Features and selection of valve actuation devices

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Features and Selection of Valve Actuation Devices I. Classification of Valve Actuation Methods Based on the movement pattern of the actuation mechanism, valve actuation devices are divided into straight-stroke and rotary-stroke types. Based on the driving mechanism, valve actuation devices are classified as follows: Manual actuation – handle and knob types (including those with reduction through intermediate gears), spring-lever types. Electric actuation – electromagnetic types, motor-driven types. Pneumatic actuation – 1) diaphragm type, 2) cylinder type: ① piston-cylinder type, ② piston-rack type, ③ piston-link type, ④ piston-fork type, ⑤ piston-screw type. 3) vane type, 4) air-engine type, 5) film and ratchet combination type. Hydraulic actuation – hydraulic-cylinder type, hydraulic-motor type. Combined actuation – electro-hydraulic combined type.

II. Characteristics of various valve actuation devices
Electric devices
Advantages:
1. High versatility, not affected by ambient temperature.
2. Wide range of output torque.
3. Easy to control; can utilize various signals such as DC, AC, short waves, and pulses; suitable for tasks like amplification, memory, logical judgment, and calculation.
4. Can be made extremely compact.
5. Possesses mechanical self-locking capability.
6. Easy to install.
7. Easy to maintain and repair.
Disadvantages:
1. Complex structure.
2. Low mechanical efficiency, generally only 25%–60%.
3. The output speed cannot be too low or too high.
4. Prone to being affected by changes in power supply voltage and frequency.

Hydraulic devices
Advantages:
1. Simple, compact structure with small size.
2. High output force.
3. Ability to achieve low or high speeds, with stepless speed adjustment possible.
4. Enables remote automatic control.
5. High efficiency due to the viscosity of hydraulic oil; also has self-lubricating and rust-resistant properties.
Disadvantages:
1. Changes in oil temperature affect oil viscosity.
2. Hydraulic components and pipes are prone to leakage.
3. Requires additional piping, making maintenance difficult.
4. Not suitable for performing various calculations on signals.

Pneumatic devices
Advantages:
1. Simple structure.
2. Air source is easily available.
3. High switching speed achievable.
4. Speed can be adjusted as needed by installing a speed regulator.
5. Gas has high compressibility, resulting in elastic closure.
Disadvantages:
1. Larger structure compared to hydraulic devices; not suitable for large-diameter, high-pressure valves.
2. Due to the compressibility of gas, it is difficult to maintain consistent speed.

III. Selection of valve actuation methods
The criteria for selecting a valve actuation method include:
1. The type, specifications, and structure of the valve.
2. The opening and closing torque of the valve (pipeline pressure, maximum pressure difference across the valve), as well as the thrust required.
3. Maximum ambient temperature and fluid properties.
4. Mode of use and number of operations performed.
5. Opening and closing speed and time required.
6. Diameter of the valve stem, pitch, and direction of rotation.
7. Connection method.
8. Parameters of the power source: voltage, number of phases, and frequency for electric drives ； Pneumatic supply pressure ； Hydraulic source pressure for hydraulics 9. Special considerations: low temperature, corrosion resistance, explosion protection, water resistance, fire resistance, radiation protection, etc