Compact fast-acting failsafe actuator

The design and manufacture of customised valve actuators is one of the main areas of activity for Rotork-Hiller, whose reputation is built on the provision of actuators for critical applications and challenging environments. Among recent examples, an enquiry to build a fast-acting failsafe stop valve actuator for a plant firefighting system demanded an exceptionally innovative design solution.

The specification called for a very compact pneumatically operated actuator, with no springs for the failsafe function, necessitating the provision of a stored energy accumulator. The addition of a conventional accumulator would have exceeded the dimensional constraints of the specification, so Rotork-Hiller engineers conceived a radical new design which incorporated the accumulator within the pneumatic actuator. The design not only eliminated the size problem but also freed-up additional space for mounting the controls to the actuator. These controls include filters, regulators, solenoid valves and pressure switches, contained within overall actuator dimensions of 470 x 584 x 680 mm (18½ x 23 x 26¾ inches).

The controls reduce the customer’s supply pressure of 45 Barg (652 psig) to 31 Barg (450 psig), which is pumped into the accumulator to provide approximately 4.4 litres (1 US gallon) of storage capacity. The actuator delivers a maximum thrust of 27,617 N (6,209 lbs).

When asked about the challenges presented by this project, Rotork-Hiller’s Engineering Manager replied: “Our biggest challenge was the ability to meet the customer’s expectations with a unique actuator design, built to stringent specifications and regulatory requirements and supplied within an expedited schedule. With the innovation applied to the design, our lead engineer on the project has confirmed that all expectations have been met or exceeded.

“One of the best features of this design is the pneumatic system redundancy with the ability to support the failsafe function of the valve in a simplified stand-alone package. The integration of the nitrogen storage accumulator within the actuator body itself can be further developed and potentially applied to all existing Rotork-Hiller failsafe pneumatic designs.”

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