6. Apparatus
6.1 Centrifuge, capable of whirling two or more filled centrifuge tubes at a speed which can be controlled to give a relative centrifugal force (rcf) of 800 +/- 60 at the tip of the tubes. The revolving head, trunnion rings, and trunnion cups, including the cushions, are to be soundly constructed to withstand the maximum centrifugal force capable of being delivered by the power source. The trunnion cups and cushions shall support the tubes when the centrifuge is in motion. The centrifuge shall be enclosed by a metal shield or case strong enough to eliminate danger if any breakage occurs.
6.2 The data in Table 1 can be used to determine the centrifuge speed setting required for the centrifuge to meet relative centrifugal force requirements for this method and was developed using the following equations:
where:
rcf = relative centrifugal force, and
d = diameter of swing, in inches, measured between tips of opposite tubes when in rotating position or
where:
rcf = relative centrifugal force, and
d = diameter of swing, in centimetres, measured between tips of opposite tubes when in rotating position.
6.3 Centrifuge Tube, cone-shaped, 100-mL with capillary tip capable of measuring 0.01 mL and readable by estimation to 0.005 %.
6.4 Centrifuge Tube, pear-shaped, 100-mL, with tube tip having graduations of 0.01 mL over the range 0 to 0.2 mL.
7. Sampling
7.1 Sampling shall be consistent with the procedures of Practice D4057.
7.2 The sample for a laboratory test will normally be an aliquot of a much larger sample taken for full or partial specification testing. The full sample should have been taken by a procedure consistent with Practice D4057. Allow the sample container and its content to equilbrate between 21 to 32°C (70 to 90°F). In general, the chosen laboratory test temperature should not be lower than that at which the fuel is stored or used as too low a temperature may cause free water haze to form from additional free water formation.