Pulseless liquid supply system for flow cytometry

Abstract

A liquid supply system for flow cytometry apparatus including a diaphragm pump, a novel liquid accumulator providing exceptionally high volume compliance, and a control of accumulator volume within narrow limits by continuous control of power to the pump motor. The accumulator achieves high volume compliance by arranging the kinematics of a main spring loading the accumulator to have a negative spring rate equal to the sum of all other positive spring rates produces by a second spring used to adjust the accumulator pressure, by the diaphragm, and by a flexure pivot support for a sensor lever. This sensor lever moves with the accumulator diaphragm to actuate an optical sensor producing an electric signal indicative of small changes in liquid volume in the accumulator. This signal in turn continuously modulates the power to the motor driving the pump so as to maintain the accumulator liquid volume close to a datum value even during a portion of the pump delivery cycle. This close control of liquid volume in a high compliance accumulator provides substantially pulse-free constant pressure liquid delivery from a pulsatile pump. The second spring may be adjusted to modify this constant pressure without disturbing the balance between positive and negative spring rates. Adjustment may be manual or automatic in response to a variable such as fluid temperature whereby liquid pressure is automatically increased with lower liquid temperatures to maintain liquid flow substantially constant through a flow cytometry apparatus used for particle analysis or particle sorting or the like.