A flow rate of unconnected first and second fluid flows is matched or not matched,
such as, but not limited to, matching or not matching the flow rate of the replacement
water stream with the waste water stream in kidney dialysis. First and second flow
paths are interconnected so substantially the same flow from a first positive displacement
pump in the first path encounters a flow-rate transducer in the second path. A
first set of transducer readings are taken for various values of the controllable
first pump speed of the first pump. The first and second flow paths are disconnected,
and a second set of transducer readings are taken for various values of the controllable
second pump speed of the second pump. The flow rates are substantially matched
or not matching by controlling one of the first and second pump speeds using the
other of the pump speeds and the first and second sets of readings.
