Dynamic Balance of hydraulic turbine runner

[21121956]

Hello everybody:

As a normal practice in the manufacture of hydraulic turbine runners, the Technical Specifications indicate to perform in the final steps of the process, the static and dynamic balancing of the runner.

In one particular case, the manufacturer agrees to perform only the static balance but not the dynamic balancing. Regardless of the Specifications, under what circumstances the dynamic balancing can be ignored? Technically, how can the manufacturer support this position? Should be the owner of the equipment rigorous in demanding the realization of this dynamic balance?

Your comments are welcome. Thanks in advance.

El que no puede andar, se sienta.

 

[RolMec]

Hi 1956,

staical and dynamical balancing cure different illnesses, see sketch. At rot-speeds where centrifugal forces have to be considered, dynamical balancing is a must. Ask the bike people, if you want to go fast you take care of the wheels, those shouldn't start "hammering" @ 35 mph or so. But don't take this number to your case...
In general, it is not only balancing as such, but in some cases this should be done for 2 or even 3 planes of the object.
The effect of disbalance is centrifugal forces, additional dynamical loads on bearings, shafts etc. Then this can induce frequencies leading to excitation --> resonance. Further effects as per your particular case.
Given all factors their due consideration --> dynamical balancing might not be necessary. Commonly seen at low rot- speeds. A case decision for the agreed specialist / appointed expert.
Regards
R.

 

[racookpe1978]

If they don't want to balance the shaft and bearings and unit dynamically, tell them to offer you a lifetime (15+ year) guarantee of it running without failure.

 

[21121956]

Hello everybody:

Thanks for your valuable opinions.

El que no puede andar, se sienta.

 

[chicopee]

What type of a hydraulic turbine is it and what is the expected RPM?

 

[MintJulep]

The owner of the equipment should purchase his equipment from a different supplier.

 

[21121956]

Hello everybody:

These are Francis turbines, with 1.035 mm in diameter and rotating at 720 RPM. The nominal water flow is 7,5 m³/s per turbine and a net head of 120 m.

El que no puede andar, se sienta.

 

[chicopee]

I would think that the manufacturer would have an obligation to have this hydraulic turbine run properly and make corrections for deficiencies before this turbine is turned over to the owner.

 

[geesamand]

You should know from the moment of startup if the dynamic balancing was necessary based on the vibration level of the rotating parts. I could see how static or dynamic balance could succeed based on the proportions of the runner, inherent imbalances, and required vibration levels in operation.

David

 

[Artisi]

--- and are the between blade volumes also being checked against each other as this can also be a source of (hydraulic)unbalance leading to vibration.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)