Pneumatic ball valves, as an important executive component in industrial automation control systems, the connection method between the actuator and the valve body directly affects the reliability, sealing performance and operational accuracy of the valve. The following will conduct an analysis from the dimensions of connection structure, common types, technical points and development trends.
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I. Connection Structure between the Actuator and the Valve Body
The actuator (pneumatic head) of the pneumatic ball valve is connected to the valve body through a **support** or a direct connection for power transmission. The core function is to convert the air source pressure into the rotational motion of the valve core. The connection structure must meet the following requirements:
1. **Torque Transmission**: Ensure that the output torque of the actuator matches the torque required for the valve to open and close.
2. **Coaxiality**: Prevent wear or jamming of the sealing surface due to eccentricity.
3. **Sealing Performance**: Prevents the leakage of the medium, especially in high-temperature, high-pressure or corrosive conditions.
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II. Common connection methods
According to the valve specifications, operating conditions and automation requirements, the connection methods between the actuator and the valve body can be classified into the following types:
#### 1. Stent Connection (Standard Type)
- **Structure**: The actuator is connected to the valve body flange via a bracket (such as a bracket in accordance with ISO5211 standards), and the bracket provides torque transmission and support functions.
- **Characteristics**
High degree of standardization, strong adaptability, and easy to replace the actuator.
Suitable for medium and small-sized diameters (DN15 - DN300) and common working conditions.
- **Application**: General-purpose pneumatic ball valves, such as those from brands like Fisher and KOSO.
#### 2. Direct Connection (Compact Type)
- **Structure**: The actuator is directly fixed to the valve body using bolts, eliminating the need for a bracket, resulting in a more compact structure.
- **Characteristics**
Small in size and light in weight, it is suitable for situations with limited space.
The torque transmission efficiency is high, but the actuator needs to be replaced by disassembling the valve body.
- **Application**: Miniature ball valves (such as those with a diameter of 10 inches or less) or integrated equipment (such as instrument valve assemblies).
#### 3. Special Connection Methods
- **High-temperature operating conditions**: Use water-cooled or air-cooled brackets to prevent the actuator from overheating and failing.
- **Explosion-proof conditions**: The actuator and the valve body are isolated by an explosion-proof junction box, meeting ATEX/IECEx standards.
- **Quick-disconnect Design**: The actuator is connected to the valve body through a quick connector, facilitating maintenance.
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III. Technical Key Points and Selection Suggestions
#### 1. Torque Matching
- **Calculation Method**:
T = 2 × μF × D
(T represents torque, F represents the frictional force of the sealing surface, D represents the diameter of the ball, μ represents the friction coefficient)
- **Selection Principle**: The output torque of the actuator should be 1.2 to 1.5 times greater than the opening and closing torque of the valve body.
#### 2. Coaxiality Control
- **Installation accuracy**: The coaxiality deviation between the output shaft of the actuator and the valve stem should be ≤ 0.1mm.
- **Adjustment method**: Fine-tuning can be achieved by using the adjustment bolts or positioning pins on the bracket.
#### 3. Sealing Design
- **Seal**: Utilizes double lip-shaped sealing rings or labyrinth seals to prevent the leakage of the medium along the valve stem.
- **Flange seal**: The connection between the valve body and the pipeline is sealed with metal wound gaskets or PTFE gaskets.
#### 4. Material Selection
- **Actuator housing**: Aluminum alloy (lightweight), stainless steel (resistant to corrosion).
- **Supporting frame**: Carbon steel (for normal conditions), duplex steel (for high temperature and high pressure).
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IV. Case Analysis
#### **Case 1: Pneumatic Ball Valve of Petrochemical Equipment**
- **Operating Conditions**: The medium is high-temperature crude oil, with a pressure of 10 MPa and a temperature of 300℃.
- **Connection method**: Water-cooled bracket + stainless steel actuator.
- **Key Points**:
The support is equipped with an internal water cooling channel, which helps to lower the temperature of the actuator.
The actuator is fixed to the valve body using locating pins to ensure coaxiality.
#### **Case 2: Pharmaceutical Clean Pipes**
- **Operating Conditions**: The medium is purified water, with a pressure of 0.6 MPa and a temperature of normal room temperature.
- **Connection method**: Direct connection + EPDM seal.
- **Key Points**
The actuator and valve body are designed as an integrated unit, reducing dead corners.
The surface of the support was polished to Ra0.4 μm, meeting GMP requirements.
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V. Development Trends
1. **Intelligentization**: Incorporates position sensors and temperature sensors to enable remote monitoring and fault diagnosis.
2. **Lightweighting**: Utilize composite materials (such as carbon fiber reinforced plastic) to reduce the weight of the actuator.
3. **Modularization**: The actuator and the valve body are quickly assembled through standardized interfaces, thereby shortening the delivery cycle.
4. **Greening**: Low-power design (such as using pneumatic proportional valves instead of electromechanical valves) to reduce energy consumption.
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VI. Summary
The connection method between the pneumatic ball valve actuator and the valve body needs to take into account factors such as torque, sealing, space and cost. **Bracket connection** is suitable for general working conditions, **direct connection** is suitable for compact designs, while **special connection** is for extreme environments such as high temperature and explosion prevention. In the future, with the advancement of Industry 4.0, intelligence, lightweighting and modularization will become the main development directions of connection technologies.
**Suggestion**: When selecting the type, it is recommended to choose the actuator and valve body combination that complies with the ISO5211 standard, as this will facilitate future maintenance and upgrades.
