Flange valve installation and connection
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For DN20 600LB flanges with a FM concave sealing surface and valves with an RF convex surface, can it be assembled using C-type metal-graphite wound gaskets? If following HGT20615, it is found that the dimensional specifications of RF are the same as those of the MFM convex surface
RF convex valves cannot be used with concave flanges; C-type gaskets can only be used with RF convex surfaces, and not with M/FM concave-convex flanges.
Strictly speaking, it’s not allowed; high pressure can easily cause leaks, and standard manufacturers do not permit this. Avoid causing yourself trouble with repairs and such. It’s better not to use it
I have a similar question; I hope experts can answer it
RF is convex; RF is used in combination with RF, along with C or D type gaskets； M is a convex surface. FM is concave; M is used in combination with FM, along with B-type gaskets. For the DN20, CLASS600 flanges mentioned by the OP, both the raised face and flat face variants have exactly the same dimensions. Therefore, two flanges of this specification can definitely be used together. However, C-type gaskets won’t work here; the simplest solution is to use B-type gaskets instead, as C-type gaskets cannot be installed.
First of all, it can be used. What is said on the upper floor (8th floor) is correct: RF has a convex surface, and RF is used in combination with another RF component, along with C or D type gaskets ； M is a convex surface. FM is concave; M is used in combination with FM, along with B-type gaskets. \"HG20592~20635-2009 Steel Flange Gaskets and Fasteners\", P249/250. The sizes are the same. Type B gaskets must be used, see P389.
Floors 8 and 9 explain it clearly: C-type gaskets of the same diameter simply cannot fit into the grooves of FM concave flanges; one must use a size smaller, namely a B-type gasket.
When the Type C gasket is forced into place, it will hang in the air on the side facing the concave surface of the flange; as a result, the gasket cannot make contact with the flange. However, it can fit tightly against the convex surface of the flange...