Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Reynolds number wikipedia , lookup
Fluid thread breakup wikipedia , lookup
Fluid dynamics wikipedia , lookup
Bernoulli's principle wikipedia , lookup
Blaise Pascal wikipedia , lookup
Hydraulic jumps in rectangular channels wikipedia , lookup
Hydraulic cylinder wikipedia , lookup
SYSTEMS AND CONTROL Electrical and Electronics Hydraulics and Pneumatics Combining Systems Work to be covered this term: Electrical and electronic systems Pneumatics and Hydraulics Pascal’s law and MA Combining systems What is a hydraulic system? It is a system that transmits energy through the use of fluid pressure by obeying Pascal’s law. The major function of a hydraulic fluid is to provide energy transmission through the system which enables work and motion to be accomplished. PASCAL’S LAW The pressure applied to a confined liquid is transmitted, without loss, throughout the entire liquid and the walls of the container Application of Pascal’s Law It wasn’t until the beginning of the industrial revolution when a British mechanic named Joseph Bramah applied the principle of Pascal’s law in the development of the first hydraulic press. In 1795, he patented his hydraulic press, known as the Bramah press. Bramah figured that if a small force on a small area would create a proportionally larger force on a larger area, the only limit to the force that a machine can exert is the area to which the pressure is applied. Simple Hydraulic system Simple hydraulic system Examples of Hydraulic systems Hydraulic jacks and many other technological advancements such as automobile brakes and dental chairs work on the basis of Pascal's Principle, named for Blaise Pascal, who lived in the seventeenth century. Hydraulic System Components The major components that make up a hydraulic system are the reservoir, pump, valve(s) and actuator(s) (motor, cylinder, etc.). Reservoir The purpose of the hydraulic reservoir is to hold a volume of fluid, transfer heat from the system, allow solid contaminants to settle and facilitate the release of air and moisture from the fluid. Pump The hydraulic pump transmits mechanical energy into hydraulic energy. This is done by the movement of fluid which is the transmission medium. There are several types of hydraulic pumps including gear, vane and piston. All of these pumps have different subtypes intended for specific applications such as a bent-axis piston pump or a variable displacement vane pump. All hydraulic pumps work on the same principle, which is to displace fluid volume against a resistant load or pressure. Valves Hydraulic valves are used in a system to start, stop and direct fluid flow. Hydraulic valves are made up of poppets or spools and can be actuated by means of pneumatic, hydraulic, electrical, manual or mechanical means. Actuators Hydraulic actuators are the end result of Pascal’s law. This is where the hydraulic energy is converted back to mechanical energy. This can be done through use of a hydraulic cylinder which converts hydraulic energy into linear motion and work, or a hydraulic motor which converts hydraulic energy into rotary motion and work. As with hydraulic pumps, hydraulic cylinders and hydraulic motors have several different subtypes, each intended for specific design applications. PASCAL’S LAW The pressure applied to a confined liquid is transmitted, without loss, throughout the entire liquid and the walls of the container PASCAL’S LAW Pascal's law means that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container. The Basic Idea The basic idea behind any hydraulic system is very simple: Force that is applied at one point is transmitted to another point using an incompressible fluid. The fluid is almost always an oil of some sort. The force is almost always multiplied in the process. The picture below shows the simplest possible hydraulic system: How does a hydraulic jack illustrate the law? Pascal’s law/principle contd. Basically, the principle states that the pressure in a closed container is the same at all points. Pressure is described mathematically by a Force divided by Area. Therefore if you have two cylinders connected together, a small one and a large one, and apply a small Force to the small cylinder, this would result in a given pressure. By Pascal's Principle, this pressure would be the same in the larger cylinder, but since the larger cylinder has more area, the force emitted by the second cylinder would be greater. Pascal’s law/principle contd. This is represented by rearranging the pressure formula P = F/A, to F = PA. The pressure stayed the same in the second cylinder, but Area was increased, resulting in a larger Force. The greater the differences in the areas of the cylinders, the greater the potential force output of the big cylinder. A hydraulic jack is simply two cylinders connected as described above. How does a hydraulic jack illustrate the law? How does a hydraulic jack work? http://www.hyjacks.net/animation.ht m How does a hydraulic jack illustrate Pascal’s law? What can you say about the pressure on piston 1 and piston 2? F1 P1 A1 •But, by Pascal’s Law, and P1 P2 F2 P2 A2 How does a hydraulic jack illustrate Pascal’s law? An enclosed fluid under pressure exerts that pressure throughout its volume and against any surface containing it. That's called 'Pascal's Principle', and allows a hydraulic lift to generate large amounts of FORCE from the application of a small FORCE. How does a hydraulic jack illustrate Pascal’s law? Assume a small piston (one square metre area) applies a weight of 1N to a confined hydraulic fluid. That provides a pressure of 1 N per square metre throughout the fluid. If another larger piston with an area of 10 square metres is in contact with the fluid, that piston will feel a force of 1N/square metre x 10 square metres = 10 N/square metre. http://www.physlink.com/educatio n/askexperts/ae526.cfm Explain the diagram! Explanation In the example, when the smaller piston moves a distance of 10 inches it displaces 10 cubic inch (163,8millilitres) of fluid. That 10 cubic inch displaced at the 10 square inch (0.000645 square metres) piston moves it only 1 inch (2.54cm), so a small force and larger distance have been exchanged for a large force through a smaller distance. Hydraulic multiplication To determine the multiplication factor in the figure above, start by looking at the size of the pistons. Assume that the piston on the left is 2 inches in diameter, while the piston on the right is 6 inches in diameter. To do: 1. Calculate the area of the two pistons. (1 inch = 2.54 cm). 2. How do the two areas compare is size? 3. What does this imply i.t.o. the force applied to the left-hand piston? 4. If you applied a 100-pound downward force to the left piston, what will the upward force be on the right piston? (First convert pounds into kg and then work out the force in Newtons). 5. What is the catch? So we can apply 1 lbs. to the small piston and get 10 lbs. of force to lift a heavy object with the large piston. Is this 'getting something for nothing'? Unfortunately, no. Just as a lever provides more force near the fulcrum in exchange for more distance further away, the hydraulic lift merely converts work (force x distance) at the smaller piston for the SAME work at the larger one. Example The pistons of a hydraulic press have a radii of 2cm and 12cm. a) What force must be applied to the smaller piston to exert a force of 5000N on the larger piston? b) What is the pressure on each piston? c) What is the actual mechanical advantage? Homework A hydraulic press has an input cylinder 2 inches in diameter and an output cylinder 6 inches in diameter. Assuming 100% efficiency, find the force exerted by the output piston when a force of 10 pounds is applied to the input piston.