Gardner Denver ELECTRA-SAVER II Service Manual page 21

MINIMUM DISCHARGE PRESSURE VALVE (Fig
ure 4.4 ) — An internal spring-loaded minimum
pressure valve is used in the final discharge line to
provide a positive pressure on the oil system of the
compressor even when the air service valve is fully
open
The valve incorporates an orifice which when air is
flowing through it maintains approximately 65
PSIG in the oil reservoir. A spring loaded piston
valve senses air pressure on the downstream
(shop air line side) of the valve When the system
pressure rises above 65 PSIG, the spring is
overridden and the valve opens to full porting
The valve does not require maintenance or
adjustment If the valve fails to function check the
valve stem 0-rings for sealing valve orifices for
restriction or valve and valve seat for burrs and
dirt
The valve is adjustable within a small range. It is adjusted by
a set screw secured by a locknut on the side of the valve
body. The minimum pressure can be adjusted as follows
I
I
REGULATOR
~–—
N)
1.
Start the compressor.
2. Reduce pressure downstream of minimum pressure
valve to below desired minimum pressure DO NOT
REDUCE DOWNSTREAM PRESSURE OR ADJUST
VALVE BELOW 65 PSIG.
3. Loosen locknut on adjusting screw.
4. Turn set screw in to increase, or out to decrease
minimum pressure to be held
5. Hold set screw at desired point and tighten locknut
CHECK VALVE (Oil Reservoir (Figure 2-1) – A renewable
seat swing type check valve in the final discharge manifold
prevents backflow of air from the shop air line when the unit
stops unloads or is shut down
COMPRESSOR CAPACITY CONTROL — On Constant
Speed Control with low demand mode switch in the ON
position the reservoir will blow down at below 20%
compressor capacity. On Automatic Start/Timed Stop
Control with low demand mode switch in the ON position, at
below 20% capacity, the reservoir will blow down and the
timer will start timing The unit will stop if air demand does
not increase before timer runs out
On Constant Speed Control and Automatic StarUTimed
Stop Control systems with the low demand mode switch in
the OFF position at 20% compressor capacity, the unit will
partially unload and continue to run.
The capacity control system pilot is protected from
moisture and dirt by a manually drained line filter located
just down stream from the inlet valve pilot The filter should
be drained periodically to prevent moisture buildup and
carryover into the control lines
INLET VALVE (Figure 7-4) — The inlet valve is a piston
actuated device which controls the compressor inlet and
operates on air pressure from the inlet valve subtractive
pilot The valve is closed when full pressure is on the system
and changes degree of opening in direct response to
system pressure changes
13-9-630
D75829
FIGURE 7-4 – INLET VALVE
The inlet valve contains piston spring "F" which returns the
unloader piston and allows the inlet valve to open as
pressure decreases and valve spring "C' which returns the
inlet valve to a closed position on shutdown of the
compressor and prevents oil back-flow from the com
pressor to the air filter.
The inlet valve piston is lubricated by a separate line which
introduces oil from the compressor oil system
BLEED AIR VALVE — A pilot-operated air valve is provided
in the inlet valve system to admit air to the compressor to
scavange oil during the unloaded cycle The inlet valve
subtractive pilot admits air to the bleed air valve piston at
the same time as air is being admitted to the inlet valve
piston at the beginning of the unloaded cycle The bleed air
valve piston shifts allowing air to pass from the oil reservoir
to the inlet valve behind the closed inlet valve providing
scavenging air as long as the compressor remains
unloaded with low demand mode switch OFF.
INLET VALVE SUBTRACTIVE PILOT (Figure 1-4) –
admits air to the inlet valve piston when a discharge
manifold pressure equal to the pilot low setting is reached
The air begins to pass through the pilot to the piston and
the inlet valve begins to close As the discharge manifold
pressure increases the pilot pressure also increases on the
inlet valve piston closing the inlet valve At full manifold
pressure (pilot unload setting) the pilot is exerting full
differential pressure on the inlet valve piston and the inlet
valve is fully closed As the discharge manifold pressure
falls the pilot exerts proportionally less pressure on the
inlet piston allowing the inlet piston spring to return the
piston and the inlet valve to open. The pilot can be adjusted
from 65 to 150 PSIG. The differential range of approxi
mately 15 PSI cannot be changed In order to obtain full
capacity at maximum operating pressure, the pilot should
be set to unload with the inlet valve fully closed at
approximately 10 PSIG above the maximum operating
pressure.
COMPRESSOR CAPACITY AND PRESSURE ADJUST-
MENTS– Any adjustment made affecting the compressor
Section 4
Page 5