Modern Building Services

MODERN BUILDING SERVICES JULY 2022 11 In addition, many older lifts using single-speed or two-speed drive systems rely on the brake for stopping and the accuracy of the car to landing threshold is reliant on the condition of the brake, the position of the lift in the shaft, and the load in the car. Types of brake failure There are many ways that a brake can fail and these include electrical and mechanical failures. In some cases, one ormore of these situations can come together to create an uncontrolled movement scenario. Examples include: • Brake solenoid going open circuit (single solenoid) • Brake solenoid going open circuit (twin polarised type) • Physical wear of brake pad • Rivets coming loose on the brake pad • Lubricant on the brake pad • Stuck in open position - release mechanism failure • Stuck in open position - other mechanical failure (such as a single line component e.g. a split pin) • Held in open position - residual magnetism • System overloaded • Poor adjustment • Overheating Standards Over the years there have beenmany improvements in braking systems for lifts including the introduction of the A3 amendment to the EN81-1 standard [Safety rules for the construction and installation of lifts. (London, BSI] for uncontrolled movement, however, this dealt with the symptomof brake failure rather than the cause. The current edition of EN81-20 (that replaced EN81-1) includes uncontrolled movement detection and also the requirement for brake components to be in two sets - thus offering redundancy and monitoring of the brake itself for correct operation. The EN81-80 (2003) standard (Improvement of the safety of existing lifts) didn’t mention inadequate braking systems however the 2019 version has been expanded to include this situation. Key takeaways 1. Older lifts with single-line components in the braking system need to be assessed. 2. It is recommended that all brakes should be fitted with lift detection switches. More information can be found at www.lecsuk.co.uk FEATURE WORKING BUILDINGS ƒMAINTENANCE, OPERATIONAND REFURBISHMENT 3. Where modernisation takes place and an old-style brake is retained and a variable frequency drive is fitted to replace an older system such as single speed, two speed, etc. there is a real risk that the lift can drive through a closed brake, especially with the lift car in the upper reaches of the shaft. 4. Prevention is better than cure. Methods of detecting the depletion of braking efficiency should be developed so as to detect rather than respond to a failure situation. The potential for uncontrolled movement should be detected before it actually happens. 5. Checking of brake condition and adjustment is still an essential part of the maintenance regime as extraneous situations such as high-speed lock tipping can affect braking performance.