Intro4u2u

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. Some manual valve actuators move rotary motion valves such as ball, butterfly, and multiturn valves a quarter-turn or more from open to close. Other manual valve actuators move linear motion valves such as gate, globe, diaphragm, pinch, and angle valves. Typically, these valves have a sliding stem that pushes the closure element open or closed. Depending on the valve’s design, the stem may rise during rotation or without rotation.  The clockwise rotation of a direct-acting actuator causes the valve to close in a clockwise direction. By contrast, the clockwise rotation of a reverse-acting actuator causes the valve to close in a counter-clockwise direction.

Selecting manual valve actuators requires an analysis of performance specifications. Manual actuators for rotary valves vary in terms of actuator torque and range of motion. 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). Manual valve actuators for linear valves differ in terms of valve stem stroke length, number of turns, and actuator force or seating thrust. Typically, stroke length is measured in inches (in) while actuator force is measuring in pounds (lbs). Other important specifications for manual valve actuators include stem diameter and, when applicable, handwheel diameter.

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.