realizing valve program control, automatic control and remote control. It is mainly used in closed-circuit valves. However, the special requirements of valve actuators cannot be ignored—it must be possible to limit the torque or axial force. Usually the valve electric device uses a torque limiting coupling.
When the specifications of the electric device are determined, its control torque is also determined. When it is running for a predetermined period of time, the motor is generally not overloaded. However, overload can occur if:
1. The power supply voltage is low and the required torque cannot be obtained, causing the motor to stop rotating.
2. The torque limit mechanism is erroneously set so that it is larger than the stopped torque, causing continuous generation of excessive torque and stopping the motor.
3. When used intermittently as a jog, the heat generated accumulates and exceeds the allowable temperature rise of the motor.
4. For some reason, the torque limiting mechanism circuit malfunctions, causing excessive torque.
5. If the ambient temperature is too high, the heat capacity of the motor is relatively reduced.
The above are some of the reasons for the occurrence of overload. The motor overheating caused by these causes should be considered in advance and measures should be taken to prevent overheating.
In the past, the method of protecting the motor was the use of fuses, over-current relays, thermal relays, thermostats, etc. However, these methods also have their own advantages and disadvantages. For electric devices that are load-changing, absolute protection is not available. of. Therefore, a combination of methods must be adopted. However, due to the different load conditions of each electric device, it is difficult to propose a unified approach. But to summarize most of the situations, you can also find common ground.
The overload protection methods adopted can be classified into two types:
1. Determine the increase or decrease of the motor input current;
2. Judging on the heat of the motor itself.
The above two methods, regardless of the kind, must take into consideration the time margin given by the motor thermal capacity. It is difficult to make it consistent with the heat capacity characteristics of the motor in a single manner. Therefore, we should choose a method based on the cause of overloading--combination and compound method, in order to achieve a full-scale overload protection.
The motors of Rotork's electric devices are embedded in the windings with a thermostat with the same insulation level as the motor. When the rated temperature is reached, the motor control circuit will be cut off. The heat capacity of the thermostat itself is small, and its time-limited characteristics are determined by the heat capacity characteristics of the motor, so this is a viable method.
The basic method of overload protection is:
1. Thermal load protection for continuous operation or jog operation of the motor;
2. Protection against motor stall using thermal relay 3. Use fuses or overcurrent relays for short circuit accidents.
The correct choice of valve electric device and the prevention of overload are closely related. Should pay attention to.
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