Knife gate valves use a blade like gate/guillotine to stop the flow of any solids or liquids in line. Unlike conventional gate valves, the blade/slide would pass through the body and a standard gland packing cannot be used. They’re extremely good for use in low pressure (PN16/Class 150) applications. They’re regularly used in handling viscous media, sludges, slurries and dry powder and are found in a range of industries – mining, food and beverage, paper, sewage and many more.
Knife gates can be produced if needed with all metal seating or a soft seat. A soft seat will give a much tighter shut off in both directions. Another advantage of using a knife gate is that when the gate moves into position it slides across the seating faces helping to keep it clean and ensure isolation is not effected when used with difficult media.
When choosing a knife gate valve you should consider the two main options which are whether you want a uni-directional or bi-directional knife gate valve.
The Uni Directional Knife Gate Valve seal on just one side. They also tend to be prone to leaking when there is a possibility of debris build up, this is because of the cutting action of the blade. Suitable for water, paper and pulp slurries, both mining, chemical and some sticky slurries, fly ash and sugar mills amongst many others. The uni-directional knife gate valve can also be used in harsh aggressive environments and high temperatures.
The Bi-Directional Knife Gate Valve will seat on either side of the gate and operate with back pressures, providing adequate water tightness and has a tendency of avoiding any build-up of solids that could prevent the valve from closing. The Bi-directional valve is generally more expensive, and you can expect to pay up to 30% more. Bi-directional valves tend to have a lower torque/thrust over the Uni-directional valves and they have the added advantage of being able to be fitted end of line.