Water is potentially the most damaging of the expected contaminants found in diesel fuel. Water destroys the lubricative properties of fuel and can quickly scour or blow injector tips/pumps. Water, in cold temperatures, can freeze and stop the fuel flow.
Water can be present in your fuel as free water (slug)
and emulsified water. Free water comes from condensation, either in bulk or engine tanks, or from
dissolved water in your fuel.
Free water gets into your fuel as storage tank
bottoms become agitated while dispersing or receiving
fuel. Dissolved water can turn to free water as the
Diesel fuel has a saturation point of water at any
given temperature. As the temperature goes down the
fuel will hold less dissolved water. This water that falls
out is free (or slug) water.
Emulsified water is what is left in the fuel. Water,
within limits, can be removed from fuel by absorption,
coalescing or by stripping. Some methods are more
efficient than others.
In this issue of Tech Tips, we will discuss the
absorption method of removing water from your fuel.
Absorption of water from fuel takes place when the media within the filter absorbs the fuel passing through it. The filter removes water from the fuel because the media contains a substance that has a high affinity for water and a low affinity for fuel. This
method of water removal is effective in absorbing free
water and other contaminants, but is fairly ineffective
way of removing emulsified water.
An example of this type of filter is the Baldwin BF956. If there is significant water contamination, the filter’s media will swell and block the fuel flow. The fuel delivery rate then drops from 15 gallons per minute to one-half gallon per minute. This would signal the user to change the filter. Typical uses for this type of filter would be on storage tanks where you do not want any free water to pass from one tank to another during fuel transfer.
In the next issue we will continue our discussion by
telling you about the coalescing method of removing
water from your fuel.
In past editions of Tech Tips, we have made you
aware of the importance of proper fuel filtration on
today’s sophisticated engines. Let’s take a look at
two of the test methods used within the filter industry to
determine if a filter actually does its job.
Remember, the job of the fuel filter is to allow proper fuel flow while filtering out any harmful contaminants within the fuel.
The two test methods we will discuss are the SAE J905
and the SAE J1985. Both test methods are industry
standard Society of Automotive Engineers (SAE) tests.
Why use SAE standardized tests? The SAE test methods
are written to test those filter characteristics that may be critical to the performance and protection of the engine in a controlled laboratory environment. The many variations in filtration requirements needed to protect fuel systems on engines and the variations in operating conditions make it difficult to specify meaningful “in-service” performance standards by which a filter may be judged. The use of this type of testing ensures consistent “apples to apples” performance comparison of
one brand versus another.
SAE J905 Life and Efficiency
This method allows us to determine how much
contaminant in the fuel is actually trapped or stopped by
the filter. By analyzing the test results, we can determine
1. How much contaminant the filter holds before it
becomes plugged and shuts off fuel flow
2. How efficient the filter is at removing the contaminant.
The contaminant used is an industry standard, which consists of a certain percentage of various
particle sizes. In this test, a specified weight of the contaminant is added to the test stand fuel stream at specified intervals until the test is terminated. Fluid samples are taken at each interval to determine the amount of contaminant that passed through the filter media during that interval.
The test averages the results at each interval to determine
the beginning, ending, and median (time-weighted)
SAE J1985 Single-Pass Efficiency This method allows us to determine how efficient the filter is at removing specific contaminant particle sizes of 5, 7, 10, 12, and 20 micron. The contaminant used is the
same as in the J905 test method.
In this test, the contaminant is added to the test stand
fuel stream. The specific particle sizes noted above are
counted as they enter the filter, then counted again after they pass through the filter. The efficiency of removing each size particle is calculated by subtracting the number of particles of that size that passed through the filter from the number of particles of that size that entered the filter, then dividing that total by the number of particles of that
size that entered the filter. In example, if 100 particles 5
micron in size were fed into the filter and 90 were trapped, then the filter is said to be 90% efficient at removing contaminant particle sizes of 5 micron or larger.