AADCO 737 Series Operating Instructions Manual page 35

13.16 If there is purge flow although the POWER switch is off (no power to the
solenoid valves or purification reactor), the problem lies with one of the
purification reactor's solenoid valves experiencing "blow by". It is due to the
weakening of the spring within the coil housing. This spring holds the spindle
against its seat when the coil is not energized, effectively closing the inlet side
of the valve at any pressure up to 100-psig. If the spring is defective, air is
admitted through the purge valve and opposite column system rather than
through the check valve, pressure regulator, etc., this air appears as purge air
through the opposite solenoid valve.
NOTE: BECAUSE OF THE 100-PSIG LIMITATION FOR THE INPUT AIR
PRESSURE, IT IS IMPERATIVE THAT THE PRESSURE SWITCH
NOT EXCEED 100-PSIG.
PRESSURE WILL CAUSE IMPROPER OPERATION OF THE
PURIFICATION REACTOR AND, THEREFORE, PRODUCTION OF
IMPURE AIR.
13.17 Further confirmation of this condition can be made by removing the connecting
tubing from the tops of the solenoid valves; i.e., the common dump connection;
and determining which solenoid valve is leaking when its coil is not energized
by feeling the flow from the top of the valve with the POWER switch off and
pressurized air being applied to the solenoid valve inlets.
solenoid valve is that valve which does not evidence purge flow since its
opposite number is leaking when non-energized. Replace solenoid valves.
13.18 If the purge flow is constant (never having no-flow conditions as described in
Section 13.10) or appears to be extremely unequal from one side of the
purification reactor to the other during normal operation with the POWER switch
on, the cause is a defective check valve on the output side of the purification
reactor. To determine which check valve is defective, disconnect a quick-
connect leading to one solenoid valve on the input to the purification reactor
with the POWER switch on and pressurized air at the valve inlets. If the purge
air is normal, the defective check valve is on the same half of the purification
reactor as the solenoid valve receiving power. If the purge air is abnormally
high, the defective check valve is on the opposite half of the purification reactor.
Replace the defective check valve.
13.19 Further confirmation can be made that one check valve is defective by: (a)
turning the POWER switch off, (b) remove the ¼-inch tubing, connecting the
output of the purification reactor to the input of the output pressure regulator,
Figure 6, or if mixer-receivers are present as in Figure 7a, the input fitting of the
rear mixer-receiver, (c) connect pressurized air to the output fitting of the
purification reactor, (d) there will be a high flow of air from the top of that
solenoid valve which is in the same half of the purification reactor which has the
EXCEEDING THE 100-PSIG INPUT
The defective
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