O2 Check Valve Riser - DISS (for operatory) O2 Check Valve Riser - DISS (for operatory) 23173-FRU Use for pre-installation of Digital Ultra™ Flushmount and Ultra PC™ % Cabinet Mount flowmeters. Includes 28085 (O2 DISS x DISS Demand Check Valve Assembly). Where to Buy x Category Dealer PartnersSales RepresentativeStrategic MarketsSchools RepresentativeAccutron™ Equipment Sales Zip Code Find RepresentativeReset Select a category, input a zip code and click on Find Representative, or explore the complete list here.