Medical fluid flow rate controlling device

An apparatus for controlling the flow rate of an intravenously administered medical liquid to a patient, from a supply of medical liquid, said apparatus comprising:

• (a) a first chamber means for containing a portion of said liquid and a gas, having a liquid inlet, a liquid outlet, and a gas phase connection, into the gas containing part of the first chamber means said liquid inlet designed to receive liquid from the supply of medical fluid;
• (b) a second chamber for containing a portion of said liquid and a gas, having a liquid inlet, a liquid outlet, and a gas phase connection, into the gas containing part of the second chamber, said first chamber means having means for moving said first chamber means vertically with respect to the second chamber;
• (c) gas phase pressure equalization means for fluidly connecting the gas phase connections of the first and second chambers so as to equalize the gas phase pressures in the first and second chambers;
• (d) first liquid connecting means fluidly connecting the liquid contact of the first chamber to the liquid inlet of the second chamber, said first liquid connecting means having at least one cannula in the fluid flow path through which a known quantity of liquid flows when a given differential pressure exists across it;
• (e) a third chamber having a liquid outlet from which liquid passes to the patient and a liquid inlet for receiving liquid from the second chamber means;
• and
• (f) second liquid connecting means fluidly connecting the liquid outlet of the second chamber to the liquid inlet of the third chamber, said second liquid connecting means having a membrane valve in the flow path which when wet passes liquid but not gas under normal operating conditions.

An apparatus for controlling the flow rate of an intravenously administered medical liquid to a patient from a supply of medical liquid, said apparatus comprising:

• (a) a first chamber means for containing a portion of said liquid and a gas, having a liquid inlet, a liquid outlet, and a gas phase connection, said liquid inlet designed to receive liquid from the supply of medical fluid;
• (b) a housing having a second chamber means for containing a portion of said liquid and a gas, with a liquid inlet, a liquid outlet, and a gas phase connection, said first chamber means having means for moving said first chamber means vertically with respect to the second chamber;
• (c) gas phase pressure equalization means for fluidly connecting the gas phase connections of the first and second chambers so as to equalize the gas phase pressures in those chambers;
• (d) first liquid connecting means fluidly connecting the liquid outlet of the first chamber to the liquid inlet of the second chamber, said first liquid connecting means having at least one cannula in the fluid flow path through which a known quantity of fluid flows when a given differential pressure exists across it, the cannula providing the only significant pressure drop in the liquid flow path comprising the liquid outlet of the first chamber, the first liquid connecting means, and the liquid inlet to the second chamber;
• (e) a third chamber means in the housing having a liquid ouetlet from which liquid passes to the patient and a liquid inlet for receiving liquid from the second chamber;
• and
• (f) a membrane valve between the liquid outlet of the second chamber and the liquid inlet of the third chamber, the membrane valve capable of passing liquid when wet but not gas under normal operating conditions.