Table 4-2. Unit Troubleshooting - Continued
TEST OR INSPECTION
FIREFIGHTING SYSTEM - Continued
PUMP FAILS TO PRIME OR LOSES PRIME - Continued
Step 7. Check for a clogged orifice in the oil line at the fitting of the priming pump head.
Refer to Direct support maintenance level to remove obstruction from orifice.
Step 8. Check vane primer pump.
After prolonged service, wear may increase primer vane clearance and reduce efficiency.
Refer to Direct support maintenance level to adjust.
Step 9. Check valve in by-pass line stuck open.
If a bypass line is installed between the pump discharge and water tank to prevent pump
from overheating with all discharge valves closed, look for a check valve in the line. If valve is
stuck open, clean it, replace it, or temporarily block off line until a new valve can be obtained.
Step 10. Estimate or measure vertical distance from water source to pump.
Do not attempt lifts exceeding 22 vertical feet (6. 7 m) except at iow altitudes and with
equipment in new condition.
Step 11. Check that end of suction hose is deep enough.
Although suction hose might be immersed enough for priming, pumping large volumes of
water may produce whirlpools, which will allow air to be drawn into suction hose. Whenever
possible, place end of suction hose at least two feet below water surface.
Step 12. Check that suction line is below pump.
If possible, avoid placing any part of suction hose higher than pump suction inlet. If high point
cannot be prevented, close discharge valve as soon as pressure drops, and reprime. This
procedure will usually eliminate air pockets in suction line, but it may have to be repeated
Step 13. Primer not operated long enough.
Refer to operating instructions for required priming time. Repeat priming procedure.
The maximum time for priming should not exceed one-half
minute for lifts up to 10 feet (3. 05 m).