I am a dialysis tech.I have a one question about cobe3 machine.Pls explain me,why cobe C3 has additional chambers in the single needle dialysis tubing set?

I am not familiar with the Cobe but if they are what I am thinking of, they are called expansion chambers.

When the blood pump is running pulling blood from the patient, a line clamp is closed so that the pump won't pull out the same blood it just returned to the patient. The chambers keep the pressure from building up too high and rupturing the dialyzer membranes. After a set amount of time, the blood pump stops, the line clamp opens and the blood flows back to the patient by the pressure stored in the expansion chambers (some machines use a 2nd blood pump to return the blood).