For selection of ESD valve actuator supply, what are factors that decide whether ESD valve shall be hydraulic or pneumatic?

Setting up a maintenace regime for a HRSG can anybody assist by telling me the time between stripdowns required of pilot operated safety valves?

The reasons for using RB valves on a pipeline and on which type of pipelines? I know only as the cost and should not be used on a pigable pipeline.

What type of valve which is called Special Valve?Perhaps for some people a special valve is one that is not available from stock or not in a catalog, etc.

I have an API 6D ball valve that shall sustain 450 bar @ 70°C. This presseure is over CL2500. Gas service, none corrosive.

Use solid ball for a 2" floater and a hollow ball for a 3" floater.Will there be any difference in performance?

Would a carbon steel valve body (for ball valves) be more suitable or equal to a ductile iron body for a glycol-water based coolant system for cooling a large diesel engine?

4" #1500 Ball valve is with seats that are pushed by springs against the ball.