When the industrial installation is planned there are plenty of options you have to go through. Some of these come with typical usage while some will have specific functions to achieve.
To make the most out of your industrial system you must have a comprehensive approach and get your desired result out of the critical process in the industrial system. The knife Gate valve is one such critical select system component that is widely used in key industrial applications.
What is a knife gate valve? Why use a Knife gate valve?
The knife gate valve was originally introduced in 1927 to be used for pulp and paper industries. Since then it has seen a huge demand for knife gate valves with various options.
The knife gate valve is engineered specifically for on-off and isolation service in the system where abrasive, slurry, and high content of Suspended solids are present.
A knife gate valve is used for handling corrosive, abrasive, slurry, and viscous media.
The valve is designed in a way that it cuts through solid particles with its knife-sharp-like blade which is known as the gate. Knife gate valves for slurry applications are more frequently used. Due to its gate being designed in stainless steel, it is best suited for wastewater applications where corrosion is a concern.
There is minimal pressure drop when it is fully open and is very cost-effective due to its lightweight.
Knife Gate valve application:
Knife Gate valves are designed in such a way that their knife-shaped gate cuts through heavy liquids, and semi-solid, abrasive material. Due to these characteristics, they have the following applications:
- Wastewater treatment plants
- Heavy liquids
- Pulp & Paper industries
- Coal and ash handling application
- Energy & Power plant
- Chemical & petrochemical industries
- Mining plant
- Cement plant
- Abrasive slurry media
- Sand & Gravel plants
- Mineral processing
- Steel plant
- Non-flammable viscous liquids
- Clean water
- Tailing & slurry transport
Parts of Knife Gate valve
How do knife gate valves work?
Knife gate valves are so-called because they have knife shape gates and their ability to cut through media containing abrasive or slurry fluids. Depending on the type of application demand It may have a round or rectangular gate that operates by lifting it up to open and down to close.
The valve operation can be manual or actuated to handle varnish, slurry, waste water, or pulp. These valves should not be used for flow regulation in a condition where the gate is partially closed.
In such conditions, the disk and seat erode over a period of time due to flow vibration. As a result, they should be used in either fully closed or fully open conditions. In addition, these Valves are designed for slow opening and closing to reduce the impact of water hammers.
Installation Guide for Knife Gate valve
- Heavy valves may require a crane system or chain block to assist in the installation process.
- Always wear protective clothing in order to safeguard eyes, face, hand, skin, and lungs from the particular fluids in the line system.
- It may be noted that whenever Air cylinders are provided they should be operated at specified input pressure only, excessive pressure could result in serious personal injury or may cause damage to both valve and cylinder.
- Before you install the valve weld any flanges if that is impossible, and protect the valve from excessive heat.
- Remove any kind of rods, debris, or tools from the pipeline before valves are installed or cycled.
- Always use fasteners in tapped holes to ensure full thread engagement of flange fasteners.
- Use appropriate fasteners for the service in compliance with applicable piping codes and standards.
- If you install a valve with an actuator in a horizontal position then you may need to support the actuator safety.
- Prepare the valve for hydro testing then hydro test system if the valve is leaking then adjust the packing and check sealing.
Types of knife gate valve:
Below you can find in-depth the types of Knife gate valves that evolved over a period of time. It is important to note that some knife gate valves are designed to operate in general-purpose conditions while some of the advanced types are used in critical applications. For reference, you can simply visualize the types of knife gate valves as:
General Purpose Knife Gate valve
- Conventional Knife Gate Valve
- Lined Knife Gate Valve
- Through Gate Valve
- Push-Through Knife Gate Valve
Severe service knife gate valve
- Guided shear Gate valve
Conventional Knife Gate valve
This type of valve was first developed in 1927 in Sweden for the Paper & pulp industry for pulp stock applications. It was an inexpensive option at that time but now it is seen as an outdated option.
Developed in: 1927
Design: This type of design was created in which the wedges of the valve were located at 5 and 7 o’clock positions at the bottom of the port. The wedges push the gate onto the seat when the valve is in fully closed condition.
Where does it work? Widely used in conditions where pressure is low, unidirectional, and general-purpose isolation where the leakage is not a major concern.
Why does it fail? The wedges are located only at the bottom of the port allowing the main area for leakage and depending on the valve size, especially at the top of the seat. The average allowable leakage is 40 cc per inch of diameter per minute. However, it is important to note that the average allowable leakage is based on a differential pressure of 40 psi. Any pressure lower than this will permit for even more leakage
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