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8. STANDARD COMPONENTS AND SUBSYSTEMS [Capacity Control System]
8.4 Capacity Control System
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
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.
STARTING
UNLOADING
RELOADING
STOPPING
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
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
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 (20Ux)
switched over to pressurize
Chamber (A)
STOP button ON
Suction throttle valve
(STV) closes
Blowoff valve opens
Internal air in discharge pipe
is exhausted to atmosphere
Compressor stops
Vacuum Valve
For 20 seconds
after starting with a
star-delta starter.
Suction Throttle Valve
1st-Stage
Air End
Intercooler
Check Valve
Aftercooler
Chamber
(C)
Chamber (B)
To Chamber (B)
To the
Atmosphere
Blowoff
Valve
3-Way Solenoid
Valve (3)
NC-COM connected for
5 seconds after reactor
is changed over to a
fullvoltage connection.
Compressed Air Discharge
Pressure Sensor
Control Line Filter
3-Way Solenoid
Valve (2)
3-Way Solenoid
Valve (1)
NC
NO
COM
NC
NO
COM
NC
NO
COM
20U
3
20U
2
20U
1
PS
Control Air Flow
Starting/Stopping
Loading
Unloading
To Chamber (A)
Chamber (A)
2nd-Stage
Air End
Check Valve
NO
NC
COM
3-Way Solenoid
Valve (20US)
3-Way Solenoid
Valve (4)
20U
4
NC
NO
COM
20US
8.4.1 Load-Unload Operation (Only for Fixed Speed Type)
