a method and apparatus for sorting particles moving through a closed channel system of capillary size comprises a bubble valve for selectively generating a pressure pulse to separate a particle having a predetermined characteristic from a stream of particles . the particle sorting system may further include a buffer for absorbing the pressure pulse . the particle sorting system may include a plurality of closely coupled sorting modules which are combined to further increase the sorting rate . the particle sorting system may comprise a multi - stage sorting device for serially sorting streams of particles , in order to decrease the error rate .