Capacity Control System - Hitachi NEXT Series Instruction Manual

8. STANDARD COMPONENTS AND SUBSYSTEMS [Capacity Control System]

8.4 Capacity Control System

8.4.1 Standard 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 sole-
noid valve (20Ux), changing its port to port connection.
The control air is now flowing to and pressurizing cham-
ber (A) of the suction throttle valve (STV), consequently
closing the suction throttle valve (STV) and unloading
STARTING
Suction throttle valve (STV) closed
START button ON
Airend starts rotation to
compress minor amounts of air
Starts in no load
switch (Reactor short)
△
3-way solenoid valve (20Ux)
switched over to connect
Chamber (A) & Chamber (C)
Suction throttle valve (STV) opens
Loading
Valve 2
Chamber
(C)
Suction Throttle Valve
1st-Stage
Air End
Intercooler
Orifice
Check Valve
2nd-Stage
Air End
62
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)
Valve 1
(Vacuum Valve)
To Chamber (A)
Chamber Chamber
(B)
Air Exhaust Valve
20U
3
3-Way Solenoid
Valve (3)
NC-COM connected for 5 seconds
after reactor is changed over to a
fullvoltage connection.
Blowoff air cooler
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.
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
Blowoff Valve
20US
3-Way Solenoid
Valve (20US)
COM
NO
NC
(A)
COM
COM
NC
NC
NO
NO
20U
2
3-Way Solenoid
Valve (2)
PS
Check Valve
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
Control Air Flow
Starting/Stopping
Loading
COM
NO Unloading
20U
NC 1
3-Way Solenoid Valve (1)
For 20 seconds after starting
with a star-delta starter.
For 15 seconds after starting
COM
with reactor starter.
NC
NO
20U
4
3-Way Solenoid
Valve (4)
Control Line Filter
Pressure Sensor
Compressed Air Discharge