This unit provides students and teachers with the information and skills they need to use the GEARS pneumatic components. Students who understand the fundamental principles involved in the operation of pneumatic components can safely design and build working pneumatic modules . Students can then integrate these modules into machines and mechanisms they design. GEARS built machines and mechanisms can be used in engineering contests played at the classroom, school, district, state or national level.The information, activities and slide shows and worksheets provided in this unit can be presented in four to five 45 minute lessons.
Introduction to Constructing Pneumatic Circuits
The purpose of this lesson is to provide students and teachers with the knowledge necessary to use the GEARS-IDS pneumatic components correctly and safely. It is advisable to build and test the operation of pneumatic modules and sub assemblies before attempting to integrate the components into a working mechanism. It is advisable that students and teachers become familiar with the feel, function and placement of the pneumatic components used in the basic GEARS-IDS circuit. This is best accomplished by building working mechanisms and developing a database of pneumatic experience. Understanding and using pneumatics correctly, safely and creatively requires time and practice.
(see Figure 2.1.1)(see Figure 2.1.2)
Note: Never build a pneumatic circuit WITHOUT A REGULATOR. The pneumatic solenoid and cylinder are rated for working pressures below that of the reservoir. Passing unregulated pressurized air from the reservoir directly to the solenoid or cylinder can damage the components and result in personal injury. ALWAYS WEAR SAFETY GLASSES WHEN WORKING WITH PNEUMATIC COMPONENTS
The GEARS Invention and Design System kit includes six pneumatic components. These components are:
The Bicycle Pump (see Figure 2.1.3)
The Pneumatic Reservoir(see Figure 2.1.4)
The 3 Way Shut Off Valve (see Figure 2.1.5)
The Regulator(see Figure 2.1.6)
The Solenoid Valve(see Figure 2.1.7)
The Pneumatic Cylinder or Linear Actuator(see Figure 2.1.8)
The quick disconnects (see Figure 2.1.9)
The Speed Controls (see Figure 2.1.10)
Pneumatic components are designed to accomplish one or more of the following tasks; store, condition, direct, control or utilize compressed air to perform useful work.
Work
Work is defined as the result of a force acting through a distance.
WORK = FORCE x DISTANCE
Example: When the piston of a pneumatic cylinder exerts a force of 10lbs through a 1 inch stroke, the amount of work = 10 inch pounds.
It all Starts with a Pump and Ends With an Actuator
Work is performed by a pump to compress and store atmospheric air in the reservoir.
The pressurized air is routed from the reservoir to the 3 way shut off valve. This valve controls the flow of air to the circuit.
From the 3 way shut off valve the air is directed to the regulator which controls the pressure of the air in the circuit.
Pressure adjusted air is fed to the solenoid valve. This valve controls the direction and flow of air to the actuator.
The actuator extracts work from the compressed air by allowing it to expand within a confined space (cylinder) and against a moving surface (piston).
Note: Speed control valves affixed to the pneumatic cylinder (actuator) control the FLOW of air into or out of the cylinder. These valves DO NOT control AIR PRESSURE.
Once the work has been extracted, the air is exhausted back through the solenoid valve and into the atmosphere.
Note: Pneumatic circuits like the one used in the GEARS-IDS kit are commonly open circuits. In an open circuit atmospheric air is pressurized, used in the pneumatic circuit and then exhausted back out into the atmosphere. This is one way that pneumatic circuits differ from hydraulic circuits. Hydraulic circuits are closed circuits. The same fluid is continually re-circulated within the circuit
In this lesson we will trace the path of the air through the circuit components, and investigate the function of each component in the circuit.
Introduction to Pneumatic Components
The pneumatic components are described in the order in which they are connected in a working pneumatic circuit.
The Bicycle Pump(see Figure 2.1.3)
Hold this component in your hands as you read the following description.
Bicycle Pump Specifications
Pump Bore is approximately 1.180 inches or 30mm
Pump Stroke is approximately 17.3/4 inches or 450mm
Hose Bore is approximately 1/4 inch or 6mm
Hose Length is approximately 44 inches or 1117 mm
A bicycle pump is comprised of a cylinder, piston and piston rod. A handle is fixed to the Piston rod. When the handle is depressed, the piston travels the length of the cylinder, reducing the interior volume of the pump cylinder and increasing the interior air pressure. This increase in air pressure is proportional to the decrease in volume. The length of the piston travel is called the stroke, and the inside diameter of the cylinder is called the bore.
Conversely, as the pump handle is extended, the piston rises and the volume inside the pump cylinder increases.
The increase in volume causes the pressure inside the pump cylinder to drop below the surrounding (atmospheric) pressure. The result is that atmospheric air is drawn into the pump through a flapper valve built into the piston. When the pump handle comes to rest at full extension the interior pump volume is at maximum and the air pressure within the pump is at normal atmospheric pressure.
Boyles Law describes the relationship between pressure and volume in a closed system like the pump. Click on the figure reference to see the mathematical expression of Boyle's Law. Note: Gas laws developed by physicists, and chemists are covered in depth in other lessons available on the GEARS website. (see Figure 2.1.11)
Charles Law describes the relationship between pressure, volume and temperature of a gas in closed system. If you pump the air into the reservoir with rapid pump strokes, the temperature of the pressurized air will increase. You will be able to feel this temperature increase if you hold the reservoir while a partner operates the pump.
Click on the figure below for an animated illustration of the relationship between pressure, volume and temperature. (see Figure 2.1.12)
The air capacity of the pump is described in terms of standard atmospheric pressure and volume. Click on the figure below to see the formula used to calculate the interior volume of the pump.(see Figure 2.1.13)
Solving for Volume we get approximately 19 cubic inches at ambient air pressure and temperature.
As the pump handle is depressed, the interior volume of the pump cylinder decreases and the pressure and temperature of the air inside the pump increases. When the pump is connected to the reservoir, the compressed air inside the pump is forced through the pump hose, through the Schrader valve and into the reservoir. The Schrader valve is a one-way (check) valve that allows higher-pressure air to enter an area of relatively lower pressure. The Schrader valve used on the reservoir is the same valve used on bicycle tires and operates in exactly the same way.
Caution: The pneumatic circuit is powered by the energy of compressed air stored in the pneumatic reservoir. To prevent accidental overpressure, The GEARS reservoir should only be filled using a bicycle pump.
In addition to adding an extra margin of safety, pressurizing a pneumatic circuit with a hand pump is a great way to appreciate and understand the amount of work (energy) necessary to store compressed air in the reservoir.
Always use Safety glasses when working with pressurized pneumatic circuits!
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