Hitachi NEXT Series Service Manual page 14

Oil-free screw compressor
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2.3.3 Capacity Control System
Air intake
Air Intake filter
1st-stage blowoff solenoid valve (1)
2nd-stage blowoff solenoid valve (1)
1st-stage
airend
2nd-stage blowoff solenoid valve (2)
Intercooler
2nd-stage
airend
■ Relationship between Air Consumption Rate and Capacity Control System
Rated
Air
Model
pressure
consumption
(%)
psi [MPa]
100 - 75 (65) 134 (136) - 108 (108)
55 kW
125 [0.86]
100 - 60 (50) 133 (137) - 80 (72)
75 kW
75 (65) - 5
55 kW
125 [0.86]
60 (50) - 5
75 kW
All 
125 [0.86]
5 - 0
model
The air compressor supports the three (3) capacity control systems as shown above.
Depending on the varying air consumption, an appropriate system is automatically selected. For more information, see
the following page. Operation frequency is shown by Digital monitor. LCD monitor displays up to first figure after
decimal place.
1st-stage blowoff solenoid valve (2)
Aftercooler
Check valve
Operating
Capacity control system
frequency (Hz)
① CPCS
speed control
82
② Two-step purge
control
66 (60)
③ Motor
Main motor stop
restart control
Air-Cooled
Water-Cooled
Purging Air Flow and Action of Blowoff Solenoid Valve
Operation phase
Starting
Loading
Purging
Stop
Power Interruption
Blowoff
silencer
Pressure sensor
PS2
※ The value in (
Control
motor
pressure
Cut-out
pressure
Cut-in
pressure
stop/
Cut-in
pressure
12
Blowoff solenoid
Blowoff solenoid
valve (1)
Fully opened
Fully closed
Fully opened
Fully opened
Fully closed
Air
discharge
) is indicated for water-cooled type.
Pressure setting
psi [MPa]
Example
Initial
of Lower
125 [0.86] 120 [0.83]
138 [0.95] 125 [0.86] AUTO ON
131 [0.90] 120 [0.83]
131 [0.90] 120 [0.83] AUTO ON
valve (2)
Fully closed
Fully closed
Fully closed
Fully opened
Fully opened
Capacity
control type
AUTO ON
VSDA
or
AUTO OFF
VSDB
VSDA
or
AUTO OFF
VSDB
VSDA

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