Air trap for liquid circulation line

摘要

An air trap comprises an air reservoir (2) to be arranged in a liquid circulation line, and a hydrophilic filter (3) which permits a liquid to permeate but does not permit gas bubbles to permeate and which is arranged in the air reservoir to separate an upstream side of the liquid circulation line from the downstream side of the liquid circulation line. The filter (3) has pores which meet conditions defined by equation (1): P<4h/d, where P represents a gas pressure, d is a diameter of the pores of the filter, and h is a surface tension of the liquid.