period two
Compressor Capacity Control
notes
6OLGH9DOYH
| GLVFKDUJH |
| SRUW |
VOLGHYDOYH | VOLGHYDOYH |
FORVHG | RSHQ |
| |
| WRVXFWLRQ |
YDOYH
RSHQLQJ
IXOOORDGSDUWORDG
Figure 38
At full load, the slide valve is closed. The compressor pumps its maximum volume of refrigerant, discharging it through the discharge port.
As the load on the compressor decreases, the slide valve modulates toward the open position. The opening created by the valve movement allows refrigerant vapor to bypass from the rotor pockets back to the suction side of the compressor. This reduces the volume of vapor available for the compression process. It also reduces the amount of rotor length available for compression. In this manner, the volume of refrigerant that is pumped by the compressor is varied, unloading it to balance the existing load.
,QOHW9DQHV
LQOHWYDQHV
LPSHOOHU
Figure 39
Inlet Vanes
A common method of modulating the capacity of a centrifugal compressor is to use a set of vanes installed at the inlet of the compressor impeller. While a survey of other centrifugal compressor designs shows that there are other
| 27 |