Method to judge the vacuum performance failure of Dewar

Generally, with the vacuum failure, the Dewar will show the phenomenon of frosting on the bottle body or a sharp increase in the pressure in the cylinder. However, for a new bottle or a gas cylinder that has not been used for a long time, because the temperature of its inner tank is higher, the pressure rises faster when filling with liquid, this phenomenon should be normal.
　　
Excessive pressure rise can be used as one of the basis for judging the vacuum failure of the pressure vessel. The shell of the gas cylinder is equipped with a vacuum plug. When the vacuum of the gas cylinder fails, the vacuum plug will loosen (under normal conditions, the vacuum plug is compressed by atmospheric pressure). Usually, the vacuum plug is covered with a plastic protective cap. Do not open the protective cap or vacuum plug. If the vacuum of the Dewar is found to be invalid, please send it back to the pressure vessel repair factory for repair.

After all, the vacuum failure of the Dewar is a rare sight. Generally, the vacuum of a gas cylinder can last for several years, or even exceed the service life of the gas cylinder. During this period, the vacuum of the gas cylinder is gradually decreasing (at a very slow rate). of. The so-called "soft" vacuum presented on the stationary Dewar can be judged by a rapid increase in pressure.
　　
If the gas cylinder vacuum plug is not abnormal, but the vacuum is suspected to be invalid, it must be judged by checking the pressure.
　　
When the pressure of the test cylinder increases, you should pay attention to:
1. First of all, we must understand the liquid temperature of the liquid filling station. The liquid temperature of the liquid filling station cannot be lower than -135 degrees.
　　
2. The liquid level of the Dewar flask should be measured at 2/3 or 1/2. 3. Decrease the pressure of the gas cylinder to 0.6MPa, close all valves, check every half an hour, check the pressure rise, and investigate for 4 hours. If the pressure rises by 0.1mpa per hour, it can be judged as a vacuum drop. Tell the after-sales personnel to judge on site .
　　
4. The liquid volume of the gas cylinder is about half, and it cannot be full, otherwise it will affect the accuracy of the judgment.
　　
5. After starting the judgment, you can tell the pressure vessel factory service personnel to go to the scene to judge.
The jacket pressure of a gas cylinder with a vacuum failure will increase at a rate of nearly 0.007MPa/min. This pressure change is very obvious; the cylinder shell, especially the more concentrated parts of the pipeline and the support adjacent temperature than other parts The temperature is low, and whether the shell is frosted or condensed depends on the temperature and humidity of the surrounding environment.

The existence of this kind of condensation cannot be used as a reliable indicator for judging the presence or absence of the vacuum degree of a gas cylinder, and the test of the cylinder pressure increase rate is the most reliable and useful way of judging.
　　
A Dewar bottle that has already failed to vacuum must be evacuated again through a special device. This operation can be carried out on the car or after the gas bottle is unloaded.