Pressure transfer unit

A pressure transfer unit comprising:

• a housing having walls defining an internal cavity;
• partition means mounted in said cavity and sealed to said walls to divide said cavity into a first pressure chamber and a second pressure chamber, and being movable to expand and contract a volume of said first chamber;
• said walls providing first port means for communicating said first chamber with a zone to be pressurized and second port means for communicating said second chamber with a reference source of fluid pressure;
• spring means biasing said partition means to move in a direction to contract the volume of said first chamber;
• liquid conduit means through which liquid is introduced into said first chamber, thereby moving said partition means against the bias of said spring means in a direction to expand the volume of said first chamber;
• valve means for limiting the volume of liquid introduced through said conduit means and received in said first chamber, said valve means having a stationary valve member and a cooperating movable valve member mounted on said partition means and actuable to close said valve means in response to movement of said partition means in a direction to expand the volume of said first chamber and to a position corresponding to a preselected volume of said first chamber, and conduit closure means in said liquid conduit means operable to close said liquid conduit means for preventing the flow of liquid outwardly from said first chamber through said liquid conduit means.