I have installed several other regulators in rifles and in some if not all, require a breathing hole or it may be ventilated. In those cases of ventilated regulators such as the HUMA, it requires to remove the valve o-ring and leave a hairline space when screwing back the air tube.
I have not seen installation instructions for the Hatsan OEM regulator, except for a video in youtube. In that particular video, the guy did not take out the valve to air cylinder o-ring and he tightened the air tube normally.
Question: Is it ok to do it as in the video or is it recommended to remove the o-ring and leave the hairline space between the valve and the air tube using the Hatsan OEM regulator. With other regulators I understand that not leaving the space for breathing, a regulator pin inside might get dislodged.