EP--85016 A Blood abstracted from a donor undergoes a first separation at the membrane on abstraction and a second separation on return without the need for more than one insertion of a needle. The blood with anticoagulant added passes through a bubble detector and first pump to the upstream chamber of the separator. The undiffused portion is drawn off by a second pump into a flexible plastics receptacle. Plasma passing through the membrane is collected in a separate receptacle.Pref. the membrane is made of PET. Transducers controlling the pumps maintain the upstream chamber inlet and outlet pressure below and above respective values during both phases. The process  is supervised by control logic.EPAB- EP--85016 B Blood abstracted from a donor undergoes a first separation at the membrane on abstraction and a second separation on return without the need for more than one insertion of a needle. The blood with anticoagulant added passes through a bubble detector and first pump to the upstream chamber of the separator. The undiffused portion is drawn off by a second pump into a flexible plastics receptacle. Plamsa passing through the membrane is collected in a separate receptacle.Pref. the membrane is made of PET. Transducers controlling the pumps maintain the upstream chamber inlet and outlet pressure below and above respective values during both phases. The process is supervised by control logic.  (25pp Dwg.No.0/2) EP--85016 B Equipment which can be used in particular for plasmapheresis, comprising: a device for withdrawing the blood from a donor, a membrane apparatus separating the blood into a fraction which has passed through the membrane and into a fraction which has not passed through the membrane, a first line connecting the withdrawal device to the inlet of the upstream compartment  of the membrane apparatus, a pump arranged on this line, a pressure sensor for the blood circulating in the line, the said sensor being located between the pumpand the inlet of the upstream compartment, an inflatable tourniquet, means making it possible to inflate or deflate the tourniquet, a second line connecting the outlet of the upstream compartment of the membrane apparatus to a vessel for collecting the fraction of the blood which has not passed through the membrane, a pump arranged on this second line and rotating in the same direction as that of the pump, a pressure sensor arranged on the line  between the said pump and the outlet of the upstream compartment of the membrane apparatus, a vessel for collecting the plasma which has passed through the membrane, this vessel being in communication with the outlet of the downstream compartment of the membrane apparatus, means for measuring the volume of blood withdrawalfrom the donor during the withdrawal stages, at the start of which the tourniquet is inflated on the limb of the donor, means for reversing the direction of rotation of the pumps when the desired amount of blood has been withdrawn during the EP--85016 B Blood abstracted from a donor undergoes a first separation at the membrane on abstraction and a second separation on return without the need for more than one insertion of a needle. The blood with anticoagulant added passes through a bubble detector and first pump to the upstream chamber of the separator. The undiffused portion is drawn off by a second pump into a flexible plastics receptacle. Plasma passing through the membrane is collected in a separate receptacle.Pref. the membrane is made of PET. Transducers controlling the pumps maintain the upstream chamber inlet and outlet pressure below and above respective values during both phases. The process is supervised by control logic. (Dwg.0/2) USAB- US4687580 A Appts. for withdrawal, fractionation and return of liq, partic. blood, comprises a cell (2) with a membrane separator/filter, and downstream (4) and upstream (3) compartments recieving respectively plasma and cellular fractions. A collecting vessel (17) is connected to the outlet end (15) of the upstream compartment, and there is a unit for determining the vol. of liq. withdrawn from the donor.Liq. from the vessel can be back-filtered and returned to the donor, and an outlet end of the downstream compartment is connected to a second collecting vessel (20). The membrane separator is pref. of a copolymer of acrylonitrile, methyl methacrylate and sodium methallyl sulphonate, and is reinforced by a web of single-filament polyester fabric with mesh opening of 75 microns