Dual converters consist of two converters or bridges. One bridge acts as a rectifier and other acts as inverter. Single-phase full converters allow only two-quadrant operations. In full-controlled converter the output voltage is reversible so the converters operate in first and fourth quadrant. The direction of load current remains same. If two full-controlled converters are connected back-to-back then a four-quadrant operation are possible and such type of converters are called dual converters. It is used in high power variable speed drives. Dual converter is operated with either circulating current or without circulating current. When both the converters conduct at the same time, there would be circulating current and the level of circulating current is restricted by provision of an inductor. It is possible to operate only one converter at any instant, but switching from one converter to the other is carried out after a small delay.
Dual cylinder roller gate is specifically designed to handle dry material in gravity flow and low pressure applications, where positive material shut-off and a dust tight seal are required. This gate is used to eliminate the frequent need for valve maintenance, production inefficiencies, and unsanitary plant environments.