Cellulose depth filtration remains one of the best oil cleaning techniques
19 Jan, 2022Cellulose depth by-pass filtration sits neatly between these two extremes
By-pass or Kidney-loop filtration is by far the best method of offline filtering and are often fixed
permanently to an application where current filtration is insufficient – usually in harsh environments or
under demanding workloads. This style of filtration is equally effective as a “quick cleanse” to alleviate
dirt levels or resolve unexpected water contamination.
What is cellulose depth filtration?
It is old but reliable technology. In this case, each metal vessel tightly holds the vital filtration cartridge
(made of tightly packed, long fiber cellulose); this allows the oil to travel up the center and push down
slowly through the entire thickness of the cellulose media. This “depth” matrix is used to trap suspended
particles, separating them from their carrying fluid. Working by adsorption and absorption, it has the
unique filtration ability to trap particles and moisture.
Depth filtration is most commonly applied in “polishing fluid” applications as it takes filtration to a much
finer level. But that is no reason to underestimate its ability and benefits of keeping any tank of oil
continuously clean and dry.
With cellulose depth filtration, slow and steady is key to the best results. Allowing fluid to move slowly
through the media optimizes results; forcing it at high flow can open up channels in the filter and
allow for by-pass. This means that during correct operation it only has one level of filtration: down to
3-micron particulate.
Know what cleanliness level you want to achieve
The most important part of any filter or filter unit is which contaminants are being filtered out. Know
what your oil cleanliness targets are (generally 3 microns for hydraulic fluid and 6 microns for gear
oils) and if you have ongoing moisture issues. In either case, its always best to determine the
source of any contamination. While filtration is always important even in clean systems, you may
be masking an issue that needs addressing first. Some companies want to achieve a suggested ISO
target, which will be reflected in your oil analysis testing or particle counting.
Never assume new oil is clean
New oil may look sparkly, but it is a rare test that sees it so. And clean
oil put into a dirty machine just gets dirty. This oil sample result is from a refurbished baler machine
that was cleaned out and filled with brand new oil. This is the first sample before the first use. The
high silicon is indicative of the work done and new seals, but contamination counts at 4, 6, and 14 are the
crucial indicators of the levels of contaminant in this small sample. New oil should have an ISO of around 18/16/13; this oil is at 22/20/16.
Know your oil type:
The type of oil inside your machine plays a significant role in determining which oil filter cart you
should buy. If you were to pump viscous oil quickly, you’ll encounter air bubbles forming inside the
machine which could damage pumps and oxidize oil. Cellulose depth works on cleaning oil slowly and
continuously and so can be more effective as a constant permanent install.
Flow rate:
You will generally want to know how much oil will be cleansed per hour; the rule of thumb on off-line filtration is to pass it through
seven times to achieve the best level of a temporary install or rotational cleanse. When you use a filter cart, oil cleanliness is
diluted by the dirty oil in the sump, since you’re taking oil from the dirty sump, filtering it, and returning it to the same. To combat
this dilution, the amount of oil in the tank must pass through the filter seven times to get the same cleanliness you would get from
single-pass filtration. As an example, a Twinset Cellulose filtration set-up with the appropriate progressive cavity pumps on standard 32 or 46-sec
hydraulic oils at 40-degree temperature will run approximately 500 lph. So a two-hour cleanse would be more than adequate.
Some sites will use a filter cart to transfer the cleanse out to an IBC, (allowing for a scrub of the tank) and then transfer cleanse back to the tank. But in doing this, never forget that sediment will be in
pipes and cylinders so as a machine starts up this sediment will push back to the tank and re-pollute
the cleansed oil. So, in a transfer cleanse it would be advised to leave the filtration on to tackle this
remaining contaminant.
Robust Simplicity
Keeping a filter cart robust and simple is key. These machines are moved around in often
harsh environments with heavy handling and challenging applications. So, a Filter Cart purchase is a worthy investment
in any location where oil cleanliness is key to efficient operation. The use of secondary
filtration can save a lot of wasted time, frustration, and resources. The application not only allows for higher
efficiency and better utilization of time and productivity but also has an impact on lowering operating costs by
reclaiming and extending the useful life of the oil and components and lowering yearly waste oil handling.
