Basic Lever The most common manual operator on smaller quarter-turn valves is the basic lever. A long handle is attached to the stem and provides the leverage needed to rotate the valve. On very small valves, where leverage is not needed, these may be replaced by ovals, tees, and various other shaped knobs. Hand Wheels Larger valves that require high torque to operate often incorporate geared hand wheels.
These operators have a large hand wheel with a gearbox that further increases the mechanical advantage. The radius of the wheel and gearing ratio determines the amount of mechanical advantage provided. These wheels will require multiple revolutions to turn the valve only 90 degrees. These type of operators are commonly found on larger butterfly valves, typically 8 inches and above.
If the valve is located high enough to be out of reach, a chain wheel will be added to the same type of gearbox so that the valve can be operated from the ground. The chain is in a long loop that hangs down to where it can be easily reached. The operator would simply pull down on one side of the chain loop to open the valve, and the other side to close it. Manual Valves with Limit Switches Many times manual valves perform a function that does not require automated actuation, but the system still needs to know what postion they are in.
Manual valves with limit switches position indicators are used in these cases. While the valve is still operated manually, the switches communicate the valve's current position to the control system. Rotary Actuators: Different Mechanical Styles There are 2 main styles of rotary pneumatic actuators for use on ball, butterfly and plug valves: Rack-n-pinion, and Scotch Yoke.
While at first they may appear drastically different, they are actually quite similar. Both operate by converting the linear motion of a piston in a cylinder into rotational motion of the stem drive. Both are available in dual shown above and single versions and both can be spring return or direct acting sometimes referred to as single acting and double acting. There is also a 3rd style of pneumatic rotary actuator that is older and far less common - Vane. In this type of actuator the piston is replaced by a vane, which is fixed to the stem drive.
The vane is enclosed in a wedge shaped chamber where the stem center is located towards the point of that wedge. Air is forced into this chamber on either side of the vane in order to move it, thus rotating the stem drive. Double Acting Double acting pneumatic actuators require air to be used to move the piston in either direction.
A solenoid valve is used to control the air flow into and venting of the actuator. Since there is no spring force to overcome, a smaller actuator can often be used. Both Vane and Rack-n-pinion style double acting actuators have an constant, linear torque output throughout the stroke in both directions.
Scotch yoke actuators, due to their mechanics, produce curved torque outputs that are identical on one stroke direction vs. Spring Return Spring return pneumatic actuators use compressed air to move the piston in one direction, and a spring to push it back in the other when the air is stopped and allowed to vent.
This requires a larger actuator since it has to overcome the force of the spring in addition to providing enough torque to operate the valve. The most important aspect of a spring return actuator is that it offers a "fail-safe" position. This means that if the air supply is lost, or electric power to the solenoid that controls the air is lost, the valve will travel to this position using the force of the spring s.
This could be either open or closed, whichever offers a safer outcome. Both Vane and Rack-n-pinion style spring return actuators have a descending, linear torque output throughout the air stroke and spring stroke. The slope of the line is caused by the spring force increasing and decreasing as it compresses and expands. Scotch yoke actuators, due to their mechanics, produce curved torque outputs that are inverse on one stroke direction vs.
The action principle of solenoid valve is the straight stroke, it sealing by the spool itself gravity and the force of the electromagnet to achieve.
So the solenoid valve can only be installed horizontally, other installation may cause it leakage. Motorized valve actuator switch action in place, then by the internal micro-switch power. Longer service life than solenoid valve, and stable performance. The structure of solenoid valve is simple, low protection level, easy to be affected by external dust and air, temperature.
Basically, protects the actuator from dust and moisture. But the general solenoid valve has no manual operation function, the pipeline needs to install bypass manual valve for backup. Solenoid valve is suitable for a wide range of media, acid, lye, water, gas, oil, steam and other media can be used.
However, the medium must not contain impurities. So we need to install the filter in front of the solenoid valve. In another case, the trim leaves the seat under the action of spring force, compressed air flows from one port to the other.
The trim is pressed against the seat to close valve port under upward force of the stem, the flow path is closed, no compressed air flows out from valve port. Solenoid valve is suitable for some special process requirements, such as leakage, special fluid media, etc. Air directional control valve is an accessory of the heating and heating system, and is generally used in electric water heaters, solar water heaters and centralized hot water supply systems.
It has good effect on gas medium and small diameter liquid, low cost and convenient maintenance. Air directional control valve has a larger working force than solenoid valve, and maximum working pressure is larger than that of solenoid valve. Switching speed of air directional control valve can be adjusted, structure is simple, and the maintenance is easy. Due to cushioning characteristics of the gas itself during operation, it is not easy to be damaged by jamming, but it must have an air supply, and its control system is also more complicated than solenoid valve.
This is particularly important in oscillatory systems. Another advantage that the voice coil provides is force control, without a feedback device, because the force output at any position in the stroke is directly proportional to the current input. This type of actuation lends itself to generally a higher force density, thus achieving higher strokes and forces in a smaller package size to the solenoid counterparts.
Cancel Search. Published October 22, The question of whether to use voice coil actuators or solenoids for small displacement motion control applications comes up often. What is a Voice Coil Actuator? What is a Solenoid?
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