This is a type of gate valve which uses a knife gate. This type of valve is suitable for use in slurries and viscous media since the knife gate can cut through such slurries or highly viscous fluids. The design of this valve helps to reduce contact between valve components. As such, there is minimal wear and tear between various components. Knife gate valve manufacturer design these valves for on and off fluid applications. These valves are not suitable for use in throttling applications. These valves can be automatic or they can be operated manually using the valve handwheel. Knife gate valve are made of different materials. The body is always made of strong metallic materials such as stainless steel, carbon steel, and ductile iron.
How does a knife gate valve work?
A knife gate valve works by using a component known as gate. The work of the gate is to close and open fluid flow. The gate gets its power to close and open from the valve actuator or handwheel via the stem. The stem is connected to the valve actuator or the valve handwheel.
To open the valve, the handwheel is rotated in the anticlockwise direction. This rotation of the handwheel makes the stem also rotate in the same direction. The stem has threads that are used to enhance the rotary motion. As the stem rotates, it moves linearly upwards which causes the gate to move upwards leaving space for the fluid to flow through the valve. To close the valve, the handwheel is rotated in the clockwise direction.
As such, the stem rotates in the same direction as it moves downwards. This downward movement of the stem makes the gate also move down until it closes the valve completely.
Types of knife gate valves
1. Through conduit knife gate valve
This is a valve that has high fugitive emissions. This type of valve is suitable for use in applications where there are scales that aid in preventing fluid leakage. This type of valve is designed with two seats and top and bottom gland packing.
2. Hopper shape knife gate valve
This is a valve that has a hopper component at the top. This valve is suitable for handling bulk media. Hopper shape knife gate valve manufacturers design this valve for use in applications such as mining, food, and chemical industries. This valve has the seat positioned in the reverse to prevent seat wear, and valve blockage as well as make it easy to close.
3. Rising stem knife gate valve
This is a knife gate valve in which the stem rises above the handwheel when the valve is being opened. When the valve is closed, the stem moves downwards. This type of valve is convenient to the valve operator as it is easy to know when the valve is closed or when it is opened. However, this type of valve occupies a lot of space and it is recommended for use in applications where space is not limited.
4. Non-rising stem knife gate valve
This is a knife gate valve in which the stem does not rise above the handwheel when the valve is opened. This type of valve is designed with an indicator that helps to know when the valve is closed or is opened. This valve is suitable for use where space is limited since it does not occupy a lot of space like the rising stem type.
Applications of knife gate valves
- Mining applications.
- Chemical industries.
- Pharmaceuticals applications.
- Foods and beverages.
- Hydrocarbon applications.
Advantages of knife gate valves
- These valves are versatile.
- They are durable.
- They have a low-pressure drop.
- They are light in weight.
- They are free from fluid leakage.
Disadvantages of knife gate valves
- These valves do not close easily like a ball or globe valves.
- They are not suitable for use in throttling fluid flow.