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Pollution classes of hydraulic oils

1 - Why clean up ?

The price of hydraulic oils and their recycling represent a significant cost for the maintenance budget.

Effective filtration increases the life of hydraulic components and fluid. Oil changes can sometimes be spaced out. All this to reduce maintenance costs, machine downtime, breakdowns...

2 - When to clean up ?

  • During oil transfer (filling or topping up the tank). It should be noted that new oils are not in acceptable pollution classes.
  • During machine operation. Efficient filtration present on the machines at different places makes it possible to trap pollution due to the wear of components, cylinder rods, etc.
  • After maintenance operations (opening of the hydraulic circuit, change of hoses, change of components, etc.) Parallel filtration using a filtration unit boosts the filtration set up. The flow through the filter is constant, low and without pressure variation, which provides optimum filter retention capacity.

3 - In what proportion to decontaminate ?

The cost of filtration is a significant budget for maintenance. Good filtration extends the life of hydraulic components and reduces breakdowns, but you don't need over-quality.

  1. Clean up beyond what is necessary:
  • It means using more efficient and more expensive filters.
  • It means changing filters more often.
  • This reduces the risk of failure.
  1. Clean up below what is necessary:

4 - The main standards related to pollution

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ISO 2941

Filter Elements: Checking the crush/burst pressure

ISO 2942

Filter elements: Verification of manufacturing conformity and determination of the *first bubble point

ISO 2943

Filtering elements: Verification of the compatibility of materials with fluids

ISO 3724

Filter elements: Verification of the characteristics of a filter by a fatigue test due to the flow

ISO 3968

Filtering elements: Evaluation of the pressure drop according to the flow rate

ISO 11170

Filter elements: Order of tests for verification of performance characteristics

ISO 16889

Filter elements: Performance evaluation by the closed circuit filtration method

ISO 23181

Filter Elements: Determination of Resistance to Fatigue Due to Flow Using High Viscosity Fluid

SAE ARP 4205

Filter elements: Dynamic efficiency evaluation method with cyclic flow

ISO 3722

Sampling bottles: Approval and control of cleaning methods

ISO 4021

Particle pollution analysis: Taking fluid samples from operating circuits

ISO 4405

Fluid pollution: Determination of particulate pollution by the gravimetric method

ISO 4406

Fluid: Method for coding the level of solid particulate pollution

ISO 4407

Pollution of fluids: Determination of particulate pollution by counting under an optical microscope

ISO 10949

Component Cleanliness: Guidelines for Obtaining and Maintaining Component Cleanliness from Manufacture to Installation

ISO 11171

Calibration of automatic suspended particle counters in liquids

ISO11500

Determination of particulate pollution by automatic light absorption counting

ISO 11943

Automated Online Counting Systems for Suspended Particles in Liquids: Calibration and Validation Methods

ISO18413

Cleanliness of components: Inspection documents, principles of extraction, analysis of contaminants and expression of results
 

5 - When to take an oil sample ?

Taking an oil sample for analysis allows you to make a report on the state of pollution at a precise moment. Regular samplings make it possible to compare the results, to define a diagnosis and the measures to be put in place.

There is no absolute rule. It is advisable to follow the manufacturer's recommendations. Sampling every 6 to 12 months or every 1000 hours corresponds to commonly encountered frequencies.

6 - How to take an oil sample ?

There are several techniques for taking oil samples.

Technique No. 1 is preferred. Sampling oil through a tank drain valve should be avoided.

It is imperative to use sterile bottles to take the samples.

As far as possible, the sample should be taken in the best environmental conditions (avoid drafts with a dusty environment, mechanical welding work nearby, etc.)

If the sampling procedures are not done correctly, the analysis result will not be representative of the actual pollution of the machine.

Ideally, the same person takes the samples in order to reproduce the same gestures, the same conditions.

 
Flacon sterile capillaire 1
  • Technique N°1: Sampling on pressure tapping. (Preferred method)
  1. Run the machine for at least 30 min performing all movements.
  2. Use a “clean and plugged” capillary, connect it to the pressure tap to rinse it. Allow about 1 liter of oil to flow.
  3. Open the sterile bottle, taking care not to pollute it.
  4. Fill part of the bottle to rinse the walls. Discard used oil. Perform this task twice.
  5. Take the oil sample. Fill the bottle ¾ full.
  6. Immediately close the bottle and identify the sample. (Date, machine number, hour meter, where in the circuit the sample was taken, type of oil, etc.)
  • Technique N°2: Sampling on an industrial valve. (To be used if technique N°1 is impossible)
  1. Run the machine for at least 30 min performing all movements.
  2. Open the valve to rinse it thoroughly. (3 to 4 liters minimum). Do not close the valve any more during sampling.
  3. Open the sterile bottle, taking care not to pollute it.
  4. Fill part of the bottle to rinse the walls. Discard used oil. Perform this task twice.
  5. Take the oil sample. Fill the bottle ¾ full.
  6. Immediately close the bottle and identify the sample. (Date, machine number, hour meter, where in the circuit the sample was taken, type of oil, etc.)
  • Technique N°3: Sampling in tank by syringe or sampling pump. (To be used if techniques N°1 and 2 are impossible)
  1. Run the machine for at least 30 min performing all movements.
  2. Thoroughly clean around the area where the sample is to be taken.
  3. Flush syringe/sample pump with filtered solvent to decontaminate tooling.
  4. Open the sterile bottle, taking care not to pollute it, and connect it to the sampling tool.
  5. Immerse the syringe/pump hose halfway up the tank. Fill part of the bottle to rinse the walls. Discard used oil. Perform this task twice.
  6. Take the oil sample. Fill the bottle ¾ full.
  7. Immediately close the bottle and identify the sample. (Date, machine number, hour meter, where in the circuit the sample was taken, type of oil, etc.)
  • Technique N°4: Taking a sample in a tank by immersing a bottle. (To be used if techniques N°1,2,3 are impossible)
  1. Run the machine for at least 30 min performing all movements.
  2. Thoroughly clean around the area where the sample is to be taken.
  3. Rinse the outer part of the sterile vial with filtered solvent to decontaminate it.
  4. Open the sterile bottle, taking care not to pollute it.
  5. Immerse the bottle in the tank. Fill part of the bottle to rinse the walls. Discard used oil. Perform this task twice.
  6. Take the oil sample. Fill the bottle ¾ full.
  7. Immediately close the bottle and identify the sample. (Date, machine number, hour meter, where in the circuit the sample was taken, type of oil, etc.)

7 - Particule size

Taille particule de pollution 1
 

There are different methods and devices for measuring particle size.

In Fig. A, a particle analyzed by microscope will retain a particle size of 13 microns while a particle analyzed by automatic counting will retain a particle size of 10 microns.

8 - Pollution classes

After analysis of the oil samples, it appears that pollution particles must be counted. There are 3 Standards.

  1. NAS 1638 standard

The NAS 1638 standard was developed in 1964 to quantify the number of particles. It was officially discontinued in 1993.

The classes are scaled from code 00 to code 12. The classes indicate the maximum number of particles contained in 100 ml of sampled fluid. The counting mode is differential.

NAS 1638

Maximum number of particles per 100 ml of fluid

Classes

5 - 15 µm

15 -20 µm

25 -50 µm

50 - 100 µm

> 100 µm

00

125

22

4

1

0

0

250

44

8

2

0

1

500

89

16

3

1

2

1000

178

32

6

1

3

2000

356

63

11

2

4

4000

712

126

22

4

5

8000

1425

253

45

8

6

16000

2850

506

90

16

7

32000

5700

1012

180

32

8

64000

11400

2025

360

64

9

128000

22800

4050

720

128

10

256000

45600

8100

1440

256

11

512000

91200

16200

2880

512

12

1024000

182400

32400

5760

1024

Example :

5 - 15 µm : 32500 particles

15 -20 µm : 1850 particles

25 -50 µm : 180 particles

50 - 100 µm : 11 particles

> 100 µm : 2 particles

Classes NAS 8
 
  1.  SAE AS4059

It was developed as a successor to NAS 1638.

The particle counting mode can be differential or cumulative.

SAE AS4059 Differential Counting

  

Classes

Maximum number of particles per 100 ml of fluid

  

5 - 15 µm

15 -20 µm

25 -50 µm

50 - 100 µm

> 100 µm

ISO 4402 (1)

6 - 14 µm(C)

14 -21 µm(C)

21 -38 µm(C)

38 - 70 µm(C)

> 70 µm(C)

ISO 11171 (2)

00

125

22

4

1

0

  

0

250

44

8

2

0

  

1

500

89

16

3

1

  

2

1000

178

32

6

1

  

3

2000

356

63

11

2

  

4

4000

712

126

22

4

  

5

8000

1425

253

45

8

  

6

16000

2850

506

90

16

  

7

32000

5700

1012

180

32

  

8

64000

11400

2025

360

64

  

9

128000

22800

4050

720

128

  

10

256000

45600

8100

1440

256

  

11

512000

91200

16200

2880

512

  

12

1024000

182400

32400

5760

1024

  

Example :

6 - 14 µm(C) : 32500 particles

14 -21 µm(C) : 1850 particles

21 -38 µm(C) : 180 particles

38 - 70 µm(C) : 11 particles

> 70 µm(C) : 2 particles

SAE AS4059 Classes 8

  1. : Counting under a microscope according to the ISO 4402 standard.
  2.  : Counting by automatic counter according to ISO 11171 standard.

(C): Certified. Indicates that the automatic particle counter has been calibrated according to ISO 11171.

 

SAE AS4059 Cumulative Count

  

Classes

Maximum number of particles per 100 ml of fluid

  

>1 µm

>5 µm

>15 µm

>25 µm

>50 µm

> 100 µm

ISO 4402 (1)

> 4 µm(C)

> 6 µm(C)

> 14µm(C)

> 21µm(C)

> 38µm(C)

> 70 µm(C)

ISO 11171 (2)

000

195

76

14

3

1

0

  

00

390

152

27

5

1

0

  

0

780

304

54

10

2

0

  

1

1560

609

109

20

4

1

  

2

3120

1217

217

39

7

1

  

3

6250

2432

432

76

13

2

  

4

12500

4864

864

152

26

4

  

5

25000

9731

1731

306

53

8

  

6

50000

19462

3462

612

106

16

  

7

100000

38924

6924

1224

212

32

  

8

200000

77849

13849

2449

424

64

  

9

400000

155698

27698

4898

848

128

  

10

800000

311396

55396

9796

1696

256

  

11

1600000

622792

110792

19592

3392

512

  

12

3200000

1245584

22584

39184

6784

1024

  

 

 

Example :

>4 µm(C) : 120000 particles

>6 µm(C) : 10500 particles

>14 µm(C) : 180 particles

>21 µm(C) : 11 particles

> 38 µm(C) : 2 particles

> 70 µm(C) : 2 particles

SAE AS4059 Classes 8

 

 

 

 

 

 

 

 

 

 

  1. : Counting under a microscope according to the ISO 4402 standard.
  2.  : Counting by automatic counter according to ISO 11171 standard.

(C): Certified. Indicates that the automatic particle counter has been calibrated according to ISO 11171.

 
  1. ISO 4406 standard

SO 4406 is the preferred method. It makes it possible to quantify the distribution of solid contaminants in a fluid sample.

There are 3 codes:

  • Code 1  : The number of particles greater than 4 µm contained in 1 ml of fluid.
  • Code 2  : The number of particles greater than 6 µm contained in 1 ml of fluid.
  • Code 3  : The number of particles greater than 14 µm contained in 1 ml of fluid.

ISO 4406

Classes

Number of particles over size per ml

Beyond

Up to

28

1300000

2500000

27

640000

1300000

26

320000

640000

25

160000

320000

24

80000

160000

23

40000

80000

22

20000

40000

21

10000

20000

20

5000

10000

19

2500

5000

18

1300

2500

17

640

1300

16

320

640

15

160

320

14

80

160

13

40

80

12

20

40

11

10

20

10

5

10

9

2,5

5

8

1,3

2,5

7

0,64

1,3

6

0,32

0,64

5

0,16

0,32

4

0,08

0,16

3

0,04

0,08

2

0,02

0,04

1

0,01

0,02

0

0

0,01

Example :

>4 µm(C) : 430 particles

>6 µm(C) : 90 particles

>14 µm(C) : 22 particles

ISO : 16/14/12

 
Graphique iso 4407
 

9 - Correspondence between standards

ISO 4406

NAS / SAE

23/21/18

12

22/20/17

11

21/19/16

10

20/18/15

9

19/17/14

8

18/16/13

7

17/15/12

6

16/14/11

5

15/13/10

4

14/12/9

3

13/11/8

2

12/10/7

1
  1. A simple method allows you to find a NAS or SAE class.
  2. Just take code 2 from the ISO standard and add the 2 digits.
  3. Example: 19/17/14: 17 = 1 + 7 = 8 (Class 8)
 

13 - Counting methods

  1. Optical particle counting (Number of particles / ml)

It provides information on the particle size distribution. The result is not affected by the opacity of the fluid or by the presence of undissolved water and air in the fluid.

The method is very technical, procedural and time consuming.

  1. Automatic particle counting (Number of particles / ml)

It is fast, accurate and repeatable. It is sensitive to sludge, water and air.

  1. Test membrane and fluid pollution comparator

The analysis is done by visual comparison with a sample. The analysis is fast and adapted to the field. It identifies the types of pollutants.

The method gives an estimate of solid pollution levels.

  1. Ferrography (Weighted number of large / small particles)

This method provides information on ferrous and magnetic particles.

The analysis does not detect non-magnetic particles (brass, silica, etc.)

  1. Spectrometry (ppm: parts per million)

This method makes it possible to identify and quantify pollutants. It does not provide information on the size of the pollutants.

  1. Gravimetry (mg/L)

This method indicates the total mass of pollutants. It does not provide information on sizes. It is not suitable for fluid < ISO 18/16/13

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11 - Recommendations

The acceptable level of cleanliness in hydraulic installations depends on:

  • Sensitivity of components to pollution.
  • Conditions of use of the installation (pressure, flow, temperature, etc.)

Expected reliability and life expectancy

 

ISO 4406

NAS / SAE

Filtration fineness

βx(c)≥1000

Standard low pressure on/off hydraulics. Occasional operation

23/21/18

12

25

Standard all-or-nothing hydraulics

20/18/14

9

15

Standard high pressure on/off hydraulics

19/17/14

8

12 à 15

Proportional & variable displacement pump

18/16/13 à 19/17/14

7 à 8

10 à 12

Servo valves

15/13/10 à 17/15/12

4 à 6

3 à 6
 

12 - Description of an oil analysis

  • Viscosity: (cSt)

This is the fluidity of the oil controlled at a temperature of 40°C. Viscosity may vary depending on:

  1. Pollution (increase or decrease)
  2. From an oxidation (increase)
  3. Thermal cracking (decrease)
  • Visual aspect :

The visual aspect (transparency, deposits) does not confirm that the oil is not contaminated, but it can provide information on pollution by another fluid.

  • Insoluble content: (in % by weight)

This measurement quantifies the solid impurities retained by filtration (5 micron millipore filter).

These pollution particles can come from external contamination or wear metals.

The "insoluble" particles are suspended in the oil. This measurement may differ from results determined by spectrometry.

  • Content of elements: (ppm)

Spectrometry makes it possible to know the contents of elements. This method doses the chemical elements present in the form of particles with a size of less than 5 microns.

The chemical elements can come from additives present in the oil, wear pollution.

  • Water content: (ppm or % weight)

0.05% water in oil is the acceptable limit in hydraulic circuits.

  • Acid value: (mg)

This measurement gives the number of mg of potash necessary to neutralize the acid compounds present in the oil.

Oxidation of the fluid increases the acid number.

  • Flash point: (°C)

This is the temperature to which a sample of oil must be brought for its vapors to ignite on contact with a source of ignition.

A drop in the flash point can be the consequence of pollution by solvent or degradation of the fluid by cracking.

  • Particle counting:

Counting can be done by different methods. The result is expressed in the form of pollution classes according to ISO or SAE standards.

  • Dielectric strength:

Property possessed by an insulating oil to prevent the formation of an arc under the effect of an electric field.

  • Deaeration:

It is the oil's ability to release the air previously introduced by mechanical agitation. (Foam formation)

The aeration of an oil can cause the following problems:

  1. Break the oil film.
  2. Accelerate oil oxidation.
  3. Increase oil compressibility.
  4. Interfere with the operation of the hydraulic controls.
  5. Cavitation phenomenon.

The causes of poor deaeration:

  1. Of pollution.
  2. Oil aging.
  3. An emulsion (mixture with another oil).
 

 

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