Abstract: In a multiblower system for cooling electronic components, each blower has a backflow preventor. The backflow preventor has two pieces of flexible material and a screen attached to the intake side of the blower assembly. Each of the pieces of flexible material is scored through to form a petaled opening through which air may pass. The scores on one of the pieces of flexible material are out of alignment with the scores on the other piece when assembled together in the blower assembly. When the blower is running, the petals in the pieces of flexible material open to allow air to pass through the blower assembly. When the blower is stopped, the petals are closed against the screen due to the pressure differential between the inside of the enclosure and the outside of the enclosure caused by the effect of the draw of the other blowers in the system.