Hydraulic elevators are considered the safest option because the cab is never suspended inside the hoistway. Elevators that use a cable-driven system hold the cab suspended in the air when they are above the ground floor. Pneumatic elevators hold the cab at higher floors by using a brake system.
Hydraulic elevators are heavy-duty elevators built for frequent, long term use. They also have an ultra-smooth ride quality and are typically very quiet. They are one of the best elevators for durability, larger weight capacities and serving a higher number of floors.
The system operates with a hydraulic pump connected to a cylinder that will raise and lower the elevator cab. The elevator will lift under pressure of the hydraulic fluid pumped into the cylinder when a call button is pressed from a higher floor.
To travel in the down direction, the controller will open a valve slowly releasing this pressure after a lower floor call has been placed. Since this type of elevator can travel down by simply opening a control valve it is also what makes them efficient in the use of power. They can even be lowered by battery backup in the event of a power failure with automatic operation.