The world’s population is increasing exponentially. The total birthrate is 4.17 per second and the total death rate 2.37 per second. The net population growth is therefore 2.37 humans per second.
People long ago started to build houses on every possible place. Ultimately and by necessity, they are now shifting to live in multi-story apartments and huge skyscrapers. Getting about in these buildings is made possible by elevators. Without elevators or lifts, these buildings would be uncomfortable places in which to live. In this article, we will discuss mainly the operation and use of hydraulic lifts.
A hydraulic lift is a device used for carrying passengers or goods from one floor to other in a multi-storeyed building. The hydraulic lifts are of two types. They are
1. Direct-acting hydraulic lift, and
2. Suspended hydraulic lift
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.
Suspended Hydraulic Lifts:
It has a cage (on which people can stand or goods can be placed), which is suspended from a wire cable, and a jigger consisting of a fixed cylinder, a sliding ram, and a set of two pulley blocks, which is provided at the foot of the hole of the cage. One pulley block is movable while the other one is fixed. The sliding ram end is connected to the movable pulley block. A wire cable, one end of which is fixed at point “A" as shown in the figure and the other end taken all round the pulleys of the movable and fixed blocks and finally over the guide pulleys, is routed as shown. The cage is suspended from the other end of the rope. The raising or lowering of the cage of the lift is done by the jigger.
Water or any hydraulic fluid at a high pressure is admitted into the fixed cylinder of the jigger. This high pressure hydraulic fluid
pushes the sliding ram to move towards left side as shown in the figure. When the sliding ram moves towards the left side, the distance between the fixed and movable pulleys increases and thus the cage is lifted up. When the water or the hydraulic fluid under high pressure inside the cylinder is released, then the distance between the two pulleys decreases and thus the cage comes down. Thus the suspended-type hydraulic lifts are more popular than direct type lifts.
www.peterrussell.com (world population count)