Cuprajake There is the odd drop, but very little, it will have no effect on the shot. What pressure were you using?
Also worth remembering that the preinfusion valve is designed to open at 4 bar, sure they put a stronger spring in, but:
- the valve never needed to seal at up to 12.5 bar like the vent valve
- I doubt they used a 13 bar spring
- there could be crud on the valve seat.