The AK pneumatic expander adopts high-precision linear guide rails, dual cylinder motion, size positioning sliders, and adjustable angle functions, solving the problems of low efficiency and high labor intensity in the worker's pants waist up and cylinder sewing process. The use of the supporting CARV digital puller can make the ordinary sewing machine a semi-automatic waist up machine, and can be equipped with CARV AT, BT, and MT series intelligent digital puller for simultaneous use, Suitable for cylindrical sewing of pants such as waist, hem, hem, cuffs, etc., and compatible with all flat, double needle, multi needle, and stretch sewing machines on the market