A control valve (10) includes a valve body with a plurality of ports (A, B, C, D, E, F) and a plurality of annular flow passages (53, 55,57). A piston (34) which includes a plurality of annular flow passages and a longitudinal flow passage is selectively movable within a bore (32) within the valve body through operation of a valve controller (70). The valve controller is selectively operative to control the position of the piston so as to enable liquid flow through a plurality of flow paths. A master controller wirelessly communicates with a plurality of slave controllers, including the valve controller. The master controller is operative to control conditions of the valve and an associated liquid treatment tank.