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How to Properly Select Electric Valves

In pipeline engineering, selecting the right electric valve is crucial to ensure the fulfillment of operational requirements. An incorrect choice can not only impact usability but also result in adverse consequences or significant losses. Therefore, it is essential to understand how to correctly use electric valves.

What is an electric valve?

An electric valve is a valve that is controlled by an electric actuator to open and close. It consists of two main parts: the upper part is the electric actuator, and the lower part is the valve itself. It is also commonly referred to as an air conditioning valve.

There are several types of electric valves:

1. Based on Valve Function:

On/Off Electric Valves: These valves are used for simple open/close operations.

Control Electric Valves: These valves are designed for precise flow regulation and control.

2. Based on Valve Design:

Electric Ball Valves: These valves have a ball-shaped closing mechanism controlled by an electric actuator.

Electric Butterfly Valves: These valves feature a disc-shaped closing mechanism controlled by an electric actuator.

3. Based on Valve Body Size:

Standard Electric Valves: These valves have a regular size for general applications.

Miniature Electric Valves: These valves are smaller in size and often used in compact systems or specific applications.

4. Electric valves are commonly available in both on/off and control types.

5. Based on Wiring:

Three-Wire Electric Valves: These valves have a three-wire connection system, commonly used in larger-sized valves.

Two-Wire Electric Valves: These valves have a two-wire connection system, often used in smaller-sized valves.

These are some of the common types of electric valves available, each serving specific purposes and applications in various industries.

When selecting an electric valve, the following points should be considered:

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

Operating Thrust: There are two main types of main structures for electric valve devices. One type does not have a thrust plate and directly outputs torque, while the other type has a thrust plate that converts the output torque into thrust through the valve stem nut.

Output Shaft Rotations: The number of rotations of the output shaft of the electric valve device depends on the nominal diameter of the valve, stem pitch, and the number of thread heads. It can be calculated using M = H / ZS, where M is the total number of rotations required by the electric device, H is the valve opening height, S is the stem transmission thread pitch, and Z is the number of stem thread heads.

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 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 rising stem. For some rotary valves and hidden stem valves in multi-turn valves, although the passage of stem diameter is not a concern, the stem diameter and key slot dimensions should be fully considered during selection and assembly to ensure proper operation.

Output Speed: If the opening and closing speed of the valve is too fast, it may cause water hammer. Therefore, the appropriate opening and closing speed should be selected based on different operating conditions.

Special Requirements: Electric valve devices have special requirements, such as the ability to limit torque or axial force. Usually, electric valve devices use couplings that limit torque. Once the specifications of the electric device are determined, the control torque is also determined.

Consider these factors to ensure the proper selection and operation of electric valves in accordance with the specific application requirements.

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