Valve upper sealing problem
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Today I read the "SH3518-2000 Valve Inspection and Management Regulations" about valve pressure test regulations. There is an upper seal pressure test. I don't know what it means. Do you open the valve and pressurize it to see if there is leakage at the valve stem packing? According to my daily work experience, when the gate valve stem rises to the top, it can seal the packing and seal the cavity. I don't know if this is correct. It would be great if the expert could provide a clear structural diagram of the gate valve. It should be easy to understand at a glance. I've searched online, but I can't seem to find it clearly.
Your guess is correct. This is how you check the upper seal of stop valves and gate valves. Generally, you need to leave it for more than ten hours after being pressurized, and then open it and listen to whether there is a deflation sound like opening a soda drink to determine whether the upper packing is leaking. .
The upper seal of the valve is an effective structure for replacing the packing under pressure when the valve stem packing seal leaks during production. I have used this method to replace the packing several times at work, and achieved good results. However, it was only used in parts with relatively low medium pressure and temperature, and I did not dare to use it in high-pressure and high-temperature parts. The structure of the upper seal is an inverted cone-shaped component on the valve stem, which can form a seal with the valve cover when the valve is fully open. After confirming that the medium does not come out, unfasten the packing gland and replace the packing. When testing the pressure of the valve, it is also necessary to unfasten the packing gland and listen to the sound to confirm whether there is any leakage.
Sealing performance The sealing performance of a valve refers to the ability of each sealing part of the valve to prevent medium leakage. It is the most important technical performance index of the valve. There are three sealing parts of the valve: The contact point between the two sealing surfaces of the opening and closing parts and the valve seat ； The matching of packing with valve stem and stuffing box ； The connection between the valve body and the valve cover. The first leakage is called internal leakage, which is commonly referred to as lax sealing. It will affect the valve's ability to cut off the medium. For cut-off valves, internal leakage is not allowed. The latter two leaks are called external leakage, that is, the medium leaks from inside the valve to outside the valve. Leakage will cause material loss, pollute the environment, and even cause accidents in severe cases. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the valve must have reliable sealing performance. I have a gate valve diagram, but I can't upload it. Give me your email and I'll send it to you! !
I have a gate valve diagram, but I can't upload it. Give me your email and I'll send it to you! !