The primary function of a hydraulic filter is to remove contaminants as oil flows through a permeable element called the media. The quality of the element determines how well a filter can function.
It may be surprising to learn that 75 per cent of all system failures in hydraulic machinery are caused by contamination. This can lead to significant economic loss for any project due to downtime (a loss of production) and the cost of replacing parts. In some mining sectors, a downtime of just an hour can cost tens of thousands of dollars.
It is obvious by this fact alone how a poor quality element can disrupt the effectiveness of a filter and cost you money. In this article, we will discuss what to consider when purchasing a hydraulic filter element so that you get one that is cost effective for your operations.
What to considerStep 1: Specifications
When looking for an element, you need to consider the following points:
Target cleanliness level (micron rating) - Microns refer to the size of contaminates. For example, a filter with a micron rating of 10 will filter out contaminants 10 microns or higher. Generally, the smaller the rating for a filter, the better it will perform.
Beta ratio - The beta ratio refers to how efficient a filter element is in capturing particles. It should have a rating of at least 200, which means for every 200 particles of contaminant that hits the filter, only 1 gets through.
Pressure rating/loss - The porosity and surface area of a filter’s media will influence the pressure loss in the system. This should be kept to a minimum. Evaluate pressure drop data of different filters for comparison
Contamination (dirt-holding) capacity – This is defined as the amount of contaminants the filter can handle before its pressure drop rises to an unacceptable level. This may be useful to compare the estimated service life of different filter elements
System/ environment - When selecting a filter, you need to factor in the characteristics of the system and the environment it will be installed in (contamination ingression rate, vibration, duty cycle, criticality of the application, potential safety issues, flow rates etc.).
Housing and Element Sizing – Your element will last longer if it is the right size for your filter. This will have a dramatic impact on the overall total cost of the filter throughout its service life.
Step 2: Selecting the right filter type
Selecting the right filter type will ultimately come down to application. Let’s look at a range of filters that you might need.
Suction – Suction filters are generally too coarse to filter fluid as they don’t meet ISO requirements. Instead, they are put in your tank to catch large items like bolts and should be considered as strainers only.
Pressure – Pressure filters are placed after your pump and protect any components downstream in the event that your pump fails. These filters must be rated in accordance with your system’s running pressure and the ISO code.
Return (in-line) – In my opinion, return filters are the best because it cleans the oil before returning it back to the hydraulic reservoir. This keeps the reservoir free from particles that could inhibit performance.
You may not need all three of these filters in your system, but it is important to have at least a pressure or return filter installed to maintain a satisfactory level of cleanliness.
Step 3: Fluid analysis
Fluid analysis is an important part of your maintenance program as it shows important indicators of filter effectiveness and ensures that the fluid performs to the manufacturer’s specifications.
This can be determined through a patch test, portable or in-line particle counter or laboratory analysis.
Good filtration practices during any operation are important. This is achieved through a rigorous maintenance schedule and a high quality hydraulic filter element. While it may be tempting to install a cheap, inferior one, please be aware that it can end up costing you money in the forms of downtime and replacement parts. Since system component life is directly related to fluid cleanliness, a good filter element is the best insurance you can take to prevent failures.
Richard Argus is the founder of fluid power service provider, Fluid Line Services based in Perth, Western Australia.