The concept of an elevator is incredibly simple -- it's just a compartment attached to a lifting system. Tie a piece of rope to a box, and you've got a basic elevator.
The main function of the pump used in hydraulic elevator is constantly pushing Liquid into the cylinder to lift the elevator, the pump is Submersible type with Variable Speed Valve Leveling. The pump and pump motor shall be mounted on one robust bedplate or within the power unit assembly if it is suitably rigid.
Of course, modern passenger and freight elevators are a lot more elaborate than this. They need advanced mechanical systems to handle the substantial weight of the elevator car and its cargo. Additionally, they need control mechanisms so passengers can operate the elevator, and they need safety devices to keep everything running smoothly.
There are two major elevator designs in common use today: hydraulic elevators and roped elevators.
Hydraulic elevator systems lift a car using a hydraulic ram, a fluid-driven piston mounted inside a cylinder. You can see how this system works in the diagram below.
The cylinder is 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:
The pump forces 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.
When the car 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.
To lower the car, the elevator control system sends a signal to the valve. The valve is operated electrically by a basic solenoid switch (check out How Electromagnets Work for information on solenoids). 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.
This system is incredibly simple and highly effective, but it does have some drawbacks. In the next section, we'll look at the main disadvantages of using hydraulics.
Hydraulic elevators are elevators which are powered by a piston that travels inside a cylinder. An electric motor pumps hydraulic oil into the cylinder to move the piston. The piston smoothly lifts the elevator cab. Electrical valves control the release of the oil for a gentle descent.
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.
All modern hydraulic pumps are either equipped with a Solid-State Contactor or a mechanical Y-Delta starter. Solid-State Contactor statrers 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. Y-Delta starters use two contactors to start the motor on a reduced speed, then kick on full speed. Old hydraulic elevators just started up abruptly, sending mains power at full blast right into the motor. This puts a lot of strain on the motor which, in turn, makes it burn out faster than motors on Y-Delta or Solid-State Contactor starters.
There are three types of hydraulic elevator; holed hydraulic, holeless hydraulic and roped hydraulic.
With holed hydraulic systems (also known as direct acting lift[1]), the elevator car is mounted on a piston that travels inside a cylinder. The cylinder extends into the ground to a depth equal to the height the elevator will rise. As hydraulic fluid is pumped into the cylinder through a valve, the car rises. As the fluid returns to the reservoir, the car descends. This system is often called Inground hydraulic.
Holeless hydraulic elevators were invented in the late 1970s or a little earlier. Holeless hydraulic elevators of pistons mounted inside the hoistway to raise and lower the car. This is especially a solution for buildings built in bedrock, a high water table or unstable soil conditions locations that can make digging the hole required for a conventional hydraulic elevator impractical. Holeless hydraulic systems use a direct-acting piston to raise the car.
Roped hydraulic elevator (also known as indirect acting lift[1]) extends the rise of the holeless elevator to 18 meters (60 ft), without the need for a belowground cylinder. As the higher power of the hydraulic cylinder and the power unit, The 1:2 ratio (power from the hydraulic power unit : elevator actual moving distance)[2][3] can be provided. Roped hydraulic elevator systems have the piston attached to a sheave which has a rope passing through it. One end is attached to the car while the other is secured at the bottom of the hoistway. Also, roped hydraulic systems require a governor because the rope is holding the car up, and there is a risk of the car freefalling when the rope breaks.
This hydraulic elevator does not require a fixed room to house the hydraulic machinery, instead, the machinery itself is usually installed on the elevator pit and the controller is installed behind a locked cabinet on the wall near the elevator. The benefit of machine room less hydraulic elevator is that it saves construction time and cost. Examples of machine room less hydraulic elevator is Otis HydroFit and thyssenkrupp Endura MRL.
Older hydraulic elevators may have a risk of leaking hydraulic oil into an aquifer and causing potential environmental contamination. This has led to the introduction of PVC liners (casings) around hydraulic cylinders which can be monitored for integrity. Additionally, older hydraulic elevator systems usually have a motor outside of the tank and cause noise when the motor is running (this layout is no longer used in the hydraulic elevators installed in mid-1990s or later, when the submersible hydraulic power unit was introduced. The motor is placed inside the tank and the motor sound is isolated by the oil in the tank).
In 2007, Kone announced that the company would stop manufacturing and producing hydraulic elevators due to environmental concern, therefore replacing them with the eco-friendly MonoSpace and EcoSpace elevators. This makes Kone the first elevator company to only produce traction elevators. Also, some other elevator manufacturers have stopped producing hydraulic elevators due to the same reason.
Elevator |
Drive systems:Traction • Winding Drum • Hydraulic Types of elevators:Double Deck • Dumbwaiter • Fireman's • Freight • Incline • Passenger • Residential • Wheelchair lift Concept:Capacity • Destination dispatch • Elevator algorithm • Elevator control system • Elevator machine room • Elevator maintenance • Elevator monitoring system • Elevator modernization • ACOP & UCMP • Machine room less elevator • Major alterations • Rated speed Elevator systems, controllers and equipments:Elevator fixtures • Elevator keys • Elevator special modes • Elevator doors • Door cam • Door interlocks (Interlock wiring communication system) • Door restrictor • Elevator Inspection Certificate • Emergency stop button • Floor designators • Gate switch • Old Deadman controls • Overspeed governor • Motor-generator set & Silicon-controlled rectifier (for DC-powered elevators) • Insulated-gate bipolar transistor (for AC-VVVF-powered elevators) • Selector • Tape head • Regenerative converter (for AC-VVVF-powered elevators) See also:List of elevator fixtures guide • List of elevator and escalator companies • Elevator door sill guide (Non-proprietary elevator component door sill guide) • Floor numbering (Unlucky floor numbers) • Elevator incidents and accidents |
Elevator drive systems |
Traction • M.R.L. • Winding Drum • Hydraulic (Oildraulic) |
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