In 1927, the Swedish pulp and paper industry sought an inexpensive valve for pulp stock applications, giving rise to the revolutionary knife gate valve design. Since then, these valves have undergone several modifications and are now used in various industries worldwide.
Interestingly, the Push-Through Knife Gate was first developed in the United States, while the Guided Shear Gate emerged in Switzerland. While all versions of this valve are referred to as “knife gate,” it’s important to note that only the Guided-Shear Gate and its advanced adaptation, the Severe Service Knife Gate Valve (SSKGV), can effectively slice through materials like a sharp knife.
If you want to explore the different types and parts of knife gate valves and learn about their applications in different industries, this blog is for you. Read on to find out more.
What is a Knife Gate Valve?
A knife gate valve is primarily used for the on-off isolation of fluids with high consistency and solid content, such as sludge or sewerage. Unlike standard gate valves, knife gate valves feature a simple metal plate for the gate, which is typically chamfered at the edge to aid in cutting through the product. These valves are typically used for uni-directional, and in some cases bi-directional, flow control, providing pressure-tight isolation of solid-liquid mixtures in various industrial applications. This valve is also ideal for applications where other valves may become clogged or fail to provide reliable isolation.
Types of Knife Gate Valves
Knife gate valves come in a variety of types, each designed to suit specific applications and industry needs. Choosing the right type of knife gate valve can help ensure the valve performs effectively and efficiently.
Through Conduit Knife Gate Valve
This valve has a smooth, unobstructed flow path with no pockets or cavities for materials to accumulate, making it ideal for handling slurries and fluids with high solid content. The design of this valve enables it to achieve a full-bore flow, minimising pressure drop and maximising flow capacity. Its usage is common in mining, chemical, and wastewater treatment applications.
Hopper Shape Knife Gate Valve
The hopper shape knife gate valve is a unidirectional valve designed for bulk handling services applications. The unique design of the valve body allows for easy passage of fluids, making it an ideal choice for use as an outlet valve for silos and other bulk storage facilities. This type of valve is commonly used in power plants, food and beverage industries, chemical plants, and mining.
To prevent issues like seat wear, difficulty in closing, and build-up in the valve body, hopper shape knife gate valves are typically installed in the reverse position with the seat facing upstream. It helps to ensure efficient and reliable performance of the valve in many demanding applications.
Rising Stem Knife Gate Valve
A rising stem knife gate valve has a stem that moves up and down as the valve is opened or closed. This design allows for a clear visual indication of the valve’s position, making it easy to tell whether the valve is open or closed. The stem also serves as a connection point for actuation, which can be manual or automated. These valves are commonly used in applications where the thread on the stem needs to be isolated from the fluid, such as in corrosive or abrasive environments.
Non-rising Stem Knife Gate Valve
This type of valve is similar to the rising stem knife gate valve but has a stem that does not rise as the gate is opened. Instead, the stem threads into a separate gate nut which is directly attached to the gate. As the stem rotates, the gate nut and subsequently the gate moves up and down. Non-rising stem knife gate valves are ideal for applications with limited vertical overhead space and are used in food processing and pharmaceutical industries.
Parts of Knife Gate Valves
Understanding the parts of a knife gate valve is important to properly maintain and operate the valve. Let’s take a closer look at the various parts of a knife gate valve.
The Gate
The gate is the primary component of a knife gate valve that slides back and forth to control the flow of fluid. It is usually made of stainless steel or other corrosion-resistant materials and has a sharp knife-like edge to cut through thick fluids and slurries. The gate’s design varies according to the type of knife gate valve.
Valve Body
It is the outer casing that holds the gate and other internal parts. It provides the necessary structural support and contains the inlet and outlet connections. The valve body can be made of various materials, such as cast iron, stainless steel, or plastic, depending on the intended use and the fluid being handled.
Valve seat
The valve seat provides a seal around the gate when it is in the closed position. It is usually made of an elastomeric material, such as rubber or polyurethane, and ensures tight shutoff to prevent leakage.
Stem
The stem connects the handwheel or actuator to the gate. It moves up and down as the handwheel is turned, raising or lowering the gate to control the flow of fluid. In a rising stem knife gate valve, the stem also provides a visual indication of the valve’s open or closed position.
Handwheel
The handwheel is used to manually operate the knife gate valve. It is usually located on top of the valve body and rotates the stem nut, which in turn opens or closes the gate. The handwheel can be made of various materials, such as cast iron, stainless steel, or plastic, and can be designed with different grips and diameters to suit the application.
Each component of the knife gate valve is designed to work together to provide reliable isolation and flow control, preventing fluid leaks and minimising the risk of downtime and costly repairs.
Applications of Knife Gate Valves
Knife gate valves have a wide range of applications due to their ability to handle high-consistency fluids and slurries. Some common industries where knife gate valves find their applications include:
- Mining Industry
In the mining industry, knife gate valves are used for abrasive slurry applications such as mine tailings, hydro cyclone feed, and thickener overflow. They are suitable for handling abrasive and corrosive media, commonly found in mining operations. - Pulp and Paper Industry
The pulp and paper industry uses knife gate valves for handling slurries such as wood pulp, paper stock, and black liquor. Knife gate valves are ideal for this industry because of their ability to slice through thick and viscous fluids, as well as their resistance to clogging and fouling. - Wastewater treatment plants
In wastewater treatment plants, knife gate valves are responsible for isolating and controlling sludge and other waste materials. The valves are designed to handle the challenging environments and corrosive fluids present in wastewater treatment facilities. - Food and Beverage Industry
The food and beverage industry uses knife gate valves for handling dairy products, sauces, and other viscous materials. The valves are ideal for food processing applications because they are easy to clean and can cut through high-viscosity fluids. - Chemical and petrochemical industry
In the chemical and petrochemical industry, knife gate valves are used for handling corrosive and hazardous materials such as acids, caustics, and solvents. The valves are of a robust construction making them suitable for use in chemical and petrochemical plants.
Advantages of Knife Gate Valves
Knife gate valves are an essential component of many industrial processes, offering a range of advantages that make them a popular choice in various applications.
High flow capacity
The full-bore design of these valves allows for an unobstructed flow path, which reduces pressure drop and enables the valve to handle high volumes of fluid. This makes them particularly suitable for applications that require the rapid opening and closing of the valve.
Compact design
Knife gate valves have a compact design that makes them ideal for applications where space is limited. They can be easily installed in tight spaces and can be fitted with actuators which allow for remote operation.
Low maintenance
Knife gate valves have a simple design with few moving parts, which result in lower maintenance requirements compared to other valve types. The valve’s gate and seat materials are also durable and resistant to wear and corrosion, which further reduces the need for maintenance. Valves fitted with resilient seats allow for the easy replacement of the seat if needed.
Cost-efficiency
Compared to other types of valves, knife gate valves are relatively inexpensive, making them a low-cost option for various industrial applications.
Bi-directional flow
Some knife gate valves are designed to allow flow in both directions, making them highly versatile and suitable for a wide range of applications.
Efficient flow control
Knife gate valves are specifically designed for handling fluids with high consistency and solid content. The flat gate with a sharp edge allows for efficient flow isolation, preventing clogging and reducing maintenance.
Where to Buy Knife Gate Valves
At John Valves, we are the leading manufacturers and go-to suppliers for high-quality knife gate valves. Our valves are designed and manufactured to the highest industry standards, ensuring reliable and efficient performance in a wide range of industrial applications. Whether you need a standard valve or a customised solution for your specific needs, we have the expertise and experience to deliver the right product for you.
Contact us today to learn more about our knife gate valves and how we can help meet your flow control needs.
