Pneumatic braking system
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pneumatic braking system
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Pneumatic braking system
- 1. TECHNICAL SEMINAR ON PNEUMATIC BRAKING SYSTEM PRSENTED BY: MADAN KUNWAR 1SJ11ME047 Department of Mechanical Engineering S.J.C institute of Technology Chickballapur-562101 2014-2015
- 2. BRAKE: A brake is a device by means of which frictional resistance is applied to a moving machine member, in order to retard or stop the motion of a machine. A brake is a mechanical device which inhibits motion, slowing or stopping a moving object or preventing its motion. Most commonly brakes use friction between two surfaces pressed together to convert the kinetic energy of the moving object into heat to slow down the motion of vehicle.
- 3. A brake which uses air as working fluid is a pneumatic brake.The system actuated to apply this phenomenon is known as Pneumatic Brake System. An pneumatic brake or a compressed air brake system, is a type of friction brake for vehicles in which compressed air pressing on a piston is used to apply the pressure to the brake pad needed to stop the vehicle. George Westinghouse first developed pneumatic brakes for use in railway service. He patented a safer air brake on March 5, 1872. Westinghouse made numerous alterations to improve his air pressured brake invention, which led to various forms of the automatic brake used in modern vehicles for more safer and advance brakeing system. In the early 20th century, after its advantages were proven in railway use, it was adopted by manufacturers of bus ,trucks and heavy road vehicles.
- 8. Brake system that is based upon a design Air patented by George Westinghouse on March 5 1872. The Westinghouse Air Brake Company (WABCO) was subsequently organized to manufacture and sell Westinghouse invention which has been universally adopted. Compressed air from compressor passes through the valve and maintains its pressure. This air is stored in the reservoir. And from the reservoir it goes to the Brake Chambers through many brake valves. In the brake chamber this pneumatic force is converted into the mechanical force and then it is converted into the rotational torque by the slack adjuster, which is connected to S-cam. This torque applies air brakes which is used to slow down the motion of the veichle.
- 9. Braking is done into three stages:
- 10. During this stage, brake pipe is charged to 5kg/cm2 pressure which in turn charges control reservoir and auxiliary reservoir to 5 kg/cm2 pressure via distributor valve. At this stage brake cylinder gets vented to atmosphere through passage in Distributor valve and there is no application of brake in the stage.
- 11. For application of brakes, the pressure in brake pipe has to be dropped. This is done by venting air from driver’s brake valve. Reduction in brake pipe pressure positions the distributor valve in such a way that the control reservoir gets disconnected from brake pipe and auxiliary reservoir gets connected to brake cylinder. The magnitude of braking force is proportional to reduction in brake pipe pressure which is done by the application of force on the brake pedal.
- 13. For releasing brakes, the brake pipe is again charged to 5 kg/cm2 pressure by compressor through driver’s brake valve. This action positions distributor valve in such a away that auxiliary reservoir gets isolated from brake cylinder. Brake cylinder is vented to atmosphere through distributor valve and thus brakes are released.
- 15. The air brake system is actually three separate systems :-
- 16. SERVICE BRAKE: This system applies and releases the brakes when the driver pushes/releases the brake pedal. Pushing the brake pedal, opens a valve to let air flow from the air tank through the airlines to a brake chamber. PARKING BRAKE : Parking brake releases air from the brake chamber which allows the brake spring to expand and forces the pushrod out which pushes a slack adjuster that turns the camshaft, twisting the S-Cam and forcing the brake linings against the brake drum.
- 17. EMERGENCY BRAKE: When there is insufficient air in the system to keep the spring in the chamber restrained, the emergency brakes automatically engage. When air pressure falls below 420 kpa, a low pressure warning light will come on along with an audible buzzer. If air pressure continues to fall, the emergency brake will automatically apply when air pressure drops to 140-310 kpa. The fail safe engineering of air brakes will not allow you to control activation of the emergency brake so look for a safe place to pull off the roadway as soon as the low pressure warning activates.
- 18. Air is available everywhere in atmosphere so the brake system can never run out of its operating fluid. Air doesnot corrode the metals so the life of pneumatic brake is more. Air line couplings are easier to attach and detach than hydraulic lines there is no danger of letting air into a pneumatic circuit. Pneumatic brake has got emergency brake which gets activated when the service brake failes, so it is very safe. Air brakes are effective even with considerable leakage, so an air brake system can be designed with sufficient fail-safe capacity to stop the vehicle safely even when leaking.
- 19. If the brakes are applied before recharging has been completed, a larger brake pipe reduction will be required in order to achieve the desired amount of braking effort. If the brake pipe pressure is too low due to an excessive no. of brake applications, an emergency application will not produce a large enough volume of air flow to trip the triple valves, leaving the engineer with no means to stop the vehicle. This system is complicated and needs trained person to use it.
- 20. The pneumatic brake is mainly used in large vehicles such as trucks, buses, trailers, and semi-trailers in addition to their use in railway train.
- 21. Operation of pneumatic brakeis different from more common hydraulic systems,so most people require additional training and licensing in order to legally drive any vehicle using an air brake system. Driving a vehicle with air brakes requires basic knowledge of proper maintenance as well. A driver should have knowledge to inspect the air pressurization system prior to driving and make sure all tanks are in working order.
- 22. Brakes are the parts of the vehicle that absorb the energy generated by a vehicle in motion in order to stop it. Pneumatic brakes became popular because of their tremendous stopping power and long life as compared to hydraulic system. In order to do this, a system with several components with prpoer functioning is required. Air provides a simple outlet to accomplish this task. Thought the pneumatic brake is complicated to use and training has to be provided for its efficient use because of its tremendous power and its effiectiveness it is very usedful in large vehicles such as trucks, buses, trailers, and semi-trailers in addition to their use in railway train.
- 23. Bennett, Sean (2010). Heavy Duty Truck Systems, 5th Ed. USA: Cengage Learning. p. 907. ISBN 1435483820. State of California, Copyright 2003, California Commercial Driver Handbook, Sec. Mechanics Corner: Understanding air brake systems. Types of Automotive Braking Systems S .Selvamani, Brake System Engineering, Sundaram Clayton limited, Chennai, (1996) S.F. Williams and R.R. Knipling, "Automatic slack adjusters for heavy Vehicle air brake systems," Research Report DOT HS, vol. 807, pp. 724, 1991. New Brunswick Department of Public Safety, "Air brake manual," [On¬ Line]. Available: http://www.gnb.ca/0276/vehicle/pdf/anual-e.pdf, accessed May 2008 S.C. Subramanian, S. Darbha, and K.R. Rajagopal, "Modeling the Pneumatic subsystem of a scam air brake system," Journal of Dynamic Systems, Measurement, and Control, vol. 126, pp. 36, 2004.