What size flange gasket or bolt kit do you use with a Class 125 cast iron reducing flange?

Unlike standard flanges (non-reducing), which are easy to match up by the size code in the part number, reducing flanges are not as straightforward to match with a gasket.

For example, for a non-reducing flange like the part number BLCF-40, a 4" x 9" Class 125 companion flange, a flange gasket can be selected by the -40 size code and uses either the 4” x 9” companion flange gasket (part number: BLCFG-40) or the 4” x 9” companion flange bolt and gasket kit ( part number: BLCFGK-40).

It is not as straight forward to choose gaskets for the BLCFR reducing flanges, however once you understand how to do the match up, it is quite easy as well. You simply match the gasket O.D. (outside diameter) to the reducing flange O.D. Alternatively, you can match the bolt circle (BC) diameters and the number of bolt holes in the gasket to the bolt holes in the flange.

For example, when selecting a gasket or bolt kit for the part number BLCFR-2090, a reducing flange with a 2” FPT thread and a 9” O.D. as indicated by the last two digits of the part number, it matches the O.D. of a 4” CI flange or 4” flange gasket. It would use either the 4” x 9” companion flange gasket (part number: BLCFG-40) or the 4” x 9” companion flange bolt and gasket kit (part number: BLCFGK-40).

Note: The same 9” O.D. gasket is used with all variations of reducing flanges with a 9” diameter regardless of the FPT pipe connection 1-1/2”, 2”, 2-1/2” or 3”. For example, all four of the following reducing flanges would use a 9” O.D. gasket:

• BLCFR-1590       1-1/2" x 9" REDUCING C.I. COMPANION FLANGE
• BLCFR-2090       2" x 9" REDUCING C.I. COMPANION FLANGE
• BLCFR-2590       2-1/2" x 9" REDUCING C.I. COMPANION FLANGE
• BLCFR-3090       3" x 9" REDUCING C.I. COMPANION FLANGE 

Additional Resources:

https://support.boshart.com/what-is-the-working-pressure-and-temperature-ratings-for-cast-iron-companion-flanges