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A vapor recovery pump for a fuel dispensing unit, comprising a housing with two chambers each having a vapor inlet valve and a vapor outlet valve, respectively, the chambers being separated by a movable piston arranged to move a distance between a first and a second end position inside the housing f

A vapor recovery pump for a fuel dispensing unit, comprising a housing with two chambers each having a vapor inlet valve and a vapor outlet valve, respectively, the chambers being separated by a movable piston arranged to move a distance between a first and a second end position inside the housing for continuously decreasing and increasing the volume of the chambers. A control element is arranged to selectively vary the location of the first end position.

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1. 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 po

1. 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; anda 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. 2. A vapor recovery pump according to claim 1, wherein the control element is arranged to selectively vary the location of the selectively variable second end position relative to the second end wall of the housing. 3. A vapor recovery pump according to claim 1, wherein the control element is arranged to oscillate the movable piston between the selectively variable first end position and the selectively variable second end position. 4. A vapor recovery pump according to claim 1, wherein the first vapor outlet valve of the first chamber is arranged to open in response to the pressure within the first chamber exceeding a specific level. 5. A vapor recovery pump according to claim 1, wherein the first vapor inlet valve is arranged to open in response to the pressure within the first chamber falling below a specific level. 6. A vapor recovery pump according to claim 1, wherein the control element is arranged to set the location of the selectively variable first end position and selectively variable second end position, and to move the movable piston between the set location of the selectively variable first end position and set location of the selectively variable second end position to continuously increase and decrease the pressure within the first chamber and the second chamber, so that the second vapor inlet valve and the second vapor outlet valve are continuously opened and closed, respectively, while the first vapor inlet valve and the second vapor inlet valve remain closed. 7. A vapor recovery pump according to claim 1, wherein the control element comprises a magnetic control element for moving the movable piston between the selectively variable first end position and the selectively variable second end position. 8. A vapor recovery pump according to claim 7, wherein the movable piston is magnetic and the magnetic control element comprise coils arranged around the housing, and a control unit arranged to selectively feed the coils with an electric current for moving the movable piston between the selectively variable first end position and the selectively variable second end position. 9. A vapor recovery pump according to claim 1, wherein the control element comprise a rotatable screw-threaded axle passing through a screw-threaded hole in the movable piston, and a control unit arranged to selectively vary the rotation of the rotatable screw-threaded axle for moving the movable piston between the selectively variable first end position and the selectively variable second end position. 10. A vapor recovery pump according to claim 1, wherein the control element comprise an intelligent device having a software application for selectively varying the location of the selectively variable first end position and the selectively variable second end position. 11. A vapor recovery pump according to claim 1, further comprising a vapor flow return line for recirculation of vapor, said vapor flow return line comprising a vapor flow control valve. 12. A vapor recovery pump according to claim 11, wherein the vapor flow return line is connected at least to the first vapor inlet valve and the second vapor outlet valve. 13. A fuel dispensing unit comprising: a 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 first end position and a second end position, the movable piston and the first end wall defining a first chamber having a first variable volume and the second end wall and the movable piston 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 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. 14. A fuel dispensing unit according to claim 13, wherein a first vapor suction nozzle is connected, via a first vapor flow line, to the first vapor inlet valve of the vapor recovery pump, and a second vapor suction nozzle is connected, via a second vapor flow line, to the second vapor inlet valve. 15. A fuel dispensing unit according to claim 14, wherein at least one of the first and second vapor flow lines comprises a control valve. 16. A fuel dispensing unit according to claim 13, wherein the at least one vapor suction nozzle is connected, via a manifold, to the first vapor inlet valve and the second vapor inlet valve. 17. A fuel dispensing unit according to claim 13, wherein the control element is arranged to selectively vary the location of the second end position relative to the second end wall of the housing. 18. A fuel dispensing unit according to claim 13, wherein the control element is arranged to oscillate the movable piston between the first and second end positions. 19. A fuel dispensing unit according to claim 13, wherein the control element is arranged to set the location of the first end position and the second end position, and to move the movable piston between the first end position and the second end position based on the first vapor flow and second vapor flow to continuously increase and decrease the pressure within the first and second chamber, so that the second vapor inlet valve and the second vapor outlet valve are continuously opened and closed, respectively, while the first vapor outlet valve and the first vapor inlet valve remain closed.