Dewar cylinder sandwich between kind of efficient insulation, including high-tech insulation, vacuum and vacuum maintenance system, plays a very important role in the service life of gas cylinder. High-tech insulation layer can effectively prevent heat radiation. Heat conduction into the liner, vacuum can effectively prevent heat convection into the liner. However, due to the release of trace gas molecules from various materials in the liner, external leakage into the liner of trace gas molecules, the liner can not reach vacuum.

Vacuum failure is a very rare phenomenon. Usually, the vacuum system of a gas cylinder can be maintained for several years. During this time, the vacuum of the cylinder (at a very slow rate) gradually decreases. If the vacuum plug of a Dewar’s cylinder is not functioning properly, but a vacuum failure is suspected, the evaporation rate (NER) of the cylinder should be tested and the results compared to the evaporation rate values in the product specification sheet.

1. First fill the bottle with liquid nitrogen at 1/2 to 2/3 of the mass of all charges;

2. Close the inlet and outlet valves. Pressurization valve . Gas use valve, open the discharge valve to discharge the gas;

3. The Dewar’s cylinder is left to stand for 24 hours, then the cylinder is accurately weighed and the weight, time and date are recorded. Record the weight, time and date;

4. Keep the cylinder static for 48 hours, then weigh the cylinder again accurately and record the secondary weight. Record the secondary weight, time and date;

5. The actual daily evaporation rate is calculated according to the following formula in kg/day.

6. The actual daily evaporation rate is calculated by the following formula in %/day.

Compare the test results with the evaporation values in the product specification sheet. Cylinder evaporation values less than twice the evaporation value of a new cylinder are considered normal. Any test result that is more than twice the value indicates that the sandwich vacuum has been or is being lost. Please contact us.

Note: The first charge of a Dewar’s bottle or overcharging of a gas cylinder can also result in high evaporation rates. The pressure in the liner of a bottle that has lost its interlayer vacuum can rise rapidly and this pressure change is very noticeable. The temperature near the support is lower than in other parts of the cylinder casing, especially where the tubing is relatively concentrated, and the casing frosts or sweats depending on the temperature and humidity of the surroundings. The existence of this condensation phenomenon can not be used as a reliable indicator to determine whether the vacuum of the gas cylinder exists or not, and the test of the daily evaporation rate of Dewar’s cylinder is reliable. Effective method of judgment.