Pneumatic diaphragm actuators are actuating devices powered by compressed air, belonging to the actuator category. They mainly consist of an actuator mechanism and a valve, using the reciprocating motion of a diaphragm to achieve the intake and discharge of media, thereby changing the fluid flow rate. The working medium is completely isolated from the transmission components, and the diaphragm is often made of corrosion-resistant materials such as fluororubber and polytetrafluoroethylene.
These actuators are self-priming, can transport liquids containing particles, and can withstand temperatures up to 150℃. They are suitable for flammable, highly toxic, and high-temperature media, and also support automatic shutdown during idling or in case of blockage. Their flow rate can be steplessly controlled by adjusting the air source pressure or a needle valve, and they are widely used in chemical, ceramic, and wastewater treatment industries.
Advantages of Pneumatic Diaphragm Actuators
Intrinsically Safe and Explosion-Proof
Powered by compressed air, there is no risk of electrical sparks, making them suitable for flammable and explosive environments (such as chemical and oil/gas sites). Meets SIL2/SIL3 safety standards; in case of air loss, a spring-loaded reset mechanism enables emergency shut-off (e.g., fuel gas systems).
Superior Corrosion Resistance and Sealing Performance
The diaphragm is made of fluoroplastics such as PFA and PTFE, resistant to strong acids (e.g., 98% sulfuric acid), strong alkalis, and organic solvents. The soft-seal structure achieves zero leakage (Class VI), and the filler-free design eliminates the risk of external leakage, making it suitable for high-purity applications (e.g., semiconductors, pharmaceuticals).
Rapid Response and Easy Maintenance
Opening and closing time is only 0.5~3 seconds, suitable for high-frequency operation (e.g., automated production lines). The simple structure, with the diaphragm being the only vulnerable component (replacement does not require valve body disassembly), results in low maintenance costs.
Wide Media Adaptability
It can transport media containing particles, high viscosity (≤25000 centipoise), or shear-sensitive media (e.g., biological agents). It has strong self-priming capability (suction lift up to 8.8 meters) and is undamaged during dry operation.
Disadvantages of Pneumatic Diaphragm Actuators
Limited Pressure and Temperature Resistance
The maximum pressure resistance is only PN2.5MPa, making them susceptible to damage in high-pressure environments; the temperature range is narrow (PTFE: -20~200℃; PFA: -40~260℃), exceeding these limits can lead to diaphragm aging or embrittlement.
Dependence on Air Source Quality and Stability
A continuous supply of clean, dry compressed air (pressure 0.4~0.7MPa) is required. Water or impurities in the air source can easily clog the air passages or corrode components. In the event of air supply interruption, double-acting valves remain in their original position, potentially affecting process safety (single-acting valves can be spring-reset).
Adjustment Accuracy and Energy Efficiency Issues
Positioning accuracy is lower than electric actuators (±1% FS), making them unsuitable for precision control applications; outlet flow exhibits pulsation, requiring dampers for smooth delivery. Energy efficiency is low (high losses during air compression), resulting in higher operating costs than electric equipment.
Not suitable for specific operating conditions
Sealing failure under vacuum or negative pressure environments; unsuitable for vacuum systems; high-viscosity media (such as slurry) can easily cause diaphragm actuation to jam.
Differences between pneumatic diaphragm actuators and ordinary diaphragm actuators
| Comparison Dimensions | Pneumatic Diaphragm Actuator | Traditional Diaphragm Actuator (Primarily Electric) |
| Drive method | Compressed air drive (pressure range 2-8.4 kg) | Electric drive (typically 380V/50Hz) |
| Explosion-proof performance | Structurally explosion-proof, suitable for flammable and explosive environments. | Requires an explosion-proof motor to achieve the same explosion-proof rating. |
| Flow rate regulation | Stepless speed regulation (0-100% linear control, accuracy ±1%) via air source pressure adjustment. | Standard models are not adjustable; a frequency converter is required for adjustment. |
| Safety | The outlet can be pressurized; it will reset via a spring in case of gas interruption. | The outlet cannot be pressurized; a safety valve/pressure relief valve must be installed. |
| Response Speed | Fast response (opening/closing completed in 0.5-3 seconds) | Slower response (motor starts and stops take longer) |
| Maintenance Costs | Simple structure, maintenance-free design (diaphragm sheet replaced approximately every six months) | Motor, reducer, and other components require regular maintenance. |
| Applicable Scenarios | Highly corrosive and explosion-proof environments such as chemical, pharmaceutical, and food industries. | Automated systems with general operating conditions and low explosion-proof requirements. |
| Price and Weight | Lower and lighter than comparable models. | Higher cost and more complex structure. |
Pneumatic diaphragm actuators offer significant advantages in safety, adjustment flexibility, and adaptability to harsh environments, making them particularly suitable for high-risk industrial scenarios. Electric diaphragm actuators, on the other hand, are better suited for automation integration in routine operating conditions, but require additional protection costs. Actual selection requires a comprehensive evaluation considering media characteristics, control requirements, and maintenance capabilities.
Newton‘s MT series pneumatic diaphragm actuators feature a single-spring or multi-spring design, providing axial output thrust. They are compact, lightweight, small in size, offer excellent performance, have a long service life, and provide significant output thrust. This actuator can be used with GLOBE control valves, shut-off valves, and other linear valves to achieve tight and convenient valve closure.
The MT actuator offers excellent versatility and interchangeability. In the field, the operating mode can be easily switched simply by flipping the upper and lower diaphragm chambers. Its unique design eliminates the need for external air supply lines; instead, air is supplied to the positioner and actuator through holes in the mounting bracket, thus eliminating external piping. Compared to traditional designs, this arrangement is more reliable and requires less space for the control valve assembly. This method ensures safe air supply to the actuator and significantly simplifies the assembly process of the positioner.
