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How should fire pump malfunction be diagnosed ?

2020-11-09
Usually fire pump in the maintenance process, the diagnosis of fire pump fault is a key link, the following gives several common faults and elimination measures, for everyone to have a targeted diagnosis of fire pump fault.

Insufficient fluid or pressure

1) the pump is not filled with water or properly vented

Elimination measures: check whether the pump shell and inlet pipeline are fully filled with liquid.

2) too low speed

Elimination measures: check whether the motor wiring is correct, whether the voltage is normal or whether the steam pressure of the turbine is normal.

3) the water head of the system is too high

Elimination measures: check system head (especially friction loss).

4) suction range is too high

Elimination measures: check the existing net head (too small or too long inlet pipe will cause great friction loss).

5) impeller or pipeline is blocked

Elimination measures: check there are no obstacles.

6) wrong rotation direction

Elimination measures: check the rotation direction.

7) produce air or leakage in the inlet pipeline

Elimination: check the inlet line for cavitation and/or air leakage.

8) the packing or seal in the packing box wear out, so that air leakage into the pump shell

Elimination measures: check packing or seal and replace as needed, check whether the lubrication is normal.

9) insufficient suction head when pumping hot or volatile liquid

Eliminate measure: increase suction head, consult manufacturer.

10) the bottom valve is too small

Elimination measures: install the correct size of the bottom valve.

11) insufficient submersion depth of bottom valve or inlet pipe

Elimination measures: consult the manufacturer about the correct depth of immersion. Use baffles to eliminate eddies.

12) impeller clearance is too large

Elimination measures: check the gap is correct.

13) impeller damage

Elimination measures: check impeller, replace as required.

14) impeller diameter is too small

Elimination measures: consult the manufacturer about the correct impeller diameter.

15) the pressure gauge is in an incorrect position

Elimination measures: check the correct location, check the outlet nozzle or pipe.

16) damaged water pump shell gasket

Elimination measures: check the condition of the gasket and replace it as required.

The power consumption of fire pump is too large

1) the rotation direction is wrong

Elimination measures: check the rotation direction.

2) impeller damage

Elimination measures: check impeller, replace as required.

3) the rotating parts bite to death

Elimination measures: check whether the internal wear parts clearance is normal.

4) axis bending

Elimination measures: alignment shaft or replacement as required.

5) too fast

Elimination measures: check the winding voltage of the motor or the steam pressure sent to the turbine.

6) the head is lower than the rated value. Pumping too much liquid

Eliminate measure: consult manufacturer. Install throttle valve, cut impeller.

7) the liquid is heavier than expected

Elimination measures: check specific gravity and viscosity.

8) stuffing box without correct stuffing (insufficient stuffing, incorrect stuffing or run-in, packing too tight)

Elimination measures: check the stuffing and reload the stuffing box.

9) improper lubrication or bearing wear

Elimination measures: check and replace as required.

10) the running gap between wear rings is not correct

Elimination measures: check the gap is correct. Replace the wear-resistant ring of the pump shell and/or impeller as required.

11) the pipe stress on the pump shell is too large

Eliminate measure: eliminate stress and manufacturer representative consultation. After the stress is removed, check the alignment.

Too much leakage in stuffing box

1) axis bending

Elimination measures: alignment shaft or replacement as required.

2) misalignment of coupling or pump and drive device

Elimination measures: check the alignment, if necessary, re-alignment.

3) improper lubrication or bearing wear

Elimination measures: check and replace as required.

Fire pump bearing temperature is too high

1) axis bending

Elimination measures: alignment shaft or replacement as required.

2) misalignment of coupling or water pump and drive device

Elimination measures: check the alignment, if necessary, re-alignment.

3) improper lubrication or bearing wear

Elimination measures: check and replace as required.

4) the pipe stress on the pump shell is too large

Elimination measures: eliminate stress and consult the representative of the manufacturer. After the stress is removed, check the alignment.

5) too much lubricant

Elimination measures: remove the plug, so that excessive oil automatic discharge. If the pump is oil-lubricated, drain the oil to the correct level.

Fire pump stuffing box overheating

1) the packing or seal in the packing box wear out, so that air leakage into the pump shell

Elimination: check packing or seal and replace as needed. Check whether the lubrication is normal.

Multistage fire pump
2) stuffing box without correct stuffing (insufficient stuffing, incorrect stuffing or run-in, packing too tight)

Elimination measures: check the stuffing and reload the stuffing box.

3) packing or mechanical seal design problem

Eliminate measure: consult manufacturer.

4) mechanical seal is damaged

Elimination measures: check and replace as required. Consult the manufacturer.

5) the shaft sleeve is scratched

Elimination measures: repair, remachining or replacement as required.

6) packing is too tight or mechanical seal is not properly adjusted

Elimination measures: check and adjust packing, replace as required. Adjust mechanical seals (refer to manufacturer's instructions with pumps or consult manufacturer).

Rotating parts of fire pump
1) axis bending

Elimination measures: alignment shaft or replacement as required.

2) the operating gap between the wear-resistant rings is not correct

Elimination measures: check the gap is correct. Replace the wear - resistant ring of the pump shell or impeller as required

3) the pipe stress on the pump shell is too large

Eliminate measure: eliminate stress and manufacturer representative consultation. After the stress is removed, check the alignment.

4) too much swing of shaft or impeller ring

Elimination measures: check rotating parts and bearings and replace worn or damaged parts as required.

5) there is dirt between the impeller and the wear-resistant ring of the pump shell. There is dirt in the wear-resistant ring of the pump shell

Elimination measures: clean and check wear - resistant rings, replace as required. Isolate and eliminate the source of dirt.

A small problem that is easy to ignore when assembling after repairing the fire pump

The middle line of impeller outlet in the vortex shell pump, that is, the middle line of impeller outlet width should be aligned with the middle line of vortex shell inlet. In case of misalignment, the impeller wheel hub and shaft shoulder should be adjusted by adding shim. The two midlines should be controlled within 0.5 mm. For pump slightly worse than the revolution of the pump has little impact on the performance of the pump, for pump with low specific speed due to the impeller outlet is very narrow, such as the impeller outlet width of only 10 mm, if the Central Line with the vortex shell 1 mm, the performance of the fire pump has a significant impact. It is suggested that the error of the two middle lines (impeller and vortex shell) should be controlled within 5% of the outlet width of the impeller.