1. Field of the Invention (Technical Field)
The present invention relates to valves, particularly to stem valves, an specifically to a valve having a sealed stem to significantly reduce or minimize liquid/gas/vapor leakage.
2. Background Art
Conventional stem valves feature a movable stem. A valve stem may have a rotating and/or sliding movement within its sleeve throughout the valve's distance of travel; the sealing of the stem must be sufficient to contend with that movement while also maintaining fluid tightness against the pressure of the fluid in the valve.
A widely used type of stem sealing (see FIG. 1, prior art) is accomplished by compressing packing 10 in a gland or stuffing box 12, which may be integral to the valve body 14, or bolted to the valve body. “Packing” is any of a wide variety of compressible materials known in the art (in early valves oakum was used) for providing a seal through which the valve stem 16 can slide. In FIG. 1, the packing 10 is disposed in any number of layers or rings (three in FIG. 1), to improve sealing under pressure while yet permitting the stem 16 to rotate or oscillate. In the stuffing box 12, which also may be called a packing chamber, compressive force is applied to the soft compression packing 10 surrounding a portion of the length of the valve stem 16. The resulting radial pressure of the packing 10 onto the stem 16 provides the desired seal, providing the radial pressure on the stem exceeds the operating pressure of the fluid in the wetted portion 20 of the valve.
Continued reference is made to FIG. 1. Compression is applied to the packing by means of packing bolts 18, which are attached at one end to the body 14 or stuffing box 12 and attached at the opposite end to a packing gland flange 24. The flange 24 may have an integral pusher 26 or other projection bearing on the packing 10, which compresses the packing when the packing bolts 18 are tightened, and therefore, provides the radial pressure for sealing the stem 16. A bushing 21 may be provided at the distal end (as shown in FIG. 1) or both ends of the packing 10 to improve packing security and performance.
It is common to attach a form of spring 28 between the nut 29 and the packing bolt 18 to tighten the flange 24 and thereby holding a constant compression force to the packing 10. The springs 28 are often “Belleville” washers, which are essentially formed as one or more (preferably a series, but one only shown in FIG. 1) elastically compressible dish-shaped washers. Belleville washers have a higher compression rating than an ordinary coil spring, and provide a “live-loaded” packing, which can automatically compensate for changes that may take place in the packing during operation of the valve. Such a “live-loaded” packing system provides a useful amount of self-adjustment to maintain sufficient pressure through the packing 10 onto the valve stem 16.
Additional reference is made to FIG. 2, which depicts a more involved variation of valve prior art. It is also known to install in a single stuffing box 12 a second set of packing 30, which is separated from a first set of packing 10 by a lantern ring 31. Proximate and distal packing rings 21, 21′ of suitable durable composition may be provided. Both sets of packing 10, 30 are compressed simultaneously by tightening a common array of packing bolts 18. Accordingly, the two sets of packing 10, 30 within a single stuffing box or packing chamber 12 provide some redundant protection against leakage, between the valve body 14 and the valve stem 16, from the valve's zone of elevated operating pressure 20. Notably, the primary packings 10, 30 can only be compressed simultaneously by the operation of the packing bolt(s) 18; individualized or custom compression of only one set of packing 10 or 30 is not possible.
Some valves known in the art provide a vent or sniffing port 34 in the axial vicinity of the lantern ring 31. By means of the port 34, pressure, sampling, and leakage tests may be performed on the primary packing chamber 12 between the two sets of primary packing 10, 30. It is possible thereby to evaluate the inadequacy of the primary packing—exposing the interior of the primary packing chamber 12 to a large fraction of the system operating pressure. Since in many valves the pressure in the primary packing chamber 12 may approach the valve operating pressure, the port 34 cannot pragmatically serve as a true vent.
As packing 10, 30 wears through use, leaks will generally start to occur where the valve stem 16 interfaces with the packing in the stuffing box 12. One way to reduce or eliminate the leaks is to increase the compression force on the packing 10, 30 by tightening the packing bolts 18. This temporary solution often eventually results in the compression being increased to the point that it is difficult for the valve stem 16 to move smoothly past the packing. Another problem which may occur, and is more severe, is the failure of the packing 10 or 30 due to over-compression, which may result in a large atmospheric release of process fluid from the valve, forcing immediate isolation of the valve from the process. Fugitive emissions from valves are an undesirable occurrence in many industries.
A number of efforts have been made to provide leak-resistant valves. Examples of these efforts are provided in the following United States Patents: U.S. Pat. No. 6,056,005 to Piotrowski, et al.; U.S. Pat. No. 5,203,370 to Block, et al.; U.S. Pat. No. 5,865,441 to Orlowski; U.S. Pat. No. 5,476,117 to Pakula; U.S. Pat. No. 5,178,363 to Icenhower, et al.; U.S. Pat. No. 5,170,991 to Heil; U.S. Pat. No. 5,129,624 to Icenhower, et al.; U.S. Pat. No. 4,901,751 to Story, et al.; U.S. Pat. No. 4,570,942 to Diehl, et al.; U.S. Pat. No. 5,979,491 to Gonsior; and U.S. Pat. No. 4,017,214 to Smith. Known devices, however, may be compromised by various drawbacks. For example, most focus exclusively on preventing any leakage at all from a single primary stuffing box or packing chamber. This often results in the need for high compression on the packings, which can be counter productive especially in high-use valves. Many devices compress simultaneously all the packings in the primary packing chamber, unnecessarily subjecting all packings—which are intended to retain fluid against the system operating pressure—to higher rates of wear.
Against the foregoing background, the present invention was developed.