sph 4c unit 4 hydraulics and pneumatic systems

SPH 4C Unit 4 Hydraulics and Pneumatic Systems

Properties of Fluids and Pressure

Learning Goal: I can explain the properties of fluids and identify associated units.

Definitions:

Fluid: A substance that flows and takes the shape of its container.

Hydraulics: The science of properties of liquids.

Pneumatics: The science of properties of gases.

Hydraulic System: A mechanical system that operates using a liquid under pressure.

Pneumatic System: A mechanical system that operates using a gas under pressure.

Examples of Hydraulic and Pnematic Systems:

Density and Compressibility

Density is the mass per unit volume of a substance. Formula:

Recall the Kinetic Molecular Theory from the previous unit:

Example: A liquid has a density of 789 kg/m3. Determine the mass of the substance if you know you have 0.5 m3 of liquid.

Compressibility is the ability of particles of a substance to be pressed closer together.

Bottle Filled with Water versus Air

Pressure

Pressure is the magnitude of the force per unit area.

Formula and units:

Example: Compare the applied pressure on snow for a 100 kg person walking on snow with just boots (0.03 m2 per foot) and then using snowshoes (0.2 m2 per foot).

Atmospheric Pressure

Atmospheric Pressure is the pressure caused by air molecules acting on an object above the Earth's surface.

Quick Facts:• Normally we do not notice atmospheric pressure because the pressure inside our bodies balances the outside pressure.• Atmospheric Pressure is measured in kPa.• Standard atmospheric pressure (what we experience on average) is 101.3 kPa.

The Relationship

Pressure (kPa

)

Altitude (km)

How a drinking straw works

SPH4CU4L2.notebook September 08, 2014

Pressure

Learning Goal: I can identify factors that affect the pressure in static fluids.

Definitions:

Altimeter is an object that uses atmospheric pressure to determine altitude.

Static Pressure Head is the height of a fluid in a column above a specific position.

Barometer is an instrument that measuresAneroid Barometer is an instrument thatatmospheric pressure. measures atmospheric pressure without using a liquid.

Although Mercury is still used today, it poses a health hazard and is not recommended for use.

Density of mercury is 13.6 times that of water.

Example: Determine the height of water in each tube.

Measuring Gauge Pressure

Absolute Pressure the true pressure, or sum of the atmospheric and gauge pressure (pabs)

Gauge Pressure the difference between absolute pressure and the atmospheric pressure (pg)

Formula:

Manometer: An instrument used to gauge pressure.


Example: If you inflate your car tire (I will use lbs/in2) to 35 psi, what does that mean?

Info: 101.3 kPa = 14.7 psi

Pressure in Liquids

Formula: pg = Dhg where:

"Dam"ed if you do! Why they build them like they do!


Pascal's Principle

Learning Goal: I can state and explain Pascal's Principle in terms of the transmission of forces in an enclosed liquid system.

Pascal's Principle Pressure applied to an enclosed liquid is transmitted equally to every part of the liquid and to the walls of the container.

The Mechanic's Saviour Enter the Hydraulic Hoist

Resulting relationship:

Example: A 1500 kg car is hoisted in the shop with a large cylinder press. The area of the large piston is 0.25 m2 (approximately a 28 cm diameter) and the area of the small piston is 0.02 m2 (approximately an 8 cm diameter). Answer the following:

A) Determine the magnitude of the force of the small piston needed to raise the car.

B) Determine the pressure, in kPa, in this hydraulic press.


Brake Technology


Fluid Systems

Learning Goal: I can describe common components used in hydraulic and pneumatic systems.

Fluid System an arrangement of components used to transmit and control forces in a fluid.

Actuator A device that transforms fluid force into mechanical force.

Common Circuit Symbols:

Electric motor: Air Storage Tank:

Airflow / Transmission line: Pressurized air and liquid tank:

Single acting cylinder: 3 way valve:

2 way valve: Filter with drain:

Relief valve: Liquid Storage tank:

Solenoid:


Robotic Applications

A Robot is an automated device that is computercontrolled and operated by hydraulic and pneumatic systems.

Generally jobs completed by robots can be classified into two general types:

Repetitive Tasks Handling Hazardous Materials

Advantages and Disadvantages of Robotics

Advantages:

• In repetitive jobs productivity is high, but not necessarily faster.

• Robots are efficient for specific tasks.

• Robots are very accurate.

• Robots can lift heavy loads.

Disadvantages:

• Not flexible in changing conditions or tasks.

• Require warmup periods and careful maintenance.

• May have slow reaction times.

• Require welltrained designers and service workers, specific to each application.


Work and Power in Fluid Systems

Learning Goal: I can analyze quantitatively and experimentally variables such as force, area, pressure, work and power in a hydraulic and pneumatic system.

It is important to be able to analyze a complete system to determine the value of multiple variables. The following table is necessary when completing this analysis.

Definitions:

Power Stroke: The time where the piston is completing the job / task it is meant to complete.

ie.

Refill Stroke: The time where the piston is being retracted and prepared to restart the cycle.

ie.

Flow Rate: The rate at which a liquid is traveling in a closed system, usually determined by the

pump.

ie.


1.5 L/s

9.0x106 Pa

rrod = 3.5 cmrhandle = 5.0 cmrhead = 10.0 cm

h = 35 cm Example: The cylinder press provided has a piston that moves back and forth regularily. The rod extends from the piston to perform a repetitive task on an assembly line. The known quantities have been provided on the diagram. Answer the following:

A) Determine the volume of liquid moved into the cylinder during the power stroke.

B) Determine the volume of liquid moved into the cylinder during the refill stroke.

C) Determine the total time of a complete cycle of the power and refill strokes.

D) Determine the magnitude of the force applied by the rod to the component during the power stroke.

E) Determine the work done by the liquid in the cylinder during the power stroke.

Laminar and Turbulent Flow

Learning Goal: I can define and describe, with examples, the concepts related to laminar flow and turbulent flow of fluids.

Definitions:

Fluid Dynamics: The study of the factors that affect fluids in motion.

Viscosity: The property of a fluid that determines its resistance to flow. ie. A HIGH viscosity means a high resistance to flow.

Laminar Flow: Fluid flow in which adjacent regions of fluid flow smoothly over one another.

Turbulent Flow: Fluid flow in which a disturbance resists the fluid's motion.

Fluid Flow

Turbulent Flow

Problem associated with turbulent flow Loss of kinetic energy.

ie. Sewage Pipes Fire Hoses

A solution is to inject plastic particles making the walls "slippery" and reducing any "sticking" to pipe walls. It works similarly with both the fire hose and human arteries!

Streamlining (Aerodynamics)

Definitions:

Drag: The forces that act against an object's motion through a fluid.

Streamlining: The process of reducing the turbulence experienced by an object moving rapidly relative to a fluid.

Drag Coefficient (cd): is a dimensionless quantity that is used to quantify

the drag or resistance of an object in a fluid environment, such as air or water.

Example: The Cyclist

Watch the demos on the website to see all these concepts in action!

Bernoulli's Principle

Learning Goal: I can state Bernoulli's Principle and explain some of its applications in such fields as technology, transportation, sports, etc...

Bernoulli's Principle

Where the speed of a fluid is low, the pressure is high. Where the speed of a fluid is high, the pressure is low.

Note: The pressure in a pipe depends on the pipe's diameter and speed of the water.

Examples and Evidence

A paint sprayer Airplane wing Car spoiler

Physics of a curveball

sph 4c unit 4 hydraulics and pneumatic systems

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