The opening and closing element of a knife gate valve is the gate disc, which moves perpendicular to the flow direction. Knife gate valves can only be fully opened and closed and cannot be adjusted or throttled. Knife gate valves primarily consist of a valve body, O-ring, gate disc, stem, and bracket. Knife gate valves utilize a wafer-type, integrated structure, resulting in a compact and lightweight design. The fully open channel prevents media from accumulating within the valve, and the replaceable seal eliminates the maintenance challenges associated with conventional slurry valves and knife gate valves. The valve body has been replaced with ductile iron, a material used in place of traditional cast steel, for improved corrosion resistance and a significantly longer service life.
The gate of a knife gate valve has two sealing surfaces. The most commonly used type is a wedge-shaped disc valve. The wedge angle varies with valve parameters, but is typically 50°. The disc of a wedge-shaped knife gate valve can be a single, rigid disc, or it can be designed to deform slightly to improve processability and compensate for deviations in the sealing surface angle during processing. This type of disc is called an elastic disc. When a knife gate valve is closed, the sealing surface relies solely on the medium pressure to press the disc's sealing surface against the valve seat, ensuring a seal. This is known as self-sealing. Most knife gate valves use a forced seal. When the valve is closed, an external force is used to force the disc against the valve seat to ensure a tight seal.
Applications of Knife Gate Valves:
Knife gate valves, due to their knife-shaped disc, offer excellent shearing properties and are ideal for difficult-to-control fluids such as slurries, powders, granules, and fibers. They are widely used in industries such as papermaking, petrochemicals, mining, drainage, and food. Knife gate valves offer a variety of seat options and can be equipped with electric or pneumatic actuators to achieve automated valve operation, depending on on-site control requirements.
Advantages of Knife Gate Valves:
1. Low fluid resistance, minimizing erosion and bruising of the sealing surface by the medium.
2. Knife gate valves require less effort to open and close.
3. Unrestricted flow direction, no flow disturbance, and no pressure drop.
4. The gate valve has a simple design, short length, and excellent manufacturing processability, making it suitable for a wide range of applications.
Disadvantages of Knife Gate Valves:
1. Erosion and scratches between the sealing surfaces are common, making maintenance difficult.
2. Large dimensions, requiring sufficient space for opening, and prolonged opening and closing times.