Steady operation method for hydraulic machine operating at variable speed

A steady operation method for a hydraulic machine operating at a variable revolution speed which is controlled in accordance with a head or load at a steady operation of the hydraulic machine, comprising the steps of:

• detecting a head or load of a hydraulic machine;
• obtaining a basic signal in response to a detected value of the head or load so as to control a revolution speed of the hydraulic machine;
• detecting parallelly a vibration or hydraulic pressure variation of the hydraulic machine;
• converting a detected value of the vibration or hydraulic pressure variation into an auxiliary signal;
• and
• controlling the revolution speed of the hydraulic machine operating at a variable speed in such a manner as that when the auxiliary signal is below a predetermined upper limit thereof regarding the vibration or the hydraulic pressure variation, said revolution speed is controlled by said basic signal, and otherwise, when the auxiliary signal is beyond said predetermined upper limit, said revolution speed is controlled by a signal other than said basic signal.