BS 1873 specifies bolted bonnet globe valves in carbon steel (WCB) and alloy steel for sizes 1/2 inch to 24 inches. Pressure-temperature ratings follow ANSI B16.34: Class 150 ranges from 275 PSI at 38°C to 180 PSI at 260°C; Class 300 from 720 PSI at 38°C to 655 PSI at 260°C; Class 600 from 1440 PSI at 38°C to 1310 PSI at 260°C. For higher temperatures, P91/P92 chrome-molydenum steel bonnets are used. For Saudi Arabian steam service above 260°C, BS 1873 forged steel globe valves with Stellited seats are specified.

Globe valves achieve tight shut-off through a flat or cone-shaped disc (plug) that seats precisely into a matching seat ring, compressing a soft or hard seat material. The stem moves axially (downward) to close, pushing the disc firmly against the seat. The contoured disc provides 360-degree seating contact, unlike gate valves which seal along a line. For critical shut-off, renewable seat rings allow regrinding or replacement without removing the valve from service. PTFE seats provide bubble-tight shut-off for general service; graphite seats handle high temperatures and slightly worn surfaces. For Saudi Arabian oil terminal leak-free requirements, globe valves with spiral wound graphite seats are specified.

Weir-type (standard) globe valves have a horizontal weir (saddle) inside the body that creates a separation between inlet and outlet flows, providing better throttling control and self-draining capability when installed with stem horizontal. Straight-through (double-ported) globe valves have flow enter one side and exit the opposite side without a weir, offering lower pressure drop but less precise throttling. For modulating control service, weir-type is preferred. For simple on-off service where minimal pressure drop is critical, straight-through design may be selected. Angle globe valves (90-degree turn) combine benefits of both for specific orientations.

Pressure seal bonnet design is used for globe valves rated Class 600 and above where bolt loading for bonnet joint sealing becomes impractical. In pressure seal design, the bonnet is held in place by pressure (from within the body) acting on a seal ring geometry, rather than by bolts. This provides: (1) more compact body design, (2) lower assembly torque requirements, (3) better reliability at high pressures. Pressure seal bonnets are standard for boiler feedwater, steam turbine bypass, and high-pressure chemical service. For Saudi Arabian refinery applications above Class 600, pressure seal globe valves are typically specified.