The globe valve can be used for both regulation and isolation. The globe is commonly called a 'stop valve' which fails to understand its main purpose of controlling flow.
The globe valve closure member is connected to a stem which is screwed up or down on to a valve seat to throttle the flow. Closure can be achieved by fully winding down the closure member onto the single seat.
The closure member comes in several designs. The most common in the energy industries are a flat disc or where fine control is a requirement a needle type disc is specified.
Globe valves are available for extreme process conditions; for instance fitted with cryogenic bonnets for low temperature service or a bellows seal design that provides a metallic gland seal where leakage to atmosphere cannot be tolerated. The globe valve can also be equipped with a floating closure member allowing it to act not only as a throttling device but also as a check valve to prevent flow reversal.
The standard globe valve design has an angled flow path resulting in a high pressure drop across the valve. This pressure drop can be reduced by using an oblique pattern or Y type body style. However for minimum pressure drop a gate or ball valve would normally be used for isolation service.
The design of the flow path in a globe valve is usually only suitable for uni-directional flow so the valve body will be marked with a flow directional arrow in order to assist in correct installation.
Typical applications are for clean process fluids or utilities. Globe valves are unsuitable for heavy or abrasive slurries where the process has particles in suspension as these can become trapped between the closure member and the seat during the closing operation. This results in leakage and permanent damage to the valve.
The main components of steel globe valves are generally manufactured from forgings from 6mm to 50mm size where end connections are normally screwed or socket weld. Castings are mostly used in larger sizes 50mm to 250mm. Flanged and butt weld connections are normally available on all sizes but usually specified as standard on sizes 50mm and above. Globe valve ratings vary from ASME class 150 to class 2500lb.
Globe valves are suited to lower pressures and smaller sizes as effective sealing is dependent on the applied stem torque being superior to the force of the media which is attempting to lift the disc off the seat. The maximum valve size generally available for this type of valve is 250mm on class 150 and 50mm on class 2500lb.