GB/T 17774-2025 Active

This document specifies the dimensions of circular and rectangular flanges for general-purpose ventilators, as well as the naming of ventilator sizes. This document does not apply to cross-flow ventilators or ventilator equipment for household or similar purposes.
For circular flanges, this document presents three different flange series: the first is used for light-duty casing thickness, and the second and third are for medium-duty and heavy-duty ventilators, respectively, which are typically used on sea vessels or in heavy industry. To avoid unduly restricting the design of ventilators,
this document only specifies the pitch circle diameter, number of holes, and hole diameter. The flange thickness and the inner and outer diameters of the flange can be freely selected within the scope of good engineering practice.