How To Sample Used Oil
General Information On Sampling
Sampling the fluid at the proper point in the machine is very important. In Figure 1 the correct location is shown to monitor how the machine is running. If samples are taken at the other points (marked off) then erroneous results may occur.
FIGURE 1
Diesel Engines
Diesel engines have two primary locations to sample from during actual operation as shown in Figure 2. Drain samples may give different results.
FIGURE 2
Gearbox Sampling
Gearboxes present a special sampling problem in that they are not usually circulating systems. Debris goes to the bottom of the gearbox, and sampling the debris gives erroneous results. One of several possible methods is shown in Figure 3 that will give a representative sample of the oil.
FIGURE 3
Sampling Methods
The ideal sampling interval is based on the point in time that the component is generating particles at approximately the same rate that particles are being removed. This is called the point of dynamic equilibrium.
There are many types of equipment that may be used. Below are five common options that are utilized. Below is a discussion of each type and how samples should be taken.
Option 1--VACUUM GUN AND TUBE ASSEMBLY
A vacuum gun and tube assembly (Figures 4 and 5) allows withdrawal of a liquid that is not under pressure. The apparatus should be cleaned between samples to prevent contamination. It is used for sampling gearboxes, transmission fluids and engine oils.
¨ When using sample pump gun make sure that oil is warm (within 1 hour of shutdown)
¨ Usually sampled through a dipstick. Tubes should be cut at length equal to reaching the middle of the reservoir
¨ Vacuum gun and repair kits are available
| FIGURE 4 | FIGURE 5 |
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This is a permanent assembly into a pressurized system. A cap is used on the assembly to keep the sample from becoming contaminated by airborne dust. A push button valve is useful in low-pressure systems. (see Figures)
¨ Installation should be in a line that represents full flow of the fluid, prior to the filter.
¨ Pump discharge.
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FIGURE 6 |
FIGURE 7 |
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Option 3--PRESSURE RELIEF VALVE (QUICK-DRAW SYSTEM)
A pressure relief valve sampling system is appropriate for higher-pressure systems. A sampling valve shown in Figure 8 is permanently installed in the circulating system. The valve is opened and sampled using a syringe-bottle system as shown in Figures 9 and 10.
Syringe bottle systems can be enclosed in a sealable plastic bag (“baggie”) to keep the sampling procedure as clean as possible in a very dirty environment, or where particle counting is needed for a sample.
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FIGURE 8 |
FIGURE 9 |
FIGURE 10 |
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¨ Ideal position is the inlet to the filter. If a quick connect/disconnect system is installed in the filter for the purpose of taking pressure readings, the valve can be installed at this point.
¨ A minimum of 4# pressure is required to use this method. The valve is tested to 3000# but you would be unable to take a sample with this much pressure. A general range is 4-100#. Check with the component manufacturer if you are in doubt as to installation.
¨ QuickDraw has a needle/cap assembly that is attached to the sample jar to take the sample through the valve. The cap/needle assembly is disposable. They should not be re-used.
Option 4--DRAIN SAMPLES
Drain samples are off of the bottom, or near bottom, of a dispenser (storage tank) or a sump. For dispensers it can be useful to look at what is actually being dispensed and whether or not a storage tank is contaminated by rust, water, etc.
However if a used oil sample is taken by the drain method, a sample may not be typical of the bulk oil unless adequate oil passes through to clean out the initial debris or water. Hence for used oil sampling for a representative sample, allow approximately a pint to a quart to pass through the drain and use the second pint or quart as the representative sample. The recommended procedure is shown in Figures 11 and 12.
| FIGURE 11 | FIGURE 12 |
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For large steam turbines or paper machines, you may need to take an internal sample from the middle of the stream of oil returning from each one of the bearings, use part of each to make a composite sample and save the remainder until a normal report is received! If an abnormal report is received then send the original 3 samples to be processed in order to pin point the source.
Centrifuge Cake Deposits
Centrifuges are commonly found in diesel engines as well as natural gas engines. Sampling oil from circulating systems using the centrifuge method proves useless since the contaminants are removed. Hence an analysis of the centrifuge cake is a better method for testing early detection of bearing failure than used oil analysis.
How To Sample Centrifuge Cakes
Please follow the instructions below. Please enclose two regular test kits for this test along with the sample. The charge is twice that of a normal analysis.
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What Causes A Report Of Low Benefit?
Poor or inconsistent sample methods!
Wrong or no equipment information supplied to the Lab.
Mislabeling the sample.
Replacing or switching of sampled units without updating the equipment information at the laboratory.
Not notifying the lab when centrifugal filters, magnets and oil sweeteners are in use.
Any time a Critical report is received or a report with Elevated Iron and/or other elements, check for possible contamination in the onsite new oil storage tank.
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