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There are different methods and tools employed to take a sample of oil from machine compartments. The most common methods are the vacuum pump method, drain stream method, and guage plug method. A WearCheck oil analysis course will provide more detailed information on taking oil samples. For information on purchasing sampling accessories contact us.

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Vacuum Pump Method

The vacuum pump sampling method is the most popular method for sampling the various compartments of mobile equipment. Samples may be taken from transmissions, engines and other machine compartments by putting the plastic tubing into the dipstick or oil access opening and using a vacuum pump to draw oil into the sample bottle.

Sampling Procedure (Vacuum Pump)

With the engine shut off, insert the two (2) meter piece of clean plastic tubing through the head of the sampling gun.
The tubing should be cut at a 45° angle for easy insertion through the cap.
Next, tighten the sampling bottle onto the cap of the vacuum pump.
For compartments with a dipstick, the tubing should be cut to the length of the dipstick.
For compartments without a dipstick, such as gearboxes, final drives and other fixed or mobile equipment, the tubing should be cut to length as necessary.
Several light pulls of the handle will fill the bottle.
In order to obtain a homogenous sample it is essential that the oil be at operating temperature.
The tubing must be used only once and then discarded.
When you discard the tubing, do not pull the tubing back through the top of the pump, as this could contaminate subsequent samples. Instead, cut the tubing just above the top of the pump, and then pull the remaining piece (that was in the bottle) from the bottom of the pump.

Drain Stream Method

This method requires care on the part of the serviceman, as external dirt entry is a likely possibility. An incorrect diagnosis will be the result.The sample must be taken from the oil when it is hot and well mixed as it flows from the compartment drain. The initial and final parts of the oil stream must not be used, as this oil is not typical of the oil in the system.

Sampling Procedure (Drain Stream Method)

All dirt and debris from around the drain plug must be cleared before the sample is taken. Compressed air can be used for this.
Remove the drain plug and allow the oil to start draining.
Once the flow is clear of visible debris the bottle can be placed under the flow and filled to the recommended level.
This bottle must be capped immediately.
Do not take the oil sample from the drain container!

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Gauge Plug Location

A gauge plug is permanently installed in the oil line or in an oil gallery. The ideal location of the gauge plug will change with the machine model, but in all installations, the gauge plug should be installed in a location where it is easy to access away from any moving parts, protected from damage, and before any in-line filtration system (if applicable).


Sampling Procedure (with Gauge Plug)

- Step 1 Remove dust cap from the gauge plug on the machine, and with the engine at low idle, purge the gauge plug by discharging a small amount in a waste container. The sample bottle should not be used for purging.


- Step 2 Push the hose assembly onto the gauge plug and fill the bottle to the indicated level. Disconnect probe and replace the dust cap on the gauge plug. When taking samples from additional equipment ensure that the hose assembly has been thoroughly flushed with used oil from the equipment before taking a representative sample.

General Sampling Guidelines


- Oil sampling must be done during normal operation of the equipment or within 30 minutes after machine shut down. This ensures that the oil is warm and truly representative of the conditions within the compartment.
- When using the vacuum pump method, ensure that the sample is drawn from about the mid point or within the working level of the oil in the compartment and not from the bottom where sludge accumulates.
- It is important that the sample container is totally clean and free of moisture before the sample is taken.
- The container should be properly sealed to prevent any contamination or loss of oil during transit.
- Ensure the sample information sheet is completely and correctly filled out.
- Courier or mail the sample to the Laboratory immediately, so as to receive the analysis results as soon as is possible.
- For more information regarding the use of sampling valves or general oil sampling questions, including vacuum sampling pumps, please contact your nearest WearCheck laboratory.