Globe versus Gate Valves
Globe versus Gate Valves
(OP)
Can anyone tell me why Globe valves seal more efficiently than Wedge Gate valves?
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Globe versus Gate Valves
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Globe versus Gate ValvesGlobe versus Gate Valves(OP)
Can anyone tell me why Globe valves seal more efficiently than Wedge Gate valves?
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RE: Globe versus Gate Valves
RE: Globe versus Gate Valves
I guess that depends on your definition of "efficient". Gate valves can provide a very tight shutoff, which gets tighter with increased pressure. For globe valves, it depends on the orientation. With flow from under the disc (the "normal" configuration for globe valves), increasing pressure results decreased sealing performance (ie, possibility of leakage). With flow from over the disc, increased pressure produces a tigher seal, but the valve can be hard to open. Globe valves, at least in my training, are not generally used as shut off valves, only for throttling.
*What to do if there's a high differential pressure?
With a gate valve, higher delta P means more torque is required to open. Use a gear (or electric) operator. As an alternative, use a bypass configuration: the torque required to open a small bypass valve is minimal, open that valve first and the let the pressure across the big gate valve equalize, then open the big gate valve.
With a globe valve, again it depends on orientation. With flow under the disc, tight shutoff requires high torque: again, think gear or electric actuator, or possibly hammer-blow handwheel. Opening is easy. For flow over the disc, closing is easy but opening requires more torque (actuator), or a bypass.
*Flow Curve
I must disagree with davfitz's assertion that globe valve flow curves are essentially linear. At least in my experience, the curve is more S-shaped and tapers off once the valve is open to about 1/3 of the pipe size. It depends on the disc design, but most globe valves should not be counted on for very fine flow control (that's what a control valve is for.) But davefitz right that gate valves should not be used for throttling.
Jonathan Nieuwsma
RE: Globe versus Gate Valves
RE: Globe versus Gate Valves
Having said that gate valves work, just make sure the application suits the valve.
As fare as the rest of the stuff that others have pointed out about globe valves, well it all depends whose product and what application. All of what’s been said isn’t necessarily so and some of what’s been said is incorrect, so just be careful and don’t rely on a single source.
RE: Globe versus Gate Valves
J. Alton Cox
www.delucatest.com
RE: Globe versus Gate Valves
Default ANSI/FCI Class II globe style control valves leak like a sieve. Control valve leakage classifications reflect the leakage in percentage terms based upon the valve sizing coefficient. Class III are normal with Class IV still leaking, Class V still leaking and Class VI still leaking. Do not compare control valve leakage rates against gates or balls as the requirements differ quite dramatically. Shutoff valves are gates and ball valves not globes.
John