20-foot suction lift. The pump consists of a split
casing, wearing rings, and rotating element.
SPLIT CASING.— The casing (fig. 4-7). is
horizontally split at the shaft centerline. This enables
easy removal of the upper casing half for inspection
and maintenance. The casing is divided into three
chambers; two suction and one discharge. The upper
half of the casing contains a flange that may connect
the pump to an air eliminator valve. Two external
seal lines on the upper casing feed fuel from the
discharge chamber to cool the mechanical seals. The
lower half of the casing contains bearing housings, a
suction flange and a discharge flange that connect
the pump to the piping system. Drain holes and drain
plugs are provided at the bottom of both flanges for
draining the pump.
WEARING RINGS.—There are four replaceable
type wearing rings (two rotating and two stationary)
installed within the pump casing. The two rotating
are installed on the impeller. The two stationary are
installed in the pump casing between the suction and
discharge chambers. The stationary rings are held in
place and prevented from rotation by the tongue-and-
groove
construction.
When
the
pump
is
assembled, the rotating wearing rings ride inside the
stationary rings. (Check the appropriate technical
manual for the correct clearance between the
stationary and rotating rings.)
Wearing rings serve two purposes: (1) owing to
their unique construction and close tolerances, they
minimize leakage between the discharge and suction
chambers and (2) they allow for the wear created
between the impeller and pump casing.
Fuel passing through the pump has a tendency
to recirculate from the discharge chamber back to the
suction chamber. As the fuel passes through the
narrow clearance between the wearing rings, a
partial seal is made by the rapid rotation of the
impeller. This seal minimizes the leakage between
the discharge and suction chambers. After prolonged
use of the pump, the clearance between the wearing
rings gradually increases due to wear. This is caused
by the friction created by the rapid rotation of the
impeller and the fuel passing between the wearing
rings. As the clearance increases, the sealing effect
decreases resulting in the loss of the rated capacity of
the pump.
Figure 4-7.—Centrifugal pump casing.
4-11
