What are the judgment standards for valve internal leakage and precautions during operation?

Method of judging valve internal leakage

After the valve is closed for 4-6 hours, use an infrared temperature measuring instrument to measure the temperature of the valve stem (near the valve body) or the metal temperature 150mm downstream of the valve body. If it is greater than 70°C, it is regarded as “internal leakage”. This judgment method is applicable to most internal leakage valves.

But in actual work, we encountered the following special situations.

01 Due to the location of the pipeline, there are disturbing high-temperature steam before and after some valves, such as traps or sewage gates connected to the pressure drain and drain pipes. Even if these valves are tight and not leaking, their stem temperature It will also exceed 70°C.

02 The drain gates or sewage gates connected side by side to the drain and drain main pipes. When the last valve is close to the main pipe, as long as any branch valve in the pipeline leaks, the temperature of other valves will rise to more than 70°C. Such as boiler blowdown valve, superheated steam drainage, etc. Therefore, other methods should be used to determine the internal leakage of these valves, generally measuring the temperature of the pipe wall in front of the door or the temperature of the valve stem in front of the door to determine the internal leakage.

Matters needing attention during valve operation:

01 For manual water release doors in various parts of the thermal system, they should be tightened again after half an hour of operation to eliminate valve gaps caused by thermal expansion and contraction.

02 For thermal pipelines with primary and secondary doors, the valve operation sequence is as follows: when opening, the door should be opened first, then the second door; when closing, the second door should be closed first, and then the door should be closed again.

03 For the operation of the gate valve, it can only be fully closed or fully open, and half open and half closed are not allowed to reduce damage to the valve.

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