Hello all i just bought vacuum gauge Testo 552 and connect it to vacuum pump and Testo 550.

So when i start to pull the vacuum is ok, after that I close the valve on the Testo 550 to isolate the pump and I turn off the pump.

So all the measurements which i can see are from the vacuum between the Testo 550, ribber hoses and Testo 551

As you can see from the video which i took the vacuum is not stable and when i close the valve from the T550 vacuum level going more weak (rise up).

Here is the video
https://www.youtube.com/watch?v=bkkVvEiyw5o

PLease let me know why is that happen?