The biggest difference between knife gate valves and gate values is that gate valves are manufactured to ANSI standards while knife gate valves comply with TAPPI standards. The gate valve is also flanged, wider dimensionally, ANSI pressure rated and its API leak tightness standards need to be met. Gate values are bi-directional, and widely used in fluid applications and they only come with metal seats. Another difference between a knife gate valve and an ANSI gate valve is within the packing gland area. A gate valve has a v-ring packing set that seals the shaft that is attached to the gate. Knife gate valves have a packing gland area that seals around the gate.
A knife gate valve has a thin profile in comparison to an ANSI gate valve. Knife gate valves are predominately uni-directional (some options are bi-directional) and feature a lugged or wafer body, without flanges. The knife gate valve seats are available in everything from resilient to the metal versions.
The most significant benefits of knife gate valves are the weight (16" usually less than 300#) and the cost. ANSI gate valves are usually over 1200# and they more expensive.