The main reason for vacuum dynamic balancing in our case is the HP that would be required to turn the rotor assembly in air to do a high speed or full speed balance. In a vacuum essentially no work is being done except rotate the mass of the rotor assembly. In most cases it allows a full speed balance.
Another reason is to take out any windage caused from not the wheels not being enclosed in a housing.
Different types of wheels or coupled wheels produce strange dynamics in air.
Will you please give me the area in this web-site that sets the policy that you refer to? I have seen comments like this before. Honestly I have tried several times to find the forum policy section --- I spent significant time doing so and found nothing.
I just went to the site policies area again and it only deals with vendors/regulators, disclaimers, and responsibilities of some types of members.
I have no doubt that these policies exist but it is hard to follow the rules if you don't know what they are.
I have confidence that you can provide this info as you have ststed that it is a policy.
This keeps people from posting the question in every Forum or as one might say "Spamming" the Forums. Most member's time, including yours, is quite valuable so one question at a time on one Forum is the way for more people to get assistance.
As a general rule, duplicate posts that are not indicated as such tend to cause people to duplicate work to answer the same question.
The experts who can answer such questions tend to subscribe to a variety of different forums, so they'll tend to such these questions, even if there is only a single posting.
Vacuum dynamic balance is a condition that is normally permitted rather than specified.
The thing that is specified is the balance speed. Always go for full speed unless unusual circumstances, or cost make it impractical.
A full speed air test would be impractical on many turbines as it could wreck the final stages, or the shaft, or both due to excessive power/torque requirement. So the vendor either has to have a boiler of sufficient capacity/condition to run the turbine, or he is required to request a vacuum balance run.
The vacuum balance also ensures that a vacuum can be held while the shaft spins; provides an informal (i.e. you wont get any results) test on the shaft gland capability.
