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Difference between hydraulic elevators and mechanical elevators

Hydraulic elevator systems: Hydraulics as we generally mean is a technology that finds its value from the use of engineering the mechanical properties and use of liquids. If we study pneumatics, hydraulics comes as its basic level evolving gases. The analysis lays down the scientific focus on how such fluid mechanics can be worked upon that in turn can be beneficial in today’s life. Power from hydraulics is one such instance where progressive engineering using the properties of fluids has been successful in providing its usefulness to the automotive industry, rail engines and most significantly, the elevator systems. Since fluid is used as a mechanism, hydraulics plays a significant role in the generation of power, its transmission and control thereof. In the case of elevator mechanisms, hydraulics is one such option that is still used by the elevator industry even today. The system is highly adopted today and installed in residential premises due to its simple and uncomplicated performance. Because hydraulic lifts do not get suspended in the air, they are the safest bet one could always go for.

IN simple terms, the crucial parts of a hydraulic lift include a pump, a cylinder and hydraulic fluid. The pump extracts oil from a tank filled with hydraulic fluid and then injects it forcefully into a cylinder. This cylinder works as a piston run by motor to push the fluid into the cylinder. Fluid input and output is regulated by a valve that controls the pressurised fluid in and out of the cylinder when desired accordingly. As the valve is closed, the fluid goes into the cylinder thereby putting pressure on the piston. As the pressure mounts, the piston the piston is pushed upwards. This in turn raises the hydraulic arm of the elevator to make elevation to the next floor. Gradually, as the valve opens, the hydraulic fluid is released and it then goes out of the cylinder back to the tank thereby making the descent possible slowly and securely. Buildings that are a few stories high only prefer using hydraulic elevators. These elevators can operate at speeds up to 150 ft. per minute. Since they are cheaper to install than other kinds and also occupy less space in a building, hydraulic lifts are the preferred ones. They surpass the lifting force of traction ropes easily. But their speed is generally slow and the oil used in hydraulics also heats up with temperature rise in the piston so an efficient machine-room system is required. Oil leakage can be common in them and its residue cause ground water pollution apart from regular worn sheaves, power failure and noisy bearings.

Hydraulic elevators are used extensively in buildings up to five or six stories high. Sometimes, but rarely, up to 8 stories high. These elevators, which can operate at speeds up to 61 meters (200 ft) per minute, do not use the large overhead hoisting machinery the way geared and gearless traction systems do. Mostly, all modern hydraulic pumps are either equipped with a Solid-State Contactor or a mechanical Y-Delta starter. Solid-State Contactor starters are better for the motor and the building's power supply, as the windings last longer and there are no voltage drops across the line of the building's power supply. Apparently even today, hydraulics is preferred for their simple logistics in smaller buildings.

Traction Elevator Systems

Traction, as the term applies means application of force to draw something closer. This physics has been applied to different mechanical usages. One such example is a roped electric elevator system also called a traction elevator system. This system is heavily based on traction by strong mechanical wires about 6 to 8 in numbers that draw weight of the cabin car and perform the elevation consequently. This drive system has been adopted preferably because it can reach any height of a building and definitely has greater speeds than steam-powered elevators. The durability of this elevator system speaks for itself. These are commonly gearless systems. There are new buildings coming up every day and traction systems are the preferred use since they require very low maintenance due to their design and it is seldom required to replace a well-maintained gearless machine. In addition to this, the speed of these elevators remarkably reaches greater than 500 feet per minute (or 2.5m/s).

A gearless traction machine employs about six to eight lengths of wire cable that are called hoisting or wire ropes that go beyond the top of the elevator. There is a drive sheave that wraps around these cables in special grooves. At the far end of the other side of the cables, a counterweight is installed on the guiderail where it can move smoothly. However, in hydraulics, we see the movement of lift was crucial by using pressurised oil. Here it is the wires that move the cabin. Since the other end of the cables is connected to the counterweight and the one end to the cable car, the combined weight of the elevator car and the counterweight mount adequate pressure on the cable into the grooves on the drive sheave that the necessary traction required is generated when the sheave turns. The counterweight reduces the load on the motor as it is calculated to match the weight of the car and a half-load of passengers. As the car rises, the counterweight descends, balancing the load. This reduces energy consumption because the motor is required to lift no more than the weight of half a car load at any time. The grooved sheave in this traditional gearless system is quite large, from 0.6 to 1.2 meters (2–4 ft) in diameter. The drive sheave is very heavy and large in size therefore, a strong electric motor is required to generate enough power to turn this sheave at 50–200 revolutions per minute in order to move the elevator at the proper rate. Additionally, to be precarious regarding safety, a governing device engages the car’s brakes in case the elevator begins to fall. There are other safety checks like a powerful clamp that stops movement of the cables and activates safety clamps installed beneath the car. The car finally stops when moveable steel jaws are held against the guiderails as sufficient force is applied to perform a smooth halt.

An alternative to hydraulic elevator systems is the mechanical elevator system, more familiar in modern building projects. While hydraulic systems use pressurized liquid, a mechanical elevator system uses strong metal ropes for elevation controlled through a motor. The sheave has grooves in it to fasten the rope tightly for lift. Also a counterweight hanging on the opposite side of the shaft helps perform the lift function smoothly. However, maintenance wise, components in mechanical elevators are more exposed to wear and tear and require regular maintenance than their counterpart. Security wise too, a hydraulic lift is the most reliable, as it can reach the nearest stop through its 12V battery if power failure persists.

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