Ring 4 is an optional Flow Ring for the Series B Duct Blaster® fan used to measure very low air flows. Ring 4 has a flow range of approximately 2.4 to 25.0 cfm (1.1 l/s, 4.0 m3/h). To install Ring 4, place the flat side of the ring against the inlet of the fan so the outer edges of the ring roughly line up with the outer edge of the inlet flange on the fan. Secure the outer edge of the ring and the fan flange together by pushing the black connecting trim over both edges all the way around the fan.
When using Ring 4, always use the pressure tap mounted on Ring 4 to connect the fan to the Channel B Input tap on your gauge (rather than the pressure tap on the fan housing).