Hale HFM - Manual (Page 16)

Many Centrifugal Pump Troubles are Due to Air Leaks
Procedure to follow to detect possible air leaks
:
A. Start engine with pump disengaged and with pump drained.
B. Tightly close pump drain valve as well as booster tank suction and discharge
valves (if connected to a booster tank). Tighten caps on suction and discharge
openings. Then pull out primer handle.
C. With engine running at idling speed, observe hand on vacuum gauge until it
reaches a stationary position. This should be 20 inches or over, depending on
vacuum producing capacity of engine.
D. Release primer handle and carefully watch vacuum gauge hand. If hand drops
back rapidly, it indicates a leak, which must be located and corrected. If it stands
stationary, or moves back very slowly, it indicates either "no leak", or a minor leak,
which will not interfere with satisfactory operation.
E. Should test indicate a leak in pump proper, the stuffing box may need adjustment.
F Now remove discharge cap. If vacuum gauge hand returns toward zero, more
rapidly than before cap was removed, it indicates that the self-closing poppet valve
within the discharge manifold is not properly seated and this condition should be
corrected. G. When difficulty is experienced in locating an air leak, it may be found
by connecting pump suction to a hydrant. With hydrant pressure on pump, look for
water leaks, any one of which indicates a possible air leak. When connected to a
booster tank, there may be an air leak in booster line valves - in valve proper, or
around valve stem. The former may necessitate replacement of complete valve
while the latter may be corrected by replacing valve stem.
H. Do not overlook possibility of air leaks in suction hose or couplings. To test for
such leaks, connect suction hose to pump suction, place pump suction cap over
the end of the suction hose, and test in the same manner as described above as to
the motion of the vacuum gauge hand.
I. It is a very good idea to make periodic tests for air leaks.
NOTE: Excessive air leakage may delay, or even prevent priming
.