Fast opening valve apparatus

A fast opening command means for rapid actuation of a valve actuator, said actuator responding to hydraulic fluid supplied to said actuator and said actuator operatively coupled to a steam flow control means for regulating steam flow of a steam turbine, comprising:

• first hydraulic fluid control means in hydraulic flow communication with said actuator for continuously controlling flow of hydraulic fluid along a first hydraulic path to said actuator from a source of hydraulic fluid;
• and
• second hydraulic fluid control means in hydraulic flow communication with said actuator for controlling flow of hydraulic fluid along a second hydraulic path to said actuator from the source of hydraulic fluid, whereby the first hydraulic path and the second hydraulic path form a parallel hydraulic fluid route between the source of hydraulic fluid and said actuator;
• wherein said first hydraulic fluid control means controls flow of hydraulic fluid to said actuator in response to a desired steam flow and to an actual steam flow of said turbine when the difference between the desired steam flow and the actual steam flow is less than a first predetermined value and controls flow of hydraulic fluid to said actuator in response to a first reference signal having a first predetermined magnitude when the difference between the desired steam flow and the actual steam flow is greater than the first predetermined value;
• and
• wherein said second hydraulic fluid control means controls flow of hydraulic fluid to said actuator in response to a fast open command signal;
• and
• said fast opening command means further comprising means for substituting a second reference signal having a second predetermined magnitude for the first reference signal in response to the fast open command signal when the steam flow control means is supplying less than a

A method for regulating an actual steam flow in a steam turbine, said steam turbine including steam flow control means for controlling said actual steam flow and an actuator operatively coupled to said steam flow control means for effecting continuous control of said actual steam flow, said actuator responsive to hydraulic fluid provided thereto, comprising:

• supplying hydraulic fluid along a first hydraulic fluid path to said actuator in response to a demanded steam flow;
• and
• supplying hydraulic fluid along a second hydraulic fluid path to said actuator when the actual steam flow is less than the demanded steam flow, wherein said second hydraulic fluid path is in parallel with said first hydraulic fluid path;
• limiting the amount of hydraulic fluid supplied along the second hydraulic path in response to a first predetermined magnitude when the actual steam flow is within a first predetermined value of maximum steam flow;
• and
• limiting the amount of hydraulic fluid supplied along the second hydraulic path in response to a second predetermined magnitude when the actual steam flow is within a second predetermined value of maximum steam flow,
• wherein a predetermined flow of hydraulic fluid is supplied along the first hydraulic fluid path at a constant hydraulic attenuation regardless of hydraulic fluid supplied along the second hydraulic fluid path.