MIL-DTL-38219D(USAF)
APPENDIX C
REFLUX VAPOR PRESSURE TEST
C1. SCOPE
This procedure is applicable for pure compounds and narrow boiling range hydrocarbon liquids. It is recommended
the test be limited to fluids that exhibit no greater than 70°C difference between the ASTM D86 IBP and FBP. This
appendix is a mandatory part of the specification. The information contained herein is intended for compliance.
C2. APPLICABLE DOCUMENTS
ASTM D86
Standard Test Method for Distillation of Petroleum Products (DoD adopted)
C3. SUMMARY OF METHOD
Three hundred mL of material are heated in a 500-mL Pyrex flask that is constructed to provide magnetic stirring,
liquid and vapor temperature observation, and ground glass fitting, for attachment to a condenser. The fuel is
outgassed by vacuum at ambient temperature for a minimum of 10 minutes. Pressure of the system is set by means
of the Whitey micro bleed valve while vacuum is maintained on the system. Heat is applied to the Pyrex fuel
container while constant pressure is maintained and the fuel stirred magnetically. After the fuel begins to boil, the
height of the fuel reflux in the condenser is observed and care taken to maintain a constant reflux height during the
entire test procedure. The reflux rate is considered to be at equilibrium when the vapor temperature and the liquid
temperature agree within 4°C. The pressure and the indicated temperatures of liquid and vapor are recorded at each
pressure point selected during the run. Higher pressure determinations are made by opening the bleed valve in
selected increments and increasing the applied heat. A minimum of four stable reflux conditions (boiling points) are
obtained and plotted on semilog paper--the reciprocal of absolute temperature on the abscissa versus the logarithm
of vapor pressure in psi on the ordinate for each boiling point.
C4. REAGENTS AND MATERIALS
The following are reagents and materials used to perform the reflux vapor pressure test:
Vacuum grease used to seal ground glass joints and seat rubber stoppers
NOTE: Silicone grease has been shown to cause foaming during post test distillations of some fuels.
Acetone, reagent grade, to clean glassware.
C5. APPARATUS
The following apparatus are used to perform the reflux vapor pressure test:
Vacuum system able to attain 0.01 psia
Variable AC voltage transformer, VWR Catalog No. 62546-251 or equivalent
Magnetic stirrer, Teflon-coated magnetic stirring bar. One-half-inch StarHead magnetic stir bars are
satisfactory.
Heating mantle, Glas-Col 500 mL or equivalent
Flask, 500 mL, Pyrex round bottom, short neck standard taper joint 24/40 with thermometer well. VWR
Catalog No. 29129-428 or equivalent
Tube, connecting, three way, joints 24/40. Upper ends have outer joints and bottom has inner ember joint.
VWR Catalog No. 62960-024 or equivalent
Condenser, Liebig, Pyrex, 41-mm OD × 300-mm long with 24/40 joint at bottom. VWR Catalog No.
23122-000 or equivalent
Rubber tubing, vacuum and medium wall
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