Valves, such as butterfly valves, having valve closing members rotatably mounted within a housing to effect opening and closing of the valve, are in widespread use throughout a wide spectrum of industrial and commercial activities including the chemical and petroleum industries, the papermaking industry, municipal and industrial water service and in commercial and residential fire suppression systems to cite a few examples.
Butterfly valves and the like often have a flexible, resilient seal mounted within the valve housing and surrounding the closure member. The seal provides a compliant, deformable interface between the valve closing member and the valve housing which effects a fluid tight seal when the closure member is rotated from the open to the closed position to compressively engage the seal.
Butterfly valves may be used to control fluids flowing under high pressure and temperature, for example, in excess of 20 atmospheres and above 200° F. Such conditions are very hard on the valve and will cause degradation unless steps are taken to protect the valve components. Especially troubling are conditions, such as large fluid temperature swings, which cause significant expansion and contraction of the valve seal. Valve seals may have a coefficient of expansion greater than the material comprising the valve housing. Since the seals are usually comprised of incompressible materials and are often captured within a groove or cavity in the valve housing, the seal must be designed so that it can expand within the cavity under high temperature conditions and yet still be deformable so as to accommodate the additional deformations caused by the compressive engagement of the valve closing member necessary to form a fluid tight seal.
A further problem associated with seal design concerns fluid which becomes trapped within the cavity between the seal and the valve housing. This usually occurs when the valve operates under high pressure and the seal deforms upon opening due to transient fluid dynamic forces occasioned by high flow rates within the partially open valve. The deformation of the seal allows the high pressure fluid to seep into the cavity between the seal and the valve housing. This presents problems when the valve closes, as the fluid in the cavity is placed under tremendous pressure as the seal is compressed radially outwardly within the cavity against the housing by the closure member. Without the ability to escape from the cavity, the pressurized fluid deforms the seal, forcing a portion of it radially inwardly from the cavity and into the fluid flow path where it may be pinched by the closure member or dragged by the high speed fluid flow and unseated from the cavity.
Clearly, the design of seals for butterfly valves and the like must take the aforementioned difficulties into consideration if such seals are to operate effectively and with a reasonable life under harsh conditions of high pressure and temperature.