An OR circuit is one in which a control signal at any one valve will produce an output. Thus, all control signals must be off in order for the output not to exist. This is accomplished in Figure 16-5 (a), in which the three valves are now hooked in parallel. If any one of the valves picks up an air pilot signal, it will produce an output at D. in Figure 16-5 (b) shows how an OR function can be implemented using one