People often have a confusion between a knife gate valve and slide gate valve. In brief, knife gate valve uses a blade to cut through thick liquids or gas; while a slide gate valve utilizes a slide plate to shut off flow of dry bulk material. In this article, we will discuss their differences in details.

Knife Gate Valve

Knife gate valves were originally designed for pulp and paper industry.  The sharp and beveled-edge knife gate can cut through thick liquids easily, like the stringy pulp, sludge and slurry. Because of its easy actuation and low cost, nowadays, knife gate valves are widely in heavy oils, light grease, slurry, paper pulp, varnish, and wastewater, especially in large size. But we should bear in mind that knife gate valve has a limitation on pressure range, usually in low pressure application.

Its function greatly diminishes when used in dry bulk applications. Its blade is seated into an elastomer seal after the blade cuts through the material. Thus, when powder or solid packs into the soft seals against the end of the gate. Overt time, the seals become abraded and influence the sealing performance, which leads to downtime, decreased production and negatively impact revenue streams

Slide Gate Valve

A slide gate valve is designed to handle dry bulk powders, pellets, and granules. Its flat rectangular slide plate can shut off or open the flow of dry material. The slide plate actuates between two, compression-loaded, hard polymer plates. The hard polymer seals are reinforced by a compressed, hard rubber backing. As a slide gate experiences frictional wear to the hard polymer seals from many actuations over time, the rubber backing ensures the hard polymer seals are constantly being forced against the slide plate.

Sometimes the hard polymer seals will wear to a degree and lose its effectiveness. At this point, we could loose the bolts and remove shim along each lateral aspect of the gate to re-tighten the bolts and the gate’s compression load will be restored.