Patent ID: 8425209

Claim:
A vapor recovery pump for a fuel dispensing unit, the vapor recovery pump comprising: a housing having a first end wall and a second end wall; a movable piston arranged to move inside the housing alternately towards a selectively variable first end position and a selectively variable second end position, the movable piston and the first end wall defining a first chamber having a first variable volume and the movable piston and the second end wall defining a second chamber having a second variable volume; a first vapor inlet valve and a first vapor outlet valve connected to the first chamber, the first vapor inlet valve and the first vapor outlet valve opening and closing in response to pressure of the vapor in the first chamber; a second vapor inlet valve and a second vapor outlet valve connected to the second chamber, the second vapor inlet valve and the second vapor outlet valve opening and closing in response to pressure of the vapor in the second chamber; a first vapor flow line coupled to the first vapor inlet valve; a second vapor flow line coupled to the second vapor inlet valve; a first vapor flow measuring device disposed on the first vapor flow line to measure a first vapor flow; a second vapor flow measuring device disposed on the second vapor flow line to measure a second vapor flow; and a control element configured to set a location of the selectively variable first end position of the movable piston relative to the first end wall of the housing, and regulate the movable piston based on the first vapor flow and the second vapor flow, such that the pressure of the vapor in the first chamber is not changed sufficiently to open the first vapor inlet valve and the first vapor outlet valve.