When people ask me, how tight our valve seats are, I usually get an increased heart rate and I most would like to say “Oh yes, they are very tight”.
But fun aside ….
Please note that I’m not talking about external tightness (stem sealing and body sealing), as there are already several accepted standards like ISO 15848-1, API 622, API 624, etc. which describe the evaluating of the valve design with respect to fugitive emissions. Those standards where driven by the legal environmental requirements and do not consider the internal tightness of the valve.
When talking about valves seat tightness, we have to differ between just a maximum leak rate of a production test and a seat performance test.