Gate Valves
Gate valves use a gate as the closing member, moving vertically along the centreline of the seat bore to open or close fully. When fully open the gate is completely withdrawn from the flow path and the medium passes almost straight through, giving the lowest flow resistance and pressure loss of any isolation valve in on/off duty. Because the travel is long, gate valves are not normally used for throttling. Gate design falls into two families: wedge type (rigid or flexible single disc) and parallel double-disc. The wedge design is simple and the most widely used; the parallel double-disc design provides reliable bidirectional sealing and resists thermal distortion and jamming, making it suitable for high-temperature steam systems. Stem configuration is either rising stem (OS&Y, visible position) or non-rising stem (NRS, compact footprint); rising stem is preferred for medium- and high-pressure steam and oil & gas service, while solids-laden duties such as mine slurry use the thin knife of a knife gate valve. Pressure ratings cover ASME B16.34 Class 150–2500 (PN 20–PN 420). Body materials include carbon steel WCB, chrome-molybdenum steel WC6/WC9 and stainless steel CF8/CF8M. Sealing surfaces can be hardfaced with 13Cr (Trim 1) or Stellite 6 (Trim 5) to suit the duty. Design and manufacture follow API 600/602, ISO 10434 and GB/T 12234.
Stainless Steel Gate Valve
The stainless steel gate valve (Stainless Steel Gate Valve) uses a CF8/CF8M stainless steel body and is intended for shutoff of water, acids, alkalis and other corrosive media, combining the low flow resistance of a gate valve with the corrosion resistance of stainless steel. It uses a wedge gate with rising-stem or non-rising-stem construction; the seating surface can be soft-seated or hardfaced with 13Cr/316 weld overlay, and the end connections are flanged or threaded. It is widely used in corrosive service in chemical, pharmaceutical, food and seawater applications.
Knife Gate Valve
Knife gate valves use a thin, blade-shaped gate. On opening and closing, the knife edge cuts through or scrapes off fibres, particles and slurry adhering to the seat, preventing blockage and jamming — making this the dedicated isolation valve for slurry and solids-laden lines. The body bore is full-port and recess-free so media do not accumulate. The seat can be metal hard-seated or a polyurethane/rubber soft seat, selected to suit the duty. Pneumatic actuators are available for fast cycling. Typical services include mineral slurry in mining, pulp and stock in papermaking, sludge in wastewater treatment and chemical slurries.
Parallel Double-Disc Gate Valve
Parallel double-disc gate valves use two parallel circular discs with a spreading mechanism. Line pressure and a spreader wedge press the discs against the seats, giving reliable bidirectional sealing without jamming from thermal distortion — a construction suited to high-temperature, high-pressure steam systems. Disc and seat sealing faces are usually hardfaced with carbide, and the pressure-seal bonnet makes sealing tighter as system pressure rises. These valves are widely used in main steam, reheat steam and high-temperature, high-pressure feedwater systems in power plants.
Cast Steel Wedge Gate Valve
Cast steel wedge gate valves use a wedge-shaped gate as the closing member, moving vertically along the seat centreline to shut off flow. When fully open the gate retracts completely out of the bore, so the medium passes straight through and flow resistance is close to zero — the isolation valve with the lowest pressure loss in fully open and fully closed service. The valve has a rising stem (OS&Y) design: the stem rises with the gate and the exposed threads give a clear indication of valve position. Sealing faces can be hardfaced with 13Cr or Stellite carbide for wear and erosion resistance at high temperature and pressure. Suitable media include steam, oil, natural gas and water; typical duties are main isolation in power plants, refineries and transmission pipelines.