Knife Gate Valves

The knife gate valve is a variant of the gate valve with a thin, sharp-edged gate that slides through the medium to close. The knife edge cuts through fibrous, viscous and settling media that would jam a conventional wedge, and the slim body needs little space between flanges. These valves are built for on/off isolation in heavy and dirty duty rather than throttling or tight bubble-tight sealing, though resilient seated versions do provide effective shut-off.

Applications concentrate in pulp and paper, mining and mineral processing, wastewater and sludge, power generation ash handling and bulk solids. The valve suits slurries, pulp stock, tailings, powders and any medium with a high solids or fibre content where a full-bore, self-clearing gate is needed. Unidirectional and bidirectional designs are available, along with variants for higher pressure and for dry bulk service.

Construction is typically a cast or fabricated body in ductile iron or stainless steel with a stainless gate and a resilient (elastomer) or metal seat. A packed gland or a deflection cone seals around the gate, and skirt or scraper arrangements clear packed solids on closing. Actuation ranges from handwheel and lever to pneumatic cylinder, electric and hydraulic, with the pneumatic cylinder common where fast cycling is required.

Design and testing follow standards such as MSS SP-81 and EN 16767 for knife gate and slurry valves, with flange drilling to EN 1092 or ASME B16.5. When specifying, confirm the bore, pressure rating, the nature and concentration of solids in the medium, the seat type (resilient or metal), whether sealing must be bidirectional and the actuation. We can then propose a suitable configuration for the service.