Uni-Directional range
These valves are designed to handle non-clean media with features that ensure minimum contact between moving parts of the valve. This is achieved by having a precision-ground gate that is held between layers of gland packing with almost no contact between the body parts and gate during most of its travel.
Seating is achieved with an almost non-sliding motion aided by jams located in the body. Avoiding sliding contact between the gate and body allows this valve to handle abrasive particles present in the media much better than conventional designs. Another feature is the beveled bottom edge of the gate (from which it derives the ‘knife’ in its name) which allows positive closure of the gate even when solid particles settle at the bottom of the body.
In handling abrasive media, deflection cones are generally used to avoid direct impingement of media on the seat surface. Hard facing of body or seating parts is sometimes used. Purge connections using gas or fluids at pressures higher than line pressure are sometimes provided on the valve body to clean seating surfaces (body purges) and packing area (chest purges). This minimises abrasive wear and tear during valve opening and closure.
Knife gate valves are excellent hopper isolation valves with their ability to cut through flowing powders and close by dislodging any material in the seating area. This is also perhaps the only valve design which can tolerate differential thermal expansion of its parts without affecting its functions, thus making an ideal choice for handling high temperature media.
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