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Gate valves (also known as knife valves or slide valves) are linear motion valves in which
a flat closure element slides into the flow stream to provide shut-off. Gate
valves are designed to minimize pressure drop across the valve in the
fully opened position and stop the flow of fluid completely. The
direction of fluid flow does not change, and the diameter through which
the process fluid passes is essentially equal to that of the pipe. Hence,
they tend to have minimal pressure drop when opened fully.
Gate valves are advantageous in applications involving slurries, as their
“gates” can cut right through the slurry. They are also used in
applications that involve viscous liquids such as heavy oils, light
grease, varnish, molasses, honey, cream and other non-flammable viscous
liquids. They are available in large sizes to better handle thick
flow. However, gate valves do have low-pressure limitations,
and are not optimal in applications that require cleanliness or sanitary
conditions. They are excellent for use anywhere a shutoff valve is
needed. They can also be used where throttling capabilities are desired,
although this is not generally recommended as erosion of the seat and disc
occurs due to the vibrations of the disk in throttling applications.
Gate valves are usually divided into two types: parallel and wedge-shaped.
The parallel gate valve uses a flat disc gate between two parallel seats,
upstream and downstream. Knife valves are of this type, but with a sharp
edge on the bottom of the gate to shear entrained solids or separate
In the double-disk parallel-seat type, the valve is closed by lowering the
disks from the valve neck to a height equal to that of the valve seats.
Once so positioned, an inclined plane mounted between the two disks
coverts downward stem force into axial force and presses the parallel
disks firmly against the valve seats sealing the two openings. These types
of valve design can accommodate asymmetric or angularly misaligned valve
Wedge-shaped gate valves use two inclined seats and a slightly mismatched
inclined gate allowing for tight shut-off. Disk flexibility is inherent to
the split wedge design. This flexibility allows the split wedge to seal
more easily and it reduces stickiness between the sealing surfaces in
cases where the valve seats are angularly misaligned.