Serial dilution of liquid samples

A valve device for use in apparatus for serial dilution of liquid samples, comprising:

• (a) a valve housing having a sample inlet connectable to a source of liquid sample, a diluent inlet connectable to a source of liquid diluent, a third inlet and a first outlet, both being connectable to a first sample recipient, a second outlet connectable to a second sample recipient, pairs of first and second pump connection ports connectable to pump means for conveying liquid sample and diluent within said valve device, said pair of second pump connection ports forming said diluent inlet;
• (b) a valve body mounted in said housing for movement therein and having a passageway of predetermined volume opening into opposite surfaces of said valve body, said passageway in a first valve body position connecting said sample inlet with one of said pair of first pump connection ports, in a second valve body position connecting one of said pair of second pump connection ports with said first outlet, in a third valve body position connecting said third inlet with the other of said pair of first pump connection ports, and in a fourth valve body position connecting the other of said pair of second pump connection ports with the second outlet;
• and
• (c) a valve body actuator for selectively moving said valve body relative to said housing into one of said aforementioned valve body positions;
• (d) said housing having recesses which are open towards said opposite valve body surfaces and in register with the path along which the ends of said passageway move during movement of said valve body between said second and third valve body positions, said recesses being connectable with a wash liquid conveying system and in at least one valve body position between said second and third valve body positions communicating simeultaneously with said passageway.