Elevators: how they are made, how they work and what types are in use

An elevator is a vertical means of transport cable-driven or hydraulically operated, which allows the movement of people between the different levels of a multi-storey structure. We also speak of lifting systemswhich generally includes both those that allow the movement of people (elevators precisely), that those that allow the movement of material and/or objects (freight elevator). The definition of his geometry and of his speed represent some of the project parameters that a technician is called to define. The technology hidden inside the casing identifies the type of elevator and the safety mechanisms present, necessary to prevent unwanted conditions from compromising the safety of users. Let’s see in this article what are the main characteristics and the different types currently in use.

How is an elevator composed?

The history of elevators has ancient origins, but the mechanical principle of operation has not substantially changed: it is a system that transmits sufficient force to a structure to allow it to rise and overcome the force of gravity, that is, descend with a set speed and without undergoing acceleration. We must generally refer to multiple components that contribute to the complete definition of the system elevator. In particular, we have:

• There Lifting cabinthat is, the structure at the service of users to ensure lifting to various levels, as well as controlling – with appropriate button panels – the desired destination.
• The plant system of the elevator, that is, that part of the electrical and mechanical organs that guarantee the actual lifting of the cabin. Among these we can also include the system of guides which outline – like tracks – the cabin’s travel path.
• The elevator shaftthat is, that part of the structure that outlines the space for positioning the cabin and the plant part of the system. The compartment can extend beyond the maximum height of the building (i.e. the roof), or deeper than the installation plane of the foundation body (in this case, we speak of pit of the elevator shaft).

Types of elevators: operating mechanisms

Let’s briefly look at the main distinction between the two operating mechanisms used to move an elevator.

Cable lifts

They are necessary when the number of floors to be served becomes considerable. In practice, the cabin contained in the elevator shaft, directed by the guides, is kept in suspension from a series of steel wire ropesUsually strands of harmonic steel (i.e. high carbon steel) firmly anchoring the cabin. These ropes extend along the elevator shaft and pass around a device located at the top of the shaft, called winch: this is what represents the actual lifting machinery, that is, the element that provides the cabin with sufficient kinetic energy to move upwards or vice versa. On the other side of the winch, a large counterweight. This counterweight moves in the opposite direction to the cabin, as it follows the movement of the cable that connects it: in essence, it is an element that partly balances the weight of the cabin and passengers, thus minimising the stresses that the winch would otherwise be forced to bear.

Hydraulic/oleodynamic lifts

Unlike cable elevators, hydraulic elevators are not “hung” by a cable. Rather, The cabins of the same are supported and pushed by a cylinder-piston system with the help of a pressurized liquidIt is precisely the liquid that, thanks to the externally governed pressure regulation, manages to generate the right lifting thrust to the support cylinder which therefore moves the cabin. In this case, therefore, there is no need for a counterweight as there is no lifting winch that must transfer energy to move the cable. On the other hand, the cylinder stroke has its own bulk and the cylinder itself has its own stability which decreases as the height to be served increases. For these reasons, the application of this technology is limited to cases where there are reduced heights to serve. Nevertheless, this type of elevator shows on average lower assembly costs and greater ease of adaptation, especially to existing buildings.

Safety devices

The elevators are equipped with real brakes which allow the cabin movements to be blocked in the event of problems. The braking mechanism is activated automatically when Falling speeds increase by 20-30% compared to ordinary operating speed and, thanks to thefriction which is generated by the contact of the brakes with the guides, the kinetic energy is dissipated until it is completely exhausted.

In the case of cable elevators, the counterweight itself is designed in such a way that it is also a protection mechanism in the event of a failure. In fact, it is capable of balance the weight of the cabin and a load equal to half the maximum design capacity. Therefore, if the failure occurs under reduced load conditions, the elevator would rise rather than fall. Safety, in these cases, is also guaranteed by the presence of a redundant number of ropes: In practice, the existing ropes work at extremely low stress values, so much so that one of the ropes alone would be able to operate the system.

Travel speeds

Cable elevators are much faster than hydraulic elevators. For the former, the travel speeds are around one meter per second (m/s), under ordinary conditions. For hydraulic elevators, these numbers can drop to half (approximately 0.5 m/s). However, the reduction in speed makes hydraulic elevators less noisy.

Elevator travel speeds are not only constrained by mechanical conditions, but also by functionality and comfort issues for passengers. Indeed, high speeds are often linked to high accelerations/decelerationswhich affect the ride comfort of the occupants. However, in some cases – for example in large skyscrapers – having high-speed elevators can be essential for the functionality of the spaces that the machine serves. For this and other reasons, usually the design scheme of elevators in these particular conditions is carried out by means of the construction of various parallel lineswhich serve specific, if not unique, levels. In this way, by increasing and limiting the travel distances (there cannot be intermediate stops), it is possible to have a longer gear and therefore higher speeds, without high increases in start and finish accelerations/decelerations. In these cases, speed values ​​of 10 m/s or more are reached.