The filter is very important to keep the hydraulic system clean and extend the service life of the hydraulic system. How to choose the right filter?
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Each machine and component in the hydraulic system has its own set of requirements, each of which affects each other and, of course, the selection of filters. To determine the size of the filter and select the right filter, you must understand the following five key pieces of information:
01
Filter performance requirements
The performance requirements of the filter are usually expressed in terms of the overworry ratio β, which is the ratio of particles entering the filter to particles exiting the filter.
Today's hydraulic filters are designed with a medium that captures and holds more pollution particles than ever before, reducing pressure drop and extending service life. For example, applications that require high-performance components will typically have an overworry ratio β of more than 1000 (i.e., 1000 particles enter the filter and only one particle passes through).
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02
Hydraulic system
After determining the performance requirements of the filter, we need to be clear about the hydraulic components installed in the hydraulic system circuit, according to industry standards, these hydraulic components need to have the corresponding standard filter type. This standard drives the ISO cleanliness code requirements and helps determine the right filter element type.
For example, a proportional valve in a loop may require a 20/18/15 ISO cleanliness code, and in order to meet the standards set by the ISO code, the circuit needs a filter with 3 µm or 6 µm absolute filtration.
When choosing the size of the filter, it is also necessary to consider the pollution capacity, pressure drop, cost and other factors, to understand what hydraulic components are attached to the filter, and to understand how these hydraulic components affect the performance requirements of the filter, which can save costs.
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03
Oil viscosity
The viscosity of the oil has a great influence on the size of the filter. When choosing a filter, many people tend to ignore this factor, often choosing a larger filter than the actual need, resulting in higher operating costs.
The filter size is too small and the pressure drop is too high, resulting in premature tripping of the blockage indicator.
If the filter size is too large, it will lead to high cost, large footprint and high replacement cost. We should fully understand the normal temperature range of the hydraulic system, according to the accurate minimum temperature to select the filter.
04
Understand the blockage indicator
Assuming that the filter of the system has a clogging indicator (analog or digital), the user should have a suitable target for the pressure drop when selecting the filter size.
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Typically, the pressure difference for the plugging indicator ranges from 1 to 8 bar, and the ratio of the plugging indicator setting to the clean pressure drop is at least 3:1. For example, assuming the filter has a 5 bar clogging indicator, the acceptable maximum clean pressure drop target is about 1.7 bar based on a 3:1 ratio.
Without understanding this principle, we may mistakenly choose the size of the filter. While too large a filter can ensure the highest amount of protection, it will increase the cost.
Understand the flow
When choosing the size of the filter, the flow rate must be considered, and we need to consider the maximum flow rate.
Note that intermittent flow may exceed the maximum flow of the pump. For example, in an accumulator loop, where the accumulator stores a certain amount of pressurized fluid and releases it into the system to supplement the pump flow, the flow through the pressure filter connected downstream of the accumulator should take into account this additional flow.
Underestimating the flow through the filter increases the pressure drop through the filter element, increasing operating and maintenance costs.
