Apparatus for sealing a fluid carrying device

Abstract

A novel sealing arrangement for fluid carrying devices and particularly for plug type valves, such as retractable double block and bleed plug valves. The sealing arrangement of the present invention adds secondary and tertiary seals to the conventional packing gland primary seal along the outer surface of the trunnion of such plug type valves. A unique isolated chamber is formed between the secondary and tertiary seals and because of the elastomeric nature of the secondary and tertiary seals, this isolated chamber is bubble tight and thus resists the gradual accumulation of minute leakage, which might otherwise cause false alarms in prior art leakage sensing equipment. Furthermore, the bubble tight feature of a chamber between isolated elastomeric seals, enables purging this chamber for making accurate observations and measurements of true leakage that might otherwise be an environmental hazard. Still more significantly, the bubble tight aspect of the chamber formed between the secondary and tertiary seals of the present invention, provides a means for providing an over-pressure in the chamber by using an inert fluid, such as nitrogen gas, which significantly increases the sealing efficacy of the present invention, as well as providing both local and remote sensing of leakage prevention status, by simply monitoring the over-pressure condition within the chamber. The chamber may also be evacuated to provide enhanced leak detection capability.