Diagnosing Specific Problems - Grundfos CR Installation And Operating Instruction Manual

15. Diagnosing specific problems

Problem
The pump does not run.
The pump runs but at reduced
capacity or does not deliver water.
22
Possible cause
1. No power at motor.
Fuses are blown or circuit
2.
breakers are tripped.
Motor starter overloads are burned
3.
or have tripped out.
4. Starter does not energize.
5. Defective controls.
6. Motor is defective.
Defective capacitor
7.
(single-phase motors).
8. Pump is bound.
1. Wrong rotation.
2. Pump is not primed or is airbound.
Strainers, check or foot valves are
3.
clogged.
4. Suction lift too large.
Suction and/or discharge piping
5.
leaks.
6. Pump worn.
Pump impeller or guide vane is
7.
clogged.
8. Incorrect drain plug is installed.
9. Improper coupling setting.
Remedy
Check voltage at motor terminal box. If no voltage at motor, check
feeder panel for tripped circuits and reset circuit.
Turn off power and remove fuses. Check for continuity with
ohmmeter. Replace blown fuses or reset circuit breaker. If new
fuses blow or circuit breaker trips, the electrical installation, motor
and wires must be checked.
Check for voltage on line and load side of starter. Replace burned
heaters or reset. Inspect starter for other damage. If heater trips
again, check the supply voltage and starter holding coil.
Energize control circuit and check for voltage at the holding coil. If
no voltage, check control circuit fuses. If voltage, check holding
coil for shorts. Replace bad coil.
Check all safety and pressure switches for operation. Inspect
contacts in control devices. Replace worn or defective parts or
controls.
Turn off power and disconnect wiring. Measure the lead to lead
resistances with ohmmeter (RX-1). Measure lead to ground values
with ohmmeter (RX-100K). Record measured values. If an open or
grounded winding is found, remove motor and repair or replace.
Turn off power and discharge capacitor. Check with ohmme-
ter (RX-100K). When the meter is connected to the capaci-
tor, the needle should jump towards 0 ohms and slowly drift
back to infinity (h). Replace if defective.
Turn off power and manually rotate pump shaft. If shaft does not
rotate easily, check coupling setting and adjust as necessary. If
shaft rotation is still tight, remove pump and inspect. Disassemble
and repair.
Check wiring for proper connections. Correct wiring.
Turn pump off, close isolation valve(s), remove priming plug.
Check fluid level. Refill the pump, replace plug and start the pump.
Long suction lines must be filled before starting the pump.
Remove strainer, screen or valve and inspect. Clean and replace.
Reprime pump.
Install compound pressure gauge at the suction side of the pump.
Start pump and compare reading to performance data. Reduce
suction lift by lowering pump, increase suction line size or
removing high friction loss devices.
Pump spins backwards when turned off. Air in suction pipe.
Suction pipe, valves and fittings must be airtight. Repair any leaks
and retighten all loose fittings.
Install pressure gauge, start pump, gradually close the discharge
valve and read pressure at shutoff. Convert measured pressure (in
psi) to head (in feet): (Measured psi x 2.31 ft/psi = ___ ft). Refer to
the specific pump curve for shutoff head for that pump model. If
head is close to curve, pump is probably OK. If not, remove pump
and inspect.
Disassemble and inspect pump passageways. Remove any
foreign materials found.
If the proper drain plug is replaced with a standard plug, water will
recirculate internally. Replace with proper plug.
Check/reset the coupling; see page 18.