Overview
This rotary stepping actuator mounts directly to the cover plate on bolted-bonnet valves to drive the valve-stem nut. This allows for simple field conversion from manual to automated operation. It also results in a compact sealed design.
Operating Principle
The actuator uses single-acting spring-return cylinders linked to ratchet-pawl mechanisms to provide the stepping action. One complete operating cycle (step) of a cylinder rotates the drive shaft by 36°, so the valve can be positioned in discreet 1/10-of-a-turn rotations of the valve-stem nut. It has been endurance tested under load to over one million cycles without maintenance or reduction in efficiency. Separate cylinders provide valve-open and valve-close operation. A direct-coupled manual override is also provided as a 1-1/2" hex extending through the top of the actuator housing.
Three styles of operating cylinders are available: pneumatic, high-thrust pneumatic, and hydraulic. This allows the actuator to be used in a variety of applications for the entire range of our surface valves.
Control:
This actuator is supplied with a transmitter to provide 4-20 mA position feedback. Limit switches are also available within the transmitter housing. Solenoid valves, quick-exhaust valves, and other accessories such as junction boxes may also be mounted to the actuator.
A control system, which is outside of Master Flo's scope of supply, is required to control the stepping function of the cylinders; the hydraulic or pneumatic supply must be pulsed with sufficient dwell time between each step to ensure full cylinder retraction.
Advantages:
- simple, robust design.
- high torque capability.
- highly reliable function.
Technical Specifications
Performance
The actuator output torque is regulated by the supply pressure to the actuator. The actuator was developed to work continuously at maximum torque loads. The actuator housing package is of ductile iron construction. This weatherproof housing protects the actuator from the external environment
POSITION FEEDBACK SYSTEM
The actuator incorporates a 4-20 mA transmitter to provide remote monitoring of the choke position. Two limit switches are included to show full open, full closed or an intermediate settings. The position transmitter and switch assembly are available with various certification options. Typical certifications include explosion proof to UL and CSA Class 1, Division 1, Groups C & D, or to CENELEC EEx d IIC T6 IP66; or intrinsically safe to EEx d IIC T6 IP66; or intrinsically safe to EEx ia IIC T4 IP66. The transmitter housing is available in anodized aluminum, bronze or stainless steel.
