Page 416 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

384 Applied Process Design for Chemical and Petrochemical Plants

How it Works: Typical of This Class of Pump (By
permission of [27])
0.60
'The Nash vacuum pump or compressor has only one
> 0.50 moving part-a balanced rotor that runs without any
o internal lubrication. Such simplicity is possible because all
c
"'
� 0.40 functions of mechanical pistons or vanes are performed
by a rotating band of liquid compressant.
Q)
§ 0.30 ' I While power to keep it rotating is transmitted by the
Q)
s: ' I rotor, this ring of liquid tends to center itself in the cylin-
f- 0.20 For one-stage drical body. Rotor axis is offset from body axis. As the
liquid-ring
schematic diagram in Figure 6-35 shows, liquid cornpres-
0.10 sant almost fills, then partly empties each rotor chamber
Multistage steam jet
during a single revolution. That sets up the piston action.
Stationary cones inside the rotor have closed sections
Suction pressure, torr between ported openings that separate gas inlet and dis-
charge flows.
Figure 6-34. Rough estimates of thermal efficiency of various vacu-
um producing systems. By permission, Ryans, J. L. and Croll, S., A portion of the liquid compressant passes out with dis-
Chem. Eng., V. 88, No. 25, 1981, p. 72 [22]. charged air or gas. It is usually taken out of the stream by

O IN THIS secroa LIQUID MOVES
OUTWARD - DRAWS GAS FROM
INl.El PORlS INTO ROTOR
CHAM8EAS
LIOUID

Nash vacuum pump schematic.

Disassembled view shows
appearance of rotor, body
and ported cones.

Figure 6-35. Diagram of liquid ring vacuum
pump features. By permission, Nash Engineer-
ing Co.