Purification Technology Edition: Daily Question [2017-11-22]

1 When there is a fault in the gas supply signal or electrical signal, or when the main components of the actuator (such as diaphragms, springs, seals, driving elements, etc.) are damaged, it is necessary to switch from automatic operation to manual operation; a handwheel mechanism can be used to maintain the regulating function of the control valve. 2 The handwheel mechanism can also be used as a limiter for adjusting the stroke of the control valve. (Limiting function) The 3-handwheel mechanism enhances the reliability of the control valve’s operation.

When the actuator of the control valve fails, a handwheel can be used to adjust the valve opening and maintain normal system operation.

1 When there is a fault in the gas supply signal or electrical signal, or when the main components of the actuator (such as diaphragms, springs, seals, driving elements, etc.) are damaged, it is necessary to switch from automatic operation to manual operation; a handwheel mechanism can be used to maintain the regulating function of the control valve. 2 The handwheel mechanism can also be used as a limiter for adjusting the stroke of the control valve. (Limiting function) The 3-handwheel mechanism enhances the reliability of the control valve’s operation. If a bypass is added to a control valve, it results in higher investment costs and larger floor space; the costs increase further when the diameter is large or precious metals are used. Using it in wheel mechanisms is cost-effective both in terms of investment expenses and floor space required. Furthermore, for single-acting diaphragm valves, the function of the handwheel and its mode of operation (the direction in which the valve moves) are directional. At the same time, diaphragm-operated valves are generally used in applications where the process pressure is relatively low and the requirements for sealing are not stringent; the force exerted is not very high, so it is sufficient to simply install a handwheel, without the need to design a lever-type handwheel (with some exceptions). The use of pins is also not practical, as pins are typically used in double-acting, piston-type actuators. Double-acting valves are not necessarily the case; generally, a double type refers to an adjustable handwheel that can be used for both opening and closing.

①The handwheel mechanism can also be used as a limiter to regulate the travel of the control valve. For example, in a pneumatic belt manual gate valve, when the signal pressure is zero, the control valve is either fully open or fully closed. If the process requires the control valve to handle a small flow rate, a handwheel mechanism can be used to achieve this. ②The handwheel mechanism can improve the reliability of the control valve’s operation. If a bypass is added to a control valve, it results in higher investment costs and larger floor space; the costs increase further when the diameter is large or precious metals are used. Using it in wheel mechanisms is cost-effective both in terms of investment expenses and floor space required. ③When there is a fault in the air supply signal for the pneumatic valve or the electrical signal for the electric ball valve, or when the main components of the actuator (such as diaphragms, springs, seals, driving elements, etc.) are damaged, it is necessary to switch from automatic operation to manual operation; a handwheel mechanism can be used to maintain the regulating function of the control valve.

In the absence of electricity or gas supply, or in manual mode, the valve can be opened or closed manually.

In normal operation, a control valve equipped with a handwheel is set to automatic mode by adjusting a switch on the valve; in this state, turning the handwheel has no effect on regulation. Conversely, when there are problems with the air supply – such as aging or leaks in the air supply lines that require replacement – the control valve is switched to manual mode, allowing the handwheel to be used for adjustment in order to prevent shutdowns.