The Cayeli concentrator designed nameplate capacity was 600,000 tonnes per year. Originally, three Rittershaus & Blecher pressure filters were installed: one for copper concentrate, one for zinc concentrate, and one standby for both copper and zinc concentrates. Mill throughput gradually increased after commissioning and was 896,700 tonnes in 1999. At these production levels, the filtration capacity created a bottleneck. In 1999, CBI decided to increase the mill capacity to one million tonnes per year and a fourth filter was installed in the year 2000 as part of the expansion plan. A LASTA M.C. automatic filter press was selected. This paper describes the selection, installation, commissioning, and operation of the new filter; and compares its performance with that of the old filters.