Gate Valves

A gate valve is a type of valve that uses a solid gate or wedge to control the flow of fluid. It operates by lifting the gate out of the path of the fluid flow to allow full flow, or lowering it to block the flow. Gate valves are designed primarily for on/off service (fully open or fully closed) and are generally not suitable for throttling or regulating flow.

Types of Gate Valves

Solid Wedge Gate Valves: Simple, robust design, suitable for general service.

Flexible Wedge Gate Valves: Wedge has a flexible design to compensate for thermal expansion or contraction, reducing seat leakage and binding.

Split Wedge Gate Valves: Two separate wedge halves, good for handling non-condensing gases and liquids at varying temperatures.

Parallel Slide Gate Valves: Use two parallel discs with springs in between, common for high-temperature steam service.

Knife Gate Valves: Feature a sharp, thin gate (like a knife) that can cut through thick liquids or slurries, common in wastewater, mining, and pulp & paper.

Rising Stem Gate Valves: The stem rises as the valve opens, indicating the valve position.

Non-Rising Stem Gate Valves: The stem rotates within the valve body, not rising externally, suitable for tight spaces.

Flanged End / Threaded End / Welded End Gate Valves: Different connection types for piping.

Applications in Various Industries

Oil & Gas: Isolation valves for pipelines, storage tanks, and processing units.

Water & Wastewater Treatment: Shut-off valves in water distribution networks, sewage treatment plants.

Chemical Processing: Isolation of chemical lines, reactors, and storage tanks.

Power Generation: Isolation valves in steam systems, cooling water, and fuel lines.

HVAC: Isolation in large piping systems.

Mining & Slurry Handling: Knife gate valves are specifically designed for abrasive slurries.

Fire Protection Systems: Isolation valves for sprinkler systems.

Technology: 

The primary mechanism involves a handwheel (manual), gearbox, or an actuator (electric, pneumatic, hydraulic) that rotates the stem. The stem is threaded into the gate, and as it rotates, the gate moves up or down. Sealing is achieved by metal-to-metal contact between the gate and the body seats, or by resilient seating materials. Design considerations include pressure rating, temperature range, material compatibility with the fluid, and ease of operation.

Material Selection Considerations

Body & Bonnet:

• Cast Iron / Ductile Iron: Economical, common for water, wastewater, low-pressure applications.
• Cast Steel (Carbon Steel, Alloy Steel): For higher pressures and temperatures, general industrial use.
• Stainless Steel (304, 316, Duplex): For corrosive fluids, food & beverage, pharmaceutical, and hygienic applications.
• Bronze / Brass: For smaller sizes, non-corrosive liquids, plumbing.
• Specialty Alloys (Hastelloy, Inconel): For highly aggressive chemicals or extreme temperatures.
• Gate/Wedge: Usually the same material as the body, or a harder material (e.g., stainless steel, often with Stellite overlay for wear resistance).
• Stem: Stainless steel (e.g., 304, 316) for corrosion resistance and strength.
• Seats: Integral with the body or separate rings. Often Stellite faced for metal seats, or resilient materials like EPDM, NBR, Viton for soft seats.
• Packing/Gaskets: Graphite, PTFE, or various elastomers selected for fluid compatibility, temperature, and pressure.
• Handwheel/Actuator Mounting: Cast iron or steel.
• Knife Gate Valves: Often feature a stainless steel blade and a cast iron or ductile iron body, with various packing options depending on the slurry.