Here is the best explanation from a very clever Dutchman (so no wonder it involves push bikes).
A push bike pump uses a connector (from pump to valve) of a very small ID, no matter how much air pressure in the tube the pump can always manage force a little more air in, due to the high velocity that connector creates.If it were a large ID the valve would never open, the pressure in the connector would just fluctuate. So only high pressure and/or high velocity gas escapes. Jan Thiel still used the step on Aprilia RSA engines. I spend lots of time welding up ducts on old mxers that have previously had the step removed.
Nice work on the TSS pipes me dips me lid.