A ball valve having an upstream seat (92) with the seat actuated by outside pressure (14, 16). Retraction members (100, 102) continuously urge seat (92) to a retracted position out of sealing engagement with the ball. A sealing member (104) fits loosely within an annular recess in the seat (92).

In combination with a gate valve comprising a valve body having an internal cavity extending between an inlet port and an outlet port, a bonnet mounted to the valve body and having an internal passageway in communication with the cavity, a valve stem rotationally supported in the passageway, a handle connected to one end of the valve stem and a gate threadedly connected to the other end of the valve stem, the improvement comprising a first packing for sealing between the bonnet and the valve stem to prevent pressure within the cavity from escaping through the passageway, a second packing for sealing between the bonnet and the valve stem to prevent pressure within the cavity from escaping through the passageway, the second packing being located between the first packing and the cavity, a bypass port extending between a first portion of the passageway below the second packing and a second portion of the passageway above the second packing, and a bypass valve for selectively closing the bypass port such that the first packing contains the pressure when the bypass port is open and the second packing contains the pressure when the bypass port is closed.

An exhaust gas obturator comprises a tubular housing (11a) having a butterfly valve (14a,15) journalled in the wall thereof. The butterfly valve spindle (14a) passes through a chamber (24,25) on one side of the housing and carries a sealing ring (26) thereon and located in the chamber (24,25). The sealing ring (26) is a close sliding fit on the butterfly valve spindle (14a) when the obturator is closed, exhaust gas pressure on the upstream side enters the chamber (24,25) and urges the seal (26) against a cover plate (23a) thereby to prevent the escape of exhaust gas to atmosphere. The chamber (24,25) is preferably vented to the downstream side. The seal may alternatively be biased by resilient means (not shown).

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.

Disclosed is a valve assembly having a slidable valve stem that passes through a bushing enclosed in a bonnet. At least one circumferential stem seal seals the valve stem to the bushing. At least one passageway is provided through the bushing for injecting a fluid between the valve stem and the bushing to wash out deposits. A second optional passageway is also provided for injecting a lubricant around the valve stem.