1. Criteria for judging internal leakage of valves
4-6 hours after the valve is closed, use an infrared thermometer 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 considered “internal leakage”. This judgment method is applicable to most internal leakage valves.
But in actual work, we encountered the following special situations:
① Due to the installation position of the pipeline, there is disturbing high-temperature steam in front and behind some valves, such as drain doors or sewage doors connected to pressure drains and jellyfish pipes. Even if these valves are tight and leak-proof, the valve stem temperature It will also exceed 70℃.
② Traps or sewage doors connected side by side to the drainage and discharge 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 the other valves will rise and even exceed 70℃, such as boiler blowdown valves, superheated steam drains, etc. Therefore, other methods must be used to determine the internal leakage of these valves. Generally, the temperature of the pipe wall in front of the door or the temperature of the valve stem in front of the door is measured to determine the internal leakage.
2. Precautions when operating the valve
① For each manual water drainage door of the thermal system, it should be tightened again half an hour after the operation is completed to eliminate valve gaps caused by thermal expansion and contraction.
② For thermal pipelines equipped with primary and secondary doors, the valve operation sequence is: when opening, the primary door should be opened first, and then the secondary door should be opened; when closing, the secondary door should be closed first, and then the door should be closed once.
③ For the operation of the gate valve, it can only be fully closed or fully opened. Half-open and half-closed states are not allowed to reduce blow damage to the valve.
3. Precautions in valve management
① Test each electric and pneumatic valve before starting the unit. During the test, a dedicated person should monitor the action of the valve and baffle on the spot, check that the connecting rod and pin of the actuator should not be loose, bent or fallen off, and check the DCS. The opening indication should be consistent with the local indication.
Electric doors with intermediate stops should be tested for normal intermediate stops.
The direction of the adjustment door switch is correct and the movement is flexible. If there is an interlocking circuit, the interlocking test must be carried out in conjunction with the relevant professional. The pneumatic adjustment device should be tested with flexible movement and no air leakage or abnormal phenomena. If any abnormality occurs during the test, the test should be stopped and notified in time. Maintenance personnel will handle it.
② Each time the unit is started, the corresponding operations should be strictly carried out according to the “Operation Ticket”. Each drain door should be checked and closed according to regulations. After 6 hours (within 10 hours) after each drain door is closed, there will be a temperature indication behind the drain door. If there is no temperature indication behind the drain door, use an infrared thermometer to measure the temperature of the pipe walls at the front and rear of the valve or use hand feel to determine whether the valve is leaking.
If there is internal leakage in the electric or pneumatic valve, the manual isolation door in front of the hydrophobic electric door or pneumatic door should be closed. If there is no manual isolation door in front of the hydrophobic electric door or pneumatic door, if the internal leakage is large, the electric door should be closed manually. And register the vacancy and contact for maintenance. If there is leakage in the manual door, log in and contact for maintenance.
③ Before each unit is shut down, a comprehensive inspection should be carried out for valve defects (leakage). Leaking valves should be logged and the relevant maintenance departments should be notified.
④ During the process of starting and stopping the machine or discharging water under pressure, after opening the water drain (drainage) door, you should check whether there is temperature behind the valve or throttle hole (steam trap) to ensure that it can drain (drain) water and prevent Corrosion caused by water accumulation in thermal pipes due to clogged valves or pipes or orifices (traps).