Page 200 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Pumping of Liquids 173

P Pressure of Liquid in Box all mechanical seals) and must not attack the material of
P': Average Presrurt Across
the O-ring shaft packing. Many other designs are avail-
able, and the manufacturers should be consulted for
advice on specific sealing problems.

Centrifugal Pump Selection

I The centrifugal pump is a versatile unit in the process
Closing Force : a (Arco"A"-Areo"C"] + Spring Loading
P
P'
Opening Force : x Area"B" plant, since its ease of control, non-pulsing flow, pressure
'h ,%"and "C"are Vorioblr limiting operation fits many small and large flow systems.
Figure 3-21. Area relationship for balanced seal construction. (By
permission, T. J. Sniffen, Power and Fluids, Winter 1958, Worthing-
ton Corp.)

pressures. Actually the maximum operating process pres-
sures are a function of the shaft speed and diameter for a
given seal design fluid and fluid temperature.
Figure 3-22 is an outside balanced seal designed for
vacuum to 150 psig and -40°F to +4OO0F. (See Table 3-4)
The process fluid must be free of solids (as for practically

Table 34
Requirements for Mechanical Seal Installations
________ ~
~
Fig.
Feature Description Remarks No.
-~
Cooling Water Jacketed Liquid must dead end 3-23 Figure 3-22. Outside balanced seal (single). (Courtesy Durametallic
Stuffing Box in stuffing box Corp.)
Cooling Gland Plate Efficient to cool 3-24
contact faces
Lubrication Dead-End Good under vacuum, 3-25
mild abrasives metal-
metal, dry seals
Lubrication Circulating Good cooling of 3-26
contact faces 3 GPM Cooling
Flushing Inside Seal Good for volatile 3-27
liquids, sol'ns tending 5 GPM Cooling
to crystallize, steam
Flushing Outside Seal Heating to prevent 3-28
solidification
Quenching Outside Seals For oxidizing and 3-29 \Pumping Temperature ,OF /
(only) corrosive liquids, seal
liquid washes process Suction Pressure
fluid, for high temp. Dead-ended in
Vent and Inside Seal Safety feature, for 3-30
Drain venting to flare, Circulation From
draining
Flushing Double Requires circulation 3-31A Internal Seal Passage.
system
Flushing Tandem Requires circulation 3-3 1 B Close Fitting
system Throat Bushing
Two Rotary Double For improved sealing 331C
Four Rotary Double For special sealing 331D
Tandem problem Figure 3-23. Water jacketed stuffing box. (By permission, H. P. Hum-
~ mer and W. J. Ramsey, Bulletin SD, 752, O&T, Durametallic Corp.)
~