5 Reasons why you cannot interchange Hydraulic and Lubrication system filters.

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On board a ship, there are various hydraulic and lubricating oil systems which employ filters to maintain oil cleanliness.  The big questions we search for an answer are ..

  • What could be the difference between a hydraulic oil and lubricating oil (system oil) filter?
  • Can we interchange a Hydraulic oil filter with engine oil filter?

Let us consider a practical example of a diesel engine L/O filter and a mooring winch hydraulic filter (assuming the dimensions are same), can these filters be interchanged?

If not, what are the factors which dictate the difference in these filters?

The Five reasons why you cannot interchange hydraulic and lubrication system filters.

Although the basic principles of filtration are the same in each case, there are slight differences in filters based on the application.

1.Location:

In most force-fed lubrication systems (diesel engines), the filter is located after the pump and before the critical machine components. This location poses several problems for the filter.  It is to be noted that the location of the filter is at the engine inlet (after the pump) for diesel engines (or) simply on the pressure side of the pump.  Whereas in hydraulic systems, the filters are usually located on the return line of the system. Thus the location of a filter on the particular system plays a major role.

2. Flow rate:

Often a filter located on the pressure side of the pumps will have to deal with 100 percent of the flow coming from the pump.  If the machine requires large amounts of oil to operate reliably (like diesel engines – where lubricating oil is used for lubrication as well as cooling), then the filter must be large enough to deal with the flow. This can be achieved by increasing the surface area of the media or changing the media type to one that utilizes a smaller fiber.

3. Pressure:

The filter must also be able to handle pressure. The pressure from the pump pushing fluid through the small pores at a high rate of speed will cause weak points in the filter.  Collapsed center tubes, blown-through media and seams, and failed end-cap adhesive are just some of the potential problems. Thus don’t be surprised to notice such damaged filters which are employed on the diesel engines, where such damages usually happens if the filters are not cleaned regularly. The solution is a more robust filter and regular cleaning, which usually means a higher cost and increase in man hours.

4. Strength:

When compared to a typical hydraulic filter located on the return line, lubrication system filters on average are slightly more robust. When installed on a low-pressure return line, these filters don’t have to be made using reinforced center tubes, sandwiched media or thicker housings.

5. Pore Size:

The basic principles of filtration include the relationship between pore size, flow rate, surface area and the differential pressure. The pore size is a major contributor to the performance of the filter to remove smaller particles.  The smaller the pore sizes found in the media, the smaller the particles it can reliably remove.  The pore size can’t be made too small with respect to the flow rate and surface area or the differential pressure will increase to a point where it opens the bypass valve and allows solid contaminants to completely bypass the filter.

These basic principles are the main difference between the many types of filters. Remember, it is driven by the application more so than the machine component type.

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