Abstract: A tube in a pumped fluid system can become obstructed by a clog. The clog is automatically cleared in response to an obstruction signal by modifying the pumping cycle which is normally used to pump the fluid. In particular, the pumping cycle is stopped after a compression stroke to apply sustained high pressure in the clogged tube, using the same fluid and the same pump, to expel the clog from the tube. The obstruction signal is derived by measuring pressure during a portion of the pumping cycle when elevated pressure due to viscosity effects have subsided. Therefore, if the pressure remains elevated, a determination of an obstructed state can reliably be made which may be caused by a clog.