Abstract: An apparatus for continuously cleaning tubular heat exchangers during use is disclosed, including a separator for continuously circulating cleaning bodies through the heat exchanger along with the heat transfer-medium being employed. The separator thus recirculates the cleaning bodies along with fresh heat transfer medium while separating out a major portion of the heat-transfer medium withdrawn from the tubular heat exchanger, and includes means for withdrawing the cleaning bodies from a downstream portion of the separator and means for withdrawing the heat-transfer medium withdrawn from the heat exchanger from an upstream portion of the separator. The separator is preferably vertically disposed, so that the cleaning bodies are aided by gravity in reaching the downstream portion of the separator, and the cleaning bodies therefore do not impinge upon any screen for separating them from the heat-transfer medium.