What Are the 6 Selection Principles for Valve Electric Actuators?

There are two types of electric actuators, including part turn electric valve actuator and multi turn electric valve actuator.

 

The former mainly controls valves that require partial rotation, such as trunnion ball valve, non return butterfly valve, etc.

 

The latter requires valves with multiple turns, such as electric actuated knife gate valve and three way gate valve.

 

The electric multi turn rotary actuator is one of the most commonly used and most reliable actuator types. A single-phase or three-phase motor is used to drive a gear or a worm gear to drive the valve stem nut, and the valve stem nut makes the valve stem move to open or close the valve. The new generation of electric single-turn actuators combines most of the complex functions of multi-turn actuators. For example, use non-entry user-friendly operation interface to realize parameter setting and diagnosis function. The single turn rotary actuator has a compact structure and can be installed on a small valve.

 

Six Selection Principles for Valve Electric Actuators

 

1. Operating torque. Operating torque is the most important parameter for selecting the valve electric device. The output torque of the electric actuator should be 1.2 to 1.5 times the maximum valve operating torque.

 

2. Operate thrust. There are two main structures of electric valve actuator. One is to directly output torque without a thrust plate. The other is to configure a thrust plate, and the output torque is converted into output thrust through the stem nut in the thrust plate.

 

3. Number of turns of the output shaft. The number of turns of the output shaft of the valve electric device is related to the nominal diameter of the valve, the pitch of the valve stem, and the number of thread heads. It should be calculated as M=H/ZS (M is the total number of turns that the electric device should meet, H is the opening height of the valve, S is the thread pitch of the valve stem, and Z is the number of stem threads).

 

4. Valve stem diameter. For multi-turn rising stem valves, if the maximum stem diameter allowed by the electric device cannot pass through the stem of the matched valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the stem of the rising stem valve. For part-turn valves and dark-stem valves in multi-turn valves, although there is no need to consider the passage of the stem diameter, the stem diameter and the size of the keyway should be fully considered when selecting and matching, so that it can work normally after assembly.

 

5. Output speed. If the opening and closing speed of the valve is too fast, water hammer is likely to occur. Therefore, the appropriate opening and closing speed should be selected according to different use conditions.

 

6. Valve electric actuators have their special requirements, that is, they must be able to limit 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. Generally run within a predetermined time, the motor will not be overloaded.

 

In the past, the way to protect the motor was to use fuses, overcurrent relays, thermal relays, thermostats, etc. But these methods have their pros and cons. There is no absolutely reliable protection method for variable load equipment such as electric devices. Therefore, various combinations must be adopted. In summary, there are two types. One is to judge the increase or decrease of the motor input current. The second is to judge the heating of the motor itself. Regardless of these two methods, the time margin given by the motor thermal capacity must be considered.