Method and system for determining vapor pressure of liquid compositions

A method for determining the true vapor pressure of a liquid composition comprising the steps of:

• providing an eductor apparatus having an inlet port, an outlet port, and a suction port interposed between said inlet port and said outlet port and downstream of a throat portion of said eductor, said eductor including means for measuring the pressure differential between said inlet port and said outlet port, and means for measuring the pressure at said suction port;
• causing said liquid composition to flow through said eductor while causing incremental changes in the pressure differential between said inlet port and said outlet port from a condition where substantially negligible pressure differential between said inlet port and said outlet port is observed to a pressure differential wherein relatively small changes in the suction pressure occur for relatively large changes in the pressure differential occur;
• and
• determining the pressure at the suction port as a function of the pressure differential between said inlet port and said outlet port and calculating the second derivative of said function to determine where said second derivative equals zero as an indication of the value of suction port pressure corresponding to the true vapor pressure of said liquid composition.

A system for determining the vapor pressure of a liquid composition comprising:

• an eductor including an inlet port, a throat portion, a suction port downstream of said throat portion and a discharge port downstream of said suction port in the direction of flow of liquid through said eductor;
• conduit means connected to said inlet port and conduit means connected to said outlet port for conducting said liquid composition through said eductor;
• pump means interposed in said conduit means connected to said outlet port for causing said liquid composition to flow through said eductor;
• means for measuring the pressure differential between said inlet port and said outlet port and means for measuring the pressure at said suction port while causing liquid to flow through said eductor;
• a pressure regulator valve disposed in said conduit means connected to said inlet port and operable to maintain a predetermined pressure in said conduit means connected to said inlet port between said pressure regulator valve and said inlet port;
• and
• means associated with said pressure regulator valve for changing the pressure of said liquid composition flowing through said eductor at said inlet port so that a set of incrementally different pressure differentials between said inlet port and said outlet port may be read together with pressures at said suction port for each incremental pressure differential between said inlet port and said outlet port for determining the vapor pressure of said liquid composition.