9
C - OPERATION
1. PRIMING
Install pet cock (248) on top of casing as shown.
CAUTION: Before starting the pump, the casing and suction
line must be ¿ lled with liquid. The pump must not be run until
it is completely ¿ lled with liquid, because of danger of injuring
some of the parts of the pump which depend upon liquid for
lubrication. Wearing rings will not seize when the pump is
¿ lled with liquid but are very liable to do so when the pump is
run dry.
Vertical units must be primed through the recirculation line at
the top inboard seal gland.
Priming By Suction Pressure
When operating with suction pressure (À ooded suction),
priming may be accomplished by bleeding all the air out of the
pump by opening the petcock located at the top of the upper
casing or at the top seal gland.
A pump operating under a suction lift may be primed by
any of the following methods, as may be best suited to the
conditions. The discharge valve should be closed during
priming operation.
Priming by Ejector or Exhauster
This method is used when steam, high pressure water, or
compressed air is available.
1. Attach an air ejector to the highest point in the pump
casing. This will remove the air from the pump and
suction line.
Vertical units must be primed through the recirculation
line at the top inboard seal gland.
2. As soon as the ejector waste pipe throws water
continuously, the pump may be started. After starting, a
steady stream of water from the waste pipe indicates
the pump is primed. If this stream of water is not
obtained, the pump must be stopped at once and the
process of priming repeated. A foot valve is unnecessary
when this kind of device is used.
3. Open the discharge valve slowly and close off the
ejector.
Priming With Foot Valve
When it is not practicable to prime by ejector or exhauster,
the pump may be primed by the use of a foot valve. The
foot valve will prevent liquid running out through the suction
inlet and the pump can be completely ¿ lled with liquid from
some outside source. Pet cocks on the top of the pump
should be opened during ¿ lling to allow the air to escape.
A tight foot valve will keep the pump constantly primed so
that the pump may be used for automatic operation. The
valve must be inspected frequently, however, to see that
it does not develop leaks and thus allow the pump to be
started dry.
Priming by Vacuum Pump
When neither of the above methods of priming are practical,
the pump may be primed by the use of a vacuum pump to
exhaust the air from the pump casing and suction line. A
wet vacuum pump is preferable, as it will not be injured
if water enters it. When a dry vacuum pump is used, the
installation must be such as to prevent liquid being taken
into the air pump. The vacuum pump manufacturer’s
instructions should be followed.
2. STARTING THE PUMP
Position of Discharge Valve on Starting
A high or medium head centrifugal pump, when primed
and operated at full speed with the discharge gate valve
closed, requires much less power than when operated at
its rated capacity and head with the discharge gate valve
open. For this reason it is usually advantageous to have
the discharge gate valve closed when the pump is being
started. The pump must not be throttled by the use of a
valve in the suction line.
WARNING! - Operating the pump with a closed
discharge valve can result in excessive heat
build-up and should be limited to the shortest
practical duration. Operating the pump at
close to shut-off head usually places greater bending
strains on the shaft than at operating points near the
best ef¿ ciency.
The following important items should be checked as pump
is started and placed in operation.
a. Pump and driver securely bolted
b. Coupling properly aligned
c. Piping complete
d. Correct pump rotation
e. Pump shaft turns freely
f. Discharge valve closed
g. Suction valve open (if used)
h. Coupling Guard installed
i. Pump fully primed
j. Pump and driver properly lubricated
k. Seal water valve (if used) open
Only after these items have been checked should the
pump be started.
3. INITIAL ADJUSTMENTS
Open discharge valve as soon as operating speed has
been reached. After the pump has been started the
packing box glands should be tightened to eliminate
excessive liquid loss. (Applies only to pumps having
packed stuf¿ ng boxes.) Packing should not be pressed too
tight, as this may result in burning the packing and scoring
the shaft or shaft sleeve. The best adjustment will allow
the liquid to drip slowly from the packing box gland. This
will permit proper lubrication of the shaft and dissipate
generated heat.
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