Not sure what you mean, but if your question is, why is a balance piston required, then normal they are at the high pressure end of the turbine. The flow there is in one direction only, a balance piston is required to balance the axial thrust on the shaft, the low end pressure of the turbine normally flows in both directions, so the thrust is balanced.
They are usually found on reaction type turbines and are kind of subtle on the drawings, look for something that can form a piston and cylinder arrangement.
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Re: balance
