Knife gate valve
A knife gate valve is drawn as a gate-valve bowtie body with a diagonal line marking the sharp gate blade. Like a gate valve it is an isolation device, fully open or fully closed, but the thin blade shears through the medium, which is why it is used on slurry, powder, and fibrous or viscous service.
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Typical usage.
Isolation on slurry, wastewater, pulp and paper stock, mining tailings, and bulk-solids lines where a standard gate or ball valve would clog or fail to seat. It is not a control valve and is never paired with a positioner. On a P&ID it reads as a gate valve with the knife blade shown, so confirm the body type from the valve schedule rather than the symbol alone.
FAQ.
How is a knife gate valve symbol different from a gate valve?
Both use the bowtie body. A knife gate valve is commonly distinguished by a diagonal line through the body representing the thin gate blade. The distinction is not always drawn, so the valve schedule or line list is the authority on the actual body type.
Is a knife gate valve a control valve?
No. A knife gate valve is an isolation device, fully open or fully closed. It is not modulated and is never fitted with a positioner. If the drawing shows a positioner or a modulating signal to the valve, it is a control valve, not an isolation knife gate.