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The filter membrane color ratings are used to determine the quality of aviation turbine fuels. Another method of determining particulate contamination is ASTM D 2276. These tests are not a substitute for required monthly tests that must be performed in a laboratory. When preflight or daily fuel samples pass the color test, use the fuel. If the fuel fails the color test, send a sample to the supporting laboratory. There are two types of field monitors used to rate filter membrane color. The first has a single membrane filter (identified by blue and red protective plugs). Use this monitor for daily checks. The second type has a double membrane filter (identified by yellow and red protective plugs) and is used to submit the monthly samples to the laboratory. Do not use the fuel until the test reports are returned from the laboratory.


The color rating when performed in the field requires the following equipment:

  • Sample valve connection.
  • Flexible pressure hose.
  • Selector valve.
  • Field monitor casing.
  • Field monitor.
  • Graduated receiver.
  • Back pressure connection (for sampling from pipes or lines in which the pressure is too low to obtain a proper sample in a reasonable time).


Insert the sampling valve connection in the fuel line of the tank vehicle. Place this connection on the downstream side of the filter/separator. After placing the sampling valve connection in the line, leave it there permanently. See Figure G-1. Follow the steps described below to take a sample for the color test.

  • Step 1. Unscrew the top of the monitor casing on the sampling assembly. Remove the protective plug from the bottom (cobweb) side of the field monitor. Place the monitor, with the bottom side down, in the body of the monitor casing.
  • Step 2. Remove the protective plug from the top of the field monitor. Put both plugs in a safe, clean place.
  • Step 3. Replace the top of the monitor casing with the monitor in the monitor body. Screw the top in place. Hand tighten it only.
  • Step 4. Attach one end of the bypass flushing hose to the selector valve and the other end to the downstream side of the monitor casing.
  • Step 5. Connect one end of the sampling line to the bottom of the monitor casing. Place the free end of the line in the sample receiver. If possible, use a graduated receiver that holds 5 liters.
  • Step 6. Remove the dust caps from the sampling valve connection in the fuel line and from the flexible pressure hose. Connect the sampling assembly to the sampling valve connection.
  • Step 7. Place the selector valve in the FLUSH position.
  • Step 8. Flush the sampling assembly with approximately 1 gallon of fuel after reaching the proper fuel flow and line pressure. The pressure on the line must be at least 25 PSI. The fuel runs through the bypass flushing hose and not through the field monitor.
  • Step 9. Turn the selector valve to the SAMPLE position. Take a 1-gallon sample. When you have the required amount of fuel in the sample receiver, turn the selector valve to the OFF position.
  • Step 10. Disconnect the sampling assembly from the sampling valve connection (allow one minute after sample is complete before disconnecting as a precaution against electrostatic discharge). Replace the two caps (one on the sampling valve connection and the other on the flexible pressure hose).
  • Step 11. Remove the field monitor from the monitor casing, and replace the protective plugs. Handle the field monitor carefully. Do not open it.
  • Step 12. Connect the field monitor to the metal syringe. Use the syringe to remove any fuel product inside the monitor. Pump the syringe two or three times to remove all of the fuel. When pumping the syringe, use slow strokes to prevent damage to the filter.


To use the color standards, match the color of the filter in the field monitor to the closest color sample in the color scale. Do this in a location shielded from direct sunlight to ensure an accurate match. Check color standards in use frequently against a new, unused set of color standards to eliminate the possibility that sunlight or soiling due to handling may have changed the colors. Use a set of color standards printed within two years for verification. Ratings between 0 to 3 can darken naturally by one number over time. When the filter has a color rating above 4 on any one of the color scales (A, B, or C), the fuel is unacceptable in its present state. Take another sample using the field monitor. If it also fails, send the fuel sample to the supporting laboratory for verification and distribution instructions. Report the following information when forwarding the field monitor: date, monitor serial number, sample location and volume of sample, and line pressure and flow rate.

Figure G-1. Sampler assembly

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