Knife Gate Valve
Knife Gate Valve
※ Wafer or Lug Type
※ Size Range: NPS 2 to NPS 24
※ Pressure Range: 150LB/ PN10~PN25
※ Design STD.: MSS SP-81/ ASME B16.34
※ Knife Gate Valve Manufacturer & Supplier
Knife Gate Valves are introduced to the world to be used in the pulp and paper industry. Where a normal gate valve is not working efficiently to cut through & stop the flow of heavy liquids.
As the name suggests, in a Knife Gate Valve the gate has a sharp knife edge to cut through the dense liquids and the liquids with a high number of suspended solids. Knife Gate Valves show a minimal pressure drop compared to other types of valves when used in a fully open position.
In this article, we will try to learn more about Knife Gate Valve and will get a brief idea of its features, application, construction, and working.
What is a Knife Gate Valve?
Knife gate valves are named from their ability to cut the medium with suspended particles. They operate by removing a circular or rectangular gate out of the media’s path. Because the sealing surfaces between the gate and the seats are flat, knife gate valves are frequently employed when a straight-line flow of fluid with the least amount of restriction is required.
Knife gate valves were specifically developed for the pulp and paper industry’s needs. This was due to sticky pulp impinging in between the edge and seat of a conventional gate valve, preventing flow shut-off.
Knife gate valves are designed to perform open and shut operations in industrial piping systems where the fluids have a high density and high content of suspended solids. The gate in these types of valves is specially made of stainless steel with a sharp edge at the bottom. This combination of the knife edge and stainless steel is highly recommended for slurries, viscous, corrosive & abrasive fluids as stainless steel has high resistance to corrosion and can also be used to make long-lasting knife edges.
Construction: Knife Gate Valve.
A knife gate valve has the same basic components as a standard gate valve, including a valve body, a gate, a stem, and a working handle (manual or automatic). The main design difference is in the design of the knife edge gate used.
Knife gate valve manufacturer provides manual and pneumatic Soft and Metal Seated Stainless Steel Knife Gate valves in unidirectional and bidirectional designs. Knife Edge Gate Valves are made to withstand extreme conditions. Knife Gate Valves have a one-piece full port cast stainless steel body that is completely lugged and exceptionally robust in design to handle the most demanding applications and assure maximum flow capacity with very little pressure drop.
Gates consisting of stainless steel and other superior alloys are machined with a super surface polish on both sides to ensure positive shutdown in Knife Gate Valves. The gland pockets are machined and carefully polished, ensuring a leak-proof gland packing and a flawless stem seal. Uni-Directional / Bi-Directional High-Performance Knife Gate Valve gives greater value and performance with numerous common features that other valves lack.
Working: 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 travels through the valve, which is how they function. Knife gate valves are now employed in a variety of processing facilities across the world and are available in a variety of sizes. This allows the valve to handle thick media flows such as grease, oils, slurry, wastewater, and paper pulp with ease. Knife gate valves have low-pressure restrictions as a result of this and are intended to seat the blade into a soft seal without causing any disturbance.
Classification: Knife Gate Valve.
Knife gate valves can be classified in four different ways:
- By Body Material: Knife gate valves are made from a wide range of materials. Common materials used include cast carbon steel, cast iron, ductile iron, gunmetal, nickel, alloy steels, stainless steel, and forged steel. Sometimes exposed parts of the knife gate valves are lined to make them thermally stable, chemically resistant and to enhance their mechanical properties. This is generally recommended for the food processing industry. The fluid service and design temperature are the most important factors in determining the material used in gate valves.
- By End Connection Type: The valve’s end connection is typically recognized by the use and compatibility of the valve; for example, screwed type ends are used with less expensive valves, bolted type ends are the most frequent of all types, and a gasket is used for sealing. Pressure seal ends are used when system characteristics such as temperature and pressure are high. Welded kinds are used for permanently placed valves, and pressure seal ends are used when system parameters such as temperature and pressure are high.
- By Sealing Method:
- Metal seated wedge gate valves were extensively employed prior to the development of the resilient seated gate valve. The conical wedge design and angular sealing devices of a metal seated wedge require a groove in the valve bottom to ensure a tight closure. The bore is still full of sand and stones. The pipe system will never be completely free of contaminants, no matter how effectively it is flushed during construction or maintenance. As a result, any metal wedge’s capacity to be drop-tight would deteriorate with time.
- The valve bottom of a resilient seated gate valve is basic, allowing sand and stones to easily flow through the valve. Impurities may travel through the valve when it shuts, causing the rubber surface to seal around them. When the valve closes, contaminants are trapped inside a high-quality rubber compound, which is flushed out when the valve is opened again. The rubber surface would revert to its previous shape, assuring that the seal was watertight.
- By Stem Type:
- Rising stems are attached to the gate and rise and fall at the same time as the valve is opened and closed, providing a visible indicator of the valve position and allowing the stem to be greased. A nut revolving around the threaded stem moves it. This type of valve has an inside screwed stem due to the up and down movement and turning motion of the stem, and the packing is prone to wear. This kind is only suitable for installation above ground.
- Non-rising stems are threaded into the gate and spin with the wedge rising and falling inside the valve. Turning the wheel opens the valve, but the stem does not come out of the housing. They take up less vertical space since the stem is enclosed inside the valve body. Non-rising valves always have a local visual signal that displays the valve’s position. Gate valves with non-rising stems can be utilized in both above-ground and below-ground applications.
Types: Knife Gate Valve.
There are 3 major types of Knife Gate Valves.
- Wafer type knife gate valve: The gate on this sort of knife gate valve is uniquely engineered to work in both directions. This type of KGV’s gate is wedged between its flanged connectors. This design prevents the valve from clogging during shut-off.
- Through conduit knife gate valve: The valve seat is replaced by two body seats and a top and bottom packing gland in this kind. When the valve is entirely closed, these seats seal it. This valve has a significant amount of through leakage and fugitive emission.
- Hopper shaped knife gate valve: This form of KGV is designed to be unidirectional. These are designed for applications requiring bulk handling services. The unique form of the body allows for smooth fluid passage, making it perfect for use as a silo discharge valve.
Technical specification: Knife Gate Valve.
- Size Range : NPS 2 to NPS 48
- Class Range : 50LB to 2500LB
- Design Standard : ISO 5208 / API 596
- End Connection : Flanged; BW; Threaded
- Operation : Manual Lever / Pneumatic / Electrical
Special Feature: Knife Gate Valve.
- It’s a full-Bore valve and allows the liquid of any density or viscosity to pass through it easily.
- There is no cavity below the gate so the accumulation of solid particles is not possible.
- These are supplied with gate scrapers and deflector cones for impure or abrasive media, these are also referred to as self-cleaning valves.
- Their unibody and rugged heavy-duty nature make them long-lasting with greater reliability, easy to maintain, and have a low-cost installation.
- These are bi-directional valves so there is no limitation of flow direction.
- It has a wafer-style construction which saves pipeline space.
Advantages: Knife Gate Valve.
- The knife gate valve has a simple and unibody design which makes them robust, maintenance-free & economical.
- They can be installed in any position.
- Flow can be in both directions.
- They are suitable for high temperatures and pressure.
- The valve length of these valves is comparatively shorter even for large diameters.
- Can be used for corrosive media.
Application and Uses: Knife Gate Valve.
Knife gate valves are built to withstand the toughest conditions, with a sharpened blade that can cut through thick and heavy liquids.
They’re particularly beneficial in wastewater applications where corrosion is a major concern. So, in addition to the valve design optimized for slurry media, having a knife made of acid-proof stainless steel is advantageous since it is less prone to corrosion damage and so requires less regular maintenance.
Knife gate valves should only be used for applications that need a totally open or completely closed position, and should not be used to control flow unless they are specifically designed for that purpose. A vibration occurs whenever fluid is pressed against a partly closed gate, progressively eroding the disc and seat.
Knife gate valves are in great demand in industries that deal with viscous materials due to their ability to manage thick liquids. These valves are designed for applications involving difficult-to-clean materials. Knife gate valves are utilized in the following industries:
- Wastewater processing Industry.
- Paper pulp Industry.
- Steel Plants.
- Slurry Transport.
- Heavy Oil Industry, etc.
To summarise, the normal type of gate valve will not beneficial in industries that handle high density and high viscosity fluids because it will clog the valve and prevent flawless sealing. To avoid this problem, valve manufacturers developed the knife gate valve.
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