INTERNORMEN Replacement Filters – Three Temperature Grades, 99.95% Efficiency, Drop-In Fit

INTERNORMEN Replacement Filter Elements – High-Precision Filtration for Hydraulic Stations

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1. Application Background & Core Functional Requirements

Hydraulic stations serve as the power source for heavy machinery, metallurgical rolling equipment, 

injection molding machines, wind turbine pitch control systems, and automated production lines. 

The circulating hydraulic oil contains multiple contaminant types generated during operation:

Contaminant Type Source

Metal wear debris Pump gears, valve spools, cylinder piston rods

Rust particles Pipeline corrosion

Thermal oxidation sludge & varnish Oil degradation at elevated temperatures

Rubber fragments Seal wear

Particles below 5 microns can abrade servo valve spool surfaces, obstruct throttle orifices,

 and induce pressure fluctuations, vibration, and elevated system noise.

Original INTERNORMEN filters are installed on main supply, return, and pressure control circuits 

of medium and large hydraulic stations. When original elements reach service limits or are subject

 to procurement delays, interchangeable replacement filters are used to maintain system 

operation.

Replacement filter requirements:

Requirement Specification

Dimensional interface Match INTERNORMEN HC, 01E, 3000, 03E series housings

Bypass valve parameters Match original opening pressure settings

Temperature rating Selected per system oil temperature range

Fatigue resistance Withstand cyclic pressure loading

Filtration performance Stable particle separation under variable flow

Structural integrity Maintain geometry under pressure shocks

Seal integrity Prevent unfiltered oil bypass

2. Filter Media – Three Temperature Grades

INTERNORMEN replacement filters use asymmetric multi-layer borosilicate glass fiber composites. 

Media performance is validated per ISO 16889 (multi-pass filtration efficiency)

 and ISO 3724 (flow cyclic fatigue).

Gradient pore structure:

Layer Function

Outer layer (coarse) Retains large metal particles and rust

Middle layer (transition) Adsorbs oil sludge and colloidal material

Inner layer (fine) Captures micron-sized abrasive particles

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Grade 1: Standard Medium-Temperature Media

Application: Systems with continuous oil temperature ≤ 100°C (cold rolling auxiliary hydraulics,

 low-load circuits without radiant heat exposure)

Structure: Three-layer borosilicate fiber, phenolic resin binder

Parameter Value

Continuous operating temperature -10°C to +100°C

Resin thermal deformation temperature 112°C

Filtration ratings available 1, 3, 5, 7 μm

Beta ratio (βₓ) ≥ 2000

Particle capture efficiency ≥ 99.95%

Oil cleanliness level NAS 1638 Class 7 or better

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

Efficiency change ≤ 3% attenuation

Area-specific dirt capacity 1300 – 1500 g/m²

Effective filtration area (vs. flat media) 3 – 4×

Associated components: NBR seals, galvanized steel support core, polyurethane end cap

 adhesive

Compatible models: 01E series return filters

Limitation: Continuous operation above 105°C causes resin softening and interlayer separation.

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Grade 2: Reinforced High-Temperature Media

Application: Systems with continuous oil temperature 100°C – 120°C (hot rolling mills, 

thermal power EH hydraulic stations)

Structure: Four-layer borosilicate fiber, high-crosslink phenolic resin (solid content 14%–16%)

Parameter Value

Continuous operating temperature -10°C to +120°C

Resin thermal deformation temperature 138°C

Transient peak tolerance ≤ 130°C for ≤ 30 minutes

Tensile strength retention (1000h cyclic 110°C–130°C) ≥ 91%

Efficiency change ≤ 1.8% attenuation

Area-specific dirt capacity 1600 – 1900 g/m²

Surface treatment Calendered isolation layer

Associated components: FKM seals, 304 stainless steel core, fluorine-epoxy end cap adhesive

Compatible models: HC series pressure filters, 3000 series return filters

Operational note: When daily average oil temperature exceeds 115°C for more than 4 hours, 

reduce system flow by 10%.

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Grade 3: Ultra-High Temperature Media

Application: Systems with continuous oil temperature 120°C – 140°C 

(furnace-front heavy-load stations, boiler actuator stations)

Structure: Fluorinated composite glass fiber with high-temperature binder

Parameter Value

Continuous operating temperature -10°C to +140°C

Transient peak tolerance Up to 150°C

Associated seals Modified full-fluorine FKM

Support core material 316L stainless steel

Operational requirements:

· Install auxiliary oil coolers; maintain daily average ≤ 130°C

· Reduce replacement interval by 30% relative to Grade 2 applications

3. Component Matching – Dimensional and Material Compatibility

All replacement elements are manufactured to the following standards:

· Dimensional parameters match original INTERNORMEN housings

· Thread specifications match original housings

· Bypass valve opening pressure matches original settings

No housing modifications are required for installation.

3.1 Seal Material by Temperature Grade

Seal Material Media Grade Continuous Temperature Range Peak Tolerance Notes

NBR Grade 1 (≤100°C) -40°C to +100°C 110°C Swelling rate 16%–22% after 500h above 105°C

FKM (Viton) Grade 2 (100°C–120°C) -20°C to +120°C 130°C Swelling ≤3% after 1000h at 120°C;

 compression rebound ≥92%

Modified FKM Grade 3 (120°C–140°C) -20°C to +140°C 150°C Specified for high-viscosity aged oil 

and radiant heat exposure

3.2 End Cap Adhesive by Temperature Grade

Adhesive Type Associated Seal/Media Maximum Service Temperature Failure Mode Above Limit

Polyurethane NBR + Grade 1 110°C Hydrolysis, delamination, bypass channels

Fluorine-epoxy hot-melt FKM + Grade 2/3 145°C Peel strength ≥50 N/cm; no delamination at 

130°C

4. Selection by Operating Condition

Condition 1: Cold Rolling Auxiliary Hydraulic Station

Parameter Value

Oil temperature ≤100°C continuous; peak ≤105°C

Specified configuration Grade 1 media + NBR seals + galvanized steel core

Compatible models 01E series return filters

Additional measures Install heat shields; drain water from tank bottom weekly

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Condition 2: Hot Rolling Mill / Thermal Power EH Station

Parameter Value

Oil temperature 100°C – 120°C continuous; peaks 125°C–130°C (<30 min)

Specified configuration Grade 2 media + FKM seals + 304 stainless steel core

Compatible models HC series pressure filters, 3000 series return filters

Coverage Applicable to >90% of steel and power industry main hydraulic stations

Additional measures Monitor cooling system performance; record differential pressure per shift

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Condition 3: Furnace-Front Heavy-Load / Boiler Actuator Station

Parameter Value

Oil temperature 120°C – 140°C continuous; peaks 140°C–150°C

Specified configuration Grade 3 media + modified FKM seals + 316L core

Compatible models Custom configuration for extreme thermal loads

Additional measures Install auxiliary coolers; maintain daily average ≤130°C;

 shorten replacement interval by 30%

5. Operating Limits

Deviation from specified flow velocity, backwash air quality, or differential pressure thresholds

 reduces service life by 30%–50%.

5.1 Maximum Oil Flow Velocity

Media Grade Maximum Velocity Operating Margin

Grade 1 0.8 m/min 20%

Grade 2 0.7 m/min 25%

Grade 3 0.6 m/min 30%

When instantaneous flow exceeds 115% of housing rated capacity, open bypass valve for

 flow division.

5.2 Backwash Air Source Quality

For housings with online backwash capability:

Parameter Requirement

Air treatment Refrigerated dryer + two-stage oil-water separator

Pressure dew point < -20°C

Residual oil content ≤ 0.1 ppm

Backwash pressure 0.4 – 0.5 MPa

Oil or water vapor in backwash air deposits as sludge on the media surface, 

permanently blocking pores and reducing service life by more than 40%.

6. Failure Modes – Causes and Corrections

Failure 1: End Cap Leakage

Observation Cause Correction

Oil seepage at end cap Adhesive temperature rating below operating temperature; 

thermal degradation Use adhesive grade matching actual oil temperature

End cap separation Extended exposure above adhesive limit Reduce oil temperature or 

select higher-grade assembly

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Failure 2: Rapid Differential Pressure Increase (New Element)

Observation Cause Correction

DP reaches alarm within days No upstream coarse pre-filter; large particles impact media 

directly Install 80–100 μm pre-filter at inlet

Immediate DP spike after installation Oil degraded; high acid value; surface blockage by sludge

 Replace oil; flush tank; remove accumulated sediment

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Failure 3: Filtration Efficiency Below Specification

Observation Cause Correction

Downstream cleanliness deteriorates Bypass due to seal swelling or shrinkage Replace with 

seal material matching temperature grade

Increased downstream particle count Media rupture from pressure spike or flow excess Verify 

flow velocity; inspect for pressure surges; use reinforced core

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Failure 4: Thermal Degradation (High-Temperature Service)

Observation Cause Correction

Media discoloration, brittleness Continuous operation above rated temperature Add cooling 

capacity; reduce thermal load

Fiber shedding downstream Resin breakdown at extreme temperature Upgrade to Grade 3 media

 with fluorinated binder

7. Installation and Maintenance Procedures

Item Procedure

Pre-installation check Verify model number; inspect seal groove and media for damage

Seals Install new seals matching temperature grade; do not reuse

Housing preparation Clean sealing surfaces before installation

Differential pressure Record per shift; replace when alarm threshold is reached

Oil analysis Test acid value, water content, particle count monthly

Storage Store in dry, dustproof location; avoid sunlight

Not permitted Do not clean used elements with solvent, water, or compressed air—the gradient 

structure is permanently damaged

8. Frequently Asked Questions

Q1: What is the filtration efficiency of these replacement elements?

A: Beta ratio ≥2000 per ISO 16889, with ≥99.95% capture efficiency at the rated micron size.

Q2: Can Grade 1 media be used at 110°C?

A: No. Continuous operation above 105°C softens the resin binder and reduces efficiency. 

Grade 2 is required for temperatures above 100°C.

Q3: When should the filter be replaced?

A: Replace when differential pressure reaches the alarm value specified for the housing.

 Fixed-interval replacement is not recommended.

Q4: Can new and old elements be used together in the same housing?

A: No. All elements in a single housing should be replaced simultaneously to maintain uniform 

flow distribution.

Q5: What documentation is supplied?

A: EN 10204 material certificates, ISO 16889 performance test reports, and dimensional 

inspection records.

9. Summary

Selection of INTERNORMEN replacement filter elements is determined by three operating

 parameters:

1. Oil temperature – specifies media and seal grade

2. System flow rate – must remain within velocity limits

3. Upstream contamination load – pre-filtration extends element life

Correct matching of media grade, sealing materials, and structural components to actual 

operating conditions maintains:

· Oil cleanliness at NAS Class 7 or better

· Specified service intervals

· Direct interchangeability with original housings—no modifications required