CMP MDV-10-04 DEL Ozone® Mixing Degas Vessel for DEL Ozone 25/50/100 Variable Speed. The Mixing De-Gas Vessel (MDV) prevents bubbles from returning to the pool, which eliminates bubble noise and visibility. The MDV should be used in all indoor, covered, and vinyl-lined pools and used in conjunction with a DEL Ozone 25, 50, or 100 unit. The MDV system may also be used in outdoor applications to eliminate bubbles from the return flow.