Knife Gate Valves (KGVs) were made in 1927 for use in the pulp and paper industry. When the least cost valve for pulp stock operation was in demand, the specialized knife gate valve was made and introduced to the world. Since then, KGVs have been used around the world. There have been some variations to meet needs, like the introduction of the push-through knife gate in the US and the guided shear gate in Switzerland.
“Knife gate” is a general term for all valve versions. The Guided-Shear Gate and its higher-caliber variant are the only knife valve versions that can cut through the media like a knife.
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In this blog article, we will describe knife gate valve classification, how it works, types, industries served in, and special applications.
What Is a Knife Gate Valve?
Knife gate valves are specifically designed for on-off and isolation operations in systems with highly dissolved solid particles. KGVs are incredibly helpful in different situations, such as abrasive, corrosive, viscous media, and slurry. When in a fully open position, there is a low drop in pressure, it is lightweight, simple to use, and highly cost-effective.
The knife gate valve design has a sharpened blade for cutting heavy liquids and thus it can be used for the hardest conditions. Since corrosion is a major issue, KGVs are incredibly helpful in wastewater applications. With valve design for slurry media, having KGV in acid-proof stainless steel is highly advantageous because it is less susceptible to corrosion and requires less frequent maintenance.
Use KGVs only for fully open and completely closed positions, and only for regulating flow when they’re specifically designed for this purpose. Vibration occurs when the liquid is pumped against a slightly closed gate that corrodes the disc and seat. Also, open and close KGVs slowly to avoid the outcome of the water hammer.
Knife Gate Valve Classification
Knife gate valves can be classified based on the various factors:
1. By Body Material
A variety of materials are used in constructing KGVs. Cast iron, ductile iron, gunmetal, nickel, alloy steels, cast carbon steel, and stainless steel are some common examples of used materials. The fluid service and the design temperature are key determining factors of the used material.
- Carbon steel knife gate valve: Carbon steel has tensile strength, impact value, and high hardness. Its frequent use is in high-temperature and high-pressure industrial plants.
- Stainless steel knife gate valve: Stainless steel is costly but is used because of its higher corrosion resistance, low-temperature resistance, mechanical strength, and heat resistance.
- Lined valves: They are naturally chemically resistant, thermally stable, and have strong mechanical properties. Their superior workability enables them to be used to offer valve-wet parts with fin lining.
2. By Stem Structure
A threaded valve stem controls the knife gate valve that connects the actuator (hand or motor) to the gate. Based on the threaded end, they are categorized as rising or non-rising stems.
- Rising stems: They are attached to the gate. As the valve operates, they rise and lower together, offering a visual indicator of the valve’s location. The nut-shaped actuator’s rotation around the threaded stem causes lifting or lowering.
- Non-rising stems: They are threaded to the gate. Stems are attached to the gate and rotate with the actuator. Because the motion is concealed in the valve, it demonstrates its location by pointing a thread to the upper end of the stem. Non-rising stems are used in places where vertical space is limited or underground.
3. By Connection Type
The requirements and perfection of the valve determine the end connection of the valve. For instance, wafer-type knife gate valves and lug-type knife gate valves have the most common flanged-type ends. A gasket is used for sealing.
4. The Sealing Method
- Metal seated knife gate valves: The use of metal seated knife gate valves was common before the introduction of resilient seated knife gate valves. A conical wedge construction and angular sealing devices of a metal-seated wedge were essential for a dip in the valve bottom. When the sand and pebbles are tapped in the bore, the pipe won’t be purified of impurities so that it can be well flushed during installation or repair. It causes metal wedges to become less drop-tight over time.
- Resilient seated knife gate: It has a simple valve bottom that allows sand and pebbles to pass freely. The rubber surface can encase impurities that go through the valve when it’s shut. In contrast, a top-notch rubber compound includes impurities and expels them when the valve is in the open position. This rubber surface gets back to its original position to provide a watertight, original-shaped seal.
5. By Design
- Hopper-shaped knife gate valve: It is uni-directional by design. Their design is for bulk handling services. The design allows easy flow of the fluid and thus it is preferable to use it as a silo outlet valve.
- Uni-directional: They are designed for general applications in the industry. The design and seat ensure the non-clogging shutoff of suspended solids.
- Bi-directional: They are for functions from inlet to outlet, or inlet outlet. It controls flows and pressures in both directions.
Knife Gate Valve vs Gate Valve
The major difference lies in the mediums they use.
- Knife Edge Valves are the best for handling slurry, powder, or granules more efficiently than Gate Valves because there’s a requirement for clear media to function properly.
- Gate valves are also not designed for highly viscous media, while knife gate valves are.
- Another difference is that gate valves follow ANSI standards and knife gate valves meet TAPPI standards.
- Gate valves are bi-directional and only have metal seating for their extensive fluid applications.
- The packing gland is another difference. A v-ring packing set ceases the shaft in the gate valve connected to the gate. In knife-gate valves, a gland region seals around the gate.
Thus, knife gate valves are efficient for industries like paper, stringy food products, process plants, stringy food products, cement, and more.
How Does a Knife Gate Valve Work?
A knife gate valve has a component with a knife used to cut through heavy liquid clogging. These valves were designed for some of the world’s harshest corrosive and abrasive conditions. The use of KGVs has become essential in viscous liquids, slurry, and other systems where impingement is an issue because of their extremely effective design.
The use of KGVs has now extended to many processing plants. They are now available in large sizes for accommodating high-density flows of varnish, slurry, wastewater, heavy oils, and more. These valves have low-pressure constraints. They are meant to be placed in an elastomer seal after use. The thick and dry material ends up on the soft seals on the gate and ends as a solid mass or powder passes through the knife gate. If it happens, seals will fail to be tight enough. Seals need to be replaced when this happens.
Advantages of Knife Gate Valves
Knife Gate Valves have several advantages that help users get things done easily and quickly.
- They are easy to activate with mechanical, electrical, or pneumatic means.
- Their lightweight design makes transport, storage, installation, and maintenance easier.
- They are extremely cost-effective.
- Many specially designed KGVs can also be used for non-volatile, non-flammable viscous fluids.
- They open and close slowly for protection against the water hammer.
Because of these advantages, knife gate valves are used for various purposes like paper production, slurry, and viscous media.
Applications of Knife Gate Valves
Knife Gate Valves are specifically designed to meet needs in some of the harshest conditions. Typically, it has a sharpened blade to cut through heavy liquids. Applications of KGVs are:
- In wastewater treatment plants corrosion is a major issue there.
- It is used in slurry media because an acid-proof stainless steel knife is less susceptible to damage due to corrosion and requires less frequent maintenance.
- KGVs are used in paper production.
- Knife gate valves also have applications in the cement industry.
- KGVs are extensively used in the oil and gas, chemical, power, and mining industries.
Make sure you don’t use them to regulate flow unless it’s designed for a specific purpose because of their use in completely open and closed positions. It can erode the disc and seat.
Maverick Valves is a solution for many industries, including water and sewage treatment, paper and pulp, oil and gas, chemicals, cement plants, and mining. Refining quality and design is done to meet these challenges.
A fully advanced range of KGVs is available to meet the expectations of each sector. Manufacturers understand the needs of customers and promise less downtime economically.
Knife Gate Valves for Special Applications
Knife gate valves have applications in several industries. With some refining, these knives are designed for different purposes. The Maverick Valves Knife is designed fully in compliance with MSS SP 81 and MSS-SP 148 standards. It is customized to meet challenges like critical media and abrasive slurry in industries like water and sewage treatment plants, metal and mining, paper and pulp, chemical, and oil and gas industries.
The compact design of valves requires less space for installation, and being lightweight makes operations and maintenance easy. The knife-like bottom design is for cutting through semi-solid and sludge media to avoid clogging. Variable metallurgy and trim options are available to make them feasible for critical applications.
Knife Gate Valve Maintenance Guide
Knife Gate Valves are used for providing isolation in several applications. It is one of the simplest, with only one moving part. It makes preventive maintenance simple and quick.
For maintenance, take the following steps:
- Ensure packaging maintenance once a month.
- Use lubricant for the stem and stem nut every 3 months. You can also use a grease machine for grease-fitting the yolk. Furthermore, lubricate the gear controller annually.
Get Your Knife Gate Valve from Trusted Distributor Ocean
Knife gate valves are super helpful in a variety of uses in different industries because they are lightweight and can be utilized in the harshest conditions economically. Key takeaways are:
- KGVs were introduced in 1927 and have since been in use with modifications in different industries.
- They are classified based on construction material, stem structure, connection type, and sealing methods.
- KGVs are available in a variety of larger sizes to accommodate the needs of different industries.
- Hopper, through conduit, uni-directional, bi-directional, etc. are different types of knife gate valves.
- Chemical, cement, oil and gas, paper, and mining are some industries where KGVs are used.
The design of knife gate valves aids in eliminating problems to allow higher production and lower costs of labor and materials.
If you are looking for a knife gate valve distributor from a reputable engineering company in Oman, Ocean is a wise choice. Our expertise services and reliability ensures that you receive the right product with exact specification and can trust for your specific needs. We offer vibration analysis services, partial discharge services, machine diagnosis services, and much more. Don’t compromise on the performance and safety of your systems; choose Ocean for your knife gate valve requirements.