Haemofiltration with filtrate flow control by adjustable venting

DETAILED DESCRIPTION OF A PREFERRED EXAMPLE EMBODIMENT AND OF THE BEST MODE OF THE INVENTION A double tube pump 1 is provided for simultaneously conveying blood and filtrate.
The upper part 1a of the pump conveys the blood of the patient which flows to the pump through the tube 2, to the filter 3 where it flows along the surface of the filter membrane 4 and then passes through the line 5 into the air trap 6.
The purpose of the air trap is to separate out and protect the patient from any air which has penetrated into the system.
From the air trap, the blood flows through the tube 7 back to the patient.
In order to replace the lost volume which occurs by the removal of the filtrate, a sterile substitute solution is added to the blood, for example by means of the tube pump 8, which conveys the substitute solution into the air trap 6 where it mixes with the blood.
In order to produce a reduced pressure and to convey the filtrate away, the lower part 1b of the double tube pump 1 is connected to the filtrate side of the filter 3 by way of the tube 9.
The filtrate which is carried away from the filter passes through the tube 10 for example into a collecting container not shown.
In the embodiment illustrated, an adjustable pressure holding valve 11 is provided to keep a preselected pressure on the filtrate side at a constant value.
In its housing, the pressure holding valve 11 includes a diaphragm 12 which is stiffened in its central portion by means of a plate and which actuates the tapered valve member 14 by way of a pin 13.
In the rest condition the tapered valve member is pressed against its seat in the housing by the setting screw member 15 by way of the spring 16, so as to prevent air from passing into the chamber on the underside of the diaphragm, by way of the inlet pipe connection 17.
It is only when the reduced pressure which is produced by the suction action of the pump 1b has reached a given value that the force thereby exerted on the diaphragm 12 can overcome the force of the spring 16