Pressure balanced actuating device

Claim 1

AN ACTUATOR FOR USE WITHIN A PRESSURIZED FLUID ENVIRONMENT COMPRISING: A BODY; AN ACTUATION FLUID PRESSURE SOURCE IN SAID BODY; A BORE IN SAID BODY COMMUNICATING SAID SOURCE WITH THE EXTERIOR OF SAID BODY; SAID BORE INCLUDING A BORE ENLARGEMENT INTERMEDIATE THE ENDS THEREOF; FIRST AND SECOND INTERCONNECTEDLY SPACED PISTONS IN SEALING SLIDABLE ENGAGEMENT RESPECTIVELY WITH SAID BORE INTERMEDIATE SAID SOURCE AND SAID BORE ENLARGEMENT AND WITH SAID BORE ENLARGEMENT; AN ACTUATOR ROD IN FORCE TRANSMITTING RELATION TO SAID SECOND PISTON AND IN SEALING SLIDABLE ENGAGEMENT WITH SAID BORE AND HAVING ONE END AREA EFFECTIVELY EXPOSED TO SAID FLUID INVIRONMENT; SAID ROD BEING EXTENDABLE FROM SAID BORE IN RESPONSE TO DISPLACEMENT TO SAID PISTONS BY PRESSURE APPLIED FROM SAID SOURCE; SAID FIRST AND SECOND INTERCONNECTEDLY SPACED PISTONS HAVING CONFRONTING EFFECTIVE AREAS OF DIFFERENT SIZE SUCH THAT THEIR AREA DIFFERENCE IS SUBSTANTIALLY EQUAL TO THE EFFECTIVE AREA OF SAID ACTUATOR ROD EXPOSED TO SAID FLUID ENVIRONMENT; AND MEANS ADMITTING FLUID FROM SAID ENVIRONMENT TO SAID BORE INTERMEDIATE SAID CONFRONTING EFFECTIVE PISTON AREAS WHEREBY THE PRESSURE OF SAID ENVIRONMENT EXERTS A NET FORCE ON SAID INTERCONNECTEDLY SPACED PISTONS WHICH IS SUBSTANTIALLY EQUAL AND OPPOSITE THE FORCE EXERTED ON SAID ACTUATOR ROD BY THE PRESSURE OF SAID FLUID ENVIRONMENT.