cryogenic gas cylinder Dewar maintenance and repair

Leak detection　In order to ensure the normal operation of the gas cylinder, the system must be regularly checked for leaks. If any leaks are found, they should be repaired immediately. You can use soapy water to accurately determine the leak.

Leak repair
　　Regarding any leakage of Dewar, it must be repaired as soon as possible:
      • If the pressure vessel is leaking from the thread of the connector pipe behind the valve, disconnect the valve after closing the valve, check the thread surface for damage, clean the thread surface of the joint if there is no damage, and reassemble using the specified sealing tape; if the thread surface is obviously damaged , Please replace the connector and reassemble.
      • If a leak is found at the root of the safety valve of the gas cylinder, the pressure gauge or bursting disc, and the ferrule of the combined regulator valve, the vent valve must be opened to relieve the pressure to atmospheric pressure before starting maintenance. After reinstallation, perform a pressure leak check.
      • If the valve or valve seat leaks, first open the discharge valve to relieve the pressure to atmospheric pressure. If the leak point is found at the inlet and outlet valve, booster valve, gas use valve and pressure regulator ferrule joint, the liquid and The gas is completely vented, and then operate according to the installation procedure of the stop valve.
　　
Dewar Parts replacement
　　This part includes the knowledge of cylinder maintenance and maintenance. Before operating according to the following procedures, you should first check the operation records of cylinders and assembly drawings of parts, and determine the correct position according to the drawings.
　　• Level gauge
　　Long-term use of the liquid level gauge may be inaccurate due to the aging of the spring, and the dewar level gauge can be calibrated again.
　　 1. First vent the pressure in the air bottle, remove the protective cover bolts, and remove the protective cover.
　　 2. Use a wrench to separate the level gauge from the bottle and take out the level gauge.
　　 3. Fully immerse the aluminum float rod of the liquid level gauge in the water. Note that the float rod must be vertical and must not touch the side wall of the water container.
　　 4. The level indicator (special for liquid oxygen cylinder) indicates the full range. If the level gauge is not taken out of the water for full scale, loosen the lock nut under the spring and turn the screw to adjust. Then immerse in water to check the set value, and tighten the lock nut after correct.
　　 5. After calibration, after the level gauge is dry, reinstall the level gauge.
　　 6. Check the sealing gasket before installation. If there is any damage, replace the gasket.
　　 7. During installation, let the level gauge droop freely and keep it vertical, and slowly put the level gauge into the gas cylinder. In order to ensure the correct position of the liquid level gauge, there is a guide ring in the bottle. If the installation position is inaccurate, it will not be fully inserted. Please pull it out and reinstall it.
　　 8. Tighten the connecting thread at last, and do pressure leak detection on the connection. Caution: The water on the level gauge will freeze under the low-temperature liquid and restrict the movement of the floating rod, making the indication inaccurate.
　　
Warning: The level gauge is extremely cold due to contact with cryogenic liquids. Please wear gloves to protect your skin.
　　•Safety valve
　　 The inner container of the Dewar is a pressure vessel. As a very important safety device, the safety valve can effectively ensure the safe use of the gas cylinder and avoid serious consequences.
　　When the pressure of the gas in the pressure vessel exceeds the opening pressure of the safety valve, the safety valve will automatically open and discharge saturated steam to the outside to reduce the pressure in the cylinder. When the gas pressure in the bottle is lower than the safety valve reseating pressure, the safety valve is automatically reseated and closed. When the safety valve leaks, the safety valve fails and the safety valve needs to be calibrated, please follow the following procedures for replacement:
　　 1. Open the discharge valve and vent the pressure in the bottle to atmospheric pressure;
　　 2. Remove the safety valve and the four-way connection;
　　 3. Clean the sealing tape on the four-way internal thread;
　　 4. Install new calibrated safety valve;
        5. Pressurize the DPL cylinder to 0.86MPa (125 psi)/2.07MPa (300 psi)/2.75MPa (400 psi), pressurize the DPW cylinder to 0.86MPa (125 psi)/2.07MPa (300 psi), Perform pressure leak detection on the connection.
　    Note: Do not repair or reset the safety valve by yourself.
　　

valve use and maintenance
       • Shut-off valve
　　 The shut-off valve of the gas cylinder may cause mechanical wear due to long-term use, affecting its sealing performance or other performance. The valve seat of the globe valve is generally not damaged, just replace the handwheel or internal parts. If it is confirmed that a valve has a problem, it should be repaired according to the following procedure:
　　 1. If the stop valve is repaired, all the liquid and gas in the bottle must be emptied;
　　 2. The valve can only be disassembled after returning to normal temperature;
　　 3. Remove the fixing screw, washer, spring and sealing washer on the hand wheel;
　　 4. Remove the handwheel, unscrew the bonnet, take out the stem and stem seal;
　　 5. Take out the spool and bushing assembly;
　　 6. Clean the valve seat to ensure that there are no contaminants and other particles inside the valve seat and the seal;
　　 7. Replace damaged parts and reinstall them in reverse steps of disassembly.
　　 8. Perform pressure leak detection on the valve.
　　Note: Valve repair parts are not provided.
　　Caution: Do not damage the inner surface of the valve seat. Any surface damage may affect the sealing performance of the valve.