Blood plasma separator using membranes - with automatic control of pressures

A membrane separator for blood plasma cooperates with a trans-membrane pressure controller responsive to blood flow conditions and having three pressure sensors whose inputs are connected to the separator inputs and outputs and to the plasma chamber, and whose outputs are connected to an addition member. The output from this member and the signal from a regulating valve setter are fed to an inertie member whose output is coupled to the rotary speed control circuit of a pump which cooperates with the plasma chamber to produce the required pressure differential. The addn. member output is also coupled with a comparator which in addn. is connected to a further regulating value setter. Output from the comparator is coupled with the control circuit input. The controller ensures effective utilisation of the membrane separator over the entire range of plasma components.