Elevator Buffers

Elevator buffers are a safety device that stop the elevator car and counterweight from sliding down to the pit floor in case of a fault. They are available in single, double and quad configurations.

Buffers are required to withstand the impact of a descending car or counterweight at 115% of the rated elevator speed. This is achieved through a minimum stroke which must be sufficient to bring the impacting mass to rest with an average deceleration of 1g.

Safety

Elevator buffers are a key safety feature of elevators. They are designed to prevent a descending car or counterweight from running into the elevator pit and potentially damaging it or the passengers in the cab. Buffers can also be used to soften the impact of an elevator car or counterweight in a free fall situation.

As with all safety devices, elevator buffers must meet a number of specific requirements. These include the way in which they bring an elevator car or counterweight to rest, as well as limiting peak deceleration force (g) and the length of time that passengers are exposed to the maximum amount of g forces.

Normally, elevator buffers are subject to type tests according to the requirements of EN81.1 and ASME A17.1, although these may vary depending on the country in which they are installed. The tests are carried out with masses that fall from a height of 0degC to 25degC and measure displacement, velocity and acceleration at a sample rate of 100Hz.

These tests ensure that the buffers meet performance specifications. They also allow the manufacturers to optimise the performance of their buffers, which can lead to better efficiency and reduced maintenance costs.

The most important of these specifications is limiting the g force for the duration that an elevator car is in contact with the buffer. The g force criterion is not necessarily a legal requirement for elevator buffers but it can be important to ensure that the buffers do not cause discomfort for passengers as the elevator car is coming to rest.

Another critical g force specification is that the peak deceleration force should not exceed 2.5g for 40 milliseconds or more. This is a key criteria in the design of buffers, which can be optimised using computer modelling and analysis.

Buffers are most often located in the elevator pit, and they can be exposed to water or flooding. They need to be cleaned and painted on a regular basis to ensure that they maintain their proper performance specifications. The oil inside elevator buffer them also needs to be checked and changed if it is exposed to any kind of flooding.

Performance

Elevator buffers are designed to bring an elevator car to a safe stopping position within an established time. They must perform to a number of technical specifications but in particular they must be capable of bringing the elevator car to rest without peak deceleration forces exceeding 1g and no more than 2.5g for more than 40 milliseconds.

There are many different technical specifications for elevator buffers in different regions around the world however all use the same basic performance criteria. This is based on drop tests where an elevator car is dropped in freefall, a measurement of the acceleration of the lift car and the time taken for the elevator car to return to its fully extended position after the test.

These performance measures are critical to ensuring that the elevator is safe for all users and can be measured with relative ease by installing a suitable test device in the bottom of an elevator shaft. The most common test used is the g force drop test but these tests can also be used to measure other important parameters such as the performance time of an elevator and the length of door opening times.

An idealised hydraulic buffer has the ability to achieve the maximum deceleration force with minimal lateral movement, achieving this is not possible for all impact masses but can be achieved by precise control of the flow of hydraulic oil across an orifice throughout the buffer stroke.

The Oleo LB gas hydraulic buffer series has been recognized for its excellent performance and reliability for over 30 years, it is a self-contained, maintenance free* unit that can be found in low, medium and high rise buildings and vehicle and service elevators. It is designed and built according to strict engineering standards and is universally approved and globally certified.

Firstly, a mathematical model is built corresponding to the working conditions of the buffer, and then the dynamic characteristics of the buffer are obtained via MATLAB. Secondly, a simplified impact model of the buffer and the mass block is built, and then the relationship between the acceleration and time of the mass block is obtained. Then, the 3D FE analysis of the elevator carriage impacting the hydraulic buffer is conducted by applying the acceleration curve of the hydraulic buffer to the 3D FE model of the elevator carriage in the form of loading curve.

Design

Elevator buffers are safety devices that are mounted at the base of an elevator shaft. They are designed to bring an impacting elevator car to rest in order to ensure the safety of the passengers who are traveling in the elevator and its supporting equipment.

There are many different types of elevator buffers, but they all have to meet certain specifications in order to be installed on an elevator. Some of the most common include oil buffers and spring buffers.

An oil buffer is a type of buffer that uses a combination of oil and springs to cushion a descending car or counterweight. These are commonly used on traction elevators, and they have to be cleaned and painted regularly to maintain their performance specifications.

The design of an elevator buffer depends on the rated speed of the elevator, as well as the load that the elevator is designed to carry. These are the most important criteria to consider when selecting an elevator buffer, as they can make a big difference in the way that the elevator is safe for its passengers and support equipment.

As for the rated speed, it is not recommended to install an elevator with a buffer that exceeds its rated speed because this can increase the risk of damage to the buffer. Also, it can reduce the braking effectiveness of the elevator, which may cause more damage to the vehicle and people on board.

Another important aspect to consider is the distance between the buffer and the counterweight. If the distance is too large, it can cause problems for the elevator and its counterweight because they elevator buffer could slip out of the buffer and hit the ground.

Generally, the distance between the counterweight and the elevator is about 3.5 feet. However, the distance can vary depending on the rated speed of the elevator and the type of buffer that is used. As an example, if the speed of the elevator is 0.5 m/s, a buffer with a clearance of 250 mm can be used to protect the counterweight from hitting the ground.

Installation

A buffer in an elevator is one of the most important safety devices in an elevator. It prevents the car from hitting the floor hard when descending to the lower floors, as it would without it.

Buffers are available in several different forms and can be installed at any point along the shaft, but they are most often located in a pit. The pit must be deep enough to provide the necessary energy-absorbing capacity, which can add to the overall cost of an elevator project.

To make sure that an elevator buffer is not damaged, it must undergo a series of tests to ensure that it will not be compromised during normal operation. These tests involve running a load cabin and counterweight onto the buffer at the same time, with each terminal limit switch inoperative.

Once the test has been conducted, a field representative of the division should examine the buffer externally to determine whether there is any visible damage. If there is any damage, the buffer should be removed from service.

Then, a second drop test should be made to confirm that the buffer will not return freely to its extended position if compressed again. This test should be made in the presence of a qualified technician who is experienced with elevators and the equipment being tested.

Another consideration is that the pit of an elevator can be susceptible to flood damage, so it is recommended that any equipment that may be located in the pit be constructed using flood-damage resistant materials. This includes electrical control panels, hydraulic pump and reservoirs, and ductwork (Figure 2 below).

When an elevator pit is subject to flooding, it is important that the equipment is located above the bottom floor elevation (BFE) to avoid water getting into the cab and damaging it. The electric motor and most other traction elevator equipment are typically located above the BFE, but other equipment, including the counterweight roller guides, compensation cable assembly, limit switches, selector tapes, governor rope assembly, and oil buffers can be installed below the BFE.

In addition, if the elevator pit is subject to flood damage, the hydraulic pump and reservoir should be located above the BFE so that it can be safely moved out of the pit. If the elevator pit is too large to permit this, it should be filled with concrete or another material that will not be affected by floodwater.