Figure 2-6.—Dehydrator operating cycle

sealed dome and the outlet line fluid. When outlet line pressure drops below dome pressure, the diaphragm moves out slightly and pushes the main valve open. This allows inlet line gas to flow through the valve until outlet line pressure builds up enough to balance the dome pressure. Then, the diaphragm moves back to throttle or closes the main valve so that dome and outlet pressures always remain in balance. Any change in dome pressure causes a corresponding change in outlet line pressure. When the dome is completely vented, the main valve shuts off bubble tight. Any trouble with the pressure regulator can usually be traced to the valve and valve seat, or to the diaphragm and O-rings being worn or deteriorated. Dehydrator The dehydrator (fig. 2-5) consists of two desiccant chambers filled with desiccant in the form of small spheres. The desiccant chambers are supported by the manifold, and they are connected to the manifold by internal air passages. A pair of two-way solenoid valves are attached to the bottom side of the manifold. The program timer controls the operation of the two solenoid valves. In one 60-second period, each solenoid valve is open for 22 seconds and closed for 38 seconds. The timing for the solenoid valves is such that both valves are closed for two 8-second dwell phases. One complete cycle takes place in each desiccant chamber every 60 seconds. Dry air is needed for reactivation of the desiccant chambers. A small quantity of dry air (figs. 2-5 and 2-6, phase I) is bypassed around the ball-check valve by a Figure 2-5.—Dehydrator. Figure 2-6.—Dehydrator operating cycle. 2-7