Control System, Functional Description - Sullair LS-10 25HP Operators Manual And Parts Lists

Section 2
DESCRIPTION
visual sight glass is located on the return line to ob-
serve this fluid flow. There is also an orifice in this
return line (protected by a strainer) to assure prop-
er flow. This separation will reduce the fluid carry---
over to less than 2 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 element replace-
ment 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
exceeds the sump tank rating. A temperature
switch will shut down the compressor if the dis-
charge temperature reaches 235_F (113_C).
DO NOT remove caps, plugs, and/or other com-
ponents when compressor is running or pressur-
ized.
Stop compressor and relieve all internal pres-
sure before doing so.
Fluid is added to the sump via a capped fluid filler
opening, placed low on the tank to prevent overfil-
ling of the sump. A sight glass enables the operator
to visually monitor the sump fluid level.
2.6 CONTROL SYSTEM,
SCRIPTION-- STANDARD ELECTRO/MECHAN-
ICAL
Refer to Figure 2---3. The purpose of the compres-
sor Control System is to regulate the compressor
air intake to match the amount of compressed air
being used. At approximately 10 psig (0.7 bar) air
line over---pressure, the control system will auto-
matically blow down the compressor and greatly
reduce the unload power consumption. The Con-
trol System consists of an inlet valve, (located on
the compressor air inlet), blowdown valve, sole-
noid valve, pressure switch, and a pressure reg-
ulator. The functional descriptions of the Control
System are given below in four distinct phases of
compressor operation. The following guidelines
apply to all LS---10 Series compressors. For ex-
planatory purposes this description will apply to a
compressor with an operating pressure range of
115 to 125 psig (7.9 to 8.6 bar). A compressor with
any other pressure range would operate in the
8
WARNING
!
FUNCTIONAL
same manner 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 in-
let valve is fully open due to inlet air flow, and the
compressor pumps at full rated capacity. The rising
compressor air pressure is isolated from the ser-
vice 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 de-
livers 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.
DE-
UNLOAD -- IN EXCESS OF 125 PSIG (8.6 BAR)
LINE PRESSURE
When no air is being used,the service line pressure
rises to the setting (cut ---out pressure) of the pres-
sure switch. the pressure switch opens, interrupt-
ing the electrical power to the solenoid valve. At this
time, the solenoid valve allows dry sump tank air
pressure or service air pressure through a shuttle
valve to be applied directly to the inlet valve piston
and keep it closed. Simultaneously, the solenoid
valve sends a pneumatic signal to the blowdown
valve. The blowdown valve opens the sump to the
compressor intake reducing the sump pressure to
approximately 25 to 27 psig (1.7to 1.9 bar). The
check valve in the air service line pressure prevents
line pressure from returning to the sump.
When the line pressure drops to the low setting
(cut ---in pressure) of the pressure switch (usually
115 psig [7.9 bar]), the pressure switch closes, re---