In Boll automatic filters, the filter candles, wedge wire candles, or wire mesh candles are automatically cleaned by back-flushing without interrupting operation. This may depend on differential pressure, time, and can be carried out using the plant’s own medium. This could be a compressed-air-supported medium or external medium.

Filters of this type are used when contamination occurs constantly, manual cleaning is uneconomic, or the plant filters are extensively automated.