Frick SGXH-4021 - Stepless Capacity Control

070.650-IOM (JUL 19)
Page 7
SGC/SGX ROTARY SCREW COMPRESSOR
INSTALLATION
Stepless capacity control
Capacity control is achieved by using a movable slide
valve. The slide valve moves axially under the rotors to
provide fully modulated capacity control from 100% to
minimum load capacity. Minimum load capacity varies
slightly with compressor model, pressure ratio, discharge
pressure level, and rotor speed. See the Table 1 for mini-
mum capacity for all SGC models.
The slide valve is positioned by hydraulic movement of its
control piston. When in the unloaded position, gas is by-
passed back to suction through a recirculation slot before
compression begins and any work is expended, providing
themostefcientunloading method available or part-load
operation of a screw compressor.
Volumizer variable volume ratio control
The FRICK compressor includes a method of varying the
internal volume ratio to match the system pressure ratio.
Control of the internal volume ratio eliminates the power
penalty associated with over- or under-compression.
Volume ratio control is achieved by using a slide stop, a
movable portion of the rotor housing that moves axially
with the rotors to control discharge port location. The slide
stop is moved by hydraulic actuation of a control piston.
The range of adjustment is listed in the Table 3.
Motor mount
SGC/SGX models through 3524 are designed with a drive
endangethatmateswithacastironmotormount(avail-
able as a sales order option). The motor mount is preci-
sion machined so that it ensures proper alignment of the
compressor and motor coupling.
Table 3: Compressor volume and capacity ratio
SGC
model
Min.
Vi
(1)
Max.
Vi
Min. capacity
%
Slide valve
and slide stop
travel
1913 2.2 5.0
Refer to
CoolWare
™
Refer to
NS-7-11
Compressor
volume
ratio
and capacity
information
1918 2.2 5.0
2313 2.2 5.0
2317 2.2 5.0
2321 2.2 5.0
2813 2.2 5.0
2817 2.2 5.0
2821 2.2 5.0
2824 2.0 4.1
3511 2.2 5.0
3515 2.2 5.0
3519 2.2 5.0
3524 2.4 4.5
4013 2.2 5.0
4018 2.2 5.0
4021 2.2 4.3
1. Optional 1.7 - 3.0 Vi