Hitachi HISCREW 2000 Series - 6.2. Capacity Control System

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6.2.1 Types 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)
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.
Pressure sensor detects pressure setting and micro
computer makes judgement thereto.
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.
Type of capacity control Purpose S-type M-type
○
◎
−
◎
−
○
MPa
MPa
MPa
0.69 0.83 0.92
0.69 0.83 0.92
0.59 0.74 0.82
Suction throttle
valve closed.
Suction throttle
valve open.
Suction throttle
valve closes partly.
Suction throttle
valve closed.
Suction throttle
valve closed.
At start : 20P (NO-COM)
20US (NC-COM)
Load : 20P (NC-COM)
20US (NO-COM)
U-type :Pressure
modulator opens.
I-type : 20P (NO-COM)
20US (NO-COM)
At stop : 20P (NO-COM)
20US (NO-COM)
Operation air flow
6. SYSTEM OF EACH COMPONENT [Capacity Control System]
6.2. Capacity Control System
Unload
☞
See page 12 for setting of capacity control mode,
page 9 for changing the capacity control settings.
Specification
discharge pressure
Cutoff pressure
Cutin pressure
(Standard setting)
At delivery from
factory.
Onlyforthe22kWmodels
Onlyforthe37kWmodels
Totheairend
Tothesuction
throttlevalve
From
theairend
NC
NC
COM
COM
NO
NO
20P
20US
SuctionThrottleValve
OilSeparator
PS
（1）
Orifice
(Onlyfor
the22kW
models)
Pressure
sensor(1)
To aftercooler
Starting
Solenoid
Valve
Modulatorvalve
Blow-off
solenoid
valve
ReliefValve
(Onlyforthe
37kWmodels)
From
suctionfilter
(Standard setting)
At delivery from
factory.