Typical Contamination Levels |
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The tables and numbers in this chapter represent typical system levels and classes of contamination as established by various organizations. Do not consider them “acceptable” levels unless they were designated as acceptable for your testing requirements. This data is helpful as a guide in establishing a reliability program if you do not have actual performance data available yet.
- Hydraulic Fluids
- ISO 4406 Hydraulic Fluid Cleanliness Codes
- Aircraft Fuels
- United States Military Land-Based Hydraulics
- CFC-Free Cleaning Solvent
- Rocket Propulsion and Service Fuels
- Ambient Air
- Cleanroom Garments
Hydraulic Fluids
This table lists the Navy Standard for Hydraulic Fluids Used for Aircraft Hydraulic Systems (NAV AIR 10-1A-17):| Size Range | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|
| 5–10 µm | 2,700 | 4,600 | 9,700 | 24,000 | 32,000 | 87,000 | 128,000 |
| 10–25 µm | 670 | 1,340 | 2,680 | 5,360 | 10,700 | 21,400 | 42,000 |
| 25–50 µm | 93 | 210 | 380 | 780 | 1,510 | 3,130 | 6,500 |
| 50–100 µm | 16 | 28 | 56 | 110 | 225 | 430 | 1,000 |
| >100 µm | 1 | 3 | 5 | 11 | 21 | 41 | 92 |
ISO 4406 Hydraulic Fluid Cleanliness Codes
ISO 4406 is a coding system designed to translate the data obtained from particle counting of hydraulic fluid samples into classes of cleanliness. It supersedes previous coding systems for hydraulic components, such as NAS 1638.This table shows how to use particle counts obtained from fluid samples to obtain the ISO 4406 rating.
Aircraft Fuels
| Activity | Total Sediment |
|---|---|
| Commercial (average) | 0.2 mg/L |
| International Air Transport Association (IATA) | 1.0 mg/USG (max) |
| Military Standards | 4.0 mg/USG (max) |
United States Military Land-Based Hydraulics
This table lists the maximum allowable particles per 100 mL in stated particle size ranges for MILH-5606, MIL-H-27601 A, and MIL-H-81019A hydraulic fluids:| Particle Size Range | Max. Allowable Particles |
|---|---|
| 5–15 µm | 2500 |
| 16–25 µm | 1000 |
| 26–50 µm | 250 |
| 51–100 µm | 25 |
| >100 µm | None |
CFC-Free Cleaning Solvent
MIL-PRF-5606H gives the following limits for petroleum-based hydraulic fluids in aircraft, missiles and ordnance:| Particle Size Range | Max. Allowable Particles |
|---|---|
| 5–15 µm | 10,000 |
| 15–25 µm | 1,000 |
| 25–50 µm | 150 |
| 50–100 µm | 25 |
| >100 µm | 5 |
Rocket Propulsion & Service Fuels*
Because of the more generous metering and pumping clearances for Missile Propellants and Service Gases, relatively high contamination levels are tolerated. The major (particulate) risk is in clogging of pump inlet screens. Fibers that will initiate clogging and silting, therefore, are specially controlled and held typically to 400 µm maximum size.| Fluid | A.F. Use Limits |
|---|---|
| LO1 (Liquid Oxygen) | 2.5 mg/L |
| LN1 (Liquid Nitrogen) | 2.5 mg/L |
| RP-1 (Rocket Engine Fuel, Grade RP-1) | 1.5 mg/L |
| GO1 (Gaseous Oxygen) | 0.01 mg/L |
| GN1 (Gaseous Nitrogen) | 0.01 mg/L |
| He (Helium) | 0.01 mg/L |
Ambient Air
This table lists the U.S. Air Force Tech. Order 00-25-203, maximum allowable particles (≥5 µm diameter) per per cubic foot:| Condition | At Rest | Operational |
|---|---|---|
| Air Force Std. Clean Room | 70 | 680 |
| Air Force Clean Work Station | 0 | 7 |
Cleanroom Garments
The ASTM Decontamination Process Garment Classification Levels are:| Class | Contamination level per square foot of fabric | Particle type |
|---|---|---|
| A | Less than 1000 | ≥5 µm particles |
| Maximum 10 | Fibers | |
| B | Less than 5000 | ≥5 µm particles |
| Maximum 25 | Fibers | |
| C | Less than 10,000 | ≥5 µm particles |
| Maximum 50 | Fibers | |
| D | Less than 15,000 | ≥5 µm particles |
| Maximum 125 | Fibers | |
| E | Less than 25,000 | ≥5 µm particles |
| Maximum 175 | Fibers |
Obviously broken fibers and lint-bearing seams on outer surfaces of garments, wiping cloths, caps, hoods, booties, and fabrics are cause for rework or rejection. Decontamination-processed clean room fabrics are free from persistent objectionable odors.