An Up and Down Business by J.O. Trundle.
At the Durrington Community Centre, 14th March, 1990.
Not an account of Mr. Trundle’s activities on the Stock Exchange, but the fascinating story of vertical movement, which he described as ‘the safest form of public transport’. Though devices for lifting objects were known by the ancient Egyptians, elevating humans awaited the invention in 1852 by Elisha Otis of a device to prevent the cage falling if the rope breaks. The weight of the cage was taken at the mid point of a cart spring: if the load was removed (by rope failure) the spring extremities would engage in ratchet bars at the side of the shaft, arresting the fall.
Having mentioned steps taken to overcome the inaccuracies of lift shaft builders, Mr. Trundle described the range of drive mechanisms available, from the single speed induction motor to the variable speed geerless unit supplied by thyristors. Hydraulic lifts are still extensively used in low rise buildings. Significant power savings result from use of the counter balance system, weight of the latter normally being (weight of car) + (half maximum load). Passenger weight is assumed to average 75 Kg. Maximum travel speeds, for limited stop lifts in high rise buildings have reached 1800 ft./min. Accuracy of landing alignment and level of passenger comfort -smoothness of acceleration/ deceleration – are primarily determined by the price the purchaser is prepared to pay. Simple control systems (the cheapest) can lead to waiting passenger frustration: modern electronics enable, for example, operating regimes to be varied as traffic flow changes during the day, approaching close to the ideal of shortest possible time for each passenger from “calling” to arrival at destination. In large, high rise blocks, all lifts but one return to ground level in the event of fire, the last is for firemen’s use. Our speaker finally described some large installations, pointing to differences required by single organisation occupation or multi company use in single or groups of floors.
In addition to slides and transparencies, we had the unusual luxury of an illustrated hand-out.
The problems created by lifts which stop between floors were first dealt with. Mr. Trundle pointed out that emergency power supply could be provided so long as the customer was prepared to pay. Hydraulic lifts, common in housing for the elderly and disabled offered a simple solution – controlled release of fluid permits slow descent to the nearest floors. Emergency brakes are nowadays progressive rather than instantaneous, though fierce enough to produce minor injury. Tapered ropes are used only in very deep mines – for hoists, not lifts, while earthquake precautions are the responsibility of the builder rather than the lift installer. Architects frequently object to the presence of machinery housed above the top floor. There are solutions, though expensive ones.