valve is positioned within the housing to control communication between said inlet and outlet a pressure proportional piston is movable within the housing and is positioned to open and close the valve a latch is positioned within the housing and cooperates with the piston to lock the piston in a position in which said valve is held in an open position providing full communication between said inlet and outlet release of the latch permits the pressure proportional piston to throttle the flow of air through said valve to provide reduced pressure at the outlet a load sensing arm is movably attached to the housing and controls operation of the latch application_number US 2370079 A description fig1 is a top view of the empty and load device with the cover removed to expose a portion of the interior fig6 is a section along plane 6 6 of fig5 and fig7 is a section similar to fig2 illustrating the device in an unloaded car position the empty and load device includes a housing indicated generally at 10 and formed of individual housing sections 12 at the left side of fig2 and 14 at the right side and an intermediate section 16 cover 18 is attached to housing section 14 a.