Gas phase space for hydraulic testing
Thread Content
1. When doing a hydraulic test, assuming the test pressure is 2MPa, is there a certain gas phase space at the top of the container? Otherwise, how can pressure be generated? Water is incompressible, but gas can be compressed. 2. There is another saying: “If the gas phase space at the top cannot be drained due to structural reasons, the test pressure cannot be reached." Is this correct?
Question 1: Under normal circumstances, the air should be exhausted, and the pressure is increased by the hydraulic pump. 2. If there is a certain gas phase space, the pressure will only rise slowly, not increase the pressure.
You should find a way to drain all the air, such as adding an outlet pipe, and the hydraulic pressure is generated by a hydraulic pump. The hydraulic test must meet the requirements of the drawing. If the test pressure is not reached, the test will be invalid.
second question: Since it is known that there is a structural reason why exhaust cannot be exhausted, it is necessary to design and process the exhaust process port and seal it after pressure testing.
Incompressible does not mean that it cannot be compressed, it is just that the compression is relatively small. Otherwise, how can we explain the numerous hydraulic cylinders! ! There is air that needs to be exhausted as much as possible. The main consideration is safety. In actual pressure, it is impossible to be absolutely free of air. There is always a small amount, so the pressure increase requires a process.
It seems that you are struggling. You feel that liquid cannot generate pressure if it cannot be compressed. If you use a pump to pump out the air, the pressure will build up quickly. Because the space for liquid to be compressed is very small, if you pump in a little more, the pressure will build up.
Thanks for everyone's answers. I basically understand it. I still have some questions. Why does the pressure increase slowly if the air is not exhausted? Talk about the principles
Gas is compressible and expandable, and its density changes greatly with pressure and temperature. According to the gas equation, the gas volume will shrink a lot from normal pressure to test pressure, so the pressure increases slowly.
If the gas cannot be exhausted, can it be understood as equivalent to a gas-liquid combined pressure test? This feels more dangerous. The change of pressure in the pressure test follows the law of conservation of energy. Gases are compressible and the pressure rises slowly. Liquids are incompressible. Energy is directly converted into pressure and the pressure rises quickly.