thousands of passes during a test temperature of the water during circulation may be controlled by valve 50 which can be used to divert water through radiator 51 for cooling one of the primary measurements made during a test with the test equipment of fig5 is the flowing pressure drop of a tube cleaner this measures the amount of energy consumed by the tube cleaner 39 s frictional drag or the force applied to clean the tube flowing pressure drop may be measured by re circulating a tube cleaner through tube 30 a under constant flow conditions pressure gauge 32 increases to a constant value after a small number of passes of the tube cleaner which is the flowing pressure drop alternatively an electronic pressure gauge having rapid response can be used in place of gauge 32 and the instantaneous maximum pressure as a tube cleaner passes can be recorded electronically preferably flowing pressure drop in tube 30 a should be in the range between about 5 per cent and about 80 per cent of the total operating pressure drop across the heat exchanger tubes to be cleaned above 80 per cent the cleaner is moving too slowly and has increased risk of stopping in a tube and below 5 per cent the cleaner is not providing sufficient cleaning action other design parameters measured by the test apparatus of fig5 are entry pressures and 34 break away 34 pressures.