Product - MSD-III Diaphragm Actuator

The MSD-III is a pneumatic diaphragm actuator with a robust rolling diaphragm and multi-spring design. Available in direct-acting (DA) and reverse-acting (RA). Fail open and close are achieved by the multi-spring force or compressed air. Additionally, the rugged one-piece cast yoke, pressed diaphragm case and special nylon-reinforced diaphragm provide dependable high force actuation performance. The MSD-III is available in five sizes to cover a wide range of applications. A manual handwheel is an optional extra on both direct-acting (DA) and reverse-acting (RA) actuators as an option.​

​Key features​

  • Multi-spring design
    • Excellent long-term accuracy and fail mode reliability are achieved through the multiple spring design with high compression force
  • Rugged one-piece yoke
    • Provides maximum strength and rigidity
  • Diaphragm case
    • Pressed steel case provides high mechanical strength and protection in the event of over-pressurisation. Further reinforcements are provided for actuator sizes greater than 290 to ensure safe operation
  • Thrust & stroke capability
    • Two​ actuator types and five sizes allow a wide range of applications

​​Key features​​

  • Diaphragm
    • Moulded elastomer with fabric insert for strength, long life and high sensitivity. The precisely formed diaphragm eliminates any friction and reduces variations in the effective areas during linear operation
  • Various air connection sizes
    • Various air connection sizes provide various accessory applications
  • Linearity
    • The moulded rolling diaphragm and deep cases minimise area change and provide a linear relation between travel and air pressure​


  • Excellent performance
    • As a multi-spring type, operation is precise and repeatability is excellent, minimising the hysteresis error 
  • Fast response
    • The actuator air chamber volume is minimised to reduce dead-time and be more responsive to changes in air pressure​
  • ​​​​Rugged construction
    • The MSD-III diaphragm actuator has undergone extreme durability tests and with numerous installations over 20 years, it has proven to be a reliable solution for control valves​

​​Technical Details

Pneumetic multi-spring ​diaphragm actuator                                                                
Spring action
DA (Direct Acting - Springs to open)
RA (Reverse Acting - Springs to close)

Refer to material table on next page 

-29 °C to 80 °C (optional -45 °C, -55 °C)

​​​Technical Details​

Operation pressure
4.2 kgf/cm2 to 5.0 kgf/cm2

Stroke range
20mm to 130mm 

Optional manual override 
Top handwheel (250, 290, 370)
Side handwheel (480, 550)



Part nameStandard material
1Sp​ringCr-Si Coil Spring Wire
2YokeA216 WCB
3Guide BushBronze
4Stem Clamp304 SS
5Diaphragm Case (Upper/Lower)Carbon Steel
6Diaphragm PlateCarbon Steel
8Actuator Stem304 SS
9Spacer​​Carbon Steel
10Diaphragm WasherCarbon Steel
11Bolt304 SS
12Nut304 SS
14Extension AdaptorAluminum

​​​​Product Dimensions​

Figure 1. Standard (without handwheel)​

Figure 2. Top handwheel type (250, 290, 370)​
Figure 3. Side handwheel type (480, 550)​

Figure 4. Top handwheel type (480, 550)​​​​

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Product - MSD-III Diaphragm Actuator