Changes And New Standards For Safety Mechanisms
When considering the applications and changes our sector has seen in safety mechanisms since the beginning of 2000s, we can see that our country has undergone extensive changes in speed regulators and brake systems.
Increasing heights of the buildings have led to the construction of faster, more comfortable and safer elevators.
The advancement of gearless machines in drive systems and the phaseout of the buffer effective brakes in elevators with a nominal speed of more than 1 mps as a result of the commissioning of regulation EN 81-1+A3 has made the safety systems considerably more comfortable and effective. While the speed regulators are only used to detect acceleration of the elevator downward, they provide functionality in both directions and whenever the elevator becomes sensitive to a possible cabin slip at any floor. The braking systems have also begun to work more comfortably in the event of excessive acceleration of the elevator car in both directions, and more precisely in unintended cabin movements.
It was not possible to instantly change production and the use of the components that were not in compliance with new regulations and standards in our country, and the problems that occurred during the transition period continued for a long time. Buffered brakes remained permissible in elevators with nominal speeds of 1 mps, and were used for many years in our country, along with the sudden stop brakes, by installing four rubber pads on the floor and ceiling of the cabin.
In 2005, 80% of elevators produced were 1 mps when it became mandatory to use a sliding brake for elevators with nominal speeds exceeding 1 mps. Because it is more economical, the use of buffered brakes continued. During this period, cabin manufacturers and assemblers who favor the comfort of sliding brakes would use them even at nominal speeds of 1 mps. However, unlike buffered brakes, sliding brakes require the rope tension of the speed regulator to be higher than normal, as described in EN-81, to ensure proper operation. During the transition from sudden brakes or buffered brakes to sliding brakes, problems with braking were encountered during the initial test phase of the installation. Because the weight under the tensioning pulleys that provided the rope tension in the speed regulators could not be set to provide a minimum tension force of 300 Nm, as permitted by EN 81, there would not be enough distance in the shaft.
For safety sudden stop and buffered mechanisms, only about 150 Nm (about 15 kg) of tension was sufficient to achieve the braking force. For this 150Nm tension, the use of 6 mm diameter hemp regulator rope was an economical solution and sufficient. In order to provide sufficient tension without increasing costs, the types of mechanisms in which the spring force and tension can be adjusted in the regulator, lower pulleys were preferred. This type of solution was economical, but after a while it was observed that the springs could not provide the same tension and that they were stretched and constantly required the maintenance personnel to go to the installations and increase tension again. Thus, it was seen that it was not economical in the long run.
We always favor locating the weighted lower tension pulley as far as possible from the hoop if there is sufficient distance within the shaft, the rope is at least 8mm in diameter with steel core, 300mm pulleys are used and the elevator has more than 10 stops so that the sufficient tension can be provided at all times.
These buffered brakes, which are preferred at nominal speeds of 1 mps, must be tested at nominal speed and with a 125% loaded cabin before the lift is activated, as referred to in EN 81. The aim of the test is to make sure that the people inside the cabin are not harmed by exposure to a force between 0.2 and 1 G (preferably an average of 0.6 G) in a possible real braking situation, and secondly to make sure that the kinetic energy generated in the braking does not damage the rails, construction, cabin and the engine gear by suddenly overloading them. The brakes are expected to be easily separated from the rails after the test. However, we have observed that some negatives occur in providing these conditions, and that the elevator installers and maintenance personnel experience major problems in such cases.
After these tests, it was determined the sliding brakes do not harm people, cabin, rails, or engine gears; but, because of the comfort they provide, have higher production costs than buffered brakes. Since the problems that arise due to the brakes that stop the cabinet at a certain distance without sliding did not occur in tests made at the revision speed, the overall robustness and comfort were not fully controlled, but at least it was confirmed that the mechanism was working. In the tests carried out at the revision speed, it could not be determined that the regulator rope had enough tension to activate the brake, or that the brakes on both rails were triggered at the same time to stop the cabin without slipping, or that the regulator pulley was in no danger of sudden locking.
Even in an elevator with a nominal speed of 1 mps is tested and used only at the revision speed, if the regulator rope is not properly tensioned after extreme acceleration, the brake will not function and, unfortunately, our colleagues who deal with installation and maintenance will be held responsible for the accident. Although the brakes and regulators have CE certifications, in order to avoid these preventable accidents, the components must be tested at real speed after assembly to ensure that they are compatible with each other.
Following the use of EN 81-1+A3 standard, in case the cabin slowly and involuntarily slips at a certain distance (UCM), the overspeed regulator should be activated even at such low speeds, triggering the brake to prevent the cabin from slipping further. Detecting and stopping this involuntary slip can be achieved by the engine or through other methods but, especially in our county, regulators are more preferred for this purpose. Therefore, the designs of the brakes and regulators have been revised and harmonized. The brakes now engage and disengage more easily, and the regulators have been redesigned with a bobbin so that when the cabin moves to any floor, they get locked, and return to their old state before moving again. In elevators with intense traffic, such as those in hotels and hospitals, failures arising from the frequent working and heating of these bobbins are among the problems experienced often. It has been observed that the bobbins cannot prevent involuntary slip when the electricity in the installations is not always exactly 24 or 190 VDC. Although disabling the bobbin is a temporary solution, we do not recommend it, because doing so is risky and against the standards.
Starting from August 2017, the EN 81-20/-50:2014 standards will be implemented in our country. Many changes have been made, especially in the elevator shaft and in the engine room; and safety devices are also updated. Buffered brakes will not be available anymore. Sudden-stop brakes can be used up to a nominal speed of 0.63 mps. If there is a living space under the counterweight, the brakes must certainly be used, and if the nominal speed exceeds 0.63 mps, there must be a sliding brake. After the braking, without any external intervention, the brakes must be turned off and separate from the rails just by moving the cabin in the other direction (EN 81-20 18.104.22.168.4.1). We believe these changes will make our elevators more comfortable and safer.
If the elevator cabin with a nominal speed of 1 mps turns on the brake immediately after triggering the overspeed regulator, it should slide for a minimum of 11 cm from the moment the brake paddle contacts the rail, and then stop thereafter. The energy released at the time of braking should not cause the brake paddles to be buried into the rail and damage it. Increasing the sliding distance means reducing the energy on the brake paddle, which can only be achieved by some materials in the brake body stretching during braking, like a shock absorber. The fact that the materials can be restored after the stretching without losing their properties allows that brake to repeat its task many times. Designed and manufactured in this way, such brakes can be restored without any intervention to the cabin from the outside.
As we have seen at the international fairs for years, before the EN 81-20/-50: 2014 standards, brake manufacturers have preferred not to use parts that are too stretchy in their design, so as to allow easy removal of the brake paddles from the rails after braking, and to be reactivated without intervention. Yet, we see that this is slowly changing. We hope that the Turkish elevator brands will increase their shares abroad with the impact of the right implementations of new regulations and standards that will go into effect in August.