Knife gate valve questions, answered

A knife gate valve closes by driving a thin, sharp-edged gate straight down across the bore. The edge cuts through solids, fibers and rags that would jam other valves, which is why knife gates are used on sludge, slurry, pulp and bulk solids lines. They are isolation valves: fully open or fully closed.

A uni-directional knife gate seals against pressure from one side, usually with a metal seat. A bi-directional knife gate seals no matter which way the pressure comes from, usually with a resilient perimeter seal or polymer seats. If flow or pressure can ever reverse, specify bi-directional. The Fabricast FIG 50, FIG 61, FIG 145 and FIG 345 are bi-directional.

For abrasive slurry and tailings, a polymer lined knife gate with replaceable liners usually outlasts a metal or rubber seated valve, because the liners take the wear and can be replaced without replacing the body. The Fabricast FIG 145 (150 psi) and FIG 345 (300 psi) use replaceable UHMWPE liners, with deflector cones and hardsurfacing available for severe service.

MSS SP-81 is the Manufacturers Standardization Society standard for stainless steel, bonnetless, flanged knife gate valves. It covers design, materials, dimensions and testing. Fabricast knife gates are designed and tested to MSS SP-81, with flanges drilled to ASME B16.5.

Choose a bonneted knife gate when the packing must be contained: enclosed or occupied spaces, odor control areas, hazardous media, or buried and submerged installations. The Fabricast FIG 240 is a bolted bonnet knife gate in cast stainless to 36 in and fabricated from 42 in.

Standard knife gates are on/off isolation valves. For limited flow control, a V-port insert shapes the opening so the gate can be positioned partly open. Talk to us about the flow range before using any knife gate to throttle.

Fabricast builds knife gates from 2 in to 120 in (DN50 to DN3000) with ratings up to 600 psi (41 bar). Catalog models are rated 150 psi or 300 psi cold working pressure; larger and higher pressure gates are engineered to order.

State which Fabricast models and configurations comply with American Iron and Steel, Build America Buy America, and the Buy American Act. Fabricast provides a signed, project-specific compliance letter with the submittal.

Fabricast Valve designs and builds knife gates at its plant in Longview, Washington. Confirm where castings and plate are sourced.

Yes. Fabricast operators mount without welding, so a handwheel gate can be converted to a pneumatic, hydraulic or electric actuator later. Give us the model, size and differential pressure and we will size the operator.

A double block and bleed knife gate has two gates in one body with a drain between them. With both gates closed and the bleed open, any leakage past the first gate drains away instead of reaching the downstream side, giving positive isolation for maintenance. The Fabricast DBB also works as a line blind.

Line size, media, maximum pressure and differential pressure, temperature, flange drilling, operator type and control voltage, quantity, and any domestic content requirement. For bid work, send the spec section and bid date.

Yes, including mining and oil sands projects. Confirm CRN registration status and provinces.

Packing leaks usually come from wrong packing material for the media, a worn or scored gate, or packing that needs adjustment. Options include live-loaded packing, a different packing material, flushing ports, or a bonneted design. Send us the details and photos and we will recommend a fix.