Control Valve - Ball or Globe type...

[reiszal]

Hi guys,

Recently i have discussion with my collegues about control valve. As far as I am concerns, in API RP 14E the most suitable control valve is globe type. But according to my colleagues, sometimes we use ball too as control valve whenever we have shearing effect in the flow.

My question are; what is shearing effect? Which one is the best preferred option actually ball or globe because I never encounter any control valve using ball disc? Please guide me.

I thank you for your guys kind assistance.

Cheerio,
ARR

 

[zdas04]

A standard ball valve (either floating or trunion) is designed as an on/off device and has terrible throttling characteristics (very non-linear open percent vs. flow percent curve).

There are a couple of companies selling a "V-Ball" device which is 1/4 turn like a ball valve, but has a seating-surface configuration that provides near-linear flow characteristics. The "V-Ball" isn't really a ball valve, but folks sometimes confuse it for one because of the increadibly clear nomenclature.

For throttling flow (even in "high shear" fluids) you can successfuly use just about any valve except a ball, a gate, a butterfly, or a plug valve. These valves are just not designed for throttling.

Globe valves are good. Needle valves (i.e., globe valves with a very steep angle on the seating surfaces), "choke" valves, and the like are designed specifically for throttling and will yield good results in most throttling or part-open service.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com