To determine whether the sealing performance of a valve is good, the following methods can be used:
1. Visual inspection
Check the surface of the valve for any wear, scratches, cracks, deformations or corrosion and other damages. These problems may lead to poor sealing. Particular attention should be paid to inspecting the sealing surface, such as the contact surface between the valve disc and the valve seat. If there are wear grooves or pits, it will affect the sealing performance.
Check whether there is any medium leakage at the valve stuffing box. If there is leakage, it indicates that there is a problem with the packing seal, which may be due to aging, wear of the packing or insufficient clamping force.
2. Pressure test
Strength test: Usually conducted before the valve is installed. Close the valve, fill the valve body with the medium (such as water or air) at the specified pressure, and keep it for a period of time (such as 5 to 15 minutes). Observe whether there is any leakage or deformation in the valve body, stuffing box and other parts. If the shell shows no cracking, no obvious deformation, and the pressure does not drop significantly, it indicates that the valve's strength is qualified and its sealing performance is initially good.
Sealing performance test
One-way seal test: For one-way seal valves, such as check valves, fill the medium from the specified inlet end. After reaching the specified pressure, observe whether there is any medium leakage at the outlet end. If there is no leakage at the outlet end, it indicates that the one-way sealing performance is good.
Bidirectional sealing test: For bidirectional sealing valves such as ball valves and gate valves, the medium is filled from both sides of the valve respectively for sealing tests. Under the specified pressure, observe whether there is any leakage on the other side and in the stuffing box and other parts. If there is no leakage on either side, it indicates that the valve has good bidirectional sealing performance.
Bubble detection method
For some valves on low-pressure pipelines, they can be placed in water. After closing the valve, a certain pressure of gas can be introduced into the valve body. Then observe whether there are any bubbles emerging around the valve. If there are bubbles, it indicates that there is a leakage and the sealing performance is poor. This method is applicable to gate valves, ball valves, butterfly valves and other valves with a nominal pressure not exceeding 1.6MPa and a nominal diameter not exceeding 400mm.
Ultrasonic detection
The leakage of the valve sealing surface is detected by using an ultrasonic detector. When the valve is closed and there is medium pressure, if there is a leakage at the sealing surface, the leaking medium will generate an ultrasonic signal. The detector can capture this signal and determine the location and degree of the leakage by analyzing it. This method can be carried out while the valve is in operation without affecting production, but it requires professional equipment and technicians to operate.
Pressure drop detection
Install pressure sensors before and after the valve to monitor the pressure changes before and after the valve when it is closed. If the pressure drop exceeds the allowable range within a certain period of time, it may be due to poor sealing performance and medium leakage causing the pressure drop. However, this method is influenced by multiple factors, such as the stability of the pipeline system and the characteristics of the medium, and a comprehensive analysis and judgment are required.
