Performance in the micro-flow rate range less than 50uL/min has been improved in the LC-20AD/AB pumps. First, a new spring-loaded check valve design has been incorporated. The spring assists in closing the check valve to prevent leak-back, resulting in more accurate and precise fl ow rates and gradient formation. This new check valve design will also increase the dependability and stability of the pump with non-polar mobile phases like hexane where static buildup can cause check valve problems. Second, the firmware has been modified for enhanced pulsation correction of the high-speed drive motor, yielding pulse-free solvent delivery. The LC-20AD/AB pumps are ideal as a front-end component for LCMS systems where stable, quiet, and precise solvent delivery is critical for optimal performance from the mass spectrometer. Of course, these improvements will enhance the performance of other detectors as well.