The ARB has the automatic sequencing feature plus the option of locking it into one sequence. The is used in control panels where two loads are required to alternate to provide equal run time on the loads. Pump Duplexor A three position switch permits the field selection of normal duplexing action, locking in the A-B sequence, or B-A sequence The output contacts will change states each time the control switch is opened, thus alternating the two loads.