Hydraulic elevator systems lift a car using a hydraulic ram and a
fluid-driven piston mounted inside a cylinder. You can see how this
system works in the diagram above.
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:
- A tank (the fluid reservoir)
- A pump, powered by an electric motor
- A valve between the cylinder and the reservoir
elevators are supported by a piston at the bottom of the elevator that
pushes the elevator up. They are used for low-rise applications of 2-8
stories and travel at a maximum speed of 200 feet per minute. The
machine room for hydraulic elevators is located at the lowest level
adjacent to the elevator shaft
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.
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.