Under normal circumstances, electric devices do not need to be operated manually. But in the accident state and the debugging process, manual operation is essential. Therefore, the hand wheel, which is an important means of manual operation, has become an indispensable part of an electric device. For hand wheels for manually operating valves, there are already some standard parts in my country, such as wave hand wheels and round flat hand wheels. Its diameters are 50-500 mm and 140-1000 mm, and are made of cast iron. For small valve hand wheels, aluminum alloy and plastic die casting can also be used.
As for the handwheels of electric devices, my country currently has no complete standards. As the starting point of the overall design of the electric device is different, the requirements of the opponent wheel are also different.
Handwheel with high manual speed ratio
In the manual-electric switching structure of the electric device, due to the size of the output torque of the electric device and the overall design considerations, the manual speed ratio can be 1:1 or greater than 1:1. The so-called high manual speed ratio means that the manual speed ratio is greater than 1:1, generally between 1:10 and 1:100. Due to the high manual speed ratio, the operating force of the handwheel is relatively small, usually a few kilograms of force, but the total number of turns of the handwheel is high, reaching tens to thousands of turns. Because of this feature, the handwheel has a small radius, generally no more than 300 mm; the handwheel is lighter, and the strength of the handwheel is lower. In order to facilitate rapid rotation, such hand wheels are equipped with handles. In order to prevent the handle from friction and heating, which affects the operation, the hand wheel should have a live sleeve. The length of the live casing shall not be less than 100 mm.
Handwheel with low manual speed ratio
Most of the hand wheels installed in low manual speed ratio electric devices are directly connected to the output shaft of the electric device through a clutch. Because of this, the operating force required for the handwheel is relatively large, generally up to tens to hundreds of kilograms. The number of turns is relatively small, ranging from a few turns to dozens of turns, or even hundreds of turns.
Analyzing the operating torque characteristics of gate valves and shut-off valves, we know that their operating torque values are only the largest at the moment of opening and closing, and are lower in the intermediate process. It is also based on this mechanism that 1:1 manual operation is possible. However, a handwheel with a force of several hundred kilograms, even if it is instantaneous, is difficult to achieve without corresponding measures. Corresponding to different measures, the handwheel structure has the following types:
Handwheel operated by casing and wrench
At the moment the valve is opened and closed, pipes can be placed on the spokes protruding outside the hub to extend the moment arm. After this moment, the required operating torque drops rapidly. At this time, the casing can be removed and operated directly by hand.
There is also a round handwheel that can be operated by a wrench. At the moment of opening and closing the valve, the wrench is stuck on the hub of the handwheel to extend the force arm for operation.
This type of handwheel has higher requirements for materials, not only having a certain strength requirement, but also a certain toughness. When in use, the spokes and the hub can neither be bent nor broken, and when engaging in this type of rated strength design, the design calculation should be carried out according to the conditions after the casing or wrench is added.
Handwheel operated by hammering
The above-mentioned handwheel operated with a casing or a wrench is not required to have a large diameter due to the use of additional tools, and there is no special requirement for the weight of the handwheel. These are their advantages. However, just because additional tools are needed for operation, which brings some inconvenience to the on-site handling of accidents, etc., a hammer-type handwheel can be used at this time.
The hammering handwheel is a handwheel with two high-strength hammering blocks. The hammer block is engaged with the clutch. When the valve is opened, the operator gives an acceleration to the hand wheel, and the hand wheel hits the clutch with its powerful hammer block to overcome the high torque required at the opening of the valve. After several impacts, the valve flap will leave. The closed position reduces the valve opening torque quickly.
As mentioned above, the hand wheel supplemented by hammering operation must not only have sufficient strength and toughness for the hammering block, but also the hand wheel itself must have sufficient weight. The magnitude of the hammering action depends on the energy of the handwheel during impact, and this energy (kinetic energy) is proportional to the mass of the handwheel and the velocity during impact.
