HYDRAULICS & PNEUMATICS Hydraulic Fluids Presented by: Dr. Abootorabi

Task for hydraulic fluids

Performance Characteristics of a Hydraulic Fluid When selecting a fluid, consider its: Lubricating power Viscosity Viscosity stability Ability to operate in cold temperatures Oxidation resistance Ability to separate from water and dirt Resistance to foaming Fire resistance The most important distinguishing feature of hydraulic fluids is viscosity.

Performance Characteristics of a Hydraulic Fluid Lubrication reduces friction between two surfaces by placing a layer of liquid between them. A properly selected liquid produces a film that separates the surfaces and allows them to freely move past each other.

Performance Characteristics of a Hydraulic Fluid Viscosity is the internal resistance to flow of a liquid (resistance to flow). A liquid with the proper viscosity provides a strong film that: Greatly reduces friction between the bearing surfaces of component parts Provides a seal between those parts

Viscosity Viscosity may be the most important property of a hydraulic fluid. If the viscosity is too high, it may results in: High resistance to flow, causing sluggish operation Increased power consumption due to frictional losses Increased pressure drop through valves and lines High temperature due to friction

Viscosity On the other hand, if the viscosity is too low, it may result in: Increased oil leakage past seals Excessive wear due to breakdown of the oil film between mating parts There are two kinds of viscosity: Absolute viscosity (μ) and kinematic viscosity (ν).

Viscosity & Temperature Hydraulic oils is directly affected by changes in temperature. For this reason, machinery should not be put into high speed or heavily loaded operation until the system fluid is warmed up to operating temperatures to provide adequate lubrication. Viscosity changes as temperature and pressure of a liquid change. Warm fluid flows easier than cold fluid.

Viscosity – temperature diagram

Viscosity – pressure characteristics At approx. 350 to 400 bar the viscosity is generally already double that at 0 bar.

Viscosity Index Viscosity index is the rate of viscosity change in relation to temperature change. The higher the viscosity index number, the lower the rate of viscosity change.

Performance Characteristics of a Hydraulic Fluid Pour point is the ability of a fluid to flow when cold and: Important to consider if a hydraulic system is exposed to cold weather Should be 20° Fahrenheit below the coldest-expected ambient system operating temperature Pour point is important in cold weather.

Performance Characteristics of a Hydraulic Fluid Pour point is 3°C above the temperature at which movement can no longer be detected in a fluid that has been cooled following an established test procedure.

Performance Characteristics of a Hydraulic Fluid Normal operating temperature range for hydraulic fluid in the reservoir is typically 110°F to 140°F (43°C to 60°C) . Operating the system in this temperature range will result in an acceptable fluid service life.

Performance Characteristics of a Hydraulic Fluid Factors causing system fluid to operate above the recommended temperature are: High ambient temperatures Reservoir is too small Reservoir inlets and outlets are too close System pump has excessive flow capacity Higher-than-required relief valve setting Slower-than-necessary circuit sequencing

Performance Characteristics of a Hydraulic Fluid A well-designed reservoir helps maintain proper fluid temperature.

Performance Characteristics of a Hydraulic Fluid Demulsibility is the ability of a fluid to separate out or reject water. Petroleum-based fluids must have the ability to easily separate from water. Select a fluid that resists emulsification Drain accumulated water from the bottom of the reservoir periodically to prevent re-emulsification and/or reaction with the fluid chemistry

Performance Characteristics of a Hydraulic Fluid Water that enters a system having a water-based fluid will modify the oil/additive/water ratio. The correct ratio is required to maintain proper fluid viscosity and other critical properties. Re-establishing the ratio requires fluid testing and adjustment of the elements to their proper proportions.

Performance Characteristics of a Hydraulic Fluid Foaming increases fluid oxidation. Caused by air being drawn into system inlet lines or churned into reservoir fluid Increases air/fluid contact because of bubble surface area

Performance Characteristics of a Hydraulic Fluid The possibility of fire exists to some extent in many hydraulic applications. Petroleum-based fluids can supply adequate safety levels in many systems Fire-resistant fluids using water or synthetic bases are required when higher fire protection is needed

Fire Resistance Fluid used in hydraulic systems must have fire resistant properties. Most fluids can be ignited under the right conditions Fire resistant fluid will not sustain combustion when an ignition source is removed Fire resistant fluid will not allow flame to flash back to the ignition source It is important to analyze the working environment of the specific application to determine fire hazards. Some fluids may continue to burn after the ignition source is removed

Types of hydraulic fluid 1. Hydraulic oils (divided into 3 classes according to DIN 51524 and 51525) HL HLP HV 2. Hydraulic fluids with low inflammability Example:

Types of hydraulic fluid 1. Hydraulic oils Most common hydraulic fluid in use consists of petroleum base blended with additives to produce the desired operating properties.

Types of hydraulic fluid 2. Hydraulic fluids with low inflammability VDMA: The VDMA (Verband Deutscher Maschinen- und Anlagenbau - German Engineering Federation) is one of the key association service providers in Europe and offers the largest engineering industry network in Europe.

Hydraulic fluids with low flammability Fire-resistant hydraulic fluids will not burn without sustained exposure to an ignition source. Oil-water (soluble oil emulsions) Water-oil emulsions Water-glycol fluids Synthetic fluids Applications: Steel works and rolling mills Automotive manufacture Offshore industry On aircraft and ships Hard coal mining Die-casting machines Control units for power station turbines

Hydraulic fluids with low flammability Oil-water (soluble oil emulsions) hydraulic fluids are used in metal forging, extrusion equipment, or other large applications. Fluid designated as an oil-in-water emulsion commonly contains only 1% to 5% oil: Extremely fire resistant Requires typical additives Subject to freezing

Hydraulic fluids with low flammability Water-in-oil emulsion fire-resistant fluids contain approximately 40% water in an oil base. Not to be confused with soluble-oil emulsions or high-water-content fluids (oil-water emulsions) Called inverted emulsions because water is suspended in oil, rather than oil in water Limited anti-wear characteristics System operating pressures limited Has limited use because of instability and maintenance needs

Hydraulic fluids with low flammability Water-glycol fire-resistant hydraulic fluids usually contain 40% to 50% water with the remainder of a polyglycol. Polyglycol is similar to automotive antifreeze An additive is added for improving the viscosity

Hydraulic fluids with low flammability All synthetic fluids provide excellent fire resistance. These are not water based. Phosphate ethers are the most common synthetic hydraulic fluids. All synthetic fluids meet the basic requirements of a hydraulic fluid: Appropriate viscosity Good high-pressure performance Good lubrication

Hydraulic fluids with low flammability Disadvantages of synthetic fluids include: Special seal material requirements Tendency to dissolve paint Environmental toxicity level must be carefully considered before using in sensitive areas

Water??? Although water is readily available and inexpensive, it is not used alone: Poor lubricant Promotes rust and corrosion Low viscosity Freezes Rapidly evaporates at temperatures within the operating range of many typical hydraulic systems

Another type of hydraulic fluids Biodegradable hydraulic fluid reduce the harmful effects of fluid spills on soil and waterways. Biodegradable fluids are: Primarily vegetable-based oils Easily broken down by organisms found in nature Biodegradable fluids are important when reducing environmental impact.

Selection of fluids The fluid supplier must understand the nature of the fluid application: Environment Types of components and their manufacture’s specifications relative to fluids Duty cycles Loads (pressure) Storage ability Temperature extremes Any unusual or special considerations in the operation of the machinery that could affect the life of the fluid or its performance

Hydraulic Fluid Additives Chemicals are used as additives in hydraulic fluids to increase the stability and overall performance of the fluid. An inhibitor is any substance that slows or prevents chemical reactions, such as corrosion or oxidation. Some common additives and inhibitors: anti-wear additives, antifoam agent, corrosion inhibitor, demulsifier, extreme pressure (EP) additive, oxidation inhibitor, pour point depressant, rust inhibitor, Viscosity-index improvers .

Hydraulic Fluid Additives Three types of anti-wear additives: Anti-wear (AW) form a protective film on the metal surface when exposed to low frictional heat Wear resistant (WR) protects the rubbing surfaces against wear, particularly from scuffing Extreme pressure (EP) Either prevent surfaces from coming into contact with one another or prevent surfaces from welding to one another when expose to high frictional heat Use when operating at pressures >3000 psi (or 200 bar)

Hydraulic Fluid Additives Demulsifier additives increase the fluid’s surface tension: Promote separation of water from petroleum-based fluids Any water that enters the system separates more quickly from the oil Antifoaming agents reduce surface tension: Allow air bubbles to break down before a sufficient quantity of foam is formed

Hydraulic Fluid Additives It’s extremely difficult to keep air and moisture out of hydraulic systems. Corrosion is a chemical reaction between a metal and a chemical-typically an acid. Rust and corrosion inhibitors protect the metal parts of system components: Rust inhibitors protect ferrous metals Corrosion inhibitors protect nonferrous metals Rust and corrosion inhibitors either: Neutralize acids Form a film on metal surfaces

Rust & Corrosion inhibitors Rust inhibitors typically coat metal parts so natural air & moisture do not interact with the metal to form oxide compounds. Corrosive elements are often created through oxidation. Care must be exercised whenever the hydraulic system is exposed to atmosphere to minimum the introduction of incompatible elements that may react with the fluid chemistry. Some materials such as alloys containing magnesium, lead and zinc are very oxidize and should be avoided in hydraulic systems.

Rust & Corrosion Protection Both rust & corrosion contaminate the system & increase component wear; increase internal leakage past the affected parts causing high temp.; and cause components to seize through heat & closure or running clearances with debris. Particular care: Operate & clean equipment to prevent the contamination of the hydraulic system with water or cleaning solvents.

Oxidation Oxidation occurs when oxygen attacks the fluid. Accelerated by heat, air entrainment in the fluid, metal catalysts and the presence of water, acids, or solid contaminants Susceptible oil to oxidation: Petroleum and vegetable Operation temperature is very important: Temps <140ºF (60ºC) , petroleum oxidizes very slow Oxidation double for every 18ºF increased in operation above 140ºF Oxidation-inhibitor additives reduce oxidation of fluids.

Inhibitor Charts

Hydraulic Fluid Specifications Kinematic viscosity is a very precise measurement for indicating hydraulic fluid viscosity. Test involves measuring the time required for a specific volume of fluid at a specified temperature to flow through a calibrated, glass capillary viscometer and then multiplying that value by a constant established for each instrument.

Hydraulic Fluid Specifications A calibrated, glass capillary viscometer is used to determine kinematic viscosity. ISO outlines 20 viscosity grades. Grades are based on kinematic viscosity tests

Hydraulic Fluid Specifications The ball viscometer can also be used to determine kinematic viscosity.

Viscosity Classes

Common viscosities Common industrial fluid power systems require fluid with viscosities in the range of ISO grades 32, 46, or 68.

Hydraulic Fluid Specifications SAE outlines several petroleum product viscosity grades: Based on kinematic viscosity ratings Extensively used with automotive products Used with hydraulic fluids in the past, but less commonly so today

SAE Viscosity Classification

Hydraulic Fluid Specifications Flash point is the temperature at which the fluid vapors form a flammable mixture with air (temporary ignition point). Fire point is the temperature at which the fluid is vaporizing rapidly enough to support combustion (the temperature the fluid must attain for continuous burning). Flash and fire points are important factors for many applications.

Handling and Maintaining Hydraulic Fluids Proper handling and maintenance of hydraulic fluids: reduces system operating cost Extends the service life of fluids Reduces the amount of maintenance time spent in cleaning and flushing systems and replacing system fluid

Handling and Maintaining Hydraulic Fluids Storing new, unused hydraulic fluids is an important consideration. Store drums in a cool, clean, dry place Place drums on their sides to reduce chances of contamination Carefully clean drum tops before removing bungs Use clean fluid-transfer equipment

Handling and Maintaining Hydraulic Fluids Reservoir and cylinder rod areas are especially susceptible to foreign materials entering the system. Seal around pipes entering the reservoir Filter air that enters the reservoir Use piston rod wiper rings or boots to prevent dirt from entering through the cylinder rod seal

Handling and Maintaining Hydraulic Fluids Cylinder rod boots help keep dirt out of the system on rod retraction. A & A Manufacturing Co., Inc., Grotite

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