2202MYJE-MY-C8-N_2018.02.
Chapter 2 Compressor Specifications and Structure
Compound 2-stage Screw Compressor 3225**C 2.5 Mechanisms
2-21
2.5.6 Capacity Control Mechanism
The capacity control mechanism, by moving a slide valve, lets suction gas (immediately before
compressed) bypass and advance to the suction side, to help shorten the rotor portion used for
compression. The slide valve is located at the bottom of the casing in which the rotors mesh together,
and is constructed to move parallel to the rotor shaft. This movement is changed by a cam mechanism
into rotation movement. Its position (namely, capacity control ratio) is indicated externally and, at the
same time, fed back to the automatic control circuit by changing the electric resistance.
Figure 2-20 Capacity Control Mechanism
2.5.7 Bearings and Balance Piston
For the load acting on the rotor perpendicular to the shaft, sleeve-type white metal-lined bearing is used.
For the load acting along the shaft direction, face-to-face combination type of angular contact ball
bearings is used.
Special care is taken to cope with the load acting along the shaft direction. Because the M rotor is a
kind of helical gear and also because the thrust force produced by discharge pressure is larger than
that for F rotor, the load applied onto the M rotor is reduced by using not only a thrust bearing but also a
balance piston that applies pressure from the opposing direction.
2.5.8 Shaft Seal Block
To prevent refrigerant gas and oil leakage, a mechanical seal assembly is used for the shaft seal of the
M rotor.
Mechanical seal assembly is mainly composed of "rotating ring" installed on the rotor shaft and
"stationary ring" installed in the seal cover. Rotating ring rotates with the shaft, and slides each other
with the stationary ring while maintaining a micron class gap. The sliding each other place is called as
the sliding surface.
For example, the BBSE (Balance Bellow Single Seal) which is currently used as standard seal,
employs a stationary ring (mating ring) made of special cast iron, a rotating ring made from carbon, and
O-rings for the packing.
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