Tested! now I am settle with the metering valve for my personal co2 system.
Takes too much turn to increase/decrease the bubble rate, miss the swagelok S series which is fast and accurate to set the bubbles. lol.
There is a problem of this metering valve though: like the Parker hannifin H2A, H3L, the brooks NRS needs higher pressure differential.
They all have the extremely small orifice and longer orifice passage(tube), so water/oil/dust can easily settled in the passage and clog the valve if the pressure differential is low. Higher pressure differential, water/oil/dust can easily be pushed through, so better to set the regulator output with higher pressure.
also, due to small orifice, need particle filters, the manual recommend a 2 micron particle filter
I guess a 7 micron particle filter is sufficient because the flow rate is about 1-2 sccm (1 bubble/second). Orifice is big enough for the 7 micron particles to pass through.