INTELLIGENCE
W
hen discussing common errors and good practice in lift maintenance, it is worth noting that misuse – that is, people not interacting with the lift in the intended manner – is probably the biggest cause of breakdowns. Holding doors, moving furniture or jumping in a lift reliably cause problems, and 70% of lift faults relate to the doors, because this area is where people interact with the lift most and can trip the safety devices. The most common sources of problems are:
ROUTINE UPKEEP
Generally, you can hear if a contactor is pulling in (being activated) correctly. You’ll often walk into a lift motor room and hear chattering relays. The chattering noise indicates that the contactors are in poor condition and possibly need replacing because of an issue with the coil or the contacts themselves. Also, after thousands of operations, terminal screws work their way loose, which, again, could increase resistance through a contact and cause it to burn up. A check to ensure correct tightness on connections is vital and is a good way to help reduce intermittent faults.
1) Door locks on landings not aligned with the lift as it arrives at the floor
3) The safety circuit switch feathers (slack rope)
Lift doors have many moving components and on average, a single door panel will be made up of rollers, pick up, hanging and kicking rollers. Any one of these rollers can cause a fault with the door opening or closing. Maintenance needs to check all locks and alignment regularly to avoid faults developing.
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Zen and the art of lift
4) There are drive issues These become common as lifts age. Over time, lifts experience brake wear and high resistance on motor contacts. Motor fields get weaker, and rope or sheave wear causes traction loss. Poor maintenance, such as not filling up the oil pots that lubricate the guides, or failing to keep the load weighing device calibrated, is often the cause of issues.
27 BUILDING ENGINEER
A contactor is an electrical device used for switching an electrical circuit on or off. Generally, they feature multiple contacts. In most cases, these contacts are usually open and provide operating power to the load when the contactor coil is energised. They are typically found with the control cabinets or containments. Determining the life-cycle of a contactor is difficult, because on-site conditions always vary. Cleanliness and temperature can play a part in reducing the lifespan of an electrical component. Dust and dirt on open contacts can cause an arc, which in turn contributes to ending up with burnt-up contacts and high resistance. This is also the case for lock contacts and other safety switches. Another difficulty is keeping everything as efficient as possible and reducing the current through the contacts. An incorrectly set brake leads to more current being drawn, overloading the contact rating. A lift running in an incorrectly balanced state would cause a rise in current and, again, reduce the lifespan of the contact – as well as the voltage variable frequency unit, which is what gives a lift smooth acceleration and deceleration, excellent speed control and reduced noise levels.
FEBRUARY 2021
2) Contactors or relays wear down, and contacts get high resistance
The safety circuit stops the lift when it detects that something is outside normal operating parameters, presenting a risk to users. Maintenance involves checking that everything is operating within tolerance. Components often require adjustment as they change over time, including the ropes, which will stretch.
5) There are position faults (proximities and magnets) Components such as magnets and proximities need to be perfectly aligned. The proximity is an electrical switch, and it needs to be aligned with the magnet for it to switch and change state, sending signals back to the control panel for many functions, including a floor level or a door over bridging function. Over time, these can come loose or be dislodged, causing breakdowns. Pencil switches and magnets usually have a set-up tolerance of between 8mm and 12mm. Any more or any less, and you get magnetic field issues, such as double pulsing if the distance is too short, or no pulsing at all if the distance is too large. If the lift car position changes because of the roller or shoe (which, again, should be maintenance checked), this can cause issues. Lifts run at high speeds with heavy loads, but with only millimetres of clearance as they travel. A lift shaft contains many safety components and can vary in vertical distance from a few metres to hundreds of metres long. It takes only the slightest anomaly or equipment defect to put a lift out of service. But the chance of this can be minimised through good knowledge of the equipment, requirements for maintenance and understanding when to take action.
maintenance Tek Hussein, Head of Technical at WeMaintain, runs through some common issues with lifts
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For more, visit wemaintain.com/en-uk
19/01/2021 09:43
