VIBRATING DRY WELL SUBMERSIBLE SEWAGE PUMP

[Berko]

Hi All,

We have a single vane, dry well submersible sewage pump (4 pole speed, 220 kW) which has an operating duty of 500 L/s @ 40M.

The pump is vertically mounted on the OEM's purpose built suction stand.

When the pump runs, the following vibration levels have been recorded.

Vibration at suction stand/volute = 5.5 mm/s (RMS)
Vibration at top of motor = 20.2 mm/s (RMS)

Top of motor is approx. 3.2M from the floor level where the Suction Stand is bolted.

Is this figure 20.2 mm/s considered excessive ?

Can anyone advise on any documents/reports/thesis, etc where I can find out what vibration limits would be considered acceptable for the motor ?

Awaiting your reply,

Cheers,

Berko

 

[CESSNA1]

BERKO:

What are the associated displacements and frequencies? Are these data the result of a PSD or did you just integrate the Acceleration curve?

Most vibration books and handbooks have a log-log chart of recommendations and ranges for acceptably smooth operation. Page 19-4 of HARRIS - Shock and Vibration Handbook lists

5.5. mm/s RMS as unsatisfactory for rigid supports and satisfactory for flexible supports.

20.2 mm/s RMS is listed as unacceptable for both.

I suggest some additional research on this system

Regards
Dave

 

[MachineryWatch]

Looks like the Hydraulic Institute standards for vertical pumps would allow nearly 8 mm/sec-rms (overall) vibration for radial vibration measurements made at the top of the motor, if the motor height is measured above the plane of the surface the that is considered the mounting floor of the motor. In other words, if the top of the motor is mounted on a floor and their is a drive shaft running to the floor below to drive the pump, you would use the measurement from the floor level the motor was mounted on to the top of the motor.

The Hydraulic Institute allows higher amplitudes the further up you go from the plane of the floor level. The number given above is a for the range from 12-20 feet above floor level.

You can see that the level you are seeing is well above the standard mentioned and above any standard I am aware of.

You don't mention the frequency of the vibration. We need more information to help diagnose the source of the problem but it is safe to say that resonance is a dominant source of problems on vertical pump/motor combinations.

Skip Hartman

http://www.machinerywatch.com