Both Gate and Knife gate valves play similar roles in a variety of industries. They are primarily used for on/off service and not to regulate flow. Typical applications include the movement of heavy oils, slurries, waste water and non-flammable viscous fluids. Although they are similar in design there are some noticeable differences.
A Gate Valve is wider, flanged and will be built to ANSI standards. Gate Valves are often used when minimum pressure loss is needed and when fully open should provide no obstruction, making it possible to use a pipe-cleaning pig. Gate Valves have a v-ring packing set that seals the shaft attached to the gate, and are only available with metal seats.
Knife Gate Valves
As its name suggests, a Knife Gate valve has a sharpened disk which serves to sever any stringent solids that may keep the valve from closing. Knife Gates were originally designed for use in the pulp and paper sector for just this reason. Knife Gate Valves are designed to TAPPI standards and is generally thinner in profile when compared to a sliding Gate Valve. The design does not incorporate flanges and the seats can be made out of a variety of materials depending on the application.
Corrosion and Wear
Both Sliding and Knife Gate Valves are unsuitable for flow control. This is because when fluid pushes against a partially closed gate vibration will occur, causing increased wear and damage, as such both these types are designed to open and close slowly to protect from the effects of fluid damage. Despite this, when used in conjunction with high viscous fluids and semi-solids and amount of wear is inevitable and this is the reason many Knife and Sliding Gates will actually be protected through Thermal Spray Coating. Tungsten Carbide is popular in this area due to its high corrosion resistance against a variety of sources and high level of hardness.
B&B produce a wide variety of valve components and can source, machine and coat a complete component working from your drawing. We are fully ISO accredited and based in West Yorkshire.