Section 1, General Information; Figure 1-1 - Compression Cycle - Gardner Denver VS200-250B Operating And Service Manual

SECTION 1
GENERAL INFORMATION
COMPRESSOR – Your Gardner Denver Rotary Screw package is fitted with one (1) single stage, positive
displacement rotary compressor using meshing helical rotors to effect compression. Each pair of rotors is
supported between high capacity anti-friction bearings located outside the compression chamber. Single
cylindrical roller bearings are used at each end of the rotors to carry the radial loads. An additional
angular contact ball bearing is located at the discharge end of each rotor to carry axial thrust loads - the
arrangement of both roller and ball bearings is designed to withstand reverse axial thrust loads. The main
rotor sits next to its gate companion, in a side-by-side configuration.
COMPRESSION PRINCIPLE (Figure 1-1) - Compression is accomplished by the main and gate rotors
synchronously meshing in a one-piece cylinder. The main rotor has four (4) helical lobes, 90 apart,
which mesh with five (5) helical grooves, 72 apart, on its matching gate rotor.
The air inlet port is located on top of the compressor cylinder, and the discharge port is located below the
compressor cylinder. The compression cycle begins as the rotors unmesh at the inlet port and air is
drawn into the cavity between the main rotor lobes and gate rotor grooves (A). When the rotors pass the
inlet port cutoff, air is trapped in the interlobe cavity and flows axially with the meshing rotors (B). As
meshing continues, more of the main rotor lobe enters the gate rotor groove, normal volume is reduced
and pressure increases.
Oil is injected into the cylinder to remove the heat of compression and seal internal clearances. Volume
reduction and pressure continues to increase until the air/oil mixture trapped in the interlobe cavity by the
rotors passes the discharge port (C). Each rotor cavity follows the same "fill-compress-discharge" cycle in
rapid succession to produce a discharge air flow that is continuous, smooth and shock free.
AIR FLOW IN THE COMPRESSOR SYSTEM (Figure 4-2, page 28) - Air enters the air filter and passes
through the inlet control (poppet) valve to the compressor inlet flange. After compression, the air/oil
mixture enters the oil reservoir where most of the entrained oil is removed by change of direction and
impingent. It is further removed by centrifugal action and drained down into the reservoir. The air and
remaining aerosols pass into twin coalescing elements where the oil is captured and drained through a
drain line back into a lower pressure region of the compressor. The nearly oil-free air passes through the
minimum pressure valve, aftercooler, optional moisture separator, and finally to the distribution network.
LUBRICATION, COOLING AND SEALING (Figure 4-2, page 28) - Oil is forced by differential pressure
from the oil reservoir through the oil cooler, servo-driven oil mixing valve, oil filter, and enters the
compressor. A portion of the oil is directed to internal passages within the compressor to lubricate the
bearings and shaft oil seals. The balance of the oil is injected into the compressor rotors to remove the
heat of compression, seal internal clearances and lubricate the rotors.
Figure 1-1 – COMPRESSION CYCLE
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