Grasso Screw compressors Types C ... XF Product Information - GEA ...

PRODUCT INFORMATION
GRASSO SCREW COMPRESSORS
Types C ... XF
INTRODUCTION; TECHNICAL FEATURES
1.3 TECHNICAL FEATURES
Rotors
The rotors are made from machined or forged tool
steel. They are designed according to low energy
consumption criteria (patented profile with optimized
main dimensions). The primary rotor is driven by the
motor, whereas the secondary rotor is directly driven
by the primary rotor by means of a thin oil film.
The drive shaft end is cylindrical and does not have
a keyway. To have a compressor in accordance with
ATEX guidelines the end of the drive shaft needs to
have a cylindrical exterior with a keyway.
Casing
The casings for operating pressures up to 28 bar are
made of laminar grey cast iron. The casings for operating
pressures up to 52 bar are made of spheroidal
cast iron. Compressors for special requirements
in accordance with API 619 are available with a cast
steel casing.
Bearings
The compressors of series AC, SH, MC and of type
CM have complete anti-friction bearings. Highperformance
cylindrical ball bearings for absorbing
radial forces and angular contact ball bearings for
absorbing axial forces provide for a theoretical live of
up to 100.000 operational hours. A hydraulically
loaded balance piston reduces the force on the axial
ball bearings and increases their lifespan. The compressors
in the LT series use the low-friction sleeve
bearings on a thin oil film to carry the radial forces in
rotor shafts with no contact and the angular contact
ball bearings absorb the axial forces.
Position indication
For position indication of the hydraulic systems of
the capacity control and the Vi adjustment, a hermetic
path sensor is used which provides an output signal
between 4 and 20 mA.
In compressor version in line with ATEX guidelines
and the required safety levels EEx ia IIC T4 or EEx
ib IIC T4, one of the position sensors from the manufacturer
shall be installed with zener diode.
For screw compressors that operate in concert with
additional compressors and have a check valve installed,
the adjustment path for the control slide in
the capacity control shall be reduced with a stop
sleeve or through parameters in the compressor
control system with a minim control slide settings
while the compressor is operating. A stop sleeve
limit the min. position of the slide and guarantees a
minimum flow rate for the compressor.
Optional equipment specifications
In addition to the specifications listed above the
compressors may also be equipped with other components.
– Doubly-working shaft seal, if the requirements in
API 619 are met.
– Axial slide bearings to fulfill API 619.
– Bearing temperature monitoring for the slide
bearings.
– Rotor positioning system for monitoring the axial
position of the rotors.
Shaft sealing
The oil blocking shaft seal with a rotating and a fixed
ring is responsible for sealing off the drive for the
male rotor shaft. Depending on the anticipated wear
on the shaft seal, various material pairings can be
used. The seal is designed to relieve load variations
whilst containing the oil charge and the thin oil film
between the rings results in a long service life. For
special cases of application the compressors can be
equipped with one doubly working axial shaft seal.
Capacity control
Through an infinitely variable control slide with a
hydraulic mechanism the swept volume can be adjusted
from 100% to a minimal value. Compressors
with a variable volume ratio operate according to a
system of combined Vi partial-load control.
10 _101011_pi_sc_gbr_2_.doc GEA Refrigeration Germany GmbH
23.03.2012