070-450 IOM (NOV 13)
Page 6
XJF ROTARY SCREW COMPRESSOR
INSTALLATION - OPERATION - MAINTENANCE
CONSTRUCTION DETAILS
HOUSING: All XJF screw compressor castings are close
grain, pressure tight, grey cast iron, to ensure structural,
mechanical, and thermal stability under all operating
conditions. Ductile iron is also available for special
applications. Contact Johnson Controls–Frick Sales for
additional information.
ROTORS: The rotors are made from the highest quality
rolled steel to exacting tolerances of the latest industry
standard asymmetric prole. The ve-lobed male rotor is
directly connected to the internal gear. The seven-lobed
female rotor is driven by the male on a thin oil lm.
GEAR:
The compressor
has an internal gear to speed up
the rotors. Each model has 3 or 4 gear ratios.
BEARINGS: Antifriction bearings with L
10
rated life in
excess of 50,000 hours (using the Frick Superlter
™
) at
design conditions are used for reduced frictional
horsepower and superior rotor positioning, resulting in
reduced power consumption, particularly at higher
pressure ratios. Cylindrical roller bearings are provided to
handle the radial loads and the thrust loads are absorbed
by four point contact or angular contact bearings. In
addition, thrust balance pistons are provided to reduce the
thrust load and improve bearing life.
SHAFT SEAL: The compressor shaft seal is a single-face
type with a spring-loaded carbon stationary surface riding
against a cast iron rotating seat. The seal is capable of
withstanding static pressure up to 400 psig. During
operation it is vented to low pressure to provide extended
life.
VOLUMIZER II ADJUSTABLE VOLUME RATIO CONTROL:
The Frick XJF compressor
adjusts to the most efcient of
three volume ratios (2.2, 3.5 or 5.0) depending upon system
requirements.
Control of the internal volume ratio eliminates
the power penalty associated with over- or under-
compression. Volume ratio control is achieved by the use of
a slide stop which is 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.
STEPLESS CAPACITY CONTROL: Capacity control is
achieved by use of a movable slide valve. The slide valve
moves axially under the rotors to provide fully modulated
capacity control from 100% to 25% of full load capacity.
The slide valve is positioned by hydraulic movement of its
control piston. When in the unloaded position, gas is
bypassed back to suction through a recirculation slot before
compression begins and any work is expended, providing
the most efcient unloading method available for part-load
operation of a screw compressor.
MOTOR MOUNT: The XJF series is designed with a drive
end ange that mates with a cast iron motor mount
(available as a sales order option). The motor mount is
precision machined so that it ensures proper alignment of
the compressor and motor coupling.
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