ACTUATOR SELECTION PROCESS

The selection of the most suitable actuator is determined by the duty cycle of the valve and the available power source. Our engineers will select and size the actuator based on the required torque and safety factor. The safety factor will increase for shutdown valves and infrequently operated valves as well as for valves used in service with particulates in the media.

Temperature, seat type and numerous other factors are also analysed and entered into actuator sizing software. We will analyse process fluid type, required operating speed, fail safe requirements, area classification, temperature and environment. Finally we will discuss with you ease of field use, maintenance, brand options, gear over-rides, positioners, solenoids etc. to come up with a valve actuation package that ensures the best balance of reliability, ease of maintenance and cost effectiveness. In-house torque testing capability provides assurance of correct sizing.

ACTUATION SELECTION CRITERIA

PNEUMATIC

Pneumatic actuators are available in spring return and double acting in 90º and 180º operation. Pneumatic actuation is inherently safe, simple, maintenance free and cost effective. Furthermore pneumatic actuators are mass produced and there is ready availability of options such as spring packs for fail-safe systems, pneumatic or electro-pneumatic positioners for modulating control as well as control accessories such as limit switches for accurate process monitoring.

Actuated ball, plug and butterfly valves require maximum torque delivery at the breakaway point (break to open). This is especially important for safety shutdown ball valves which are infrequently operated resulting in increased torque requirements to break open the valve. Depending on the factors mentioned above in the “actuation selection process” section, the required safety factor can be over 100%.

ELECTRIC

Electric actuators are compact and efficient and are used where air and hydraulic supply is not available. They are generally only for on-off service, not fail-safe service. Electric actuators are available in isolating, regulating and modulating and can be supplied in 3 phase as well as single-phase AC and DC.

HYDRAULIC

Hydraulic actuators are suited to operating 90º turn valves such as ball, plug and butterfly valves. Linear piston style is also available for gate and globe valves. Double-acting and fail-safe spring return styles are available, utilizing hydraulic oil up to 35,000 kPa.

Hydraulic actuators are generally used when very high torque is required to operate larger valves or where pneumatic or electric supply sources are not available. A major advantage (especially for off-shore rigs etc) is the size and weight of hydraulic actuators is much smaller.