I found this online at www.woodessence.com.

"Turbine HVLP Spray systems such as Kremlin/Apollo, Fuji and others typically do not benefit from the venturi effect to create a vacuum that will draw fluid from the collapsible liner. These systems often require a pressurized cup to force fluid to the spray nozzle. 3M offers H/O Pressurized Cups for these systems and other applications where pressure feed is helpful.

H/O Pressure Cups are available only in the Mini or the Large size and are fabricated from rigid plastic and include a full coverage lid/collar assembly. An integrated pressure relief valve is built into these cups and they include a rubber pressure tube to connect to the Spray Gun pressure port.

H/O Pressure Cups utilize the standard lids/liners that are used with the gravity/siphon feed cups."