Control System, Functional Description- Electro-Mechanical Valve - Sullair LS20 Operator's Manual And Parts List

Section 2
DESCRIPTION
The spiral valve provides a modulation range from
100 to 50%. During this period, the pressure rises
approximately from 100 to 105 psig (6.9 to 7.2 bar).
As the air pressure exceeds 105 psig (7.2 bar), the
differential pressure regulator controlling the inlet
poppet valve starts opening and forcing the poppet
closed, thus throttling inlet air flow to the compres-
sor. The inlet poppet valve provides a modulation
range from 50 to 40%. During this period, the pres-
sure rises approximately from 106 to 110 psig (7.3
to 7.6 bar). During this range, the spiral valve
remains in the unload position.
UNLOAD MODE - IN EXCESS OF 110 PSIG (7.6
BAR)
When a relatively small amount or no air is being
used, the service line pressure continues to rise.
When it exceeds 110 psig (7.6 bar), the Supervisor
Control System de-energizes the solenoid valve
allowing sump air pressure to be supplied directly to
close the inlet valve. Simultaneously, the solenoid
valve sends a pneumatic signal to the blowdown
valve. The blowdown valve opens to the atmos-
phere, reducing the sump pressure to approximate-
ly 15 to 20 psig (1.0 to 1.4 bar). The minimum pres-
sure check valve prevents line pressure from
returning to the sump.
When the line pressure drops to the low setting
(cut-in pressure; usually 100 psig [6.9 bar] on low
pressure ["L"] compressors; 125 psig [8.6 bar] on
high pressure ["H"] compressors; 150 psig [10.3
bar] on ["HH"] compressors; and 175 psig [12.0
bar] ["XH"] . Supervisor energizes the solenoid
valve and allows the blowdown valve to close. The
re-energized solenoid valve again prevents line
pressure from reaching the inlet control valve.
Should the pressure begin to rise, the pressure reg-
ulator will resume its normal function as previously
described.
AUTOMATIC OPERATION
For applications with varied periods of time when
there are no air requirements, Supervisor's AUTO-
MATIC mode allows the compressor to shutdown
(time delayed) when no compressed air require-
ment is present and restart as compressed air is
needed.
2.7 CONTROL SYSTEM, FUNCTIONAL DESCRIP-
TION- ELECTRO-MECHANICAL VALVE
Refer to Figure 2-5B. 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 automat-
12
ically blow down the compressor and greatly reduce
the unload power consumption. The Control
System consists of an inlet valve, (located on the
compressor air inlet), blowdown valve, solenoid
valve, pressure switch, and a pressure regula-
tor. The functional descriptions of the Control
System are given below in four distinct phases of
compressor operation. The following guidelines
apply to all LS20 Series compressors. For explana-
tory purposes this description will apply to a com-
pressor with an operating pressure range of 100 to
110 psig (6.9 to 7.6 bar). A compressor with any
other pressure range would operate in the 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
inlet 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 service
line in this phase by the minimum pressure valve,
set at approximately 50 psig (3.5 bar).
Closed Inlet Start- (Wye-delta or Solid-State start-
ing) applies dry-sump or service air pressure
through a solenoid valve to hold the inlet valve
closed allowing the compressor to start unloaded.
After a preset time (4-6 seconds) the controller will
discontinue applying pressure to the inlet valve, and
allow the compressor to continued with the start
mode.
NORMAL OPERATING MODE - 50 TO 100 PSIG
(3.5 TO 6.9 BAR )
When the pressure air rises above 50 psig (3.5 bar),
the minimum pressure/check valve opens and
delivers compressed air to the service line. From
this point on, the line air pressure is continually
monitored by a line pressure gauge and a pressure
switch usually set at 100 psig (6.9 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 (STANDARD CONTROL) -
100 TO 110 PSIG (6.9 TO 7.6 BAR)
If less than the rated capacity of compressed air is
being used, the line pressure will rise above 100
psig (6.9 bar), and a pressure regulator starts feed-
ing an air signal to close the inlet poppet valve,
throttling the mass of air entering the compressor
and thereby reducing the latter's air delivery. The air
throttling of the inlet poppet valve system increases