Knife gate valves for slurry, sludge and solids: where standard valves fail

Why do standard valves struggle with solids?

A standard wedge gate valve closes into a seat at the bottom of the body. Solids can settle there and stop the gate closing fully. A butterfly valve’s disc sits in the flow even when open, so fibres and rags can wrap around it.
The result is the same: a valve that leaks when shut, jams part way, or needs taking out and cleaning far more often than it should.

How does a knife gate valve work?

Instead of a wedge, it has a thin blade with a sharp, chamfered edge. As it closes, the blade cuts through the media rather than trying to push it aside. When it’s open, the blade is fully out of the flow.
Our knife gate valve is a one-piece, resilient-seated, wafer-pattern design with a round-bottomed, chamfered stainless steel blade. It is bi-directional, so it seals with flow from either side, and it gives a tight shut-off on everything from heavy sludges to clean fluids.

What are the key details?

• Sizes: DN50 to DN1000.
• Pressure: up to 10 bar working pressure. The allowable pressure difference across the closed valve falls on larger sizes, so check the datasheet for your size.
• Body: ductile iron, powder coated inside and out.
• Blade: 304 stainless steel, with an NBR seal.
• Maintenance: the gland packing can be replaced without taking the valve out of the pipeline.

How can it be operated?

By handwheel with a non-rising spindle, which is useful where headroom is tight. Or with a double-acting pneumatic cylinder or electric actuator, for automated or remote operation on process lines.

Where are knife gate valves used?

• Quarry and mining slurry and dewatering lines.
• Anaerobic digestion plants, for digestate and feedstock.
• Food waste and food processing effluent.
• Sludge lines at industrial and municipal treatment works.
• Paper and pulp stock.

Quick tip: tell us what’s actually in the pipe. “Slurry” can mean anything from muddy water to a thick paste, and it changes the seal and operator we’d recommend.

Before you enquire, have ready: pipe size, working pressure, what the media contains and how thick it is, temperature, and how you want to operate the valve.

Related reading: Butterfly or gate valve? Can air valves be manufactured in specialist materials?