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CMC TECHNICAL REFERENCE MANUAL
1X36003 Version 2.52
1996-1999 Ingersoll-Rand Company
Date of Issue: 18-Oct-1999
5
Once loaded, the compressor
will operate along the constant
pressure line until the user
switches to Unload or presses
the stop button.
Control is accomplished by
modulating the inlet valve within
the compressor's throttle range.
When system demand is less
than the minimum throttled
capacity, the discharge
pressure is maintained by
modulating the bypass valve and
venting some or all of the air to
atmosphere. This valve is
opened just prior to reaching the
surge line. Whenever the
bypass valve is open, the inlet
valve maintains its position at
the minimum throttled capacity
setting. Modulate provides a
constant discharge pressure
with variable capacity from
design to zero.
This control method is used
when reliable control of the
discharge pressure is required.
Modulate is the most commonly
used control method for Centac
and X-FLO compressors.
Energy Saving Control - Autodual
Autodual automatically loads the
machine when demand is high
and unloads the machine when
demand is low.
When the compressor is
controlling to pressure setpoint
and demand is within the inlet
valve throttle range, constant
pressure is maintained in the
same manner as Modulate.
When the machine is controlling
to the pressure setpoint and
system demand is low, the
compressor is operated in the
bypass valve throttle range.
Discharge
Pressure
Power at
Coupling
Capacity
Surge Line
Natural
Curve
Design
Point
Natural
Curve
Unload
Point
Unloaded
Unloaded
Inlet
Valve
Throttle
Range
Bypass
Valve
Throttle
Range
Reload Point
(Reload Percent)
Unload
Point
Figure 2: Autodual Control
Discharge
Pressure
Power at
Coupling
Capacity
Inlet
Valve
Throttle
Range
Surge Line
Natural
Pressure
Curve
Design
Point
Maximum
Throttle Point
(MinLoad)
Constant Pressure Line
Unloaded
Bypass
Valve
Throttle
Range
Natural
Power
Curve
Surge Line
Constant Power Line
Unloaded
Figure 3: Modulate Control