[diesel_john]

I started to make a recirculating ball meter out of common plastic pipe and this is the concept using a 0.12gram plastic BB. But it could made as small as needed. Those are 1/4" bolts in the pic. The groove in the inside ring was made by mounting a length of 1/2" water pipe on a 5/8" bolt and chucking the bolt in a drill press. Then used a 6mm round file to make the groove. The various size pipes were cut to 1/4" long and sanded/lapped down to almost 6 mm (the ball size). Fluid would enter through the bottom plate between the outer and second ring. Then through a small port drilled at an angle to propel the ball in the second ring. And exit through the center ring or top plate.