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Capacity Control System - Hitachi NEXT Series Instruction Manual

Oil-free rotary screw air compressor
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8. STANDARD COMPONENTS AND SUBSYSTEMS [Capacity Control System]

8.4 Capacity Control System

8.4.1 Load-Unload Operation (Only for Fixed Speed Type)
The unloading process occurs when the compressed air
demand decreases and the discharge pressure rises as
high as cut-out pressure. The pressure sensor (PS)
detects the high pressure and energizes the 3-way solenoid
valve (20Ux), changing its port to port connection. The
control air is now flowing to and pressurizing chamber
(A) of the suction throttle valve (STV), consequently
closing the suction throttle valve (STV) and unloading the
STARTING
Suction throttle valve (STV) closed
START button ON
Airend starts rotation to
compress minor amounts of air
Starts in no load
Changes to full voltage delta connection
3-way solenoid valve (20Ux)
switched over to connect
Chamber (A) & Chamber (C)
Suction throttle valve (STV) opens
Loading
Vacuum Valve
Chamber
Suction Throttle Valve
1st-Stage
Air End
Intercooler
Check Valve
2nd-Stage
Air End
UNLOADING
Air demand decreases
Discharge pipe pressure rises
Pressure sensor (PS) operates
3-way solenoid valve (20Ux)
switched over to pressurize
Chamber (A)
Suction throttle valve
(STV) closes
Blowoff valve opens
Internal air in discharge pipe is
exhausted to atmosphere
To Chamber (B)
To Chamber (A)
Chamber (B)
Chamber (A)
(C)
NC
20U
3
3-Way Solenoid
Valve (3)
NC-COM connected for
5 seconds after reactor
is changed over to a
fullvoltage connection.
Check Valve
airend while the blowoff valve opens and exhausts the
internal compressed air to atmosphere.
The loading process occurs when the compressed air
demand increases and the discharge pressure dropped as
low as cut-in pressure. The pressure sensor (PS) detects
the low pressure and 3-way solenoid valve (20Ux), suction
throttle valve (STV), and blowoff valve work in reverse
action and the airend reloads.
RELOADING
Air demand increases
Discharge pipe pressure drops
Pressure sensor (PS) operates
3-way solenoid valve (20Ux)
switched over to pressurize
Chamber (B)
Suction throttle valve
(STV) opens
Blowoff valve closes
Loading
3-Way Solenoid
Valve (4)
3-Way Solenoid
Blowoff
Valve (20US)
Valve
20US
NO
To the
Atmosphere
COM
NC
NO
20U
2
3-Way Solenoid
Valve (2)
Aftercooler
STOPPING
STOP button ON
3-way solenoid valve (20Ux)
switched over to pressurize
Chamber (A)
Suction throttle valve
(STV) closes
Blowoff valve opens
Internal air in discharge pipe
is exhausted to atmosphere
Compressor stops
3-Way Solenoid
Valve (1)
20U
4
Control Air Flow
COM
NO
Starting/Stopping
NC
Loading
Unloading
COM
COM
NC
NC
NO
For 20 seconds
COM
after starting with a
star-delta starter.
NO
Control Line Filter
Pressure Sensor
PS
Compressed Air Discharge
20U
1
67

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