Some of the most common repairs needed for an elevator or a stair lift include replacement cables for a cable drive or hydraulic system of the elevator, replacement chain for chain drive systems, fixing a ruptured hydraulic fluid line in hydraulic systems, and cleaning and seal maintenance for pneumatic systems. Newer elevators are often outfitted with automated or computerized controls that may experience occasional electronic glitches, which interfere with optimal system performance. Drive chain adjustments are another common repair performed to ensure that the stair lift chair stops or the elevator opens at the proper place. Malfunctioning door operators account for nearly three-quarters of elevator repair requests.