What is the sealing performance of manual knife gate valve

Manual knife type gate valves are widely used in industrial pipelines, especially in handling media such as mud and slurry, which have great advantages. One of its important functions is "sealing", which means ensuring that the medium does not leak out of the valve. So what is the sealing performance of manual knife gate valves? Let's talk about it in detail below.

How is sealing achieved?

The sealing of manual knife gate valve relies on the tight fit between the gate and the valve seat. When you turn the handwheel to close the valve, the gate is pressed against the valve seat, sealing the passage and preventing the medium from flowing through.

2. Different sealing structures

There are several common sealing methods for manual knife gate valves, each with its own characteristics:

Metal to metal sealing: suitable for high temperature and high pressure applications. Its wear resistance is good, but the sealing effect is relatively average, which means there may be a slight leakage.

Soft seal: The sealing material used here is some soft elastic material, such as PTFE (polytetrafluoroethylene) or rubber. It has a good sealing effect and almost no leakage, but it cannot be used in particularly high temperature and high pressure environments.

Bidirectional sealing: This type of seal is equipped with sealing components on both sides of the gate, so regardless of which direction the medium flows through, the valve can effectively block it, making it more suitable for a wider range of scenarios.

3. Level of sealing performance

The sealing performance of manual knife type gate valves also has levels, which are divided into three common levels according to industry standards:

Class IV: Minor leakage is allowed, but it does not affect use.

Class V: The leakage is very small and almost imperceptible.

● Class VI: No leakage.

What factors affect the sealing effect?

There are many factors that affect the sealing effect, mainly including the following aspects:

Material selection: The sealing material should be able to withstand the medium inside the valve, such as corrosion resistance, high temperature resistance, etc.

Surface smoothness: The smoother the sealing surface, the less likely it is to leak.

● Compression force: When the valve is closed, sufficient pressure is required to press the gate and valve seat tightly to ensure the sealing effect.

Temperature changes: An increase or decrease in temperature can affect the expansion or contraction of materials, which can also affect sealing.

● Medium characteristics: If there are particles or corrosive substances in the medium, it will also affect the sealing.

5. How to improve sealing performance?

To improve the sealing effect, we can start from the following aspects:

Choose high-performance sealing materials such as PTFE and graphite for better sealing effect and longer service life.

Optimization design: For example, using a wedge-shaped design can make the gate and valve seat fit more tightly.

● Increase sealing area: Increasing the sealing area or using multiple seals can improve the sealing effect.

● Regular maintenance: The valve may experience wear and tear on the seals over time. Regular inspection and replacement can maintain good sealing performance.

● Use auxiliary devices: Sometimes auxiliary sealing devices such as stuffing boxes can be added in special applications to further enhance the sealing effect.

6. How to test the sealing effect?

To determine whether the sealing effect is good or not, several tests are usually conducted:

Static pressure test: Simply put, it is to close the valve and apply static pressure to see if it leaks.

Dynamic testing: Simulate the operation of valves under actual working conditions to observe their sealing performance under different conditions.

● Airtightness test: Use gas to detect for minor leaks and measure with sensitive instruments.

Through these tests, we can determine the sealing performance of the valve and whether it can meet the requirements of actual working conditions.

Overall, the sealing performance of manual knife gate valves is one of their core functions, which determines whether the valve can effectively block the medium. Understanding the sealing principle and influencing factors of valves can help us better select and use knife gate valves, and achieve better sealing effects in practical operations.