TSM 363 Fluid Power Systems

TSM 363 Fluid Power Systems Hydraulic Fluids & Conditioning

Water based Vegetable based Synthetic based Synthetic based Types of Fluids Hydraulic Fluids Fire Resistant Petroleum based oils Biological degradable Water-based

Basic Requirement for Fluids Mobile fluid power systems use mainly liquid fluids, and we are discussing liquid fluids only. • efficient power transmission • effective cooling • reliable lubricating • efficient sealing • effective contaminants removing • compatible with component materials • resistant to foaming • used over wide operating temperature

V0 Power Transmission m1 m2 V1 V2 Efficient power transmission requires a consistent & reliable response, and optimum efficiency. It requires a “stiff” fluid power system. The “stiffness” of the system is mainly determined by the compressibility of the fluids!

Lubrication Lubricants are widely used in mechanical systems to reduce the friction between components surfaces. In hydraulic systems, many components have relative motion in operation. Hydraulic fluids should be able to provide lubrication in between those surfaces.

Sealing Clearances inside hydraulic components cause internal leakage. It relies on the fluid (viscosity) to minimize the leakage across these clearances to improve efficiencies and reduce the production of heat.

Contaminants Removal There are debris in the hydraulic systems due to wearness of the components. It relies on the fluid motion to remove those debris away from the system (especially from the clearances of between the components of moving relatively.

Cooling Hydraulic fluids will absorb and carry away the heat generated in the system (mainly at valves, cylinder and/or motor). --> The fluids act like the coolant in the hydraulic system. The heat must be dissipated in the tank (or sometimes uses a heat exchanger) before it can be reenter the system.

Fluid Properties To adequately carry out the desired functions of hydraulic fluids, the following are the fluid properties we should pay attention to in selection. • viscosity • lubricating ability • pour point, oxidation resistance • compatibility with system elements • rust/corrosion protection • demulsibility • etc.

Fluid Selection The general categories of available hydraulic fluids are petroleum oils and fire resistant fluids. Bio-degradable fluids are becoming popular recently. Water hydraulics is a relative new technology. • No single fluids can meet all the requirements. • Lubricating & viscosity are important for mobile systems. • Concerns on environment increased interests in biodegradable oils (required in many European countries). • Fire resistance is important for machinery working at the flammable environment.

ISO Viscosity Grade SAE Summer # SAE Winter # 120 26 110 24 10000 ISOVG100 100 22 9000 SAE 50 SAE 20W 90 20 8000 80 18 7000 ISOVG68 70 16 6000 SAE 40 60 14 5000 SAE 15W 50 12 4000 ISOVG46 SAE 30 40 10 3000 ISOVG32 30 8 2000 SAE 10W SAE 20 ISOVG22 20 6 1000 10 4 SAE 5W cSt@40C cSt@210 F cP@0 F Viscosity • Viscosity of a fluid is defined as its resistance to flow at a given temperature. It affects the fluid’s ability to be pumped, transmitted, and its ability of lubricating and sealing. • Both ISO and SAE have established a viscosity grade (number) to specify the ranges of viscosity.

Fluid Conditioning & Devices Fluid conditioning includes: • Fluids storage & preparation • Contamination prevention & control • Temperature control The main fluid conditioning devices include: • Reservoir • Filter • Seals • Cooler

Typical Structure of Reservoirs

Key Functions of Reservoir • Fluids container • Provides a space on the vehicle to store hydraulic fluids. • Fluids cooling device • Discharges heat generated in the fluid power system. • Air separator • Removes as mush air as possible from the fluids. • Debris separator • Filters out debris to prevent possible damages. • Inlet fluid conditioner • Prepares the supplying fluids to the pump with a good inlet condition for maximizing the pump efficiency.

Criteria for Sizing a Reservoirs • Must make allowance for dirt and chips to settleand for air to escape • Must be able to hold all the oil that might drain into it from the system • Must maintain the oil level high enough to preventa whirlpool effect at the pump inlet line opening • Should have a surface area large enough to dissipate most of the heat generated by the system • Should have adequate air space to allow for thermal expansion of the oil In General: Reservoir size = 3pump flow-rate(gal or L) (GPM or L/min)

Types of Contaminations Most of the times, fluids contamination is the major contributor to failures of hydraulic system. • Solid contamination:It may consists of dirt, metal particles, seal materials, etc. It is the most common cause for failure of mobile hydraulic systems. • Thermal contamination:The useful life of most hydraulic fluids will be significantly reduced by overheat. • Air/gas contamination:Dissolved air affects system stiffness, results in poor performance. • Water contamination:Water will degrade the fluids in numerous ways (max of 700 ppm is allowed).

Major Sources of Solid Contaminations Contamination can be introduced into the system from both external and internal sources. • Built-in contamination:Much of the solid contamination is resulted from the manufacture and assembly of the hydraulic systems. • External contamination:Much of dirt, air, and water contamination is resulted from operating environment. • Internally generated contamination:It mainly caused by the wear (esp. at break-in & wear out periods). • Maintenance contamination:Could be all kinds of contamination due improper maintenance procedure.

Typical Hydraulic Fluid Filters

Definition of Filtration Rating

ISO Fluid cleanliness measurements

Use of Heater Exchangers

Correct Use of Seals

Lecture Summary • Introduced the basic characteristics of fluids: • Physical properties • Functionalities • Introduced the basic fluid conditioning devices: • Reservoir • Filters • Heat exchangers • Seals

TSM 363 Fluid Power Systems