Coaxial vapor flow indicator with pump speed control

A method for monitoring vapor-to-liquid flow rate in a fuel dispensing system with a vacuum assisted vapor recovery system having a fuel conduit for delivery of fuel and a vapor conduit for recovery of vapor, said method comprising the steps of:

• determining vapor flow rate in the vapor conduit by measuring differential of pressure between a first location in the vapor conduit at a narrow upstream neck of a Venturi section formed in the vapor conduit and a second location in the vapor conduit upstream of the Venturi section using a flexible member disposed between a first chamber in communication with the first location and a second chamber in communication with a second location, positioning of the flexible member being responsive to and indicative of the differential of pressure between the first location and the second location, and, in turn positioning a vapor flow indicator assembly comprising a magnet and a Hall Effect sensor;
• using the Hall Effect sensor, issuing a signal indicative of the vapor flow rate, the signal by the Hall Effect sensor being indicative of proximity of the magnet to the Hall Effect sensor, which in turn is indicative of the position of the flexible member between the first chamber and the second chamber;
• determining liquid fuel flow rate in the fuel conduit;
• issuing a signal indicative of the liquid fuel flow rate;
• comparing the signal indicative of the vapor flow rate and the signal indicative of the liquid fuel flow rate;
• and,
• when vapor-to-liquid flow rate is outside a predetermined range, issuing a controlling signal.