Hydraulic servo system for steam turbines

Claim 1

In a hydraulic servo system for steam turbines and the like for actuating the main valve between the turbine and the steam source in addition to other normal operational functions, including feeding source means for supplying hydraulic fluid of a predetermined pressure to said system and a servo motor having a connection to said system and actuated by the hydraulic fluid normally so as to maintain the main valve in opening position to supply steam to the turbine; the improvement enabling drainage of the servo motor and the system independent of one another comprising a. drainage means operative to drain hydraulic fluid from said servo motor to rapidly close said main valve; b. adjustable valve means connected to said hydraulic fluid supply means and to said drainage means between the two; c. hydraulic conduit means located between said adjustable valve and said drainage means for feeding hydraulic fluid from the supply means to said servo system, d. throttling means located in the hydraulic conduit means between said drainage means and said valve means for forming a throttled portion in said system; e. said valve means being provided with control means controlled by the pressure drop between said throttling means and said servo motor to drain hydraulic fluid from said throttled portion and the servo system and effective to interrupt the supply of hydraulic fluid thereto in response to the pressure drop resulting from rapid drainage of hydraulic fluid from the servo motor through said drainage means.