Securing and centering devices for a split mechanical seal
The mechanical seal includes a pair of resilient biasing elements disposed about each seal ring, and the resilient biasing element is preferably an elastomeric member.
The axial biasing element is associated with at least one seal ring for generating and applying, in cooperation with the elastomeric member, a second radially inward force; the second force operating to bias the segment sealing faces together when the mechanical seal is exposed to a selected pressure condition. The axial biasing element is an abutment, integrally formed with the segments of both seal rings, that has a radially outwardly slanted outer surface. The abutment transforms the axial force into an axial force component and a second radially inward force component.
This second radially inward component also operates to bias the sealing faces of the seal ring segments into sealing contact with each other. The seal further includes integrally formed screw housings that have formed therethrough a fastener-receiving aperture. The aperture has a tapped smaller-diameter portion and an untapped larger diameter portion. The aperture mounts a screw that has a screw-head and a shaft. The shaft has a tapped larger-diameter distal end and a smaller-diameter proximal end.
Split mechanical seals with resiliently mounted faces are employed in a wide variety of mechanical apparatuses to provide a pressure-tight and fluid-tight seal. The mechanical seal is usually positioned about a rotating shaft that is mounted in and protruding from a stationary housing. The seal is usually bolted to the housing at the shaft exit, thus preventing the loss of pressurized process fluid from the housing.
Conventional split mechanical seals include face type mechanical seals, which include a pair of sealing rings that are concentrically disposed about the shaft, and axially spaced from each other. The sealing rings each have sealing faces that are biased into sealing contact with each other. Usually, one seal ring remains stationary, while the other ring contacts the shaft and rotates therewith. The mechanical seal prevents leakage of the pressurized process fluid to the external environment by biasing the seal ring sealing faces in sealing contact with each other. The rotary seal ring is usually mounted in a holder assembly which is disposed in a chamber formed by a gland assembly. The holder assembly has a pair of holder halves, each having a pair of sealing faces, that are secured together by a number of screws. Likewise, the gland assembly has a pair of gland halves, each having a pair of sealing faces, that are also secured together by a number of screws. The sealing rings are often divided into segments, each segment having a pair of sealing faces, thereby resulting in each ring being a split ring that can be mounted about the shaft without the necessity of freeing one end of the shaft ends.
Each holder and gland half has formed on one of the sealing faces a gasket groove for mounting a sealing gasket. When the gasket is mounted within the groove and the halves are secured together by the screws, the gasket is placed in intimate facing contact with the opposite sealing face of the holder or gland half. This facing contact forms a pressure-tight and a fluid-tight seal between the respective gland and holder halves.
The gland assembly is usually centered on the stationary housing prior to securing thereto by centering the shaft and holder assembly disposed within the chamber formed by the gland assembly, thereby determining the proper mounting position of the gland assembly. Conventional methods for centering the gland assembly include using a number of plastic elongated tabs mounted on the exterior seal housing at an outboard end of the seal. The plastic tabs protrude evenly into the gland chamber, centering the shaft and holder assembly.
Another drawback of conventional split seals is that the screws which secure the gland and holder segments together are usually mounted in predetermined tapholes, which typically necessitate rotating the shaft after securing one screw, to affix the other screws. Additionally, during disassembly of the mechanical seal, the screws can become disengaged from either segment of the gland and holder, thereby increasing the likelihood that the screws can become detached and damage other components of the housing, or lost.
Still another drawback of the conventional seals is that the conventional centering mechanisms center off the shaft at the outboard end of the seal. In applications where there is a minimal distance between the seal outboard end and an axial obstruction it is difficult to insert the centering mechanism. Consequently, it is difficult to center the gland assembly relative to the shaft. Additionally, the plastic tabs can become disengaged from the seal, increasing the likelihood that the tabs can become lost. Further conventional seals employing integrally formed centering mechanisms add distance to the overall length of the seal, which can preclude the use of the seal.
As the above described and other prior art sealing systems have proven less than optimal, an object of this invention is to provide an improved mechanical seal that provides a fluid-tight seal under a variety of operating pressure conditions.
Another object of the invention is to provide a single split mechanical seal that can function under different operating pressures, thereby eliminating the need for employing different seals.
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