Duplex Gate Valve Manufacturer in Africa

Isolation valves used in saline water, produced water and chloride-bearing process lines must resist localised corrosion around the wedge, seat pockets and stem area. A duplex gate valve combines a straight flow passage with higher strength than common austenitic stainless steel. African Valve is a leading Duplex Gate Valve Manufacturer  in Africa, supplying South Africa, Nigeria, Egypt, Angola, other African markets and international project requirements.

Gate Movement and Flow Passage

The wedge moves vertically between two seats. When fully raised, it withdraws from the bore and leaves a nearly straight flow path. This keeps pressure loss lower than in a globe valve and makes the design suitable for full-open or full-closed isolation.

A gate valve should not remain partly open for control duty. High local velocity can cause vibration, wedge movement and erosion at the seat edges.

Duplex Body and Trim Materials

Cast bodies may use ASTM A995 Grade 4A, while compact forged designs may use ASTM A182 F51. The bonnet, wedge, stem and seat rings should use compatible duplex grades or another corrosion-resistant trim selected for the fluid. ASTM A995 covers duplex castings for pressure-containing components, and ASTM A182 covers forged valve parts.

Duplex stainless steel offers improved resistance to chloride stress-corrosion cracking and pitting compared with common 300-series stainless steel. Heat treatment, ferrite balance and welding practice remain critical. An incorrect thermal cycle can reduce corrosion resistance even when the material certificate lists the correct grade.

Wedge, Stem and Bonnet Design

Solid or flexible wedges may be supplied depending on size, temperature and design standard. A flexible wedge can accommodate limited seat movement caused by thermal or pipeline loads.

A rising-stem outside-screw-and-yoke arrangement keeps the threaded section outside the main pressure boundary and gives visible valve position. Bolted bonnets allow maintenance access, while welded or pressure-seal bonnets may be selected for compactness or higher-pressure service.

Technical Specifications

Size Range: DN15 to DN600

Pressure Ratings: ASME Class 150 to Class 1500

Design Standards: API 602 for compact forged valves; API 603 or ASME B16.34 for applicable larger designs

Testing Standard: API 598

End Connections: Flanged RF, RTJ, socket weld or butt weld

Operation: Handwheel, gearbox, pneumatic actuator or electric actuator

Body Materials: ASTM A995 Grade 4A or ASTM A182 F51

Gate Design: Solid wedge or flexible wedge

Bonnet Design: Bolted, welded or pressure seal

Stem Design: Rising stem, OS&Y

Seat and Packing Arrangement

Integral or renewable seat rings may be used according to the body design. Hard-facing can reduce galling and erosion where the valve cycles frequently or closes against high differential pressure.

Flexible graphite packing is commonly selected for elevated temperature. Low-emission arrangements may be added where fugitive-emission control is required. Packing choice must also suit the external marine or chemical environment.

Industrial Applications

Duplex gate valves are used in desalination plants, produced-water systems, marine utilities, pulp and paper lines, chemical processing and selected oil and gas services. For warm seawater, concentrated brine or severe crevice conditions, Super Duplex may provide a better corrosion margin.