Hydraulic Power Principles of Engineering © 2012 Project Lead The Way, Inc.

Hydraulic Power Hydraulic power Hydraulics vs. pneumatics Early hydraulic uses Hydrodynamic systems Hydrostatic systems Liquid flow Mechanical advantage Bernoulli's principle Viscosity Common hydraulic system components Emerging hydraulic application example

Hydraulic Power Hydraulics The use of a liquid flowing under pressure to transmit power from one location to another Liquid in a hydraulic system behaves like a solid since it compresses very little Oil is most often used in hydraulic systems, although other systems also may use synthetic oils or water.

Hydraulic Power At least two examples of hydraulic power are visible on the fire truck.

Hydraulics vs. Pneumatics Hydraulic Systems Use a relatively incompressible liquid Have a slower, smoother motion Are generally more precise Lubricate naturally Are not as clean as pneumatics when leakage occurs Often operate at pressures of 500–5000 psi Generally produce more power The slower, smoother motion of hydraulics is what makes hydraulic systems more precise than pneumatic systems.

Early Hydraulic Uses Water Wheels Create rotational motion Descriptions exist as early as 1st century BC Several examples in ancient China Grist mill is pictured Modern turbines in hydro-powered dams are a sophisticated version of the water wheel used to create electricity.

Early Hydraulic Uses Roman Aqueducts Delivered water to buildings, agricultural fields, and fountains Used gravity to create flow Fountains were decorative and used by people to collect water for practical use

Water Turbine Propeller Hydrodynamic Systems Fluid is in motion Force and energy are transmitted by flow Water Turbine Propeller Pneumatic systems can also be referred to as hydrodynamic. Windmills are an example of such a system. The early hydraulic examples in this presentation are hydrodynamic systems. The picture is of a turbine that could be used to produce electricity.

Hydrostatic Systems Fluid does not flow quickly or continuously Fluid is pressurized Force and energy transmitted by pressure Most common in industrial settings National Fluid Power Association & Fluid Power Distributors Association Pneumatic systems can also be referred to as hydrostatic since such systems are often pressurized.

Hydrostatic Systems Pascal’s Law Pressure exerted by a confined fluid acts undiminished equally in all directions Click the arrows to activate the hydraulic press.

Liquid Flow Flow Rate The volume of fluid that moves through a system in a given period of time Flow Velocity The distance the fluid travels through a system in a given period of time Symbol Definition Example Units Q Flow Rate gpm or gal/min (gallons per minute) in.3 / min v Flow Velocity fps or ft/s (feet per second) in. / min A Area in.2 fps = feet per second fpm = feet per minute gpm = gallons per minutes

Liquid Flow Example Q = 15 gal/min d = 2 in. v = ? A flow meter attached to the main line in a hydraulic system measures the flow rate at 15 gpm. The line has an inside diameter of 2 in. What is the flow velocity in the meter? Q = 15 gal/min d = 2 in. v = ? Convert 15 gal/min to in.3 /min 1 gal = 231 in.3 Float Many types of flow meters can be used to measure flow rate. The image in this slide is a variable flow meter. The float is lifted by gravity, so this type of meter is placed in a vertical line system. Reprinted with permission from Introduction to Fluid Power, by James L. Johnson. Copyright © 2002 Thomson Delmar Learning.

Liquid Flow Example Q = 3465 in.3/min d = 2 in. v = ? A flow meter attached to the main line in a hydraulic system measures the flow rate at 15 gpm. The line has an inside diameter of 2 in. What is the flow velocity in the meter? Q = 3465 in.3/min d = 2 in. v = ?

Mechanical Advantage The following formula solves for ideal mechanical advantage. Actual mechanical advantage is always less than the ideal calculation. National Fluid Power Association & Fluid Power Distributors Association

Mechanical Advantage Example A force of 100. lbf is applied to the input cylinder of the hydraulic press seen below. What is the pressure in the system? How much force can the output cylinder lift? What is the mechanical advantage of the system? Fin = 100. lbf Fin = 100. lbf Fout = ? din = 4.0 in. dout = 12.0 in. Ain = ? Aout = ? p = ? MA = ? din = 4.0 in. dout = 12.0 in.

Mechanical Advantage Example Find the area of each cylinder. Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in. Ain=? Aout=? p=? MA=?

Mechanical Advantage Example Find the pressure in the system. Fin=100. lb Fout=? Rin=2.0 in. Rout=6.00 in. Ain=12.57 in.2 Aout=113.10 in.2 p=? MA=?

Mechanical Advantage Example Find the force that the output cylinder can lift. Fin=100. lb Fout=? Rin=2.0 in. Rout =6.00 in. Ain=12.57 in.2 Aout=113.10 in.2 p=7.955 lb/in.2 MA=?

Mechanical Advantage Example Find the mechanical advantage of the system. Fin=100. lb Fout=900.28 lb Rin=2.0 in. Rout =6.00 in. Ain=12.57 in.2 Aout=113.10 in.2 p=7.96 lb/in.2 MA=?

Bernoulli’s Principle Conservation of Energy: An increase in velocity results in a decrease in pressure. Likewise, a decrease in velocity results in an increase in pressure. This example portrays a venturi which is represented by a decrease in diameter. At the narrowed point, speed increases and pressure decreases. This is important in hydraulic systems because the size of conduit or piping in a system will likely vary and impact the system based on this principle. Bernoulli’s Principle also applies to pneumatic power, but it is a more important consideration for hydraulic power.

Viscosity The measure of a fluid’s thickness or resistance to flow Crucial for lubricating a system Measured in slugs/sec-ft (US) or centistokes (metric) Hydraulic oil is usually around 1.4 slugs/sec-ft Decreases as temperature increases Absolute pressure is used to complete pneumatic calculations.

Common Hydraulic System Components Cylinder Directional Control Valve Transmission Lines Filter Pump Reservoir—the tank that holds fluid in a hydraulic system. Transmission lines—used to transport fluid in a circuit. Pump—used to create flow in the system. Cylinder—also called an actuator. Used to convert fluid power to linear mechanical power. Filter—used to remove contamination from fluids. Filters are also often next to lubricators. Lubrication helps prevent wear on the components in the system. Directional control valve—used to control which path a fluid takes in a circuit. All systems also require seals and gaskets between components to reduce leakage in the system. Reservoir National Fluid Power Association & Fluid Power Distributors Association

Click the lever on the valve to extend and retract the cylinder. Common Hydraulic System Components Click the lever on the valve to extend and retract the cylinder. Cylinder Valve Reservoir Pump

Image Resources Johnson, J.L. (2002). Introduction to fluid power. United States: Thomson Learning, Inc. Microsoft, Inc. (2008). Clip Art. Retrieved January 10, 2008, from http://office.microsoft.com/en-us/clipart/default.aspx National Fluid Power Association. (2008). What is fluid power. Retrieved February 15, 2008, from http://www.nfpa.com/OurIndustry/OurInd_AboutFP_WhatIsFluidPower.asp National Fluid Power Association & Fluid Power Distributors Association. (n.d.). Fluid power: The active partner in motion control technology. [Brochure]. Milwaukee, WI: Author.