Gas-Over-Oil Actuators

Gas over Oil actuators are used on gas transmission systems where the hydrocarbons are “sour” (have high concentrations of Hydrogen Suplhide). Due to the lack of other power sources in remote locations, the pipeline gas is used to power the actuator, although in the case of gas-over-oil actuators it is isolated from the actuator internals by the oil with which the actuator is filled.

The pipeline gas enters the Actautor via a tapping in the pipeline and is directed to the Gas/Oil chambers. Inside, the gas acts on the surface of the Oil, exerting a pressure which is transmitted to the actuator cylinder. During a shut-down scenario (generally a pipeline rupture), instrumentation in the Control Panel senses a pressure drop and vents the gas from one side of the system. Hydraulic pressure from the other side of the system causes the Valve to close and protects the total contents of the pipeline from leaking into the environment.

Our range of Gas-over-Oil Actuators includes heavy duty scotch yoke, Helical Spline, Vane type and heavy duty linear cylinder.


  • Double Acting (DA)
  • Spring Return (SR)
  • Line-break control – pneumatic or electronic
  • Nitrogen bottle re-set
  • Torque range – up to 400,000NM
  • Thrust range – up to 50KN
  • Temperature down to -60C
  • Supply – pipeline fluid
  • Approvals – CE, ATEX, SIL4, GOST, CSA/UL
  • Painting – Epoxy paint to customer or project specification
  • Accessories – see Component supply
  • Automation systems – see Automation systems

Additional Services

  • Automation system design using CAD
  • Design and supply of valve to actuator adaption kits
  • Design and supply of control systems and panels
  • Supply of complete assembled and tested automated Valves
  • Fitting of automation assembly to free-issue Valves
  • Fitting and Testing of customer supplied components (engineering and labour only)