Manual Valve Actuators Information
Manual valve actuators do not require an outside power source to move a valve to a desired position. Instead, they use a handwheel, chainwheel, lever, or declutchable mechanism to drive a series of gears whose ratio results in a higher output torque compared to the input (manual) torque. Most manual valve actuators use worm gears, mechanical devices that transmit motion between non-intersecting right-angle axes.
The advantage of using a manual valve actuator is that the devices are inexpensive, reliable and do not require a power source. They are usually self-contained and since they use the same motion to open and close it is often easy to spot an error or cause of a discrepancy. The disadvantage is that they are not automated and therefore need to be manually controlled each time.
Due to the wide variety of applications that valves perform, there are two different methods of flow control available.
Rotary motion valves rotate through a quarter-turn (90 degrees) or more from open to close. The closing element is generally a disc or ellipse which turns about an angular shaft. Some common examples include ball, butterfly, and multi-turn valves.
Linear motion valves have a sliding stem designed to push the closure element open or closed. The valve stem may rise while rotating (multi-turn) or may rise without rotating. The closing element can be a disc or plug pushed against or slid down in front of an orifice. Examples of linear motion valves include gate, globe, diaphragm, pinch, and angle valves.
More information on rotary and linear motion valves can be found on IEEE GlobalSpec's Valve Types page.
Selecting manual valve actuators requires an analysis of performance specifications.
Stem diameter- The stem diameter describes the diameter of the valve stem and can be combined with the lead and pitch of the valve stem thread in order to size the automation required for the valve.
Handwheel diameter- The handwheel diameter describes the size of the handwheel devices used to control the manual valve actuator.
Direct acting or reverse acting- Direct acting actuators use a clockwise rotation of the actuator/handwheel to close the valve. Reverse acting actuators use a counterclockwise motion to close the valve.
Operating environment- The operating environment includes the range of temperatures, average level of humidity, and stableness of the environment in which the valve actuator will operate. It is important to ensure the valve actuator is protected and is able to tolerate the conditions to prevent failures or accidents.
Actuator specifications. Image Credit: Cleaning Technologies Group
Rotary actuators vary in terms of actuator torque and range of motion. Depending on the valve’s design, the stem may rise during rotation or without rotation.
Torque, the measure of force needed to produce rotary motion, is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied.
Common ranges of motion include 90° (quarter-turn), 180°, 270°, and 360° (multi-turn).
Linear valve actuators differ in terms of valve stem stroke length, number of turns, and actuator force or seating thrust.
Stroke length is measured in inches (in). The term stroke is used to define the travel required to have the valve fully opened to fully closed. Using an actuator with fewer strokes than the valve will "short stroke" the valve and the full CV rating of the valve will not be realized.
Actuator force is measured in pounds (lbs). The actuator must supply enough force to overcome the pressure in the system to close the closing element and keep it closed.
More information on the specifications for rotary and linear motion valves can be found on IEEE GlobalSpec's Valve Actuators Specification Guide.
Manual valve actuators are often housed in enclosures that are rated by the National Electrical Manufacturers Association (NEMA), a trade organization which defines safety standards for electrical equipment.
Type 4 NEMA enclosures are rated for indoor and outdoor use and provide protection from falling dirt, rain, sleet, snow, windblown dust, splashing water and hose-directed water.
Type 4X NEMA enclosures provide protection against these same environmental variables and can also resist corrosion.
Type 7 NEMA enclosures are constructed for indoor use in hazardous locations categorized as Class I; Division 1; Groups A, B, C, or D in NFPA70, a directive from the National Fire Protection Association (NFPA).
Type 9 NEMA enclosures are constructed for indoor use in hazardous locations classified as Class II; Division 1; Groups E, F, or G in NFPA70.
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