Capacity Control System Standard - Hitachi NEXT Series Service Manual

2.3 Capacity Control System Standard

2.3.1 Fix speed type (Load-Unload Operation)
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 por t to por t
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 airend while the blowoff valve
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
(C)
Suction Throttle Valve
1st-stage
airend
Intercooler
Check valve
2nd-stage
airend
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)
COM
NC
NO
3-Way Solenoid Valve (3)
20U
3
NC-COM connected for
5 seconds after reactor
is changed over to a
fullvoltage connection.
Check valve Aftercooler
Air-Cooled Water-Cooled
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. When the pressure sensor
(PS) detects the low pressure, 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)
20U
4
COM
3-Way Solenoid Valve (20US)
Blowoff
20US
valve
NO
COM
NC
To the
Atmosphere
COM
NC
NO
20U
2
3-Way Solenoid
Valve (2)
Control Line Filter
Pressure sensor
PS
10
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
Control air flow
NO
Starting/Stopping
NC
Loading
Unloading
COM
NO NC
For 20 seconds
after starting with
a star-delta starter.
Compressed Air Discharge
1