Page 245 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Pumping of Liquids 215

Choice of leak-resistant packing or
standard mechanical seal (illustrated).
Special mechanical seals available to
Positive-lock thrust control for preci- fit equipment.
sion rotor and shaft positioning to Integral safety relief valve works to
protect system against excessive
maintain original perfonnance and pressure.
minimize wear for extended pump life.

Cushioned, positive-flow action of Specially designed and machined
rotor and idler combination provides ....____ revolvable casing provides eight
non-pulsating, low-shear transmis- port positions to suit application.
sion of liquid.
Figure 3-658. Typical rotary gear pump. (By permission, Viking Pump, Inc., Unit of ldex Corporation.)

selection of these pumps, it is sometimes better to select a Significant Features in Reciprocating Pump
larger pump running at low speeds than a smaller pump Arrangements
at high speeds when dealing with viscous materials.
I. Liquid Pump End
As a general guide, speed is reduced 25-35 percent A. Pump Pressure Component
below rating for each tenfold increase in viscosity above
1000 SSU. Also, generally, the mechanical efficiency of I. Piston
the pump is decreased 10 percent for each ten fold 2. Plunger
increase in viscosity above 1000 SSU, and referenced to B. Types
a maximum efficiency of 55 percent at this point. [1] 1. Simplex, one piston
2. Duplex, two piston (Figure 3-66)
3. Triplex, three piston (not used as steam driven)
Reciprocating Pumps
C. Piston or Plunger Action
1. Single acting, one stroke per rpm
Reciprocating pumps are positive displacement pis-
ton units driven by a direct connected steam cylinder 2. Double acting, two strokes per rpm, cylinder
or by an external power source connected to the crank- fills and discharges each stroke (Figure 3-67)
shaft of the pump piston. Being positive displacement, D. Packing for Piston or Plunger
these pumps can develop very high pressures ( 10,000 1. Piston packed: packing mounted on piston and
psi and higher) for very low or high capacities (up to moves with piston; applied to comparatively low
1000 GPM). pressures