Capacity Control System - Hitachi HISCREW 2000 Series Instruction Manual

6.2. Capacity Control System

Only for the 22 kW models
Only for the 37 kW models
Orifice
20US
(Only for
the 22 kW Starting
NC
models) Solenoid
Valve
From
suction filter
Suction Throttle Valve
6.2.1 Types of Capacity Control
Type of capacity control
I-type (Integral unload type): Fully closes the suction
throttle valve when discharge pressure reaches to cut-
off pressure, and fully opens by cutin pressure. At full
close, pressure inside the oil separator is discharged
until it reaches to the atmosphere and economize
power consumption more .
The discharge pressure of the compressor is variable
within the pressure range as follows: (Each pressure
value is set by digital monitor on the panel)
Specification
MPa
discharge pressure
Cutoff pressure MPa
Cutin pressure MPa
Pressure sensor detects pressure setting and micro
computer makes judgement thereto.
P-type (Motor ON-OFF control type): In addition to
U-type and I-type control, the system automatically
stops the motor when a consumed air capacity is less.
(This type fluctuates pressure like I-type.)
U-type (Suction unload type): Gradually controls dis-
charge air capacity by opening or closing the suction
throttle valve according to the increase in discharge
pressure.
6. SYSTEM OF EACH COMPONENT [Capacity Control System]
Modulator valve
COM COM NC
Blow-off
20P
NO solenoid
NO
valve
Relief Valve
(Only for the
37 kW models)
To the suction
throttle valve
To the air end
0.69 0.83 0.92
0.69 0.83 0.92
0.59 0.74 0.82
Operation air flow
At start : 20P (NO-COM)
Load :
At stop : 20P (NO-COM)
From
the air end
Oil Separator
See page 12 for setting of capacity control mode,
page 9 for changing the capacity control settings.
Purpose
This is applicable when air con-
sumption is less and the unit is in
continuous use, and when the
power consumption at unload op-
eration must be kept less.
This is applicable when the unit
is very often operated unloaded,
or when the air consumption in-
termittently fluctuates.
This is applicable when fluctua-
tion of discharge pressure must
be kept less.
Suction throttle
20US (NC-COM)
20P (NC-COM) Suction throttle
20US (NO-COM)
U-type: Pressure Suction throttle
modulator opens. valve closes partly.
I-type: 20P (NO-COM) Suction throttle
20US (NO-COM)
Suction throttle
20US (NO-COM)
Pressure
PS
（1）
sensor (1)
To aftercooler
S-type M-type
◎
(Standard setting)
At delivery from
factory.
−
(Standard setting)
At delivery from
○
valve closed.
valve open.
valve closed.
valve closed.
○
◎
factory.
−
29