Page 193 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

166 Applied Process Design for Chemical and Petrochemical Plants

Table 3-3 ance between these two faces prevents leak-
Basic Parts of a Centrifugal Pump age of liquid out or air in.
Shaft sleeve Protects the shaft where it passes through the
Part Purpose stuffing box. Usually used in pumps with
Impeller Imparts velocity to the liquid, resulting from packing but often eliminated if mechanical
centrifugal force as the impeller is rotated. seals are employed.
Casing Gives direction to the flow from the impeller Wearing rings Keeps internal recirculation down to a mini-
and converts this velocity energy into pres- mum. Having these rings as replaceable wear-
sure energy which is usually measured in feet ing surfaces permits renewal of clearances to
of head. keep pump efficiencies high. On mall types
only one ring is used in the casing and on
Shaft Transmits power from the driver to the im- larger sizes, companion rings are used in the
peller. casing and on the impeller.
Stuffing box This is a means of throttling the leakage
which would otherwise oc~w at the point of Wearing plates With open type impellers or end clearance
entry of the shaft into the casing. Usually not wearing fits, these perform the same purpose
a separate part, but rather made up of a as wearing rings do with radial clearances.
group of small details, as “A” to “D”. Bearings Accurately locate shaft and carry radial and
(A) Packing This is the most common means of throttling thrust loads.
the leakage between the inside and outside of
the casing. Frame To mount unit rigidly and support bearings.
(B) Gland To position and adjust the packing pressure. In most single suction pumps this is a sepa-
(C) Seal gage Provides passage to distribute the sealing me- rate piece. In many double suction pumps, the
(also called dium uniformly around the portion of the support is through feet cast as part of the
water-seal shaft that passes through the stuffing box. casing. In some special suction pumps, the
OF lantern This is very essential when suction lift con- feet are also part of the casing and the bear-
ring ditions prevail to seal against in-leakage of air. ing assembly is overhung. With close coupled
single suction types, this support is provided
(D) Mechanical Provides a mechanical sealing arrangement by the motor or by special supporting adap-
seal that takes the place of the packing. Basically ters.
it has one surface rotating with the shaft and
one stationary face. The minutely close clear- Coupling Connects the pump to the driver.
MODIFIED STUFFING BOX.. . avail- CASING is horizontally split to permit STANDARD DEEP STUFF-
able with John Crane Type 1 mechqni- removal of top half without disturbing ING BOX carries generous
tal seals. These mechanical seals are piping. Suction and discharge connec- packing; is easily access-
easy to install in the field and are car- tions are in lower half of casing. ible. Stuffing box contains
lied in stock. split seal cages and split
glonds. Gland bolts are
c o m p I e t e I y removable.
Bushing at bottom of stuff-
ing box is close fitting and
readily reploceable.

SHAFT is heat treated, ex-
tra heavy to take maximum
radial thrust. Shaft sup- /
ports impeller between
bearings for longer bear- ALL BEARINGS, grease-
ing, wearing ring and pack- ibricated, held in bearing
ing life. wring of heavy one-piece
/ mstruction - are excep-
Pnally well sealed against
housing are cost integral
WEARING RINGS pro- I \ moisture. Brackets holding
tect casing, are easily re- with the casing. Bearing
placed, assure continuous covers are also of heavy
high efficiency. Impeller IMPELLER, hydraulically one-piece construction and
rings and tongue and balanced - double suction are interchangeable end
groove casing rings are enclosed type for better for end.. . and contain sta-
available at nominal performance under critical tionary member of laby-
extra cost. suction conditions. rinth seal.
Figure 3-4. Centrifugal Pump, double suction single-stage impeller. (Courtesy Allis-Chalmers Mfg. Co.)