The present invention relates to a compression chamber unit (1) of an air pump, comprising a cylindrical body part (3) provided with at least one outlet nozzle (4), a number of connecting flanges (6) and a number of connecting bosses (7), wherein the cylindrical body part (3) is an extruded cylinder and a cap (2) is formed with outlet nozzle (4), connecting flanges (6) and connecting bosses (7), where the cap (2) is adapted to engage with a first end part (10) of the cylindrical body part (3). The present invention further more relates to a method for forming a compression chamber unit (1) which method comprises the following steps: the cylindrical body part (3) is extruded, and the cap (2) is moulded onto the cylindrical body part (3).