Welch ProBoost Air-Cooled Diffusion PumpWelch ProBoost Air Cooled Diffusion Pump Product Details Use Welch ProBoost in conjunction with a backing pump like the CRVpro to get deeper vacuum and higher flow. High Vacuum to 10 torr Use with high vacuum and Schlenk lines Employs air cooled diffusion pump Easy Attachment to backing pump Welch ProBoost is an air cooled gas jet pump (commonly called a diffusion pump). The gas jet is formed by directing boiling silicone vapors through a hollow cone.