Apparatus for aspirating and dispensing liquid samples in an analytical instrument, e.g., a hematology instrument, includes a liquid-sampling valve that, while operating to segment and position for dispensing one or more precise volumes of a liquid sample that has been aspirated into the valve by a pump, simultaneously enables the apparatus to be operated in an aspirate/dispense (suck-and-spit) mode in which a liquid sample can be selectively driven through the valve in opposite directions by a pump, e.g., a syringe pump.