A valve actuator is a mechanical device that is used for opening and closing a valve. This power source can be electric, pneumatic (compressed air), manual, or hydraulic (the flow of oil).
Usually, manually actuated valves always need someone in attendance to adjust them using a direct or geared mechanism attached to the valve stem. Whereas, power-operated actuators uses gas pressure, hydraulic pressure or electricity pressure allowing a valve to be adjusted on its own, or it allows rapid operation of large valves.
Though, actuators may be only to open and close the valve, or may be for intermediate positioning, but there are some valve actuators include switches or some other ways to remotely indicate the position of the valve.
Manual actuators are found in all kinds of process plants as they are used for the automation of industrial valves. Manual actuators are used in food factories, mining and nuclear processes, wastewater treatment plants, power plants, refineries, and pipelines. These manual valve actuators actually play a major part in automating process control. Normally, the valves to be automated differ both in design and dimension. The diameters of these valves can vary from one-tenth of an inch to several feet.
A manual valve actuator includes levers, gears, or wheels to move the valve stem. Manual valve actuators are powered by hand. The best thing about manual actuators are, they are cost effective. Manual valve actuators are typically self-contained and easy to operate. However, only in case of large valves it becomes impossible to operate manually, or if some valves are located in remote, toxic or hostile environments that also prohibits manual operations.
More often than not, for the matter of safety, certain types of valves or situations may require quicker operation and that can be best done by the manual actuators as it is easy to close the valve immediately manually.
Below are the types of Manual Valve Actuators
Basic leaver is the most common manual operator on smaller quarter-turn valves. For the purpose, a long handle is attached to the stem that provides the leverage needed to rotate the valve.
Ball and Butterfly valves shown with manual lever operators:
If the valves are very small where no leverage is needed, then they can be replaced by ovals, tees, and various other shaped knobs.
Hand wheels are geared when large valves that require high torque to operate is used. They have a large hand wheel with a gearbox, which further increases the mechanical advantage.
Geared hand wheel operator alone and on a butterfly valve:
If the valve is located high enough somewhat out of reach then a chain wheel is added to the gearbox in order to operate valve from the ground. The chain hung down where it is easily reachable, and the operator can simply pull down on one side of the chain loop to open the valve, and the other side to close the valve.
Manual Valves with Limit Switches:
Manual valves with limit switches-position indicators, are used where manual valves perform a function that does not require automated actuation usually, but at the same time the system needs to know what position they are in. However, the valve is operated manually, but the switches communicate the valve's current position to the control system.