In the on-line process, the cleaning body moves through the tubes with the conveying medium and cleans them by means of its oversize compared to the tube diameter. In the range of diameters of up to 50 mm these cleaning bodies consist of sponge rubber, in larger diameters up to the size of oil pipelines it is a matter of scrapers or so-called pigs. Sponge rubber balls are applied mainly for cooling water, like sea, river, or cooling tower water. For the chemical or pharmaceutical industry, specially adapted cleaning bodies are imaginable but the conveying media flows are so weak that off-line processes are employed in most cases. Given the fact that the cleaning bodies are not allowed to remain in the conveying medium they have to be collected after passing through the tubes. In the case of sponge rubber balls this is done through special strainer sections; for scrapers or pigs an outward transfer station is provided. According to the Taprogge process, the sponge rubber balls are re-injected upstream of the system to be cleaned by a corresponding ball recirculating unit whereas the scraper or pig is mostly taken out by hand and re-injected into another collector. Sponge rubber balls therefore safeguard a continuous cleaning while the scraper or pig system is discontinuous.