Table 4-2 Unit Troubleshooting - Continued
TEST OR INSPECTION
FIREFIGHTING SYSTEM - Continued
"HUNTING" (FLUCTUATING PRESSURE)
Hunting can result from a combination of suction and discharge
conditions involving the pump, relief valve, and engine. When
the elasticity of the suction and discharge system and the
response rate (reaction time) of the engine, pilot valve, and
relief valve are such that the system never stabilizes, hunting
results. Changing one or more of these factors enough to
disrupt this timing should eliminate hunting.
Step 1. Inspect suction hoses and connections for worn seals or loose connections.
Tighten connections or replace seals in suction hoses (see para 4-1 0 and 4-1 1).
Step 2. Check for sticky pilot valve.
Repair pilot valve (see para 4-36).
Step 3. Check for sticking relief valve.
Repair relief valve (see para 4-35).
Check for plugged filter or line.
Clean lines and filter.
FIRE PUMP WILL NOT ENGAGE
Step 1. Check correct switching sequence has been carried out.
Carry out correct switching sequence (see para 2-13).
Step 2. Check for electric shift disengaged.
Push in manual disengage handle (on left hand side of pump body).