I've installed a Welch WOB-L 2546B-01 at each end station to replace the Gast 523 pumps that we have been using. I've set the pressure to -19inHg and checked the flow at the dust monitor on the floor was 2.8L/min. The new pumps are much quieter, ~84dB vs ~67dB, but at a lower frequency. I'll post more photos of the setup and more details tomorrow after we see how they run over night.