You need to talk to the valve manufacturer and find out what their thrust requirement for the valve is at the specific line pressure. Once you know this you can size a linear actuator based on the pneumatic pressure available.
The pneumatic actuator will generally be much faster in operation...
In my experience the certifcate must state 3.1.b. If it does not, it can be very dificult, most of the time impossible, to have the paperwork accepted by third party inspection authorities.
Take a look at this pdf file reference table 8. It appears to show the various equivalents. I think the specification now is BS EN 10083-1 CR22E.
www.dstan.mod.uk/data/03/016/00000200.pdf
It is worth mentioning, as you can see below, BS3602 has now been superceded and withdrawn.
Pub Id : BS 3602
Status : Superseded , Withdrawn
Title : Specification for steel pipes and tubes for pressure purposes: carbon and carbon manganese steel with specified elevated temperature...
I assume that when you say welding you are referring to socket weld flanged valves. If this is the case then it is normal practice to remove the centre section of the valve and weld the flanges to the pipe. When welding is complete and the pipe/flange assembly cooled, the valve centre section...
In my experience it could be that you are seeing the result of a certain amuount of ovality casused by distortion during the threading and possibly other machining processes.
For example, is there a lot of other machining taking place before the thread is cut thus causing the distortion to...
