The proven better stem seal
Written on July 25, 2018 | Back to the overview
Graphite stem seals for valves combined with emission directives are a recurrent topic. First of all it is for the valve not sufficient to specify just TÜV TA Luft or ISO 15848. Various allowable emission values in different norms. We will elaborate on this detail in future posts.
Primarily, the method of assembly in the valve is crucial. Graphite seals are best compressed (deformed) during the final assembly. More to this, each single ring should be compressed individually. Should multiple seal rings be pressurized simultaneously, then only the upper seal ring will be compressed. This is where the initial force is being exercised. Extra force on the gland ring, perhaps combined with cup springs, could result in yet another issue, that is an unacceptable increased torque. Multiple graphite seal rings will only seal individually when all rings are compressed in the very same way.
Most stem seal sets are being delivered as a “ready to assemble” set. Usually there is no possibility to compress the rings individually. If one knows this is a better solution, then it is probably still not clear on how to perform such an assembly. For critical applications this is off course of the highest interest.
The picture below shows a cutaway assembly of a stem seal where the separate rings have been compressed.