The device is placed in the sealing sleeve, the sealing device is sealed with the external seal, and then to the empty tank filled with 8~12bar compressed gas, the tank outside the vacuum to pressure 0.2~0.4bar; thus the internal and external pressure difference; pressure sensor placed in the real space, the beginning and end of the pressure inside the time to read a numerical and compared, if more than set value, the system will be considered as a waste;