When there is an abnormality in the gas source data signal or electronic signal, or when the key components of the implementing mechanism (such as membranes, elastic yellow, hydraulic seals, transmission components, etc.) are damaged, the fully automatic actual operation should be changed to manual actual operation. A handwheel mechanism can be used to continue maintaining the adjustment effect of the regulating valve. The handwheel mechanism can also be used as a limit switch to adjust the valve stroke arrangement. The handwheel mechanism can improve the credibility of the regulating valve operation. If a dual circuit power supply is added to the regulating valve, the project investment cost and land occupation will be high. When the specification is large or precious metals are used, the cost will be higher. Applying it to the wheel mechanism, regardless of project investment cost or land occupation considerations, is considered cost-effective.
    In addition, for single acting diaphragm valves, the function and method of action of the handwheel (the position and orientation of the valve are specific). In addition, diaphragm valves are generally used in areas where the processing pressure is very low and the closing regulations are not strict, and the interaction force is not very large. Therefore, immediately installing the handwheel function is sufficient, without the need for a design scheme to save energy equipment handwheel (except for uniqueness, using a plug is not very practical, and the plug is generally used on the double acting, piston type actuator. Double acting valves are not necessarily, and double acting handwheels are generally arbitrary and can be opened and closed).
      1. The principle and method of top mounted handwheel limit is to use the thrust generated by the handwheel shaft when rotating the handwheel to replace the thrust generated by the diaphragm head under the action of the gas signal to overcome the reaction force of the spring and push the valve stem to move. When the handwheel exerts force on the valve stem and places it in a certain position (not the original position), the thrust generated by the diaphragm head under the action of the gas signal can only form a combined force with the thrust of the handwheel, causing the valve stem to continue moving in the same direction and not to exceed a certain position in the opposite direction. Therefore, the top mounted handwheel has a one-way limit function. When it is necessary to limit the regulating valve of the top mounted handwheel, first remove the gas signal inside the diaphragm head, or adjust the current signal to 4mA, and then rotate the handwheel to move the valve stem to the desired limit position.
    2. The principle and method of side mounted handwheel limit is to use the slider on the handwheel shaft to push the A-end of lever c horizontally (L-shaped lever) or vertically (straight plate lever) when rotating the handwheel. The thrust is transformed into a vertical movement of the B-end of the lever through the fulcrum d, thereby causing the valve stem to move up and down. The slider can exert force on both sides of the bar hole on the lever, which means that the regulating valve can perform bidirectional forced operation on the valve stem regardless of whether there is a signal. Therefore, the side mounted handwheel has the function of bi-directional limiting of the regulating valve. However, it is not possible to limit the regulating valve in both directions simultaneously, and only one direction can be selected to limit the regulating valve. When it is necessary to limit the regulating valve, the direction of the limit must be determined first before proceeding with the operation. If the regulating valve is limited in the same direction as the membrane head force, first adjust the current signal to 20mA, and then operate the handwheel to move the valve stem to the desired position; If the regulating valve is limited in the opposite direction of the membrane head force, first adjust the current signal to 4mA, and then operate the handwheel in the opposite direction to bring the valve stem to the desired position.
     When there is a malfunction in the gas source signal or electrical signal, or when the main components of the actuator, such as membranes, springs, seals, transmission components, etc., are damaged, automatic operation should be changed to manual operation. A handwheel mechanism can be used to continue maintaining the adjustment function of the regulating valve.