185 T3 Kubota User Manual 2: Description
02250223-054 R01
Subject to EAR, ECCN EAR99 and related export control restrictions. 19
2.6 Capacity control system,
functional description
Refer to Figure 2-3 or Figure 2-4. The purpose of the
control system is to regulate the amount of air intake and
match it to the demand (required output) on the compres-
sor. The control system consists of a pressure regulating
valve(
s), air inlet valve, system blow
down valve, engine
speed control, and tubing connecting the various compo-
nents of the compressor and engine. The functional
desc
riptions of th
e control system are described by relat-
ing them to four distinct phases of operation. They apply
to any contr
ol system with the exception of those with
specified pressures which are dependent on pressure
requirements. The given values apply to a compressor
with an operating pressure range of 100 to 125 psig (6.9
to 8.6 bar).
Start—0 to 58 psig (0 to 4.0 bar)
When the compressor is started, the sump pressure
quickly rises from 0 to 58 psig (0 to 4.0 bar). During this
peri
od the pressure regulator valve is inactive. At this
pressure range the idle warm-up control keeps the inlet
valve closed for engine idle operation. Within 30 seconds
of starting the compressor (the instrument panel annunci-
ator light goes off after 30 seconds) turn the handle of the
war
m-up selector
valve (located on the instrument panel)
from the START to the RUN position. The inlet valve is
fully open due to inlet pressure, and the compressor
operates at full capacity. When the compressor operates
at full capacity, the engine runs at full speed.
Normal operation—80 to 100 psig (5.6 to 6.9 bar)
When the warm-up control selector valve handle is
moved to the RUN position, the sump pressure rises
above 80 psig (5.6 bar). At this time, the inlet valve
r
emains fu
lly open for maximum air output. The engine
will continue to run at full speed during this phase of
operation.
Modulation—100 to 125 psig (6.9 to 8.6 bar)
If the demand on the compressor is less than its rated
capacity, the service line pressure will rise above
100 psig (6.9 bar). The pressure regulating valve gradu-
ally opens, applying pressure to the inlet valve piston and
en
gine
speed control. This causes the inlet valve to par-
tially close and reduces the engine speed. As the pres-
sure increases, the inlet valve pis
ton will further close the
inlet va
lve and the engine speed will decrease until it
reaches its preset idle speed. When the demand on the
compressor increases, the sump pressure falls below
125 psig (8.6 bar). The pressure regulating valve closes,
the air
inlet
valve opens fully, and the engine speed
increases to its preset full load rating.
Between the pressure regulating valve and the inlet
valve, there is a
small orifice that vents a small amount of
air into the atmosphere when the pressure regulating
valve is open. This allows changes in air output to con-
form to air demand. This orifice also discharges any
accumu
lated mo
isture from the regulator.
Shutdown
The blowdown valve is normally closed. At shutdown the
back pressure in the compressor inlet signals the blow-
down valve to vent the sump pressure into the atmo-
sphere.
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