Gardner Denver ELECTRA-SAVER II Service Manual page 23

will blow down If the system pressure does not fall to the
pressure switch low setting within the time set on the timer,
the unit will stop
The ON indicator light will remain on as long as the On-Off
switch ON pushbutton is depressed When air is again
required the unit will start the timer will reset and the
loaded unloaded stop cycle will repeat
The timer must never be set at a time less than that indicated by
the minimum run time caution plate on the instrument panel
Use of less time of run interval will allow excessive motor
starts and cause shortened motor life or failure
When the low demand mode switch is in the ON position
and timer is positioned so the letter "N' in MINUTE is
opposite the green arrow mark on the escutcheon the
compressor will build to full pressure unload and blow
down At this setting the motor will not time out and stop
ing the compressor to load up and operate normally.
The control consists of a flow controlcheck valve, a small
surge changer, a normally open three-way air valve, and a
shuttle valve.
The Flow Control-Check Valve consists of a check valve
and an adjustable orifice in one body see Figure 8-4.
The Three-Wey Valve (Figure 9-4) requires 15 PSIG
control pressure to shift the valve
L .-—
-.J
>
ADJUSTABLE CONTROLLED FLOW
FREE FLOW THRU CHECK VALVE
MINIMUM RUN TIME SETTING
FOR AUTOMATIC START/TIMED STOP CONTROL
Size Time (Minutes)
All 6
Electrical Wiring — Figures 16-4 and 17-4 are the wiring
diagrams for the units with Automatic Start/Timed Stop
Control System
VIBRATION SWITCH (Optional Equipment) — The op
tional vibration shutdown switch, mounted on the com-
pressor coupling cover, detects an increase in vibration that
could be an indication of impending damage to the unit The
switch actuates when the selected level of vibration is
exceeded
The switch MUST BE ADJUSTED when the unit is first
installed. Refer to switch manufacturer's instruction manual
for complete details
AUXILIARY AIR RECEIVER— An auxiliary air receiver with
adequate volume must be used with both control systems
to prevent rapid cycling of the unit Occasionally shop air
lines are of such a length as to provide adequate volume
but this should be carefully checked before using the unit
without an auxiliary air receiver.
LOW STARTING TORQUE (Unloaded Start) CONTROL
(Optional Equipment) — When a reduced voltage closed
transition starter is used problems may arise as the torque
required by the compressor may exceed that available from
the compressor drive motor during and just after the
starting cycle This is especially true when a unit uses full
motor horsepower at some pressure lower than 100 PSIG.
The Low Starting Torque Controls holds the compressor
inlet valve closed for a short period while the motor is
starting and reduces internal air loads and the compressor
torque
The control allows the compressor to build up a pressure of
approximately 15 PSIG in the oil reservoir which is directed
to the pilot on the inlet valve to close the valve and unload
the compressor while the motor reaches full load speed A
pneumatic timing circuit then bleeds the pressure off the
inlet valve pilot after approximately 10-15 seconds allow
FIGURE 8-4 — FLOW CONTROUCHECK VALVE
3
0-15
pSIG
15 PSIG
DE-ENERGIZED
ENERGIZED
FIGURE 9-4 – THREE-WAY VALVE
CAuTiON
This control will function properly only when the
low
Demand switch if OFF If the Low Demand switch is
ON the Low Torque control will react to all demands
for air as initial start-up and delay buildup in air
pressure for the time delay built into the system
In operation (Figure 10-4), the adjustable orifice in the flow
control check valve controls the rate at which pressure will
build in the surge chamber the unloaded starting time is
proportional to the pressure buildup time When the
pressure in the surge chamber reaches 15 PSIG, the three
way valve will shift bleed control pressure from the inlet
valve and purge valve, and allow the compressor to load
See Figure 10-4 for the complete Low Starting Torque
Control assembly. Figure 11-4 is the unit tubing diagram
with control in place
RESERVOIR PRESSURE SWITCH – The reservoir pres-
sure switch will prevent motor damage if an attempt to start
motor is made before the reservoir is completely blown
down The pressure switch will not allow the motor to be
restarted after the unit has stopped until the pressure in
the reservoir is below 5 PSIG. The switch pressure is
sensed at the separator tower section of the oil reservoir.
The switch is factory set at 5 PSIG, with an adjustable range
of 3-30 PSIG.
, WARNING
Do not set pressure switch to pressure above 5 PSI.
13-9-630
Section 4 Page 7