Industrial Valves

10Valve Operation

10.1 Introduction

A valve must have a means of operation in order to function properly. It may be possible to divide all valves operating in the same way, except for pressure relief and check valves, into two groups; those which are controlled by hand and those which are controlled with actuators. There are valves that are manually controlled or manual valves that are operated by either a lever or a handwheel and a gearbox. As seen in Figure 10.1, a manually operated valve with a handwheel and a gearbox that is being driven by an individual (a human) is shown.

The calculations in this section are focused primarily on the torque and forces generated by the manual operator or actuator to operate the valve. Additionally, the generated loads from the operator or actuator are transferred through the valve stem to the internals of the valve in order to operate (open or close) the valve. Therefore, the valve internals, especially the stem, must be designed robustly in order to withstand the forces applied by the operator or actuator. There are also several valves which are used in cryogenic or extremely cold service environments like liquefied natural gas (LNG), and nitrogen. In fact, some of these valves are capable of operating at –196 °C. It is no surprise that LNG has since become a very popular source of energy as a clean and environmentally friendly fuel. So many investments have been made in LNG plants, and more investments will be made in the future. Cryogenic ...