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Determine the emission values for fuel-powered engines. A higher EURO standard means stricter emission requirements or lower emissions. Both fuel and oil play an important role in keeping emissions low. For example, an engine oil developed for the EURO3 standard cannot be used for EURO6 engines. Using the wrong or inferior oil can damage your engine and clog the entire exhaust system.

"Measure of the fluidity of a lubricating oil or hydraulic fluid.

The higher the viscosity (given in centistokes cSt), the thicker the oil.

The lower the viscosity of an oil, the thinner it is. Low-viscosity oils are also referred to as low-viscosity, while viscous oils are also referred to as high-viscosity.

The viscosity describes the flow property of a hydraulic oil and is dependent on the temperature and can be additionally influenced by additives.

It can change during use due to temperature, operating pressure, oxidation or contamination.

A distinction is made between dynamic and kinematic viscosity.

In practice, kinematic viscosity is used for determination due to the lower testing effort. It describes the viscosity-density ratio and has the SI unit: mm²/s or "centistoke" cSt.

There are different methods (also using online sensors) for the determination of kinematic viscosity."

Can be modified with additive packages to improve their performance and extend their range of applications. The current trend is clearly towards semi-synthetic and fully synthetic oils.

They are somewhere between a mineral and a fully synthetic oil. The different molecular structures of semi-synthetic oils ensure optimum lubrication of older engines with greater tolerances. These oils also offer longer service intervals and better lubricating properties than pure mineral oils, without the high cost of fully synthetic oils.

They use complex additive packages to achieve viscosity values that mineral or semi-synthetic oils cannot produce. Fully synthetic oils are mainly used in modern engines with smaller tolerances, higher performance and longer maintenance intervals. They are also generally more expensive than mineral or semi-synthetic oils.

Defines the quality standards and requirements for engine oil in Europe. ACEA categorizes products with a combination of letters, numbers and year. For example: A3/B3 describes different properties than A1/B1, but higher numbers do not necessarily mean better quality.

Is an American interest group (like the ACEA) of the oil and gas industry. The API defines technical standards and requirements for Lubricants and assigns quality levels for engine oils. In general, the higher the letters, the higher the quality requirements for the crude oil. These values only apply to crude oil, not to finished products. However, the API values alone are not specific enough to determine the overall quality of the engine oil and its performance.

A - Passenger cars (gasoline engines)

B - Passenger cars, vans, light commercial vehicles (diesel engines)

C - Passenger cars for petrol and diesel engines with new exhaust aftertreatment systems (e.g. DPF)

E - Heavy-duty diesel engines

Founded in 1911 to standardize oil and its viscosities. A distinction is made between monograde oils (e.g. SAE 20) and multigrade oils (e.g. SAE 15W40). Monograde oils are mainly used for applications with unchanging operating conditions. Monograde oils are no longer used in modern engines or applications.

Consist of five types of oil from which all engine and Transmission oils are made:

Group I

Most natural base oils for blending oil products with low performance requirements.

Group II

Common base oils for blending mineral oil-based products. The lubricating properties are rated as sufficient to good.

Group III

Group III oils are refined to the highest level. The oil molecules remain stable and uniform and offer a wide range of applications. Although not chemically produced, these base oils are often used for blending fully and semi-synthetic oils.

Group IV

Chemically produced base oils that offer amazing performance potential for Lubricants. Stable compounds and uniform molecules make these oils a perfect base for blending fully and semi-synthetic oils.

Group V

Mainly used for the production of additives to improve other base oils and not as a base oil itself.

Cellulose features high stability and strength as a base material in filtration.

Filter efficiency:

X50 = 19 – 24 μm

T4 μm = 60 – 80 %

Total filtration efficiency = 97 – 99 %

Standard:

ISO 4548-12

ISO 19438

ISO 5011

Use:

Oil, fuel and air filters

Cellulose and polyester improve efficiency and dust absorption in filtration.

Filter efficiency:

X50 = 13 – 25 μm

T4 μm = 70 – 85 %

Total filtration efficiency = 97 – 99 %

Standard:

ISO 4548-12

ISO 19438

ISO 5011

Use:

Oil, fuel and air filters

Fully synthetic media are additionally resistant to extreme temperatures and water.

Filter efficiency:

X50 = 5 – 25 μm

T4 μm = 90 – 99.8 %

Total filtration efficiency = 99 – 99.9 %

Standard:

ISO 4548-12

ISO 19438

ISO 5011

Use:

Oil, fuel and air filters

Melt-down media additionally feature high dust retention capacity.

Filter efficiency:

T4 μm = 90 – 99.8 %

Total filtration efficiency = 99.9 – 99.98 %

Standard:

ISO 19438

EN60335

Use:

Fuel and air filters

Features:

· Filtration of acidic gases, vapors, pollen, microorganisms

Filter efficiency:

PM 2.5

Standard:

DIN EN ISO

16890-1

Use:

Cabin air filters

Features:

· F1 flame retardancy

· Energy-saving construction

Filter efficiency:

Total filtration efficiency > 99.95 %

Use:

Air filtration

Oil filtration is possible in a full flow and partial flow arrangement, as well as a combined system. Each drive

component is equipped with a full flow filter. The filter is usually located directly downstream from the oil pump in the oil circuit (a filter always generates a certain pressure drop), so that the entire volume of oil flows through the filter once per circulation. As a result, the particles that could cause wear are filtered out on each pass. The engine oil flows directly from the full flow filter to the areas of the engine that require lubrication.

The partial flow oil filter is located in an oil bypass flow, parallel to the full flow. Only about five to ten percent of the total oil flows in this secondary flow. The partial flow oil filter is equipped with a finer filter medium, which filters out extremely fine particles (soot particles < 1 μm) from the oil. The partial flow oil filter therefore guarantees continuous ultra-fine filtration of the oil. The task of filtration is performed by a depth filter medium. The flow rate is reduced as filter loading increases, resulting in a higher filtration grade. Partial flow filters are used in addition to the full flow filter, primarily in diesel engines with high soot input and in commercial vehicles with high mileage and long service intervals.

Spin-on oil filters, or spin-ons, consist of a metal housing containing a filter element, which is supported by a perforated plate inner frame. The spin-on oil filter screws onto the motor block and is designed for easy replacement. Spin-on oil filters can be used in both full flow filtration and partial flow filtration. To prevent the filter from running dry, an anti-drain valve with silicone wings is integrated in the filter. Spin-on filters often contain a filter bypass valve, which opens to allow for continous oil flow to ensure necessary lubrictaion of the engine in the case of high oil pressure or a plugged filter. Although this allows unfiltered oil to enter the circuit, it ensures the supply of lubricating oil. The opening pressures are generally between 0.8 and 2.5 bar. High differential pressures can also occur during the cold-running phase of the engine at high oil viscosities or in the case of exhausted or aged and plugged filter elements.

Oil filter inserts use screw-on fittings. The oil filter insert is replaced separately and is located inside a filter housing that is permanently connected to the engine or the oil filter module. The Hengst filter insert consists of a filter medium

sandwiched between two temperature-resistant or welded thermoplastic end plates. In modern vehicles, this filter element is made of metal-free components and is thermally recyclable. This means that insert filters can be incinerated with no residue, unlike metal spin on filters which typically cannot be incinerated. In the case of Energetic® oil filter inserts, the inner dome can be integrated in the filter element or located in the filter housing. In another series, the valve stem and compression spring are integrated in the inner dome. For servicing, the technician opens the oil filter housing and replaces only the filter insert. The housing and the screw-on cap are lifetime components. Due to

their resistance to chemicals and wet tensile and tear strength, the service life of filter inserts used in passenger cars is between 30,000 km and 50,000 km, and in commercial vehicles 100,000 km or more (depending on the driving profile and the quality of oil used). The longer the replacement interval, the more important it is to use a quality oil filter. Replacing only the filter element and the gaskets results in a very economical and ecological solution with high-intensity utilization.

In a direct injection combustion engine, the fuel filter must also have a high filtration grade (in contrast to former indirect injection systems). Current regulations for reducing hydrocarbon emissions require an assembly consisting of the fuel pump, fuel filter and pressure control valve in the tank unit. These filter elements are often designed with complex geometries. Otherwise, solutions exist for some vehicle types with “simple” in-line filters, fuel filter inserts and spin-on filters. Depth filters using fuel-resistant cellulose are used to achieve required performance levels.

The particulate filter (also known as a pollen filter) protects the vehicle’s inhabitants from solid particles such as pollen and fine dust (PM 10 μm up to 99 percent). The pleated or folded filter paper of the particulate filter is made of high-performance fleece material. Through electrostatic charging, the particles are attracted by the fibers and filtered out of the air. In addition to electrostatic filtration, mechanical filtration is also used. A multi-layer fiber structure ensures that the particles adhere to the fine fibers as they flow through the filter.

In addition to a pre-filter and a microfiber fleece element, combination filters also have an activated carbon layer. This granular activated carbon layer absorbs fine particles (PM 2.5 μm up to 99 percent) as well as bunpleasant and toxic gases such as ozone, smog and exhaust fumes. The open-pored surface of the activated carbon absorbs odor and gas molecules like a sponge. The molecules then enter the labyrinthine channels, where they are retained. The activated carbon layer consists of natural materials, such as coconut shells.

Pollen, bacteria and mold spores in the ambient air can cause undesirable reactions in people with allergies. This can affect concentration and endanger road traffic. So-called biofunctional cabin air filters, such as Blue. care, bind allergy-causing substances, or allergens, and prevent bacteria and mold spores from entering the cabin through the ventilation system. In addition to a particulate filter layer and an activated carbon layer, the cabin air filter also has a third layer. This special biofunctional coating has an antiallergenic and antimicrobial function to protect the vehicle inhabitants against allergens, bacteria and mold. Biofunctional cabin air filters from Hengst are coated with silver ions, for a purifying effect that is both antibacterial and antiallergenic.

Air dryers use special granules to remove moisture from compressed air. This prevents corrosion of the control and regulating valves of the brake system and air suspension system. Air dryers are used primarily in commercial vehicles with very high braking pressures.

The abbreviations MTF (manual transmission fluid) and ATF (automatic transmission fluid) are self-explanatory. ATF fluids have a higher additive content and must be replaced at regular intervals. Together with the transmission oil, the ATF filter insert must also be replaced. MTF and ATF fluids must never be mixed!

The ISO code is a numerical key for the degree of contamination by solid particles.

Since 1999, ISO 4406 has specified three classes >4μ, >6 μ and >14μ.

The particles counted in an oil sample always refer to 100ml and are assigned to a purity class per size class.

Example after determining the particle numbers:

190.000 Particle > 4µm(c) / 100 ml => Class 18

58.600 Particle > 6µm(c) / 100 ml => Class 16

1.525 Particle > 14µm(c) / 100 ml => Class 11

=> Result: ISO-Class 18 / 16 / 11

Size classes of particles per 100 ml according to ISO4406 (excerpt)

Particle count from to => ISO Code

from 1,000.000 to 2,000, 000 => ISO Code 21

from 500,000 to 1,000, 000 => ISO Code 20

from 250,000 to 500,000 => ISO Code 19

from 130,000 to 250,000 => ISO Code 18

from 64,000 to 130,000 => ISO Code 17

from 32,000 to 64,000 => ISO Code 16

from 16,000 to 32,000 => ISO Code 15

from 8,000 to 16,000 => ISO Code 14

from 4,000 to 8,000 => ISO Code 13

from 2,000 to 4,000 => ISO Code 12

from 1,000 to 2,000 => ISO Code 11

from 500 to 1,000 => ISO Code 10

from 250 to 500 => ISO Code 9

from 130 to 250 => ISO Code 8

from 64 to 130 => ISO Code 7

from 32 to 64 => ISO Code 6

from 16 to 32 => ISO Code 5

"The most commonly used hydraulic fluids are produced on a mineral oil basis with appropriate additives.

In Germany, the designations H, HL, HLP, HVLP according to DIN 51 524 are common.

H: without active ingredient additives, correspond to the lubricating oils according to DIN 51 517. These hydraulic oils are hardly used today.

HLP: with active ingredients to increase corrosion protection, with high-pressure additives and ageing resistance (also HLP according to DIN 51 524, Part 2). They are used at pressures to and above 200 bar and meet the usual thermal loads.

HV: with active ingredients to increase corrosion protection, ageing stability, to reduce scuffing wear in the mixed friction area and to improve viscosity-temperature behaviour (also HVLP DIN 51 524, Part 3)

HLPD: with active ingredients to increase corrosion protection, ageing resistance and detergent additives (German name, not standardised)"

For use in biologically critical environments (construction machinery in water protection areas, forestry machines in the forest, snow groomers in the mountains, etc.), hydraulic fluids have been developed that are biodegradable. These fluids can be produced from mineral oil, but they are often produced on the basis of renewable raw materials, such as vegetable oils.

The following types of environmentally friendly hydraulic fluids are distinguished:

HETG (base triglycerides = vegetable oils): These fluids are very biodegradable and usually not hazardous to water. Compared to mineral oils, they have a lower ageing stability and can only be used to a limited extent under temperature stress.

HEPG (based on polyglycols): Polyglycols are made from mineral oil, they are very biodegradable and not hazardous to water. Their properties are comparable to those of mineral oils, they are water-soluble and cannot be mixed with mineral oils or vegetable oils.

HEES (based on synthetic esters): Synthetic esters can be produced on the basis of renewable raw materials as well as on the basis of mineral oil. They are very biodegradable and not hazardous to water or meet water hazard class 1. They have a high ageing stability and are insensitive to extreme working temperatures.

HEPR (other base fluids, primarily poly-alpha-olefins).

Flame retardant liquids are used where mineral oils cannot be used due to high fire risks. In hard coal mining and civil aviation, the use of flame-retardant liquids is mandatory. Other main applications are systems where the hydraulic fluid may come into contact with red-hot or hot metal or open flames in the event of leaks (die casting foundries, forging presses, power plant turbines, metallurgical and rolling mills).

The flame retardant liquids are divided into the following groups:

HFA: Oil-in-water emulsions or solution products with a water content of more than 80 % and a mineral oil-based concentrate or a hydrosoluble polyglycol concentrate. With mineral oil base, there is a risk of segregation and microbial growth. The fluid can be used between +5 °C to +55 °C, the low viscosity leads to high leakage losses.

HFB: Water-in-oil emulsions with a water content of more than 40% and mineral oil.

In Germany, it is not approved due to poor fire properties and is rarely used.

HFC: Water glycols with a water content above 35% and polyglycol solution. The fluid can be used for temperatures between −20 °C to +60 °C and pressures from 250 bar.

It is the most common hydraulic fluid among flame retardant fluids.

When it comes into contact with zinc in the piping system, zinc soaps are formed, which can clog pressure filters, for example.

HFD: Anhydrous synthetic fluids with a higher density than mineral oil or water (not HFD-U), can cause problems with the suction behavior of pumps and attack many sealing materials and plastics.

The liquid is suitable for temperatures between −20 °C to +150 °C.

Depending on the main component, these are the following types:

HFD-R: Phosphoric acid ester

HFD-U: anhydrous other compositions (consisting of fatty acid esters or polyglycols) are to be classified as non-flame retardant, since they do not reach the RI value >25 in the Buxton test, which is decisive for flame retardancy.

Additives are added to strengthen or improve various properties.

In principle, hydraulic fluids consist of a base fluid (e.g. mineral oil) and other ingredients called additives.

The tribological properties of the lubricant are improved with the following additives:

Wear reducers, so-called AW additives (Anti wear additives)

Friction Modifiers

Scuffing protection additives, so-called EP additives (Extreme pressure additives)

Viscosity Index Improver (VI Improvers)

The following additives are required to meet other lubricant requirements:

Anti-corrosion additives, so-called Corrosion inhibitors,

Anti-aging agents, so-called antioxidants (e.g. antioxidants)

Anti-foam additives

Biocides in water-miscible lubricants (biocides)

Surfactants/Emulsifiers

Dispersants/Wetting agents

If necessary, alkaline additives for acid neutralization (indicated by the so-called base number).

The additives are added to the base oil (up to 30%). Depending on the type of application, the additives are selected to ensure the required properties. In the case of gear oils, additives are essential for certain purposes, e.g. to increase compressive and shear strength.

"Low solids contamination in the delivery state

Good filterability (the ability to flow continuously through a filter without changing its pressure loss)

High detergizing (suspending) effect

Flat V/T gradient

Good oxidation stability

Good air separation capacity

Neutral behaviour towards materials

Minimum conductivity (> 300 pS/m) recommended due to electrostatic charge"

"The ISO 4406 purity classes specify how many solid particles may be in oil or another fluid. An assessment of the size of these particles is taken into account. Since 1999, ISO 4406 has specified three classes >4μ, >6 μ and >14μ.

When counting manually on a filter, only 2 purity classes (>5μ and >15μ) can still be specified.

In ISO particle counting, the particles are indicated cumulatively.

The particles counted in an oil sample always refer to 100ml and are assigned to a purity class per size class."

"Method for coding the degree of pollution based on the number of particles per unit volume, divided into size classes. The NAS 1638 standard is still in use, but is considered obsolete. The classification according to NAS 1638 was officially withdrawn several years ago and replaced by SAE AS 4059.

For more information, see e.g. Oilcheck: https://de.oelcheck.com/wiki/elementbestimmung-oel-kraftstoff-reinheitsklassen/"

"Gives a statement about the flow properties of a hydraulic fluid at temperatures in the minus range.

The cloudpoint is the clouding of an oil due to the appearance of solid paraffin crystals, which form in an oil when cooled and make it viscous and unfilterable.

The pour point refers to the solidification of an oil at low temperatures. By accumulating the paraffin excretions, the oil solidifies so much that it no longer moves, it can no longer be delivered or pumped."

The lower the value of the dirt carrying capacity, the less the additive package of the oil is able to transport soot and dirt.

Dispersants are the indispensable counterpart to detergents. They keep the detached dirt in suspension and ensure that it cannot form new deposits. In doing so, they literally envelop the dirt particles and enable them to be transported to the filter.

"The analysis of filter residues (i.e. the particles trapped in the filter) can provide important information, as these residues can of course no longer be analysed in oil samples.

In extreme cases, very fine filters can also filter out active ingredients in the oil and damage the hydraulic fluid. Additives such as silicone defoamers, viscosity index improvers or detergents are particularly affected.

Abrasion particles from wear processes or foreign particles introduced from outside can and should be retained by the filter. During sampling, such particles do not enter the sample container. This deprives the oil of important information carriers that would otherwise inform about problems during lubricant analysis.

A used oil from a plant with optimal filtration therefore often only reflects an incomplete picture of the oil and plant condition. In these cases, only the analysis of the filter residue completes the actual findings."

Infrared spectroscopy is used to compare the respective fresh oil with the used oil. A lower correlation of the spectra (e.g. 70% instead of 99%) indicates an aging of the oil.

"Similar to CO2 in water, air also dissolves in oil. The air can lead to the oil foaming up and dissolves especially when the pressure drops rapidly.

This leads to

-increasing compressibility of the oil – the response of the hydraulics suffers

-decreasing flow rate of pumps,

-impaired lubricating effect up to insufficient lubrication,

-decreasing cooling capacity,

-increased oil oxidation

-Diesel effect, in which air bubbles are compressed so much that a diesel-like combustion of the surrounding oil is induced. This process produces soot particles and the oil turns black."

In order to keep these negative effects as low as possible, an oil should be able to separate excess air as quickly as possible. This behavior is determined as air separation capacity (ASC) in the laboratory.

"An oil is worse the higher the neutralization number in the fresh oil comparison.

Mineral oil-based or synthetic base oils are usually neutral at the beginning. Oil aging and degradation products from additives can lower the pH value of the oil.

Free acids lead to increased oxidation on oil-wetted metal surfaces and reduced service life of seals."

Lubricants age over the course of their service life. Hydrocarbon chains are destroyed or react with moisture and air penetration. Additives degrade over time.

"Oxidation is usually used as a synonym for classic oil aging.

Oils oxidize under the influence of heat and oxygen. Acids and oil-insoluble components are formed. These, in turn, are often the cause of paint-like resin formation or sludge-like deposits. Anti-oxidants neutralize oxygen-containing compounds and deactivate catalytic wear particles that accelerate oxidation.

Once the additives are used up, the aging process of the oil accelerates."

"The criteria for the flame retardancy of a hydraulic oil are specified in regulations, norms and standards (ISO 6743/4, DIN EN ISO 12922, DIN 24317, VDMA 24317, ANSI/NFPA, CETOP, etc.).

A flame-retardant hydraulic fluid of the HFC type, for example, should not start to burn even at temperatures above 600°C ("flame-retardant" does not mean that they cannot burn at all). In simplified terms, "flame retardancy" means that fire safety can be increased and, in the event of a fire, additional time can be gained to initiate protection and extinguishing measures.

In general, flame-retardant hydraulic fluids can be divided into two categories: water-containing and anhydrous fluids. "

"Measure of the fluidity of a lubricating oil or hydraulic fluid.

The higher the viscosity (given in centistokes cSt), the thicker the oil.

The lower the viscosity of an oil, the thinner it is. Low-viscosity oils are also referred to as low-viscosity, while viscous oils are also referred to as high-viscosity.

The viscosity describes the flow property of a hydraulic oil and is dependent on the temperature and can be additionally influenced by additives.

It can change during use due to temperature, operating pressure, oxidation or contamination.

A distinction is made between dynamic and kinematic viscosity.

In practice, kinematic viscosity is used for determination due to the lower testing effort. It describes the viscosity-density ratio and has the SI unit: mm²/s or "centistoke" cSt.

There are different methods (also using online sensors) for the determination of kinematic viscosity."

"Electrical conductivity describes the electrostatic chargeability of liquids and depends on the type of liquid and the concentration of moving charge carriers contained in it.

The electrical conductivity of a hydraulic fluid depends on various criteria such as its base oil, additives and polarity.

Unit: pS/m (pico Siemens/meter = 10-12 ohms)

Zinc and ash-free hydraulic fluids with Group II to IV base oils and less than 300 pS/m can cause electrostatic charges and discharges when used at low temperatures.

In addition, however, there are other influencing factors such as flow velocity, diameter of pipeline, etc."

"The filterability of a hydraulic fluid influences the differential pressure and thus the performance of the entire system.

The development requires higher operating pressures using more precise, more powerful hydraulic components with a smaller tank volume.

In order to protect the system and thus ensure operation and service life, ever finer filter elements are used. In addition to increased differential pressure and lower dirt holding capacity, it can also lead to blockage and ultimately to more frequent change intervals.

For this reason, oil and component manufacturers carry out a wide range of tests, such as determining filterability, during the development of new products.

See also "Evaluation of Hydraulic Fluids for Rexroth Hydraulic Components" D90235

Testing based on ISO 13357-2

Petroleum products - Determination of the filterability of lubricating oils - Part 2:

Dry Oil Process

Infrared spectroscopy is one of the most important analyses in the assessment of used oil.

IR spectroscopy detects impurities and changes due to oxidation in the lubricant.

The method is based on the use of infrared light.

Changes in the chemical structure are indicated by differences in the absorption of IR light.

An IR spectrum is created as an "absorption image". Changes that become visible when comparing the used oil spectrum with that of fresh oil are identified as additive degradation, impurities, aging products and oxidation.

By comparing the fresh oil with the used oil, IR spectroscopy provides information about oil oxidation.

"Since 1997, ISO 12103-A3 has provided for the test dust ISO MTD (ISO Medium Test Dust).

The ISO MTD is used to calibrate automatic particle counters within the framework of the ISO 11171:1999 and ISO 11943:1999 calibration standards.

Particle sizes

In the case of the ACFTD dust used in the past, the longest expansion of the particles was used as the quantity.

With the introduction of ISO 11171:1999, a redefinition of particle sizes was carried out at the same time.

The standard defines the diameter of an equal-area particle of ISO MTD as particle size.

Particle size specifications according to the new calibration standard ISO 11171:1999 are obtained as a marker for the calibration.

Calibration material used, certified and traceable to a national standard has the index(c), e.g. 4 μm(c).

This notation is also used in the context of the revised ISO 4406:1999 and the new ISO 11943:1999."

Basically, water in oil behaves similarly to water in the air

Here, too, a distinction must be made between the water content [PPM] or milliliters per 1000 liters

and the humidity [%] or the aw value [0-1]

Each fluid can absorb a certain amount of dissolved water.

The maximum amount that a fluid can contain in dissolved form is called its saturation point.

Once the saturation point is reached, the water is separated from the oil when the water content increases further.

The oil moisture is always given as a function of the saturation point of the oil.

The saturation point (the ability to keep water in solution) increases (similar to air) as the temperature rises.

The saturation curve is oil-specific.

As a result, an aW value of 0.4 and an aW value of 0.9 at 20°C can be measured for the same oil with the same water content (e.g. 500 PPM) at 40°C.

If the temperature of the oil is further reduced, the proportion of water above the the saturation point precipitates as free water. The saturation point of an oil is a function of various factors, such as the composition of its basic substances (mineral or synthetic) as well as the types of additives, emulsifiers and oxidizers used.

The conventional unit of measurement for determining the water content in oil is ppm (parts per million).

The unit of measurement ppm is a parameter for the absolute moisture content, which describes the volume or mass ratio of water to oil:

In terms of volume: 1 ppm water = 1 ml water / 1 m³ oil

or

Based on mass: 1 ppm water = 1 g water / 1000 kg oil

A ppm measurement does not tell you how close the moisture content is to the saturation point of an oil.

This becomes especially critical when the water content approaches the saturation point of the oil.

Then there is a risk that the saturation point will be exceeded and free water will form.

"Water activity (also known as Activity of Water or aw-value) is a measure of freely available water in a material. It is defined as the quotient of the water vapor pressure over a material (p) to the water vapor pressure over pure water (p0) at a given temperature:

aw = p / p0

where

p = Partial pressure of water in a substance over the material

p0 = saturation vapor pressure of pure water at the same temperature

In the example above, aw changes as a function of the saturation point (p0, in the denominator).

Water activity will also prove to be a function of the actual

water content in the oil, i.e. water that is absorbed or released by the oil.

In other words, aw always indicates the actual difference to the saturation point.

It is possible to derive an interrelation between aw and ppm for each oil.

The significance of this ratio decreases over the life of a dynamic oil system (e.g. lubricating oil).

The composition of a fluid changes over time as chemical reactions take place that change not only its saturation point, but also the relationship to water activity.

"The Karl Fischer method is the quantitative determination of water by titration, hence Karl Fischer titration or simply KFT.

The method was developed in 1935 by the German chemist Karl Fischer.

The decisive factor for the process is the fact that sulphur dioxide and iodine only react with each other in the presence of water.

The yellow-brown iodine is reduced to colorless iodide:

This process consumes water, so the reaction can only take place until all the water is used up.

If there is no more water, added iodine is no longer reduced. The resulting brown coloration serves as a visual endpoint indication.

More advanced methods work in a similar way.

Strong hygroscopic reagent reacts with water.

With the rapid test, the resulting pressure is used to infer the water content."

"They are installed directly in front of the component to be protected in order to protect it in the event of sudden failure of e.g. pumps/motors.

They are always installed WITHOUT a bypass valve.

Significantly coarser filter fineness than the installed working filters.

Not responsible for the purity of the fluid

Usually high-pressure filters that have to be installed in the main stream (full-flow filtration).

Filter fluids of the actual hydraulic working group.

Rarely constant volume flow (resulting in poorer filtration).

They work depending on the operating cycles of the system (filter change only in the event of system downtime – or double filter)."