Get current pricing for Knapp, 6 Long 6M40-V21-25-5 Knapp, 8 Inch, 6 Membrane Reverse Osmosis Housings. End Cap Ports Are 1 1/2 Inch Victaulic Fittings. Vessel Pressure Rating Is 400 Psi. . Product Category: Process Equipment, Sub Category: Reverse Osmosis Equipment: