Modern Building Services

10 MODERN BUILDING SERVICES JULY 2022 B rake failures affect many types of equipment and while efforts have been made in standards to improve the outcome of a brake failure – unfortunately, they still occur. This can be because many lifts were installed prior to the introduction of current standards. The consequences of a failure can range froma ‘near-miss’ to fatalities. Many service technicians take the view that with the introduction of variable frequency drives into the lift and escalator industry that the brake no longer needsmaintaining. Nothing could be further than the truth. Thankfully recent standards have been developed to reduce the risk of brake failure, but there are key areas to be aware of and key recommendations that everyone responsible for lifts, whether in commercial or private settings, should be aware of. The function of a lift brake has changed over recent years with developments in drive systems. Older systems such as single- speed and two-speed designs relied on the brake itself to bring the lift to a stop during an ordinary journey and the leveling accuracy would be dependent upon the condition of the brake pads, the load in the lift car relative to balance, and the position of the lift in its shaft. With these drive systems, the brake was also used to bring the lift to a safe stop in the event of a power supply fault or a control system situation (such as a high-speed lock tip). The regular maintenance of the brake with these drive types is vital. Older but more sophisticated drive systems [such as the DC Ward Leonard system or the DC static converter drive] were designed so that the motor would bring the lift to a stop at a landing and then the brake would apply to hold the lift car for loading/ unloading. Similarly, these drive systems were required to bring the lift to a safe stop in the event of a power supply fault or control circuit situation. Modern drive systems [such as the AC VV and the variable frequency drives] are similar to these however maintenance is still required as situations such as high-speed lock tips can still occur and cause premature wear of brake pads. What happens when a brake fails? A lift can be compared to a set of scales with the heaviest side of the balance equation between the car and the counterweight being the side that descends when left to gravity. In many cases when a brake fails the lift car will run upwards due to the counterweight being heavier than a lightly loaded lift car. As the counterweight descends, where no compensation exists, the lift car ascent increases in speed as the suspension ropes payout onto the counter-weight side. Modern lifts are fitted with uncontrolledmovement devices that will detect and arrest a runaway conditionbutmany liftswere installed prior to this recommendation in the standards and do not have such a facility. It should be remembered that uncontrolled movement may be caused by situations other than a brake failure too. EUR ING Dave Cooper , CEO of LECS UK and CIBSE board member, outlines the latest developments within BSI standards that govern brakes on lifts and outlines his key recommendations to keep brakes operating safely. Brake failures on lifts, consequences and recommendations FEATURE WORKING BUILDINGS ƒMAINTENANCE, OPERATIONAND REFURBISHMENT