Gate valves use a flat wedge that moves perpendicular to flow for on-off service with minimal pressure drop when fully open. Globe valves use a plug that seats against a horizontal weir for throttling and precise flow control. Gate valves should not be used for throttling; globe valves should not be used where full flow with minimal pressure drop is required. For Saudi Arabian pipeline isolation, gate valves are standard. For modulating control in process lines, globe valves or control valves are used. Gate valves are cheaper and lighter for the same pressure class and size.

On-off (isolation) service: Use gate valve for full bore flow and minimal pressure drop, ball valve for quick quarter-turn operation, butterfly valve for large sizes (above 24 inch) where gate/ball cost is prohibitive. Throttling service: Use globe valve for precise flow control, control valve with positioner for automated modulation. Consider: (1) Required control range (gate/ball limited to 10:1, globe 50:1, control valve 100:1), (2) Pressure drop availability (throttling requires 10-20% system pressure loss), (3) Operating frequency (frequent cycling wears soft seats). For Saudi Arabian oil terminal pump discharge, on-off gate or ball valves are used; for chemical injection, globe needle valves provide fine control.

BS (British Standards) and ANSI/ASME (American) are the dominant global valve standards. Key differences: Face-to-face dimensions: BS vs ANSI differ for some sizes, causing compatibility issues. Pressure ratings: Both use Class system (150, 300, 600) but BS also has PN (Pressure Number) ratings not directly interchangeable. Flange dimensions: ANSI B16.5 vs BS 4504 have different bolt circles and flange OD for same rating. Gate, globe, check valves: BS 5153 (cast iron), BS 5154 (bronze), BS 1873 (steel) vs ANSI B16.34. For Saudi Arabian projects, ANSI/API standards dominate (Aramco, ADNOC preference). For European-engineered plants (Jubail / Yanbu), BS may be specified. Always verify compatibility before ordering.

Valve body materials use casting designations: WCB (ASTM A216 Carbon Steel, max temp 425°C), WC6 (1.25Cr-0.5Mo, to 540°C), WC9 (2.25Cr-1Mo, to 570°C), C5 (5Cr-0.5Mo). Stainless steel: CF8 (304 SS), CF8M (316 SS), CF3 (304L), CF3M (316L), CN7M (Alloy 20). Forging designations: A105 (carbon steel), F22 (2.25Cr-1Mo), F91 (9Cr-1Mo-V). Trim materials use AISI designations: 304, 316, 410 (13Chrome), 440C (for seats). Example: Gate valve with WCB body and 316 trim means carbon steel body with stainless steel disc and stem. For Saudi Arabian sour service, verify H2S content and select NACE-compliant materials per MR0175.