Abstract: A chamber assembly for infusion and transfusion apparatus comprising a drip chamber having a pump chamber and an observation chamber connected together and connecting a tubing adaptor to a piercing device assembly. The cross-sectional area of the observation chamber is smaller than the cross-sectional area of the pump chamber and the observation chamber is short relative to the pump chamber. Changes in pressure in the pump chamber are transmitted through the observation chamber faster than such pressure changes are transmitted through the pump chamber because of the difference in length of the two chambers. The difference in cross-sectional areas of the two chambers causes the pressure wave in the observation chamber to be more uniform than that wave is in the pump chamber. The assembly including the observation and pump chambers accurately controls the flow rate of fluid into the tubing, so that only a single drop is present in the observation chamber at any one time.