What is Handwheels?
Handwheels are most common valve actuator. Handwheels are used to actuate control valve manually where automatic controlling is out of option and also in many cases, handwheels are used to override the control system and to operate the valve manually.
There are various designs available in handwheel,including those that can stroke the valve in either direction and those that stroke the valve in one direction, relying on the valve spring for the return stroke.
A handwheel should be designed to operate in the following manner.
- Handwheels should be installed on the yoke for globe valves, arranged in order to jack the valve stem in either direction.
- Neutral position should be clearly indicated.
- Handwheel operation should not add friction to the actuator.
- Clutch / link mechanisms should be intended for handwheels on rotary valves so that control of the valve position is not lost when the handwheel is engaged.
Types of handwheels:
Types of handwheels include handwheels fixed to the stem, hammer handwheels, and handwheels connected to the stem through gears.
Top-mounted & Side-mounted handwheels:
Top-mounted handwheels should be for the valves mounted relatively low.
For valves at greater altitudes, side-mounted handwheels should be selected. A chain drop plus chains can also operate the side-mounted handwheels to release and rest the locking levers.
Handwheels Fixed to Stem:
Only the mechanical advantage of the wheel is provided by handwheels attached to the stem. Valve binding makes operation hard when these valves are subjected to elevated operating temperatures.
Hammer Handwheel:
The hammer handwheel passes freely through a part of its turn, as demonstrated below Figure, and then strikes a lug on a secondary wheel.
The secondary wheel is mounted on the stem of the valve. With this arrangement, if it is stuck closed, the valve can be shut down for tight closure or pounded open.
Gears:
If a manually operated valve requires extra mechanical advantage, the valve bonnet is equipped with manually operated gear heads as shown in the figure below.
A unique wrench or handwheel connected to the pinion shaft allows one person to run the valve when two people are required without the benefit of the equipment.
Because it takes several pinion turns to generate one turn of the valve stem, big valve working time is extremely long. Gear handwheels can decreases the valve operating time.