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Manual, Fixed, and Hammer Actuators
Although manual actuators are able to displace the valve in any disposition, they are not capable of operating directly. The handwheel pneumatic actuators are the most common-seen type of mechanical actuator. Among this type are handwheels fixed to the stem, hammer handwheels, and handwheels connected to the stem through gears.
Handwheels Fixed to Stem
As illustrated in the image below handwheels fixed to the stem gives only the mechanical advantage of the wheel. Under the circumstance of high operationg temperatures, the manual handwheel actuator will be hindered by valve binding
As illustrated in the image, the hammer handwheel walks rapidly across a portion of its turn and then lashes against a lug on a secondary wheel. The secondary wheel is fixed to the valve stem. With this kind of design, the valve can be hammered shut for tight closure or hammered open if it is stuck shut.
The Handwheel Working Princle
There are many choice for handwheel actuator’s driving force. For manual mechanical methods, the driving force includes the lead screw systems of vises and clamps, and levers fitted in manual juicers or can crushers. Wheels with pistons powered by compressed air are used to move parts of machines. Hydraulic wheels with pistons can give large forces of strokes to constructive equipment such as shovels, lifts and jacks, and short throw cylinders for braking systems. The solenoid coils are short distance electromagnetic linear electric actuators . These actuators flip switches and move on and off as well as lock and unlock car doors. It is for trams, people movers and material conveyors that the linear movements of electromagnetic motor poles are used.
As the pressure generated by the air comes into the middle chamber between two wheels from the air port, it will separate the two wheels and make them move towards the opposite side of the chamber. The rack of two wheels rotate in counterclockwise direction in order to simultaneously emit the shaft .
On the contrary, when the pressure of the air enters the air chamber on both sides, it will drive the two wheels move towards the middle of the chamber, whilst, the air is emitted from the air port and make the rack of two pistons simultaneously rotate in clockwise direction thus to drive the output shaft. (If the wheel is fixed in the opposite direction, the output air will be in opposite direction)
Another common actuators with the handwheel working principle is the pneumatic actuator. This kind of actuator decodes an air signal into valve stem motion by air pressure performing on a diaphragm or piston connected to the stem. Used in throttle valves for open-close positioning, Pneumatic actuators are required capable of moving at fast speed. When air pressure closes the valve and spring action opens the valve, the actuator is termed directacting. When air pressure opens the valve and spring action closes the valve, the actuator is termed reverseacting.