Sullair LS20T Operator's Manual And Parts List page 14

Section 2
DESCRIPTION
The receiver is an ASME pressure vessel. A combi-
nation minimum pressure/check valve, located
downstream from the separator, assures a mini-
mum receiver pressure of 170 psig (11.7 bar) during
full load operation. This pressure is necessary for
proper air/fluid separation and proper fluid circula-
tion while supplying air to the system. This valve
also acts as a check valve preventing compressed
air in the service line from bleeding back into the
receiver on shutdown and during operation on the
compressor in an unloaded condition.
A pressure relief valve (located on the wet side of
the separator) is set to open at rated tank pressure.
The compressor is also equipped with high pres-
sure shutdown protection to shut down at high MAX
P1 setpoint. This prevents the relief valve from
opening. High temperature probes are provided to
shut down the compressor.
DO NOT remove caps, plugs, and/or other compo-
nents when compressor is running or pressurized.
Stop compressor and relieve all internal pressure
before doing so.
Fluid is added to the sump via a capped fluid filler
opening, located on the tank to prevent overfilling of
the sump. A sight glass enables the operator to
visually monitor the sump fluid level.
2.6 CAPACITY CONTROL SYSTEM, FUNCTIONAL
DESCRIPTION
Refer to Figures 2-3, 2-4A, 2-4B, 2-C,
4E. The purpose of the compressor control system
is to regulate the compressor air intake to match the
amount of compressed air being utilized. At 0 to 10
percent air output, the control system will automati-
cally unload the compressor and reduce power con-
sumption. The unload sump pressure can be set
using the unload control regulator valve (150 psig/
10.3 bar).
The Control System consists of an inlet poppet
valve, startup solenoid valve, reference (equal-
izing) pressure regulator, blowdown solenoid
valve, pneumatic blowdown valve, control pres-
sure regulator, unload pressure regulator,
sequencing solenoid valve, and a control line fil-
ter located prior to the controls.
The functional description of the Control System is
described below in five distinct phases of the com-
pressor operation. For explanation purposes, this
description will apply to compressors with an oper-
ating range of 525 to 535 psig (36.1 to 36.8 bar). A
8
compressor with any other pressure range would
operate in a similar manner except for the stated
pressures.
START MODE - TO 170 PSIG (11.7 BAR)
When the compressor start button is depressed, the
pressure will rise from 0 to 170 psig (0 to 11.7 bar).
During this period, the control inlet solenoid is
closed, which keeps the inlet poppet valve closed.
The control pressure regulator is also closed at this
time. After the startup timer times out, the startup
solenoid valve changes state and the reference
pressure regulator controls the pressure signal to
the poppet valve at a maximum 60 psig (4 bar). The
inlet poppet valve opens allowing full airflow to the
compressor inlet and the discharge pressure builds
to approximately 170 psig (11.7 bar). No air is sup-
plied to the system service line during this phase by
the minimum pressure valve. When the discharge
pressure exceeds approximately 170 psig (11.7
bar), the minimum pressure valve may start to open
and allow air to flow to the system service line.
NORMAL OPERATION MODE - 170 TO 525 PSIG
(11.7 TO 36.1 BAR)
When the sump pressure rises above 170 psig
(11.7 bar), the minimum pressure valve opens and
delivers compressed air to the system service line.
From this point on, a line air pressure transducer
continually monitors the air pressure. The control
pressure regulator valve remains closed during this
phase, keeping the inlet poppet valve wide open.
The blowdown solenoid valve also remains closed
2-4D and 2-
during this phase. Flow will occur when the dis-
charge pressure is higher than the line pressure.
The check valve, which is built into the minimum
pressure valve, will prevent back flow into the com-
pressor.
MODULATING MODE - 525 TO 535 PSIG (36.1 TO
36.8 BAR)
If less than the rated capacity of compressed air is
being used, the system service line pressure will
rise above 525 psig (36.1 bar). The control pres-
sure regulator valve gradually opens applying air
pressure to the control side of the inlet poppet
valve, which modulates the position of the inlet pop-
pet valve. This reduces the amount of air entering
the compressor until it matches the amount of air
being utilized. The control system functions contin-
ually in this manner, between the limits of 525 to
535 psig (36.1 to 36.8 bar) in response to varying
demands from system service line. The control
pressure regulator valve has an orifice, which vents
a small amount of air to the atmosphere when the