Axial type fans cause gas to flow through in an axial direction which is parallel to the shaft where the blades rotate, making the flow axial at exit and entry. Axial fans are designed to create a pressure difference and force which produces a flow through the fan. line break Timer Controlled Timer controlled Extractor fans with a built-in timer control means that the fan will operate with the bathroom light switch and then overrun for a set amount of time to continue removing moisture from the air. This is great for steamy bathrooms, allowing you to turn the light off but continue with extraction for a short time.