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b) While the tank is out, look into the lower end of the tank. Make sure the drain screen is in
place. Also check for accumulations of lime at the bottom of the tank. Refer to "Steam
Generator Disassembly" and "Cleaning Procedure" sections to rectify these problems.
3) If the tank drains well when the water level is high but poorly or not at all when it is low, check the
duct pressure where the dispersion tube is mounted. A negative
duct pressure can cause
drainage problems. While this is relatively rare, it has been known to happen.
4) If the water backs up into the drain pan inside the unit, check for a blocked drain cup under the
pan. If the drain cup is OK, check the drain piping for an accumulation of solids. Clean as required
and increase the pitch of the drain piping if necessary. If long runs of horizontal drain pipe cannot
be avoided, it may be necessary to develop some kind of drain flushing system. An air gap in
between drain piping and drain hose from the EHU will allow "burping" of air from drain piping.
Fill System Failure:
Make sure the drain valve is not leaking. A leaking drain valve may appear to the humidifier as a fill
system failure.
Check to see that the fill valve is operating. While the fill light is on, disconnect one of the fill valve
leads (Figure 28-1, 28-2), then momentarily touch the lug to the coil terminal. You should be able to
hear the valve operate.
1) If the fill light is on, but the valve is not operating, check for 24 VAC between the valve lead wires.
After checking, TURN OFF THE POWER.
a) If 24 VAC WAS NOT found, check the continuity of the wires back to the circuit board.
Repair broken wires as necessary. If wires are intact, call the factory for assistance.
b) If 24 VAC W
AS found, disconnect the fill valve leads and check the coil resistance. It should be
18 ohms. Replace the coil if necessary.
2) If the fill valve is operating but the unit fills too slowly, check for either low water pressure (less
than 25 psi) or a partially plugged screen inside the inlet fitting. If the screen tends to plug too
easily, it may well be removed and replaced by a larger filter in the water line external to the unit.
(NOTE: the nominal flow rate valve should be 0.31 gal/min. for each tank. The flow rate is
regulated by a flow washer in the valve inlet or on the EHU-704 by flow washers in the brass tee
immediately downstream of the fill valve.)
3) If the valve makes humming or buzzing noises but fails to open:
a) Check for high water pressure (over 125 psi).
b) If a backflow preventer is used, crack open a fitting between the backflow preventer and the fill
valve. If this causes the fill valve to open, remove the backflow preventer from the system.
Backflow preventers are not needed as the Series EHU-700 incorporates a 1 inch air gap as
an anti-syphon feature.
For additional information on Armstrong Series EHU-700 Humidifiers, contact your Armstrong
Representative and request Bulletin No. 596.
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