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How are Dewars (jars) safe to use?

Views: 2     Author: Site Editor     Publish Time: 2022-06-15      Origin: Site

Dewar flasks are stainless steel pressure vessels with super vacuum insulation, designed for the storage, transportation and use of liquid oxygen, liquid nitrogen, liquid argon or carbon dioxide, liquefied natural gas, for reliable and economical transport of cryogenic liquid gases, and on-site storage and supply of liquid gas.

The structure of the dewar flask

The upper part has a protective ring and a pipeline valve system. The middle bottle body has a stainless steel outer shell, a thermal insulation layer, a stainless steel inner tank, a vacuum interlayer, and the innermost part is the liquid medium.

Use of Dewar flasks

The liquid supply and use process of the Dewar bottle: first, make sure that the main pipe valve of the spare bottle group is closed, open the gas valve and the liquid outlet valve on the cylinder to be used, and then open the corresponding valve on the header skid of the bottle group connected to the steel cylinder , and then open the corresponding main valve of the pipeline. Finally, open the valve at the inlet of the vaporizer, and the liquid is vaporized through the vaporizer and then supplied to the user after being regulated by the pressure regulator. When supplying liquid, if the pressure of the cylinder is not enough, you can open the booster valve of the cylinder, and pressurize the cylinder through the pressure boosting system built in the cylinder, so as to obtain sufficient liquid supply pressure.

Advantages of Dewar flasks

The first is that it can hold large quantities of gas at relatively low pressures compared to compressed gas cylinders. The second is that he provides an easily manipulated source of cryogenic liquid. Due to the firmness and reliability of the Dewar flask, its long holding time, and its own gas supply system, the built-in vaporizer can continuously output normal temperature gas (oxygen, nitrogen, argon) with a flow rate of up to 10m3/h, and the high constant output pressure of the gas reaches 1.2Mpa (Medium pressure type) 2.2Mpa (high pressure type), fully meet the gas requirements under normal circumstances.

Dewar bottle gas supply operation

>>> Preparation 1. It should be kept at a safe distance between the Dewar bottle and the oxygen cylinder (the distance between the two bottles should be kept more than 5 meters). 2. There should be no open flame devices around the bottles and cans, and there should be fire protection devices nearby. 3. Check whether the Dewar bottle (can) is well connected with the end user. 4. Check that all valves, pressure gauges, safety valves, and valve fixtures for Dewar bottles (tanks) in the system should be complete and easy to use. 5. There shall be no grease and leakage in the air supply system. >>>Operation procedure In order to make the Dewar bottle (tank) gas supply system continuous, stable, safe and economical gas supply, when the Dewar bottle (tank) gas supply system is used, a single Dewar bottle (tank) can be used for calibration The terminal is used for gas supply, and two Dewars (cans) or three or more Dewars (cans) can be switched alternately through the bus bar.

Notes on filling

Before filling the dewar bottle (tank) with cryogenic liquid, first determine the filling medium and filling quality of the gas cylinder. The filling quality can be found in the product specification table. To ensure accurate filling, use a scale. 1. Use a special delivery hose to connect the gas cylinder inlet and outlet valve (DPW gas cylinder is the inlet valve) to the supply source, and tighten it without leakage. 2. Open the discharge valve and the liquid inlet and outlet valves of the gas cylinder, then open the supply valve and start filling. 3. During the filling process, monitor the pressure in the bottle with a pressure gauge and adjust the discharge valve to keep the pressure at 0.07~0.1MPa (10~15 psi). 4. When the required filling quality is achieved, close the inlet and outlet valves, discharge valves and supply valves. 5. Remove the delivery hose and remove the gas cylinder from the scale.

Warning: Do not overfill gas cylinders. Warning: Before filling, confirm the medium in the bottle and the filling medium. Warning: Filling should be carried out in a well-ventilated place, because the accumulation of gas is very dangerous. NOTE: A fully filled cylinder will have a very rapid rise in pressure that may cause the safety valve to open. Note: After working on liquid oxygen or liquefied natural gas, please be careful not to smoke immediately or get close to the place with fire, as liquid oxygen or liquefied natural gas is likely to be splashed in the clothes.

Other considerations

1. When working with cryogenic liquids, you must wear protective equipment to prevent frostbite. 2. In the operation of liquid oxygen, the opening and closing of the valve should be carried out slowly, and the sudden opening and closing of the oxygen flow will cause any pollution in the system to catch fire. 3. Except for liquid oxygen, all liquid vapors can suffocate people. 4. The filling volume cannot exceed: liquid oxygen 192㎏, liquid nitrogen 136㎏, liquid argon 230㎏. 5. When using liquid, it is recommended to reduce the pressure in the bottle as much as possible. 6. The gas cylinder must be kept upright during operation, and should be avoided from overturning, and the gas cylinder must not be rolled horizontally. 7. Open fire is strictly prohibited within 5m around the storage, vaporization, filling, and use site of liquid oxygen, and all fire sources should be eliminated, and there should be obvious fire prohibition signs. 8. There must be no openings leading to low places (such as basements, pits, wells, ditches) around the storage, vaporization, filling and use sites of liquid oxygen at least 5m; there must be a liquid retaining weir at the entrance of the ditches . 9. When filling or handling liquid oxygen, operators are not allowed to wear work clothes and personal protective equipment contaminated with grease. All clothes and protective equipment contaminated with grease must be replaced.



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