ppt team 18

ppt team 18

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  Elevators By Sushma ,Shrishail , Rajat Putlekar
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  INTRODUCTION  In the1800s, new iron and steel production processes revolutionized the world of construction. With sturdy metal beams as their building blocks, architects and engineers could erect monumental skyscrapers hundreds of feet in the air.  But these towers would have been basically unusable if it weren't for another technological innovation that came along around the same time. Modern elevators are the crucial element that makes it practical to live and work dozens of stories above ground.
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   Even insmaller multi-story buildings, elevators are essential for making offices and apartments accessible to handicapped people.
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   Types ofElevator : 1. Hydraulic elevator 2. Roped elevator
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  HYDRAULIC ELEVATOR  Hydraulicelevator systems lift a car using a hydraulic ram, a fluid-driven piston mounted inside a cylinder.
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  WORKING.
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   The cylinderis connected to a fluid- pumping system (typically, hydraulic systems like this use oil, but other incompressible fluids would also work). The hydraulic system has three parts:  A tank (the fluid reservoir)  A pump, powered by an electric motor  A valve between the cylinder and the reservoir
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   The pumpforces fluid from the tank into a pipe leading to the cylinder.  When the valve is opened, the pressurized fluid will take the path of least resistance and return to the fluid reservoir.  But when the valve is closed, the pressurized fluid has nowhere to go except into the cylinder.  As the fluid collects in the cylinder, it pushes the piston up, lifting the elevator car.
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   When thecar approaches the correct floor, the control system sends a signal to the electric motor to gradually shut off the pump.  With the pump off, there is no more fluid flowing into the cylinder, but the fluid that is already in the cylinder cannot escape (it can't flow backward through the pump, and the valve is still closed).  The piston rests on the fluid, and the car stays where it is.
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   To lowerthe car, the elevator control system sends a signal to the valve.  The valve is operated electrically by a basic solenoid switch .  When the solenoid opens the valve, the fluid that has collected in the cylinder can flow out into the fluid reservoir.  The weight of the car and the cargo pushes down on the piston, which drives the fluid into the reservoir.  The car gradually descends.  To stop the car at a lower floor, the control system closes the valve again.
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  Pros and Consof Hydraulics  Pros(advantages):The main advantage of hydraulic systems is they can easily multiply the relatively weak force of the pump to generate the stronger force needed to lift the elevator car  Cons:Size of the equipment,expensive, Inefficiency [The energy of position (potential energy) only works to push the fluid back into the reservoir. To raise the elevator car again, the hydraulic system has to generate the energy all over again]
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  • The ropesare attached to the elevator car, and looped around a sheave (3). • The sheave is connected to an electric motor(2). When the motor turns one way, the sheave raises the elevator; when the motor turns the other way, the sheave lowers the elevator. • Typically, the sheave, the motor and the control system(1) are all housed in a machine room above the elevator shaft. • The ropes that lift the car are also connected to a counterweight (4), which hangs on the other side of the sheave. The counterweight weighs about the same as the car filled to 40-percent capacity. • Both the elevator car and the counterweight ride on guide rails (5) along the sides of the elevator shaft. The rails keep the car and counterweight from swaying back and forth, and they also work with the safety system to stop the car in an emergency. CABLE SYSTEM(Roped elevator):
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  • How counter weightbalances the weight on both sides.
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  Safety Systems:  Safetiesare activated by a governor when the elevator moves too quickly.  Most governor systems are built around a sheave positioned at the top of the elevator shaft.  The governor rope is looped around the governor sheave and another weighted sheave at the bottom of the shaft.  The rope is also connected to the elevator car, so it moves when the car goes up or down. As the car speeds up, so does the governor.  The diagram below shows one representative governor design.
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   Elevators alsohave electromagnetic brakes that engage when the car comes to a stop. The electromagnets actually keep the brakes in the open position, instead of closing them. With this design, the brakes will automatically clamp shut if the elevator loses power.  Elevators also have automatic braking systems near the top and the bottom of the elevator shaft.  The bottom of the shaft has a heavy-duty shock absorber system -- typically a piston mounted in an oil-filled cylinder. The shock absorber works like a giant cushion to soften the elevator car's landing.
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   Elevators usetwo different sets of doors: doors on the cars and doors opening into the elevator shaft.  The doors on the cars are operated by an electric motor, which is hooked up to the elevator computer.
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   The electricmotor turns a wheel, which is attached to a long metal arm.  The metal arm is linked to another arm, which is attached to the door. The door can slide back and forth on a metal rail.  When the motor turns the wheel, it rotates the first metal arm, which pulls the second metal arm and the attached door to the left.  The door is made of two panels that close in on each other when the door opens and extend out when the door closes.  The computer turns the motor to open the doors when the car arrives at a floor and close the doors before the car starts moving again.  Many elevators have a motion sensor system that keeps the doors from closing if somebody is between them.
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  Thank you