Patent ID: 7997074

Claim:
A method of controlling pressure in a hydraulic system of a wind turbine, the hydraulic system including a hydraulic station with a tank for storing working fluid, first and second pumps fluidly connected to the tank, first and second flow paths extending from the respective first and second pumps to a hydraulic circuit, and first and second relief valves in fluid communication with the respective first and second flow paths, the method comprising: controlling the first pump and first relief valve based on maintaining pressure of the working fluid in the hydraulic circuit between a first minimum limit and first maximum limit; controlling the second pump and second relief valve in addition to the first pump and first relief valve if the pressure of the working fluid in the hydraulic circuit falls below the first minimum limit; verifying that the first or second pumps operate when the first or second pumps are requested to do so by a control system; and closing the first or second relief valves only if the operation of the respective first or second pumps has been verified.