Industrial gate valves

Gate valves are designed for full-open or full-closed service. When partially open, the gate wedge experiences severe erosion and vibration from turbulent flow across the disc edge, leading to premature seat damage and wire-drawing (cutting) in steam or gas service. For flow control in African mining slurry systems or refinery process units, specify globe valves or control valves with characterized trim designed for throttling. Gate valves in partially open positions also exhibit unstable flow characteristics unsuitable for process control.

Solid wedge gates are single-piece construction offering maximum strength and simplicity, preferred for high-pressure services. Flexible wedges incorporate a shallow cut through the disc, allowing slight deflection to compensate for thermal expansion, seat wear, and pipeline stress—critical in high-temperature steam applications common to South African power plants. Split wedge (two-piece) designs offer bidirectional sealing without worrying about installation direction, beneficial for African water systems where valve orientation may be uncertain.

Pressure seal bonnets are standard for Class 900 and higher (ANSI 900, 1500, 2500) where internal pressure energizes the seal, becoming tighter under pressure. This design reduces bolting requirements, overall weight, and maintenance complexity—advantages for offshore platforms in Nigerian waters or remote mining installations. Bolted bonnets suit Class 150-600 applications and provide easier access for seat replacement in maintenance-intensive services. For Nigerian offshore and Angolan deepwater projects, pressure seal designs reduce topside weight while improving reliability.

Thermal binding occurs when temperature differentials cause uneven expansion between the wedge and body seats. Solutions include: (1) Flexible wedge designs that accommodate thermal stresses, (2) Parallel slide (slab) gates that eliminate wedging forces entirely, (3) Proper warm-up procedures before full operation, and (4) Stellite-hardfaced seats to resist galling. For Kenyan geothermal facilities operating at 300°C or Egyptian power plants with supercritical steam, specify parallel slide gates or flexible wedge with hardened seats. Never leave gate valves partially open during thermal transients.

Sour service (H₂S-containing) requires NACE MR0175/ISO 15156 compliance with material restrictions: (1) Carbon steel bodies must meet hardness limits (HRC 22 max for C-Mn steels), (2) Avoid zinc coatings, copper alloys, and certain stainless steels prone to sulfide stress cracking, (3) Trim materials typically 13Cr, 15Cr, 316 SST, or Inconel depending on chloride content and temperature. For Nigerian and Ghanaian offshore fields with significant H₂S, request material certificates demonstrating NACE compliance. Our engineering team provides material selection guidance based on partial pressure calculations and operating envelope.