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water--flow regulating valve (not shown) which oper-
ates to conserve water during periods of varying
load on the compressor. This same valve automati-
cally shuts off the water supply when the compres-
sor is shut down. In addition, water--cooled models
have a water pressure switch to prevent operation
with inadequate water pressure.
2.5 COMPRESSOR DISCHARGE SYSTEM, FUNC-
TIONAL DESCRIPTION .
Refer t o F igur es
2 -- 3
discharges the compressed air/fluid mixture into the
combination receiver/sump.
The receiver has three basic functions:
1. It acts as a primary fluid separator.
2. Serves as the compressor fluid sump.
3. Houses the final fluid separator.
The compressed air/fluid mixture enters the receiv-
er and is directed against the internal baffle. The
direction of movement is changed and its velocity
significantly reduced, thus causing large droplets of
fluid to form and fall to the bottom of the receiver/
sump. The fractional percentage of fluid remaining
in the compressed air collects on the surface of the
separator element as the compressed air flows
through the separator. A return line (or scavenge
tube) leads from the bottom of the separator ele-
ment to the inlet region of the compressor unit. Fluid
collecting on the bottom of the separator is returned
to the compressor by a pressure differential be-
tween the receiver and the compressor inlet. A visu-
al sight glass is located on the return line to observe
this fluid flow. There is also an orifice in this return
line (protected by a strainer) to assure proper flow.
A secondary separator element with a separate re-
turn line, strainer, sight glass and orifice further re-
duce the fluid carry--over to less than 1 ppm (parts
per million). A gauge, located on the instrument
panel, shows red if abnormal pressure drop through
the separator develops. At this time, separator ele-
ment replacement is necessary. This gauge must
be checked with the compressor running fully
loaded.
A minimum pressure/check valve, located down-
stream from the separator, assures a minimum re-
ceiver pressure of 55 psig (3.8 bar) during loaded
conditions. This pressure is necessary for proper
air/fluid separation and proper fluid circulation.
A terminal check valve is incorporated into the mini-
mum pressure/check valve to prevent compressed
air in the service line from bleeding back into the re-
ceiver on shutdown and during operation of the
compressor in an unloaded condition.
A pressure relief valve (located on the wet side of
the separator) is set to open if the sump pressure ex-
ceeds the sump tank rating. A temperature switch
will shut down the compressor if the discharge tem-
perature reaches 235_F (113_C).
and
2 --
4. T he c ompr es s or unit
2.6 CONTROL SYSTEM,
SCRIPTION- STANDARD ELECTRO-MECHANI-
CAL
Refer t o F igur e
2 --
5. T he pur pos e of t he c ompr es s or
Control System is to regulate the compressor air in-
take to match the amount of compressed air being
used. At approximately 10 psig (0.7 bar) air line
over--pressure, the control system will automatically
blow down the compressor and greatly reduce the
unload power consumption. The Control System
consists of an inlet valve, (located on the compres-
sor air inlet), blowdown valve, solenoid valve,
pressure switch, and a pressure regulator. The
functional descriptions of the Control System are
given below in four distinct phases of compressor
operation. The following guidelines apply to all
LS--12 and LS--16 Series compressors. For explan-
atory purposes this description will apply to a com-
pressor with an operating pressure range of 115 to
125 psig (7.9 to 8.6 bar). A compressor with any oth-
er pressure range would operate in the same man-
ner excepting stated pressures.
START - 0 TO 50 PSIG (0 TO 3.5 BAR)
When the compressor START button is depressed,
the sump pressure will quickly rise from 0 to 50 psig
(0 to 3.5 bar). During this period both the pressure
regulator and the solenoid valve are closed, the inlet
valve is fully open due to inlet air flow, and the com-
pressor pumps at full rated capacity. The rising com-
pressor air pressure is isolated from the service line
in this phase by the minimum pressure valve, set at
approximately 50 psig (3.5 bar).
NORMAL OPERATING MODE - 50 TO 115 PSIG
(3.5 TO 7.9 BAR )
When the pressure air rises above 50 psig (3.5 bar),
the minimum pressure/check valve opens and deliv-
ers compressed air to the service line. From this
point on, the line air pressure is continually moni-
tored by a line pressure gauge and a pressure
switch usually set at 125 psig (8.6 bar). The pres-
sure regulator and the solenoid valve remain closed
during this phase. The inlet valve remains fully open
for maximum capacity.
MODULATING MODE - 115 TO 125 PSIG (7.9 TO
8.6 BAR)
If less than the rated capacity of compressed air is
being used, the service line pressure will rise above
115 psig (7.9 bar). The pressure regulator valve
gradually opens, applying air pressure through the
control line to the inlet valve piston. This causes the
inlet valve to partially close reducing the amount of
air entering the compressor until it matches the
amount of air being used. The control system func-
tions continually in this manner, between the limits
of 115 to 125 psig (7.9 to 8.6 bar), in response to
varying demands from the service line.
The pressure regulator has an orifice which vents a
small amount of air to the atmosphere when the
pressure regulator controls the inlet valve. The ori-
fice also bleeds any accumulated moisture from the
control lines.
Section 2
DESCRIPTION
FUNCTIONAL
DE-
9
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