via tube 54 into first chamber 22 the liquid then passes through tube 28 into second chamber 24 near its bottom second chamber 24 is rigidly mounted within third chamber 26 and fluid leaving the second chamber through orifice 74a falls to the bottom of third chamber 26 having conventional drip chamber 126 tube 32 leads the fluid from drip chamber 126 to needle 34 located within arm 36 of the patient second chamber 24 is open at its top and since third chamber 26 is vented to the atmosphere second chamber 24 is subjected to atmospheric pressure the fluid inside first chamber 22 is likewise subjected to atmospheric pressure through its vent both vents contain hydrophobic filters to prevent liquid from passing through the vents and to prevent air borne contaminants from entering through the vents fig2 shows third chamber 26 mounted on first chamber 22 by means of retaining clip 40 chamber 26 may be moved vertically within clip 40 to vary the desired flow rate in fig3 flow rate indicia 38 are located on the wall of third chamber 26 indicia 38 are typically in units of milliliters per hour and are located at heights corresponding to the indicated flows through the one or more thin plate orifices used herein first chamber 22 is equipped with fluid inlet 44 fluid outlet 46 and vent 42 third chamber 26 has liquid outlet 48 vent 50 and liquid inlet 70 fig4 is an overhead view showing float 56 described below located within first chamber 22 fig5 is a partial sectional view of the device fluid in tube 54 from the supply enters first chamber 22 through inlet 44 and flows out of the chamber through liquid outlet 46 through tube 28 and into third chamber 26.