ASTM D4953 Vapor Pressure of Gasoline and Gasoline-Oxygenate Blends
ASTM D4953 Standard Test Method for Vapor Pressure of Gasoline and Gasoline-Oxygenate Blends (Dry Method)
8. Procedure
8.1 Sample Transfer - Remove the sample from the cooling bath, dry the exterior of the container with absorbent material, uncap, and insert the chilled transfer tube (see Fig. 1). Remove the liquid chamber from the cooling bath and, using an absorbent material, dry the threaded top and place the chamber in an inverted position over the top of the transfer tube. Invert the entire system rapidly so that the liquid chamber is upright with the end of the transfer tube approximately 6 mm (0.25 in.) from the bottom of the liquid chamber. Fill the chamber to overflowing. Withdraw the transfer tube from the liquid chamber while allowing the sample to continue flowing up to complete withdrawal.
NOTE 8 - Warning: Provision shall be made for suitable containment and disposal of the overflowing sample to avoid fire hazard.
8.2 Assembly of Apparatus - Immediately remove the vapor chamber from the water bath and, as quickly as possible, dry the exterior of the chamber with absorbent material with particular care given to the connection between the vapor chamber and the liquid chamber. Remove the closure from the vapor chamber and couple the filled liquid chamber to the vapor chamber as quickly as possible without spillage. When the vapor chamber is removed from the water bath and dried and the closure is removed, connect it to the liquid chamber without undue movement that could promote exchange of room temperature air with the 37.8°C (100°F) air in the chamber. Not more than 10 s should elapse between removing the vapor chamber from the water bath and completion of the coupling of the two chambers. With Procedure B it is necessary to disconnect the spiral tubing at the quick action disconnect after removing from the water bath and before making the connection to the vapor chamber.
8.3 Introduction of the Apparatus into Bath:
8.3.1 Procedure A - Turn the assembled apparatus upside down and allow all the sample in the liquid chamber to drain into the vapor chamber. With the apparatus still inverted, shake it vigorously eight times lengthwise. With the gage end up, immerse the assembled apparatus in the bath, maintained at 37.8 +/- 0.1°C (100 +/- 0.2°F), in an inclined position so that the connection of the liquid and vapor chambers is below the water level. Carefully examine for leaks. If no leaks are observed, further immerse the apparatus to at least 25 mm (1 in.) above the top of the vapor chamber. Observe the apparatus for leaks throughout the test and discard the test at anytime a leak is detected.
8.3.2 Procedure B - While holding the apparatus in a vertical position immediately reconnect the spiral tubing at the quick action disconnect. Tilt the apparatus to 20 to 30° downward for 4 or 5 s to allow the sample to flow into the vapor chamber without getting into the tube extending into the vapor chamber from the gage or pressure transducer. Place the assembled apparatus into the water bath maintained at 38.7 +/- 0.1°C (100 +/- 0.2°F) in such a way that the bottom of the liquid chamber engages the drive coupling and the other end of the apparatus rests on the support bearing. Observe the apparatus for leakage throughout the test. Discard the test anytime a leak is detected.
8.4 Verification of Single Phase Sample - After the apparatus has been immersed in the bath, check the remaining sample for phase separation. If the sample is contained in a transparent container, this observation can be made prior to sample transfer (8.1). If the sample is contained in a non-transparent container, mix the sample thoroughly and immediately pour a portion of the remaining sample into a clear glass container and observe for evidence of phase separation. A hazy appearance is to be carefully distinguished from separation into two distinct phases. The hazy appearance shall not be considered grounds for rejection of the fuel. If a second phase is observed, discard the test and the sample. Hazy samples may be analyzed (see Report section).
8.5 Measurement of Vapor Pressure:
8.5.1 Procedure A - After the assembled apparatus has been in the water bath for at least 5 min, tap the pressure gage lightly and observe the reading. Withdraw the apparatus from the bath and repeat the instructions of 8.3. At intervals of not less than 2 min, tap the gage, observe the reading and repeat the instructions given in 8.3 until a total of not less than five shakings and gage readings have been made and continuing thereafter if necessary until the last two consecutive gage readings are constant, indicating that equilibrium has been attained. Read the final gage pressure to the nearest 0.25 kPa (0.05 psi) and record this value as the uncorrected vapor pressure of the sample. Without undue delay remove the pressure gage from the apparatus and, without attempting to remove any liquid that may be trapped in the gage, check its reading against that of the pressure measuring device while both are subjected to a common steady pressure that is not more than 1.0 kPa (0.2 psi) from the recorded uncorrected vapor pressure. If a difference is observed between the gage and the pressure measuring device readings, add to or subtract the difference from the uncorrected vapor pressure and record the resulting value as the vapor pressure of the sample.
8.5.2 Procedure B - After the assembled apparatus has been in the bath for at least 5 min, tap the pressure gage lightly and observe the reading. Repeat the tapping and reading at intervals of not less than 2 min, until 2 consecutive readings are constant. (Tapping is not necessary with transducer model but the reading intervals are the same.) Read the final gage or transducer pressure to the nearest 0.25 kPa (0.05 psi) and record this value as the uncorrected vapor pressure. Without undue delay, disconnect the gage or pressure transducer from the apparatus and check its reading against that of the pressure measuring device while both are subjected to a common steady pressure that is not more than 1.0 kPa (0.2 psi) different from the recorded uncorrected vapor pressure. If a difference is observed between the gage or transducer and the pressure measuring device, add to or subtract the difference from the uncorrected vapor pressure and record the resulting value as the vapor pressure of the sample.
NOTE 9 - If it is suspected that phase separation of the sample may have occurred during the test procedure, the following procedure can be performed to verify the integrity of the test sample. Perform the following operations as quickly as possible after removing the apparatus from the water bath in order to maintain the temperature of the sample at or near the test temperature. Quickly dry the exterior surfaces of the liquid and vapor chambers with absorbent material. With the apparatus in an upright position, disconnect the vapor and liquid chambers. Quickly drain the contents of the liquid chamber into a dry, clear, glass container and observe the sample. If the sample is not clear and bright and free of a second phase, cap the container, reheat the sample to 37.8°C (100°F), mix the sample well, and observe the sample again. If the sample is still not clear and bright and free of a second phase, phase separation has occurred and the test may not be valid.
8.6 Preparation of Apparatus for Next Test - Thoroughly purge the vapor chamber of residual sample by filling it with warm water above 32°C (90°F) and allowing it to drain. Repeat this purging at least five times. Purge the liquid chamber in the same manner. Rinse both chambers and the transfer tube several times with petroleum naphtha, then several times with acetone, then blow dry using dried air. Appropriately close the liquid chamber and place it in the cooling bath or refrigerator in preparation for the next test. Use an appropriate closure for the bottom connection (where liquid chamber attaches) of the vapor chamber and attach the gage after the gage has been prepared in accordance with 8.6.2.
8.6.1 If the purging of the vapor chamber is done in a bath, be sure to avoid small films of floating sample by keeping the bottom and top openings of the chamber closed as they pass through the water surface.
8.6.2 Preparation of Gage - Procedure A - Disconnect the gage from its manifold connection with the pressure measuring device, remove trapped liquid in the Bourdon tube of the gage by repeated centrifugal thrusts. Accomplish this in the following manner: hold the gage between the palms of the hands with the right palm on the face of the gage and the threaded connection of the gage forward, extend the arms forward and upward at an angle of 45°, and swing the arms rapidly downward through an arc of about 135° so that centrifugal force aids gravity in removing trapped liquid. Repeat this operation at least 3 times or until all liquid has been expelled from the gage. Connect the gage to the vapor chamber with the liquid connection closed and place in the 37.8°C (100°F) bath to condition for the next test.
8.6.3 Preparation of Gage or Transducer - Procedure B - In the correct operation of Procedure B liquid does not reach the gage or transducer. If it is observed or suspected that liquid has reached the gage, purge the gage as described in 8.6.2. The transducer has no cavity to trap liquid. Ensure that no liquid is present in the T-handle fitting or spiral tubing by forcing a stream of dry air through the tubing. Connect the gage or transducer to the vapor chamber with the liquid connection closed and place in the 37.8°C (100°F) bath to condition for the next test.
