Blood pumping system

A blood pumping system comprising a pair of pumps each having a pumping chamber defined by a flexible enclosure expandable to a full condition and compressible to an empty condition;

• means defining blood inlets to both said chambers;
• means defining blood outlets from both said chambers;
• inlet valves for controlling flow through said inlets;
• outlet valves for controlling flow through said outlets;
• first actuators for said inlet valves;
• second actuators for said outlet valves;
• third actuators movable in one direction for compressing said enclosures to said empty condition and movable in the reverse direction to permit said enclosures to expand to full condition;
• electric controllers for said first, second and third actuators;
• means responsive to movement of said third actuator to its extreme positions to provide position signals;
• means for regulating the rate of operation of said controllers including a variable oscillator supplying a sequence of timed signals to repeatedly and sequentially open said inlet valves, close said outlet valves and permit said pumping chamber to expand to full condition then close said inlet valves, open said outlet valves and move said third actuators in said one direction;
• a signal comparator;
• means for supplying said oscillator signals to said comparator;
• means for supplying said position signal to said comparator;
• and
• means controlled by said comparator in response to differences in the time of receipt of said position signals and said oscillator signals for varying the frequency of said oscillator.