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.
Holeless hydraulic consists 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 extends the rise of the holeless elevator to 18 meters (60 ft), without the need for a belowground cylinder. 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.
Machine room less hydraulic
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.
Benefits of Hydraulic Elevators
- No need for reinforcement. The cylinder that lifts the elevator cab is supported by the ground underneath.
- Are usually cheaper than traction units.
- If the line breaks, the elevator will fall no faster than oil can escape.
Detriments of Hydraulic Elevators
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 system no longer exists in the hydraulic elevators installed in mid-1990s or later when the submersible hydraulic power unit introduced which placed the motor inside the tank to make some of the motor sound isolated in the oil 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 has stopped produce hydraulic elevators due to the same reason.
Notable hydraulic elevator models
- Oildraulic (1937 – 2012) – notable hydraulic elevator system invented by Automobile Rotary Lift Co., normally used on Dover and ThyssenKrupp elevators in the United States and Canada.
- Schindler 300A (1995 – 2001)
- Schindler 321A (1998 – 2001)
- Schindler 330A (2001 – present)
- Otis 211 (1987 – 2013) Common hydraulic controller used on Otis elevators.
- Otis HydroFit (2011 – present) Otis’s new hydraulic system. Also comes with MRL option.
- ThyssenKrupp Endura (2012 – present) – successor to the Oildraulic.
- ThyssenKrupp Endura MRL (2014 – Present) Successor to the Oildraulic; MRL version of Endura.