Each ball and seat set is individually matched to ensure a lock-and-key fit. This guarantees 3 bubbles/minute or less in the industry standard nitrogen bubble test; common acceptable standards are 12 bubbles or less. We have also minimized the ball travel distance within the check valve; less travel distance equals quicker seating and more accurate pump metering. Simply put, tighter specifications make a better valve. A single OPTI-MAX® cartridge is interchangeable across multiple pump brands, and will function in either the inlet or outlet position. The same replacement cartridge will fit into OPTI-MAX® housings for pumps made by Waters, Shimadzu, Agilent/HP, and most other OEM solvent delivery systems. This allows you to minimize the number of spare check valve cartridges you keep on hand, and dramatically reduce the cost of inventory required to cover your maintenance needs.