Oil Sampling Procedures


Use of Metal Cylinders for the Collection of Gas-in-Oil Samples

Metal cylinders can be used effectively to collect oil samples from transformers. To obtain a representative sample it is necessary to use the proper sampling technique. Following the procedure below will ensure that the sample received by the laboratory is reflective of the oil in the main tank of the transformer. Refer to ASTM D3613 for complete instructions on the sampling of transformer insulating fluids.

Hold the cylinder in a vertical position at all times.
This will ensure all air bubbles rise to the top and exit the container.

Drain the Sampling Valve
Stagnant oil from the lower drain valve of the transformer must be removed before the sample is collected. Also moisture that may be present in the depression of the drain valve must be removed. To achieve this, remove the plug from the drain valve and drain approximately one-half to one gallon of oil into an oil-waste container. To the drain valve, attach a plug fitted with a tubing connector and a section of clear plastic tubing.
Attach the Tubing to the Container
Attach the cylinder's lower valve fitting to the tubing connected the transformer. Attach the cylinder's upper valve fitting to the tubing discharging to the waste oil container.
Open Valves in Ordered Sequence
  • Open the valve on the transformer.
  • Open the lower cylinder valve (A).
  • Open the upper cylinder valve (B).
    Allow about 1 quart of oil to flow through the cylinder into the waste container. Tap the sides of the cylinder with a tool to dislodge air bubbles. Oil running though the tubing should be free of air bubbles.
  • Shut Valves in Reverse Order
  • Shut the upper cylinder valve (B).
  • Shut the lower cylinder valve (A).
  • Shut the transformer drain valve.
    Shake the cylinder then listen and feel for signs of incomplete filling. If not completely filled, redo from step 1 of Open Valves in Ordered Sequence.
  • Re-Assemble Transformer Valve and Plug
    Disconnect the tubing and remove the connector from the drain valve. Replace the original plug on the drain valve. Apply pipe dope or Teflon tape on the plug threads to insure a good seal and to prevent rust.


    That's it. You should now have a representative sample of the oil from within the transformer ready to be shipped to the laboratory.

    Complete the information on the sample data sheet and prepare the sample for shipment. Be sure to write down all pertinent information on the sample data sheet.


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