Sewage Pump Problem

All the usual:

• shaft misalignment
• bearing seal leak
• incorrect bearing lubrication
• fluid carries too many, too aggressive solids
• chemical compatibility attack: H₂S?
• cavitation
• running against a closed discharge valve
• etc.

What is the composition of the waste water? Does your impeller show signs of damage? Open or closed impeller?

i really can't recognize the type of impeller,i actually have some pics for it if you can help.

Any pictures of the shafts?

Do I understand that the pump puts out 465 liters/second at 32 Meters of head?

Make and model of the pump would be useful information, as would an indication of where the shaft breaks, its material and a photograph of the fracture surface.

Did the fracture surface look something like this. Is there any change of section of the shaft at the crack propagation region? What type of coupling is installed? What was the vibration level and frequency? What were the last alignment figures?

Basically if the fracture is due to some sort of bending fatigue you have to look at what could cause the bending, and alignment comes to mind.

Are you having the same problem on all the pumps?

If all the pumps are failing at the same rate, it may be an hydraulic problem (most likely cavitation or pushing against a dead head), if it' s only this one pump failing, I would look more closely at alignment and lubrication.

by the way, the piping seems well designed with the eccentric reducer and the Long radius elbow.

good luck

IS the type of impeller 2 Vanes mixed flow?

By the way Shaft and Bearings failure occur in all the pumps !!!

What might be the hydraulic causes (IN some Details)?

Check the specs on the pump. 32 meters seems a lot for a non-clog impeller. You may need a higher speed pump.

I have seen similar frequent failures on pumps like you have.

The odd situation is that the pipelines are too heavy for the slender pump support. After several failures, we were forced do some analysis on these kind of pumps. The interesting findings were as below:

· Pipe lines, suction and discharge, were drained off.

· Pump/Motor was decoupled.

· Two Dial gauges at right angle, were mounted on the rim.

· Pipelines were charged.

· Surprised to see huge readings (about 5/8 mm, not microns), both vertically and horizontally.

Analysis:

· The loaded pipes at pump suction and discharge flanges distort the pump's centerline.

· The pump's support (with fewer bolts compared to suction and discharge bolts, in size and numbers) and the probe (the long, slender support at bearing bracket) are too week to hold the pumps preferred position.

· Though pump doesn't move much, keeping pump support as fulcrum, the shaft end deviates from the preferred central axis.

· Pump runs with great 'misalignment', ultimately leads shear at shaft's weakest section.

Remedy:

· Stronger supports were made for suction and discharge lines at very close to pump suction and discharge flanges. These supports include heavy clamps, which would prevent any possible slide or sidewise shift on loading or thermal expansion.

· The influence of pipe loading on coupling end was tested with decoupled condition.

· The probe support was kept loose during this test.

· Objectionable movements were still noticed. Supports were further firmed with stubs welded to pipe around the supports.

· 0.1 mm on the dial was final satisfying figure at the coupling.

· Alignment was carried out with suction/discharge flanges disconnected and loosening the probe support.

· 0.05 mm misalignment was the target.

· Dials on coupling rims, suction/discharge flanges and the probe support were tightened. Pipelines were charged.

· Still all these precautions, deviations around 0.05 mm (further to misalignment) were noticed which were left helpless.

The results were very much satisfying, no shaft fracture and fewer bearing failures.