High-precision Replacement InterNormen Filter for Hydraulic Station Oil Circuit

1. Working Condition Profile & Core Functional Demands

Hydraulic stations serve as the power core of heavy machinery, metallurgical rolling equipment, injection molding machines,

 wind turbine pitch control systems, and automated production lines. The circulating hydraulic oil inside these systems 

carries multiple types of pollutants generated during long-term continuous operation:

· Metal wear debris from pump gears, valve spools, and cylinder piston rods

· Pipeline rust particles and scale

· Thermal oxidation oil sludge and varnish precipitates

· Tiny rubber sealing fragments

Even micro-scale particulate contaminants below 5 microns will scratch the matching surfaces of precision servo valves,

 block tiny throttle orifices, and cause unstable pressure output, vibration, and abnormal noise throughout the entire hydraulic 

system.

Original Internormen filters are widely installed on main oil supply circuits, return oil circuits, and pressure control branches 

of medium and large hydraulic stations to maintain long-term oil cleanliness. When original parts reach their service limit 

or face procurement cycle constraints, interchangeable Internormen replacement filter elements become the core consumable 

for sustained stable operation of hydraulic stations.

High-precision filtration working conditions impose rigid multi-dimensional requirements on replacement filter elements, 

which must fully match the dimensional interfaces, internal bypass valve parameters, temperature resistance, and fatigue 

resistance benchmarks of standard Internormen HC, 01E, 3000, and 03E series filter elements. Any mismatch in filter media

 grade, skeleton material, or adhesive formula will lead to premature performance attenuation—such as rapid differential 

pressure surge, filtration efficiency decline, and medium leakage—which further trigger secondary wear of precision hydraulic

 components and unplanned production shutdowns.

2. Multi-Layer Gradient Glass Fiber Filter Media Grading

All filter media adopted for Internormen interchangeable filter elements utilize asymmetric multi-layer borosilicate glass

 fiber composite structures, which pass ISO 16889 multi-pass filtration efficiency testing and ISO 3724 flow cyclic fatigue testing.

 Three temperature-resistant grades are divided according to the long-term average oil temperature of hydraulic station oil

 circuits, with clear matching boundaries for cold auxiliary hydraulic stations, conventional main hydraulic stations, 

and high-temperature furnace front hydraulic stations.

The gradient pore structure realizes staged interception of pollutants:

· Outer loose fiber layer – captures large metal wear debris and rust particles

· Middle transition fiber layer – adsorbs oxidized oil sludge and colloidal precipitates

· Inner dense precision fiber layer – traps micron-level abrasive fine particles

This design effectively avoids early surface blockage and balances dirt holding capacity with filtration precision.

Grade One: Standard Medium-Temperature Glass Fiber Media (Oil Temperature ≤100°C)

Applicable to cold rolling auxiliary hydraulic stations, small auxiliary pump lubrication circuits, and low-load hydraulic

 stations without furnace radiant heat interference.

Parameter Specification

Continuous temperature range –10°C to +100°C

Resin thermal deformation temp 112°C

Optional filtration precision 1μm, 3μm, 5μm, 7μm

Beta ratio (βₓ) 2000 (≥99.95% efficiency)

Tensile strength retention ≥83% after 500h at 100°C

Efficiency attenuation <3%

Dirt holding capacity 1,300–1,500 g/m²

Seal material NBR nitrile rubber

Skeleton material Galvanized carbon steel

Applicable models 01E series return oil filters

Grade Two: Reinforced High-Temperature Glass Fiber Media (100°C to 120°C)

The most widely adopted media grade for medium and large industrial hydraulic stations, compatible with most Internormen 

HC and 3000 series original filter element dimensions.

Parameter Specification

Continuous temperature range –10°C to +120°C

Resin thermal deformation temp 138°C

Peak temperature tolerance 130°C (≤30 min)

Tensile strength retention ≥91% after 1,000h cyclic aging

Efficiency attenuation ≤1.8%

Dirt holding capacity 1,600–1,900 g/m²

Surface treatment Calendered for sludge resistance

Seal material FKM fluororubber

Skeleton material 304 stainless steel

Applicable models HC series pressure filters, 3000 series return filters

Grade Three: Ultra-High Temperature Custom Media (120°C to 140°C)

Exclusive solution for extreme thermal load hydraulic stations where standard filters show rapid performance attenuation.

Parameter Specification

Continuous temperature range –10°C to +140°C

Peak temperature tolerance 150°C

Tensile strength retention ≥88% after 1,200h severe aging

Seal material Modified full-fluorine FKM

Skeleton material 316L stainless steel

Application Furnace front hydraulic stations, boiler actuator systems

3. Complete Structural Accessory Matching Standards

The overall temperature and pressure fatigue resistance of the complete filter assembly relies on coordinated matching of all

 components. Mismatch of any single accessory will cause medium leakage and bypass pollution before the filter media

 reaches its service limit.

Sealing Ring Matching Rules

Media Grade Seal Material Continuous Temp Range Peak Temp Tolerance

Grade One NBR nitrile –40°C to +100°C 110°C

Grade Two FKM fluororubber –20°C to +120°C 130°C

Grade Three Modified full-fluorine FKM –20°C to +140°C 150°C

Critical restrictions: NBR seals are strictly prohibited for hot rolling and power plant hydraulic circuits with oil temperature 

exceeding 100°C. After 500 hours of immersion in oxidized high-temperature oil, NBR volume swelling can reach 16%–22%, 

forming leakage paths.

End Cap Bonding Adhesives

Adhesive Type Matched Media Grade Temp Limit Peel Strength

Polyurethane Grade One ≤110°C N/A

Fluorinated epoxy hot-melt Grade Two & Three ≤145°C ≥50 N/cm

4. Graded Matching Selection Schemes for Typical Working Conditions

Condition One: Cold Rolling Auxiliary Hydraulic Station

· Oil temperature: ≤100°C continuous, ≤105°C peak

· Recommended configuration: Grade One media + NBR seals + galvanized carbon steel skeleton

· Compatible with: 01E series return oil filters

· Key operation measures: Install heat insulation baffles; weekly water drainage from tank bottom

Condition Two: Hot Rolling Mills & Thermal Power EH Stations

· Oil temperature: 100°C–120°C continuous, 125°C–130°C peak (≤30 min)

· Recommended configuration: Grade Two media + FKM seals + 304 stainless steel skeleton

· Compatible with: HC series pressure filters, 3000 series return filters

· Coverage: Over 90% of mainstream hydraulic station applications in steel and power industries

· Key operation measures: Optimize cooling system to avoid >120°C for >4 consecutive hours; record differential pressure

 per shift

Condition Three: Furnace Front Heavy-Load Hydraulic Stations

· Oil temperature: 120°C–140°C continuous, peaks 140°C–150°C

· Recommended configuration: Grade Three media + modified full-fluorine FKM seals + 316L stainless steel skeleton

· Key operation measures: Install auxiliary oil coolers to keep daily average below 130°C; shorten replacement cycle by 30%

5. System Operation Parameter Control Standards

Unreasonable control of oil circuit flow velocity, backwash air source cleanliness, and differential pressure thresholds will 

cause 30%–50% loss of the rated service cycle.

Flow Velocity Limits

Media Grade Max Velocity Flow Margin

Grade One 0.8 m/min 20%

Grade Two 0.7 m/min 25%

Grade Three 0.6 m/min 30%

When instantaneous peak flow exceeds design rating by >15%, open bypass regulating valve for flow splitting.

Compressed Air Source Standards for Backwash Systems

· Must include refrigerated dryer + dual-stage oil-water separator

· Air source dew point: ≤ –20°C

· Residual oil content: ≤0.1 ppm

· Warning: Oil/moisture-mixed air forms sticky tar sludge, permanently blocking fiber pores and shortening service life 

by >40%

· Backwash pressure: 0.4–0.5 MPa (prevents pleat collapse)

6. Common Failure Analysis & Solutions

Failure 1: Oil leakage at filter element end cap seals

· Root causes: NBR seals used beyond 100°C; seal hardening, cracking, or swelling

· Solutions: Upgrade to FKM or full-fluorine FKM seals matching actual oil temperature; replace seals during every filter 

element change

Failure 2: Rapid differential pressure surge after short operation

· Root causes: Excessive filtration velocity; media grade mismatch; missing front-end pre-filtration

· Solutions: Verify flow velocity within limits; upgrade to higher dirt-holding Grade Two/Three media; install coarse strainer 

upstream

Failure 3: Unstable filtration efficiency (oil cleanliness deteriorates)

· Root causes: Adhesive delamination creating internal bypass; skeleton deformation causing media collapse

· Solutions: Use fluorinated epoxy hot-melt adhesive (Grade Two/Three); upgrade to 304/316L stainless steel skeleton;

 verify bypass valve setting

Failure 4: Glass fiber media delamination and breakage

· Root causes: Oil temperature exceeding resin thermal deformation point; excessive backwash pressure or flow impact

· Solutions: Select correct temperature grade with safe margin; reduce backwash pressure to 0.4–0.5 MPa; 

install heat insulation

7. FAQ (Frequently Asked Questions)

Q1: Are these replacement filter elements fully interchangeable with original Internormen filters?

A: Yes. All dimensional parameters, thread specifications, and built-in bypass valve opening pressures maintain full consistency 

with corresponding Internormen original HC, 01E, 3000, and 03E series filter housings. Direct drop-in replacement requires no 

mechanical modification.

Q2: How do I select the correct temperature grade for my hydraulic station?

A: Measure the long-term average oil temperature at the filter housing. For ≤100°C, choose Grade One. For 100°C–120°C, 

choose Grade Two (covers 90% of applications). For 120°C–140°C, choose Grade Three. Always allow 5–10°C safety margin 

above measured temperature.

Q3: What is the difference between NBR and FKM seals, and why does it matter?

A: NBR (nitrile) is rated for ≤100°C and is suitable for low-temperature auxiliary circuits. FKM (fluororubber) is rated 

for ≤120°C–140°C depending on grade. Using NBR above 100°C causes swelling, hardening, and leakage—this is the #1 cause 

of premature filter failure.

Q4: What filtration precision options are available?

A: Standard options include 1μm, 3μm, 5μm, and 7μm for Grade One; 3μm, 5μm, and 10μm for Grade Two; and 5μm and 

10μm for Grade Three. Custom precision grades are available upon request.

Q5: What is the typical service life of these replacement filter elements?

A: Under normal operating conditions with proper matching, Grade One lasts 6–12 months; Grade Two lasts 8–14 months;

 Grade Three lasts 4–8 months due to more severe thermal stress. Actual service life depends on oil contamination level and 

operating hours.

Q6: Can the filter element be cleaned and reused?

A: No. Glass fiber media filter elements are disposable. Attempting to clean them with compressed air or solvents will damage

 the delicate fiber structure and permanently reduce filtration efficiency. Always replace with new elements.

Q7: What is the significance of the Beta ratio (βₓ > 2000)?

A: Beta ratio measures filtration efficiency. βₓ = 2000 means the filter captures 99.95% of particles at the rated size (x microns). 

This high efficiency ensures precision servo valves and pumps receive adequately clean oil.

Q8: What should I do if the differential pressure rises rapidly after installing a new element?

A: Check that the media grade matches your oil temperature; verify flow velocity is within limits; inspect for collapsed pleats or

 media damage from improper handling; confirm the housing bypass valve is not stuck closed; ensure no upstream coarse 

strainer is blocked.

Q9: Are these elements compatible with fire-resistant hydraulic fluids (phosphate esters, water-glycol)?

A: For phosphate ester fluids, we recommend upgrading to FKM seals and verifying media chemical compatibility. 

For water-glycol fluids, please consult our technical team for specific recommendations. Standard glass fiber media is

 compatible with mineral oils.

Q10: Do you offer custom sizes for non-standard Internormen housings?

A: Yes. We can custom-manufacture filter elements to your specific dimensional, precision, and temperature requirements. 

Please provide your housing specifications, oil type, and operating conditions.

Q11: How does the gradient pore structure improve filtration performance?

A: The outer coarse layer captures large particles, preventing early surface blinding. The middle layer handles intermediate

 contaminants. The inner fine layer traps micron-sized particles. This staged design increases dirt holding capacity by 30–50% 

compared to single-layer media.

Q12: What quality certifications do your replacement elements comply with?

A: Our elements are manufactured and tested in accordance with ISO 16889 (multi-pass efficiency), ISO 3724 (flow fatigue), 

ISO 2941 (burst resistance), and ISO 2943 (fluid compatibility). Factory test reports are available upon request.