The Well Designed Remote Actuated Valve

Remote actuated valves must be chosen to match process requirements. Design decisions include materials of construction, valve seat material, valve t q)e, actuator type and controls characteristics. The design must match utility supply levels (air pressure, hydraulic pressure, flow capacity) and tolerances with actuator design to provide the correct torque/thrust to the valve. The torque/thrust must be above breakaway requirements and must be below stress limits of the drive train. With some valves, the ratio of these values may limit the available operating safety factor. 

Process material, pressures, temperatures and flow rates will have a major impact of valve type chosen. Matching process needs, including the need for tight shut-off and other safety requirements must also be done. Valve manufacturers often customize the valve design to match specific needs. It is recommended to consult with experts from the valve manufacturer to assure a well-designed final element. 

The pneumatic or hydraulic controls must also be carefully designed to not only provide the required torque/thrust levels but also to perform their function in the correct time period. This may require the addition of pneumatic boosters or quick exhaust valves. The final element must close fast enough to provide tiie safety protection function but not so fast as to induce excessive and possibly dangerous stresses in the piping due to the system dynamics. 

Fortunately for the safety instrumented function designer, many valve manufacturers are getting their products and their design processes assessed to lEC 61508 (Ref. 1). These manufacturers supply a safety manual and all failure rate data (typically assuming a well designed final element) needed for SIF probabilistic verification. Some manufacturers are 

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