Knife gate valve vs wedge gate valve for slurry, sludge and water
A knife gate valve looks like an ordinary gate valve but is built for different conditions: thick and abrasive media at low pressure. It should not replace a wedge gate valve on water mains or steam, and the reverse is also true.
TAZ Engineering Team · · 5 min
Differences
In a knife gate valve a thin bevelled blade cuts through the medium and closes against a seal in a short wafer or lug body. In a wedge gate valve a solid wedge enters between two body seats and is pressed against them by line pressure and stem thrust.
Pressure and tightness
Knife gate valves are usually rated PN 10 or lower, less at large sizes, and many are unidirectional. Wedge gate valves are made up to PN 160 and above and are normally bidirectional.
Abrasive and fibrous media
On slurry, tailings and sewage with fibres and sediment, a wedge gate valve clogs because solids settle in the bottom of the body and the wedge cannot reach the seat. A knife gate blade cuts through deposits, which is why it is standard in mineral processing, pulp and paper and wastewater treatment.
How to choose
Clean water, steam, oil products or pressure above PN 16: wedge gate valve. Slurry, sludge, sediment and bulk solids at low pressure: knife gate valve, with attention to blade and seal materials, flushing ports and replaceable liners.
Checklist
- medium and solids content
- operating pressure
- flow direction
- DN
- blade and seal materials
- flushing ports
- actuation