Knife Gate Valves: Working Principle & Function
Knife Gate Valves are generally employed in systems with high suspended particle concentrations for on-off and isolation operations. Knife gate valves come in handy when dealing with slurry, viscous, corrosive, or abrasive fluids. In the fully open position, the valves have a little pressure drop, are easy to use, lightweight, and cost-effective. A knife gate valve cuts through heavy liquid blockages with a blade, whereas a slide gate valve utilizes a slide plate to manage better or regulate the flow of dry bulk material. Knife gate valves were designed specifically for the pulp and paper sector.
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What is Knife Gate Valve?
Knife gate valves are primarily used for on-off and isolation functions in systems with a high suspended solids concentration. Knife gate valves are particularly useful when dealing with slurry, viscous, corrosive, or abrasive fluids. The valves have a modest pressure drop in the fully open position, are simple to operate, have a light weight, and are cost-effective.
Function of A Knife Gate Valve
Knife gate valves get their name from their ability to cut through solid-containing mediums. They operate by elevating a circular or rectangular gate out of the media's path. Knife gate valves are commonly utilized when a straight-line fluid flow with minimal restriction is required. The sealing surfaces between the gate and seats are flat.
Knife gate valves were created with the pulp and paper industry in mind. Stringy pulp impinged between the wedge and seat of a standard gate valve, blocking flow shut-off.
A knife gate valve allows thick media to flow freely over soft seals without being obstructed. The material is chopped up as it passes through the valve, which is how they work. Knife gate valves are now used in a variety of processing plants across the world and are available in a variety of sizes. A thick media flow such as grease, oils, slurry, paper pulp, and waste water can be handled easily with this valve. Knife gate valves have low-pressure restrictions due to this and are designed to seat the blade into a soft seal without causing any disruption.
Working Principle of A Knife Gate Valve
Although the knife edge valve and the butterfly valve have similar appearances, their operating principles are vastly different. The valve disc in a butterfly valve swivels around any fixed axis, performing the valve's opening and closing functions. In the case of a knife edge valve, however, the disc is replaced by a gate that slides up and down to open and close the valve. The gate's edge is sharp enough to easily pierce the flowing media before taking its seat and closing the valve. The viscous flowing fluid may wedge between the edge of the gate and the seats if the gate's edge is not sharpened. This may or may not include effective valve sealing, causing the flow to be hampered. The following diagram depicts the overall operation of the knife edge valve, which was previously discussed.
Types of Knife Edge Gate Valve
The knife edge valve, on the other hand, is a sort of parallel gate valve in and of itself, but it can be further classified based on its shape, actuation, and materials. Knife edge valves come in two basic shapes: round and square, as seen in the diagram below. The shape of the gate's knife edge varies depending on the valve type; for example, a circular valve uses a circular edged gate, whereas a square valve has a straight edged gate.
The knife edge valve can be classified into three types based on how it is operated: manual, electrical, and mechanical. The manual type uses a hand wheel, the electric type uses a stepper motor, and the mechanical type uses a pneumatic cylinder. The valve body and gate are made of stainless steel (SS304 and SS316). It is, however, sometimes manufactured of mild steel to save money.
Advantages and Disadvantages of Knife Gate Valves
Knife gate valves are common because they are low-cost, easy-to-use, and portable. They can also be found in a wide range of businesses and processes. Knife gate valves have a sharp edge that seals the pulp by cutting through it. In applications that require slurry, viscous fluids, and other systems where collision is a concern, the knife gate valve has proven to be highly effective.
Knife gate valves should be used only for applications requiring a completely open or completely closed position and should not be used to regulate flow unless specifically designed for that purpose. When fluid presses against a partially closed gate, a vibration gradually erodes the disc and seat.
Applications of Knife Gate Valves
A knife gate valve can be found in various processing sectors. Larger sizes are offered for thicker flows of heavy oils, slurry, light grease, varnish, pulp, and wastewater. Knife gate valves, on the other hand, have low-pressure limitations.
FAQs about Knife Gate Valve
- What is the purpose of a knife gate valve?
A knife gate valve allows thick media to flow freely over soft seals without being obstructed. The material is chopped up as it passes through the valve, which is how they work. Knife gate valves are now applied in a variety of processing plants across the world and are available in a variety of sizes.
- What is the difference between a knife gate valve and a gate valve?
The most significant distinction between these two types of valves is that gate valves are manufactured to ANSI specifications, whereas knife gate valves are built to TAPPI specifications. A v-ring packing set seals the shaft attached to the gate on a gate valve, whereas a packing gland seals around the gate on a knife gate valve.
- Where are knife gate valves used?
Knife gate valves are used in wastewater treatment plants, chemical plants, mining, cement plants, and a variety of other industrial applications, whereas gate valves are used in drinking water mains, distribution networks, and pump stations.
- What is the difference between a globe valve and a gate valve?
Gate valves: these valves are used to control the flow of water. Globe valves are used to control the flow of water by starting, stopping, and regulating it. The spherical valve body shape that forms around the plug/disc stopper gives it its name.