Direct acting hydraulic lifts:
The system consists of a ram which slides inside a fixed cylinder. The cylinder has suitable openings at the bottom for the hydraulic fluid to enter and also suitably designed to allow the ram to slide up and down. The ram has a cage attached to its top, which acts as a capsule carrying people or goods. The ram is pushed up by the pressure of hydraulic fluid acting beneath. Thus the cage moves up to various floors as per the need. The cage is moved in downward direction by allowing oil to get drained from the cylinder back to the oil reservoir.
Working: When the pump delivers oil to the bottom of the cylinder, as the valve meant for the re-circulation remains closed, the oil beneath the bottom of the ram gets pressurized and this pressurized oil lifts the ram (cage). When the cage has to be lowered, the oil is drained back to the oil reservoir by keeping the valve open. The time for which the valve is kept open is decided by the electro-magnetic switch, which gets its signal from the people who use the lift.
1. The cylinder has to be designed too long if the building is too high. If the building is twenty meters high, the cylinder has to be dug nineteen meters deep below the building. So, this type of elevator cannot be used for tall buildings.
2. The energy utilized is more for the hydraulic systems and thus they are comparatively inefficient.
3. Maintenance of hydraulic fluids is frequently required. They have to be replenished if required which is expensive.
To overcome the above disadvantages, a suspended type can be used for tall buildings.