Heavy Duty Hydraulic Filters
Frequently Asked Questions
Q: What is the micron rating of the filter?
A: A micron rating is a value assigned to a filter, indicating that filters ability to remove a certain size of particle. To accurately determine the filter’s ability in removing a certain particle size, Beta Ratios from multi-pass testing should be used.
(Reference FMC TSB-89-5R3 under revisions)
Q: What micron rating do I need for my application?
A: The ISO cleanliness code publishes a recommended cleanliness guideline for typical hydraulic system components; however, always check component manufacturer recommended ratings.
Q: What is the difference between absolute and nominal ratings?
A: Nominal rating usually means the filter can capture a given percentage of particles of a stated size (e.g. 50% @ 10 micron). Absolute rating is the smallest typical particle size retained by a filter media at 98+% efficiency. This is also referred to as the Beta=75 or 98.67% efficiency rating.
For additional information about nominal and absolute micron ratings: (Reference FMC TSB-89-5R2 under revisions)
Q: What is the burst Rating of the filter?
A: The burst rating of a spin-on hydraulic filter is the minimum pressure the filter can withstand without deforming to the point where the filter fails. Hydraulic filters are typically designed to have a minimum burst pressure that is twice that of the normal operating pressure of the application. Therefore, hydraulic filters will have different burst ratings depending on the requirements of their application.
Q: Why don’t cartridge filters have a burst rating?
A: Cartridge filters do not have a burst rating because the pressure is retained by the housing on the application rather than the filter.
Q: What is the collapse rating?
A: Both spin-on hydraulic filters and cartridge hydraulic filters have a collapse rating. The collapse rating is a rating of the filter’s ability to resist collapse. Collapse ratings are given in PSID (differential pressure). Differential pressure is the difference in pressure from the inlet of the filter to the outlet of the filter.
Reference FMC TSB-96-2R1
Q: What controls the flow rate of the filter?
A: The flow rate of a filter is the filters ability to pass a volume of fluid in a given time. Flow rate is affected by the amount of media and the restriction of that mediA: Generally, a filter that has high efficiency at removing small particles is going to be more restrictive to flow than a filter of the same size with same amount of media that has a lower efficiency at removing small particles.
Q: How can flow-rate be increased without sacrificing filtration performance?
A: To increase the flow-rate without sacrificing filter performance, a filter with more media surface area may be used. While the media has the same restriction per sq: in., the larger surface area of the media will provide a higher flow rate. An increase in flow-rate can also be accommodated by adding another filter in parallel. Other media types are also available that may provide increased flow without sacrificing filtration performance.
Q: What is the difference between cellulose and synthetic media?
A: Synthetic media is typically considered superior to cellulose media for many applications. Fiber size is smaller and more consistent allowing it to filter smaller particles, hold greater amounts of contaminant, yet provide less resistance to flow.
Q: Why do some hydraulic cartridges have a center tube support while others do not?
A: Some hydraulic applications create a large pressure differential across the element. Therefore, a center tube support is designed into the center tube to increase the element’s resistance to collapse.
Q: What is the difference between ISO and SAE ratings?
A: There is no significant difference between ISO (International Standards Organization) or SAE (Society of Automotive Engineering). Both organizations provide test standards to allow the ability to reliably compare published filter ratings among manufacturers.
Q: What is an ISO cleanliness code?
A: ISO cleanliness code is a data format for rating fluid contamination level and plotting filter media performance.
Q: What fluids are my filters compatible with? (eg. fuel, 90 wt gear oil etc.)
A: There are many types of hydraulic fluids used for power, but they can basically be called petroleum base, biodegradeable or fire resistant. Check with the filter manufacturer for fluid compatibility.
Q: How do I know I have the correct pressure rating for my equipment?
A: Reference FMC TSB-97-1R1
Q: Do hydraulic filters have bypass valves?
A: Hydraulic filter bypass valves if present are typically located in the filter head assembly or a separate component to the hydraulic system.
Q: What system characteristics should be considered when specifying a hydraulic filter?
A: Some of the characteristics to consider are filter location, hydraulic system hose size, gallons per minute flow requirements, fluid reservoir size and approximate fluid working temperature.
Reference FMC TSB-97-1R1
Q: Where does hydraulic system pressure originate?
A: Hydraulic pumps do not generate pressure, they only generate flow. It is resistance to flow in the system that generates system pressure.
Q: What types of hydraulic pumps are available?
A: The most popular types are gear (also known as rotary) pumps, vane pumps, and piston pumps. Pumps are rated by horse power (hp), shaft type, shaft size, direction of shaft rotation, gallons per minute (gpm) flow and pounds per square inch (psi) pressure.
Q: In mobile hydraulics, where is the filter located?
A: On a mobile hydraulic system, the filter or filters can be located in several different areas based on the system’s design and intended use. The most common locations are:
Suction side – a strainer on the end of the pick-up line in the reservoir or a filter in the line between the reservoir and the hydraulic pump.
PRESSURE SIDE – a filter in the line between the hydraulic pump and the rest of the system.
RETURN SIDE – a filter in the fluid return line from the actuator going back to the reservoir.
OFF-LINE – an entire filtration system that is added on to filter the fluid in the reservoir independently from any other filters in the system. This is sometimes referred to as a kidney loop system.
Q: Where can I find some basic hydraulic information?
A: Reference FMC TSB-96-1
Q: What causes the center tube of my hydraulic filter to collapse?
A: Reference FMC TSB-96-2R1