Vilter VSM 71-701 Operation And Service Manual Download

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COMPRESSOR

The Vilter Single Screw Compressor is a positive
displacement, capacity and volume controlled, oil
flooded, rotary compressor which uses a single
main screw intermeshed by two opposing gate ro-
tors. Gas compression occurs when the individual
fingers of each gate rotor sweep through the
grooves, or flutes, of the main screw as the screw
rotates. Compression occurs from the time the
screw flute is first closed off by the gate rotor fin-
ger, until the time when the screw flute has ro-
tated to the point of lining up with the discharge
port in the compressor housing. A labyrinth type
seal is used to prevent gas at discharge pressure
from leaking past the end of the screw. Any dis-
charge gas leakage past the labyrinth seal is vented
back to suction via four longitudinal holes drilled
through the body of the screw.

By venting the discharge end of the main screw
back to suction, forces on each end of the screw
are equal. This results in zero net axial forces on
the main bearings. With twin opposing gate ro-
tors, all radial forces are cancelled out also. Main
shaft bearings have no net forces except the weight
of the screw and the shaft assembly.

The compressors are comprised of three rotating
assemblies: the main screw assembly and the two
gate rotor assemblies. Each of these rotating as-
semblies use a common bearing configuration con-
sisting of a single, cylindrical rolling element bear-
ing at one end, and a pair of angular contact ball
bearings at the other end. The pair of angular
contact ball bearings are used to axially fix one
end of the rotating shafts, and to absorb the small
amount of thrust loads on the shafts. The inner
races of the ball bearings are securely clamped to
the rotating shafts, while the outer races are se-
curely held in the bearing housing, thus fixing the
axial position of the shaft in relation to the bear-
ing housings. The cylindrical roller bearings at
the opposite end of the shafts allow for axial growth
of the shafts while supporting the radial loads from
the shafts.

The suction gas enters the compressor housing
through the top inlet flange, at the driven end of
the unit. The driven end of the compressor hous-

ing is flooded with gas at suction pressure. The
gas enters the open end of the main screw flutes at
the driven end, and becomes trapped in the screw
flute as the screw rotates and the gate rotor tooth
enters the end of the flute. At this point, the com-
pression process begins. Directly after the screw
flute is closed off by the gate rotor tooth, oil is in-
jected into the groove.

The oil enters the compressor through a connec-
tion at the top of the compressor. The purpose of
the injected oil is to absorb the heat of compres-
sion, to seal the gate rotor tooth in the groove, and
to lubricate the moving parts.

Additional internal oiling ports are provided at the
main and gate rotor bearings to cool and lubricate
the bearings. The mechanical shaft seal housing
also contains oiling ports to lubricate, cool and pro-
vide a sealing film of oil for the mechanical shafts
seal. Excess oil flows through the check valves on
the sealing baffle plate. This oil is directed at the
main rotor roller bearing, which cools and lubri-
cates the front roller bearing.

As the main screw rotates, the gate rotor is also
driven, causing the gate rotor tooth to sweep the
groove in the main screw. This sweeping action
reduces the volume of the groove ahead of the gate
rotor tooth and causes the trapped gas and oil to be
compressed in the reduced volume. As the main
screw continues to rotate, the gate rotor tooth con-
tinues to reduce the groove volume to a minimum,
thus compressing the trapped gas to a maximum
pressure. A labyrinth seal arrangement prevents
the compressed gas from leaking past the end of
the screw. As the gate rotor tooth reaches the end
of the groove, the groove rotates to a position that
lines up with the discharge port in the compressor
housing and the gas/oil mixture is discharged from
the screw at high pressure. This completes the com-
pression cycle for a single flute of the main screw.

Once the gas is swept from the main screw flute
through the discharge port, it passes into the dis-
charge manifold of the compressor. From the dis-
charge manifold, the gas/oil exits the compressor
housing

Vilter VSM 71-701, Operation And Service Manual

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