Linear-Stroke Piston-Type Pneumatic

Linear-Stroke Piston-Type Pneumatic Actuator
I. Product Overview
The linear-stroke piston-type pneumatic actuator is a high-power linear drive device designed specifically for control valves. Utilizing a cylinder-piston transmission structure, it differs from standard diaphragm actuators by offering higher output thrust, superior pressure resistance, and excellent fatigue and vibration resistance, making it suitable for demanding operating conditions involving high pressure differentials. Powered by compressed air to achieve linear reciprocating motion of the pushrod, it is designed for use with all linear-stroke valves—such as sleeve control valves, single-seat control valves, globe valves, and gate valves. When paired with a pneumatic positioner that accepts 4–20mA analog signals, it enables precise proportional control as well as on/off shut-off functionality.
This series of actuators is available in two configurations: single-acting (spring-return) and double-acting (piston-driven). They offer advantages such as high thrust, stable stroke, high linearity, high-temperature resistance, and durability against aging. They overcome the limitations of diaphragm actuators—namely insufficient thrust, fragile diaphragms, and an inability to operate under high pressure—making them widely applicable in automatic control systems for power plants, chemical processing, petrochemical industries, and high-temperature/high-pressure fluid handling.
II. Model and Structure Definitions

• ZSA: Direct-acting linear-stroke piston actuator (signal increase causes pushrod extension)

1. ZSB: Reverse-acting linear-stroke piston actuator (signal increase causes pushrod retraction)
2. Single-acting: Air intake drives the valve; loss of air triggers automatic spring return (fail-safe design)
3. Double-acting: Dual-side air intake drive; delivers ultra-high thrust; suitable for heavy-duty valves operating under high pressure differentials
   III. Working Principle
   After the air supply is regulated by the positioner, it enters the upper or lower chamber of the cylinder, driving the piston to generate linear thrust that moves the valve stem vertically. A built-in precision balancing spring provides real-time pressure feedback, ensuring that the pushrod displacement maintains a precise linear proportion to the input air pressure signal, thereby accurately controlling valve opening, flow rate, pressure, and liquid level. The piston-style structure offers a significantly higher pressure-bearing capacity than diaphragm designs, allowing for higher supply pressures and exponentially increased output thrust; it is particularly well-suited for heavy-duty control valve applications involving high pressure differentials and large bore sizes.
   IV. Key Structural Features
4. High Piston Thrust & Heavy-Duty Capability: The large piston surface area generates powerful output thrust, easily overcoming unbalanced forces from high-pressure-differential media; this ensures stable regulation and jitter-free valve operation.
5. No Vulnerable Diaphragms & Extended Service Life: Eliminating traditional diaphragm designs in favor of a metal piston and wear-resistant seals, this structure eliminates the risk of aging or rupture; it offers high-temperature and fatigue resistance, making it ideal for long-term, continuous operation.
6. Precise Linear Regulation: Utilizing matched sets of precision springs, the design ensures high stroke linearity, minimal hysteresis, and high repeatability, resulting in negligible regulation errors within the automatic control system.

• Flexible Action Reversal: Direct and reverse action modes can be quickly switched on-site to accommodate “air-to-open” or “air-to-close” safety configurations.

2. Adjustable Stroke Limits: Upper and lower mechanical limits are adjustable, precisely locking the valve’s fully open and fully closed positions to prevent over-travel damage to internal components.
3. Multiple Sealing Protections: Wear- and temperature-resistant sealing rings ensure excellent airtightness and zero leakage, maintaining stability and reliability across high- and low-temperature conditions.
4. Comprehensive Compatibility & Versatility: Compatible with smart positioners, solenoid valves, valve position feedback units, manual override handwheels, and explosion-proof accessories; fully compatible with DCS automatic control systems. V. Material Specifications

• Cylinder body: High-strength aluminum alloy (hard-anodized) / Carbon steel (baked enamel finish)
• Piston and push rod: Precision-machined stainless steel
• Return spring: High-strength precision alloy spring (fatigue-resistant, deformation-resistant)
• Seals: Standard NBR; optional high-temperature FKM or low-temperature HNBR
• End caps and fasteners: Corrosion-resistant and rust-proof treated
  VI. Technical Parameters
• Operating air supply pressure: 0.2–1.0 MPa
• Output stroke: 20 mm–100 mm (multiple specifications available)
• Action type: Single-acting (spring return) / Double-acting (piston-driven)
• Control signal: 4–20 mA DC analog modulation signal
• Linearity accuracy: ≤±1.5%; Hysteresis: ≤1.0%
• Operating temperature: -20°C to +120°C (upgradable seals available for higher temperatures)
• Protection class: IP65
• Explosion-proof rating: Ex d IIC T6 (explosion-proof configuration optional)
• Compatible valves: Single-seat control valves, sleeve control valves, high-pressure multi-stage control valves, globe-style control valves, and other linear-motion valves
  VII. Applicable Operating Conditions
  ✅ Recommended Applications
• Power plants and thermal power stations: High-pressure feedwater, steam desuperheating and pressure reduction, high-temperature/high-pressure control systems
• Petrochemical, coal-to-chemical, and hydrogenation units: High-pressure-drop, high-thrust, heavy-duty control valve applications
• Chemical industry and environmental protection: Acid/alkali media, high-temperature fluids, continuous automatic control pipelines
• Retrofitting applications where standard diaphragm actuators suffer from insufficient thrust, valve oscillation, or unstable regulation
• Automated process systems requiring high precision, high stability, and long-term continuous operation
  ❌ Inapplicable Conditions
• Direct exposure of the cylinder body to highly corrosive gases (requires anti-corrosion protection) Operation exceeding rated temperature or pressure parameters
  VIII. Applicable Standards

1. Design and Manufacturing: GB/T 4213, IEC 60534
2. Protection Class: IP65
3. Explosion-proof Standard: Ex d IIC T6
4. Inspection Standard: JB/T 8219 (Standard for Industrial Process Control Actuators)
   IX. Installation and Operating Instructions
5. The actuator must be installed vertically and upright, maintaining coaxial alignment with the valve stem; eccentric installation is prohibited to prevent push-rod bending, jamming, or air leakage.

• The air supply must be clean and dry; an air service unit (filter-regulator-lubricator) should be installed upstream to filter out condensate, oil, and impurities, thereby extending the service life of the cylinder and seals.

1. Perform zero-point and span calibration after installation; verify full-stroke linearity by inputting 4mA, 12mA, and 20mA signals.

• For high-differential-pressure applications, prioritize double-acting, high-thrust models to ensure stable valve regulation without oscillation.
• Single-acting models feature an automatic reset function upon air supply loss, meeting fail-safe interlock requirements.
• Periodically inspect cylinder airtightness, push-rod seals, and spring condition; recalibrate accuracy every six months during long-term operation.
  X. Summary of Product Advantages
  Compared to traditional diaphragm actuators, linear-stroke pneumatic piston actuators offer higher thrust, higher pressure resistance, superior vibration and aging resistance, longer service life, and more stable regulation. They effectively resolve common issues in high-differential-pressure applications—such as valve oscillation, incomplete shut-off, and insufficient thrust. With a reliable structure, high precision, and low maintenance requirements, they represent the optimal actuation solution for industrial linear-stroke control valves operating under high-pressure, high-temperature, and high-differential-pressure conditions.