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.
However, modern passenger & cargo lifts have advanced mechanical systems to handle the substantial weight of the elevator, passenger and its cargo. Additionally, they need control mechanisms so that the passengers can operate the elevator, and they need safety devices to keep everything running smoothly and reliably in compliance to safety norms.
There are two major elevator designs in common use today: Hydraulic elevators and Roped elevators. This blog discusses the working principle of hydraulic elevators.
Hydraulic elevator systems lift a passenger and cargo using a hydraulic arm, 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:
• A tank (the fluid reservoir
• A pump powered by an electric moto
• A valve between the cylinder and the reservoir
The pump forces fluid from the tank into a pipe leading to the cylinder. When the valve is opened, the pressurized fluid takes the path of least resistance and returns to the tank. 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.
When the cargo 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. The piston rests on the fluid, and the cargo stays where it is.
To lower the cargo, 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 cargo and passenger pushes down on the piston, which drives the fluid into the reservoir. The cargo gradually descends. To stop the cargo at a lower floor, the control system closes the valve again
This system is incredibly simple and highly effective for common uses.