The knife gate is a straight-through isolation valve whose gate travels at right angles to the flow and cuts through fibrous, granular and slurry media instead of wedging into them — which is why it works where a wedge gate packs solid and stops closing. A pair of independent, replaceable seats gives a seal that can be renewed on site, and the body has no pocket for solids to bridge. DN25–DN1200, 10 bar to DN600 and 6.9 bar to DN1000, −29 to 200 °C or 425 °C by seat material. It isolates; it does not throttle.
General Specifications
Size RangeDN25 – DN1200 (larger sizes on request)
Design StandardMSS SP-81
Face-to-FaceMSS SP-81 (custom lengths on request)
Flange DrillingEN 1092 / ASME B16.5 / HG/T 20592 / GB/T 9124.1 / AS 2129 / AS 4087
Working Pressure10 bar (DN50–DN600) · 6.9 bar (DN700–DN1000) · DN25–DN50 and above DN1000 on request
Flow ControlOn / off isolation — not for continuous throttling
Sealing DirectionUni-directional, bi-directional on request
OperationHandwheel, bevel gear, pneumatic, electric or hydraulic
MediaHigh-viscosity, particle- and fibre-laden and slurry media
Temperature−29 to 200 °C / −29 to 425 °C depending on seat material
Pressure RatingPN10 / PN16 / 150LB (table D/E drilling)
Materials & Coating
BodyCarbon steel / stainless steel / duplex steel / special material
GatePrecision-machined knife gate with a cutting edge
SeatIndependent replaceable seat — metal (hard) or resilient (soft)
Stem SealingMoulded packing, upper seal
Body ConstructionCompact one-piece body, no solids pocket
Applications
Municipal wastewater plants Paper and pulp stock lines Power plant auxiliary water Chemical light-sludge service
Uni-directional sealing, and what it costs you
A general knife gate seats on one face. That is what allows the gate to wipe the seat clean on every stroke, and it is why the valve is specified with a flow direction. Fitting it the other way round puts the pressure behind the seat and the valve will pass.
Where reverse pressure is a real condition, the bi-directional seat variants or a different valve type have to be selected at enquiry stage — this is not something to decide on site.
Seat type and operator are separate decisions
Seat material follows the medium: resilient rubber for water and non-aggressive slurry, metal for high temperature and abrasive duty, PTFE where chemical resistance matters, U-section where the seat has to be replaceable from the pipeline side.
Operation is chosen on cycle frequency and access: handwheel with rising stem for infrequent manual duty, pneumatic cylinder where the valve is part of an automated sequence, and full-lug body where the valve has to be bolted to both flanges and dead-end the line.
More from this series
Related guides
