This machine is to be installed directly to the production line, on line eliminate the defective cans (with pin holes, cracked welding, dented flanges etc.) The working principle of this machine is: detect and get a first pressure value after the cans vacuumed when the cans pass through the working heads, keeping some time, then detect again to get a second pressure value, by the calculation of the PLC, compare with the machine setted standard value. If the value is in the standard range, the cans will pass smoothly and go to the next procedure palletizing; if the value is not in the standard range, then means this can is a defective can and will be rejected automatically on the outlet conveyor and collected to a container for factory analyzing use, this is the whole detecting procedure.