Popup valves have a 40gpm flow rate while this basin says 348gpm. Won’t that cause a bottleneck?

Justin, for NDS Part #1215 (Galv Grate), the inlet capacity is 348 gpm. You will also have a flow rate from your outlet coming out of the catch basin which will depend on what size the connection/outlet is. If you have a 4 inch pipe and a #1242/1243 connection, that would be either a 3" or 4" inside opening depending on how it was connected. If it is a 3", that capacity is limited to around 83 gpm, if it's a 4" then you have around 153 gpm. You are correct in that the pop-up emitter allows for a 40 gpm flow rate. It depends on the area and amount of water you have coming into the catch basin in order to determine the pipe size and the number of pop-up emitters that may be required. It is possible that you may need additional pop-ups or increase the size of the pop-up to a 6" to achieve a release rate of 88 gpm. We would be glad to discuss this further with you and ensure that your system meets the design constraints for your application. Please call our Technical Services Team at 1-800-726-1994 if you'd like and select prompt "3".