Originally Posted by bumsdeclaf
seems like it initially gets sent back with pressure on the rear o-ring but then the weep hole starts to leak and somehow it still makes it to the plunger.
That is indeed what happens, pressure from the front is constant against the sail o-ring, unlike most other dump valve markers.
The bleed hole is partially isolated while the bolt is forward, but once the hole gets past the air inlet on the rearward stroke, it starts leaking more; the pressure differential of the LP air Vs the empty valve chamber drives the bolt backwards very fast, even with that small leak, accounting for the relatively high efficiency of the valve design. In the end the bleed hole goes past the bolt pin and feeds the valve chamber.
The valve opens and closes very fast which accounts for the loud pop signature of the marker without the muffler. The muffler is IMO a half assed fix to a design problem, it strips the air burst from a considerable part of it's energy and delays the pressure differential, making it more likely for the bolt not to reset completely and go full auto, as the infamous youtube video demonstrates.
IMO a FASOR spool valve would've been a better fix, slow to open and fast to close, it could've quieted the sound signature down without sacrificing energy transfer, retaining the efficiency (think automag, but with a lower OP and an appropriately sized valve chamber).