Abstract

A metering pump for determining the quantity of a fluid flowing at an externally-determined rate, e.g., for measuring the volume of a gas, such as air, flowing through a flow-restrictive element, such as a filter, has a variable-volume chamber (e.g., a bellows) including a movable wall which is urged in one direction (e.g., toward expansion if an inspirator) by resilient means and is driven in the opposite direction by mechanical means, such as a reciprocable lever arm which engages the wall but leaves it during a part of its movement, said means having electrical contacts in a circuit which powers an electrical motor driving the mechanical means, the contacts being open when the mechanical means leaves the wall, permitting the wall to move at a rate determined by the fluid flow rate. Counting means, such as a counter, are coupled to the electric motor or circuit for counting the movements of the wall.