Patent Application
20200362968
Conventional seals for valves that have a bonnet and stem have problems preventing the escape of pressurized fluid from the valve body. In the cargo tank industry, valves of this type are commonly used, and depending on the type of liquid being loaded/unloaded the prevention of pressurized fluid from escaping is of utmost concern. These seals are often exposed to harsh and volatile fluids, where conventional seals and methods have fallen short. Periodic maintenance is generally required to maintain seal performance which is costly. In some cases, loading/unloading facilities often require specialized testing to hold back pressurized fluid for a timed period before being accepted.
Prior art seals have often consisted of rope packing seals, u-seals, or stacked vee packing seals to name a few. These types of seals have often underperformed when preventing pressurized fluid from escaping. Chemical compatibility also becomes a major factor when dealing with sealability and longevity in volatile service. PTFE materials are often used in the design of these seals which adds another level of complexity. Seals of this material have good chemical resistance when exposed to harsh and volatile fluids over a wide range of temperatures and pressures but can lose resiliency an important sealing property over time. PTFE material will creep and deform over time and lose its ability to seal. Springs are often used to hold the PTFE seals in compression. Rope packing usually consists of a non-asbestos aramid fiber w/PTFE impregnation rope that is cut in pieces and installed in the bonnet of a valve, and a packing gland and packing nut are used to compress the packing around a stem. These seals often weep, are difficult to install, and can take a compression set requiring the packing nut to be tightened in order to maintain the required sealing force. U-cup seals sit in a gland that seals against a bonnet and stem and are orientation specific. These seals cannot be tightened and rely on the pressurized fluid to energize the lips of the u-cup. In some cases, these seals will use springs or energizers to help keep the u-cup in shape, but often weep in low pressure applications. Vee packing seals are also difficult to install because there are multiple pieces, require a spring or Belville to energize, and are orientation specific.
The disadvantages of prior art are overcome by the system and method presented and provided herein.
A seal for a valve stem comprises an upper gland, a lower gland, a packing nut and an accordion type seal that further comprises a seal body that has a plurality of convolutions that are compressible when pressure is applied to the seal body, and an energizer mounted in the interior or exterior root of at least one convolution. The accordion type seal is positioned between the upper gland and the lower gland. The packing nut is threaded onto the valve stem to compress the accordion type seal between the upper gland and the lower gland.
In some embodiments, a first energizer is mounted in the interior root of at least one convolution and a second energizer is mounted in the exterior root of at least one convolution. In some embodiments, a plurality of energizers are each mounted to one interior root of a convolution. In some embodiments, a plurality of energizers each mounted one exterior root of a convolution. The energizer could be any of o-rings, coil springs, foams, elastomers, or garter springs.
This invention is capable of embodiments that are different from those shown; thus details of the devices and methods can be changed in various manners without departing from the scope of this invention. Accordingly, the drawings and descriptions are to be regarded as including such equivalent embodiments as to not depart from the spirit and scope of this invention.
For a more complete understanding and appreciation of this invention, and its many advantages, reference will be made to the following detailed description taken in conjunction with the accompanying drawing:
In the cargo tank industry, valves are used in the loading and unloading process and commonly have bonnets and stems to facilitate actuation of the valve. It is of great importance that the joint between the stem and bonnet does not allow the escape of pressurized fluid from the tanker.
The energizer 14 may be o-rings, coil springs, foams, elastomers, garter springs, or other device or a combination of such that can fit within the convolutions of the seal body 12. O-rings, as shown in the figures are preferred as they can provide additional sealing between the seal body 12 and the valve bonnet 20. Such multiple-point sealing gives redundancy and a better seal. Unlike some valve seals in the prior art that are typically unidirectional, the accordion style seal 10 provides a fluid seal in both directions.
The accordion style seal 10 with the energizers 14 improves the sealing between the valve bonnet 20 and the valve stem 22. The energizers 14 improve sealing engagement as well as provides additional sealing capability—essentially the energizers 14 push or hold the sealing material, in this case the seal body 12, in position. This accordion style seal 10 greatly reduces the problem of the seal collapsing and compressing thus losing the ability of the seal to be adjusted.
The seal body 12 is preferably made of PTFE Teflon®, and the O-rings 14 are preferably made of FEP Teflon® encapsulated silicon or similar elastomer. The materials chosen provide low friction characteristics and chemical compatibility across a wide range of fluids at different temperatures and concentrations.
It will be understood that the number of convolutions on the seal body 12 could vary with the application. Furthermore, not every convolution needs to have a corresponding energizer 14 and there may be some convolutions on the seal body 12 that do not have any corresponding energizer.
This invention has been described with reference to several preferred embodiments. Many modifications and alterations will occur to others upon reading and understanding the preceding specification. It is intended that the invention be construed as including all such alterations and modifications in so far as they come within the scope of the appended claims or the equivalents of these claims.
| Number | Date | Country | |
|---|---|---|---|
| 62848263 | May 2019 | US |
