Seal for a joint or juncture – Process of dynamic sealing – Contained or compressed by gland member in packing box
Utility Patent
1998-08-26
2001-01-02
Dayoan, B. (Department: 3626)
Seal for a joint or juncture
Process of dynamic sealing
Contained or compressed by gland member in packing box
C277S511000, C277S530000, C411S165000, C411S539000, C411S535000, C411S546000
Utility Patent
active
06168161
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of Invention
The present invention relates generally to rotary valves and more particularly to a rotary valve with an improved shaft seal. Rotary valves such as plug and butterfly valves have been in common use in the water and wastewater industries for over 75 years. Rotary valves have a rotating element or shaft that penetrates the body of the valve. Various operating mechanisms such as hand levers, gear actuators, or power actuators are connected to the rotating shaft to drive the valve open, closed, or hold it in an intermediate position. A shaft seal is required to prevent fluid media from escaping the pressure boundary of the valve or pipeline via the opening in the body where the shaft penetrates. There are many types of seals such as O-rings, U-cups, rope packings, or V-type packings to name a few. Historically, valves and pumps have been equipped with rope packing which requires constant pressure from a gland ring and regular adjustment to prevent leakage.
One embodiment of the current invention relates specifically to the application of V-type packing used in rotary valves. V-type packing is relatively new (i.e. 30 years) in some rotary valve applications. One characteristic of V-type packing is that it is wear compensating, which means that as it is worn due to rubbing and friction with the rotating shaft, it flexes outward further to effect a seal. Another characteristic of V-type packing is that it is self-energizing. The V-shaped rings are pushed outward by internal pressure and provide a tight seal due to the force against the shaft and the outside wall of the bearing bore. Hence, V-type packing differs from the historical rope packing in that it does not require regular adjustment.
Historically though, users of valves have been trained to adjust packing regularly because of the once common use of rope packing. While packing adjustment is needed on rope type packing, over adjustment of V-type packing can have damaging consequences. If V-type packing is over adjusted, the V-rings will wear prematurely and excess shaft friction will develop. The current invention is designed to prevent over adjustment of the packing gland by the user who is not aware of the correct application of V-type, or other, packing. Further, the invention allows simple adjustment of the follower several years down the road should excessive wear cause leakage.
DESCRIPTION OF RELATED ART
Rotary valves such as plug and butterfly valves may be used in any application which involves the flow of fluids (including gasses and particulates) through a closed system, especially a closed system under pressure.
Some traditional rotary valve seals are shown in U.S. Pat. Nos. 4,863,144 and 4,697,786. The '144 patent shows a rigid packing gland, with no means of adjustment, as part of an eccentric plug valve. The '786 patent shows an eccentric plug valve with a more traditional packing follower secured to the valve cap by fasteners which may be adjusted over time.
As shown in the '786 patent, a typical rotary valve has a valve body defining a valve chamber. The valve body includes a valve cover through which a shaft extends to a valve plug within the valve chamber. The shaft is guided on journal bearings and a seal is provided by packing material in the annular space between the shaft and valve body. A packing follower is provided to hold the packing material in place and is fastened to the body by fasteners. The current art allows for the packing follower to be fastened down against the packing until the user judges that sufficient force is exerted on the packing. However, threaded fasteners can exert extreme forces on the packing causing premature wear and increased friction on the shaft. Further, wear over time may require that the fasteners be adjusted after a certain period of use to compensate for lost packing. In either event, the user is required to judge the degree of tightening necessary and many users are unlikely to make this judgment in accord with the optimum performance of the particular packing material.
U.S. Pat. No. 5,478,048 describes a number of the possible shapes of packing materials for use in a rotary shaft seal. Specifically, the '048 patent discusses graphite V-type packing and various ring adapters for placement at the top or bottom of the ring stack, as well as packing with cross-sections that are truncated-wedge shapes or arcuate in shape. The '048 does not contemplate the differences in required packing maintenance for the new packing configurations and materials.
Another problem of prior art followers and fasteners is that they are subject to loosening as a result of vibration in certain applications. Vibration is a common occurrence because of flow turbulence and valve operation. Loosening of the fasteners and relaxation of the pressure from the packing follower to the packing can easily result in losing the seal and may require further tightening maintenance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved rotary shaft seal by placing one or more slotted spacers between the packing follower and the valve body. The slotted spacers allow the fasteners to be tightened to the full strength of the fastener while the actual pressure on the packing material is controlled by the factory prescribed spacers. The length of the follower portion of the packing follower, the height of the packing, the depth of the cover bore, and the thickness and quantity of the spacers control the initial compression of the packing.
Another object of the present invention is to provide a plurality of spacers in small thickness increments so that the removal or insertion of one spacer will provide a small increment of difference in compression on the packing. Depending on the shaft size, the quantity of the spacers can be set at the factory to provide a preset amount of adjustment over the life of the valve. All the user is required to do is remove a spacer at intervals predetermined by the factory and re-tighten the fasteners.
Another object of the present invention is to provide a spacer that is easy to use and manufacture. The spacer includes an inside slot which is marginally larger than the outside diameter of the fastener so that the spacer can be pulled out from under the packing follower without removing the fastener. The spacer provides a tab which protrudes beyond the packing follower so that the spacer can be extracted from under the packing gland with a simple tool such as pliers. The spacer is further designed to contain opposite symmetry along a straight line in jig saw like precision so that the parts can be economically fabricated from strip metal with minimal waste.
Another object of the present invention is to provide a locking mechanism for the spacers to prevent loosening of the fasteners in applications subject to vibration. Locking tabs within the spacer slot prevent rotation and decrease the likelihood of the fasteners backing out of the valve body.
One embodiment of the invention is a rotary shaft seal assembly with a shaft extending from a chamber through a body. Packing material is disposed in the annular space between the shaft and the body to provide a seal. A follower member is connected to the body by threaded fasteners and applies pressure to the packing material to maintain the seal. The amount of pressure exerted is adjusted by rotating the threaded fastener. At least one spacer is positioned between the follower member and the body to determine the maximum pressure which the follower member can exert on the packing when the threaded fastener is fully tightened.
The assembly can also include a valve body and a plug member at the end of the shaft within the chamber so that the assembly acts as a plug valve and the shaft can be rotated to vary the fluid flow through the chamber.
Some specific examples of packing material may be a V-type set including a top adapter, a bottom adapter, and at least one v-shaped ring or one or more rings of rectangular or V-shaped packing.
A plural
Dayoan B.
Pickard Alison K.
Sonnenschein Nath & Rosenthal
Val-Matic Valve & Manufacturing Corp.
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