Patent Description:
The invention relates to valves, and more particularly, to valves that form a seal using packing.

For critical valve applications where even the smallest amount of external valve leakage is not acceptable, a bellows seal valve is typically used.

With reference to the sectional diagram of <FIG>, a bellows seal valve comprises an accordion-like bellows <NUM>. One end <NUM> of the bellows <NUM> is welded or attached to the valve stem <NUM>. The other end <NUM> of the bellows <NUM> is welded to a part <NUM> that can be clamped or otherwise attached to the valve bonnet <NUM>. When operating the valve, the valve stem <NUM> is moved in a linear valve stroke so as to control the position of a valve plug <NUM> relative to a valve seat <NUM>. During the valve stroke, the bellows <NUM> compresses or expands along with the linear motion of the sliding valve stem <NUM>.

Since the bellows <NUM> has a static seal at each end <NUM>, <NUM>, and the circumference of the valve stem <NUM> is covered by the bellows <NUM>, a metal barrier between the process fluid inside of the valve and the external atmosphere is provided, eliminating leakage at the valve stem <NUM>. In the example of <FIG>, the process fluid is outside of the bellows <NUM>, and the atmosphere is inside of the bellows <NUM>. For other bellows valves, the process fluid is inside of the bellows <NUM> and the atmosphere is outside of the bellows <NUM>.

Because the metal bellows <NUM> is flexed as the valve stem <NUM> is moved, over time the bellows <NUM> will ultimately crack and fail. To prevent leakage due to a bellows failure, a set of packing <NUM> is provided above the bellows <NUM> to provide a second seal.

Unfortunately, implementing a bellows valve can be costly. Furthermore, if the bellows <NUM> were to develop a leak path, the process fluid in the example of <FIG> would leak from the outside surface of the bellows <NUM>, through the leak path, into the inside area of the bellows <NUM>. The valve fluid would then be sealed from the outside environment only by the valve stem packing <NUM> in the gland area <NUM> of the valve. If the valve stem packing <NUM> were to leak, then the process fluid would escape to the outside atmosphere. Since valve stem packing <NUM> typically allows a higher level of leakage than a bellows <NUM>, there is a high probability that if the bellows <NUM> were to develop a leak path, at least some process fluid would escape through the bellows <NUM> and valve stem packing <NUM> to the outside environment.

Document <CIT> discloses a seal system, particularly suitable for process valves. Document <CIT> discloses a seal assembly for a valve stem. Document <CIT> discloses a gas pressurized packing system for control valves. Document <CIT> discloses a pressure vessel.

What is needed, therefore, is a reliable valve design that is less prone to leakage than conventional bellows valves, while also being less expensive than conventional bellows valves.

The present invention is a reliable valve design that is less prone to leakage than conventional bellows valves, while also being less expensive than conventional bellows valves.

According to the present invention, a linear stroke valve includes a pair of packing seals that are spaced apart by a gap space along the valve stem, for example within a gland area of the valve. Leakage through the packing seals is prevented by introducing a pressurizing fluid, such as nitrogen, into the gap space between the packing seals and maintaining the pressurizing fluid at a gap pressure that is higher than the process fluid pressure so as to ensure that any leakage past the packing seals will be of the pressurizing fluid into the process fluid or into the environment, while any escape of the process fluid into the environment is prevented.

Assuming that there is little or no leakage past the packing seals, the volume between the packing seals will normally be constant and static, and there will normally be no flow of the pressurization fluid into the valve once the desired pressure of the pressurizing fluid is established within the valve. In embodiments, the pressure and/or flow rate of the pressurizing fluid is monitored, so that any leakage of the pressurizing fluid through either or both of the packing seals is easily detected as a decrease in the pressure and/or as an increased flow rate of the pressurizing fluid into the valve. Depending on the application of the valve, leakage of small amounts of the pressurizing fluid into the process fluid and/or into the environment may be tolerable. However, once the flow rate and/or pressure drop of the pressurizing fluid exceeds a specified maximum, then a maintenance action can be applied to the valve, for example by re-tightening or replacing the packing, or replacing the valve.

In some embodiments where the disclosed valve is implemented for a high temperature oxidizing application, the pressurizing gas can serve to protect inner rings of the packing seals by displacing oxygen away from them. Oxidizing resistant rings of packing can be placed on the outsides of the packing seals to protect inner rings that might otherwise be oxidized. In some of these embodiments, this arrangement further protects the valve fluid from oxygen ingress when the process fluid is drained from the system and a vacuum is created that might otherwise suck air into the valve from the outside environment.

One general aspect of the present invention is a valve system comprising a valve. The valve includes a valve seat; a valve plug configured to control a flow of process fluid through the valve according to a separation between the valve plug and the valve seat; a valve stem in mechanical communication with the valve plug and configured such that linear actuation of the valve stem controls the separation between the valve plug and the valve seat; first and second packing seals surrounding the valve stem, each of the packing seals forming a seal between the valve stem and a surrounding gland housing, the first and second packing seals being separated from each other along the valve stem by a seal gap, and a seal pressurization port configured to allow a seal pressurizing fluid to enter into the seal gap and to be pressurized within the seal gap to a desired gap pressure.

Embodiments according to the claimed invention further include a pressurization fluid source, a pressurizing fluid pressure regulating apparatus, and a pressurization fluid line that provides fluid communication between the pressurization fluid source and the seal pressurization port of the valve. Some of these embodiments further include a pressure measuring device configured to measure a pressure of the pressurizing fluid within the gap space. Embodiments according to the claimed invention further include a flow measuring device configured to measure a flow rate of the pressurizing fluid into the gap space.

Another general aspect of the present invention is a method of preventing process fluid leakage along a valve stem of a linear stroke valve. The method includes providing a valve system according to the first general aspect, determining or estimating a process pressure of the process fluid, and applying a pressurizing fluid to the seal pressurization port, the pressurizing fluid being pressurized to a gap pressure that is higher than the process pressure.

Embodiments according to the claimed invention further include monitoring a flow rate of the pressurizing fluid and, optionally, monitoring a pressure of the pressurizing fluid.

In the embodiments according to the claimed invention, the method further includes, if the monitored pressure or the monitored flow rate changes by more than a specified amount, determining that a leak has developed in the valve, and applying a maintenance action to the valve. In some of these embodiments, the maintenance action includes at least one of re-tightening at least one of the packing seals, replacing at least one of the packing seals, and replacing the valve.

And in any of the above embodiments, the pressurizing fluid can be nitrogen gas.

The features and advantages described herein are not all-inclusive and, in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, specification, and claims. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes, and not to limit the scope of the inventive subject matter as defined by the appended claims.

With reference to <FIG>, according to the present invention a seal is formed with the valve stem <NUM> of a linear stroke valve by a pair of packing seals <NUM>, <NUM> that are separated from each other along the valve stem <NUM> by a seal gap <NUM>. In the example of <FIG>, the packing seals <NUM>, <NUM> are both located within a gland area of the valve, and a spacer <NUM> is provided within the gap space <NUM>.

The valve further includes a pressurization port <NUM>. With reference to <FIG>, the pressurization port <NUM> can be used to inject a pressurizing fluid, such as nitrogen gas <NUM>, through a pressurizing fluid transfer line <NUM> into the gap space <NUM> between the packing seals <NUM>, <NUM>. A pressure regulating device <NUM> is then used to establish and maintain the pressurizing fluid within the gap space <NUM> at a higher pressure than the process fluid, thereby ensuring that any leakage past the packing seals <NUM>, <NUM> will be of the pressurizing fluid into the process fluid and/or into the environment, while any escape of the process fluid into the environment will be prevented.

Assuming that there is little or no leakage past the packing seals <NUM>, <NUM>, the volume of the gap space <NUM> between the packing seals <NUM>, <NUM> will normally be constant and static, and there will normally be no flow <NUM> of the pressurization fluid into the valve once the desired gap pressure of the pressurizing fluid is established within the gap space <NUM>.

With reference to <FIG>, in embodiments according to the claimed invention, after placing the valve in service <NUM> and establishing <NUM> the pressurizing fluid within the gap space <NUM> between the packing seals <NUM>, <NUM> at the desired gap pressure, the flow rate and, optionally, the pressure of the pressurizing fluid is monitored <NUM>, for example using a flow gage <NUM> as shown in <FIG>, so that any leakage of the pressurizing fluid past either or both of the packing seals <NUM>, <NUM> is easily detected and quantified as a decrease in the pressure and/or increase in the flow rate of the pressurizing fluid. Depending on the application of the valve, leakage of small amounts of the pressurizing fluid into the process fluid and/or into the environment may be tolerable. However, once the flow rate and/or pressure drop of the pressurizing fluid exceeds a specified maximum level <NUM>, a maintenance action can be applied <NUM> to the valve, for example by re-tightening or replacing one or both of the packing seals <NUM>, <NUM>, or replacing the valve.

In some embodiments where the disclosed valve is implemented for a high temperature oxidizing application, the pressurizing gas can serve to protect the inner rings of the packing seals <NUM>, <NUM> by displacing oxygen away from them. Oxidizing resistant rings of packing can be placed on the outsides of the packing seals <NUM>, <NUM> to protect inner rings that might otherwise be oxidized. In some of these embodiments, the invention further protects the process fluid from oxygen ingress when the process fluid is drained from the system and a vacuum is created that might otherwise suck air into the valve from the outside environment.

The foregoing description of the embodiments of the invention has been presented for the purposes of illustration and description. Each and every page of this submission, and all contents thereon, however characterized, identified, or numbered, is considered a substantive part of this application for all purposes, irrespective of form or placement within the application. This specification is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of this disclosure.

Claim 1:
A valve system comprising a valve, the valve comprising:
a valve seat (<NUM>);
a valve plug (<NUM>) configured to control a flow of process fluid through the valve according to a separation between the valve plug (<NUM>) and the valve seat (<NUM>);
a valve stem (<NUM>) in mechanical communication with the valve plug (<NUM>) and configured such that linear actuation of the valve stem (<NUM>) controls the separation between the valve plug (<NUM>) and the valve seat (<NUM>);
first and second packing seals (<NUM>, <NUM>) surrounding the valve stem (<NUM>), each of the packing seals (<NUM>, <NUM>) forming a seal between the valve stem (<NUM>) and a surrounding gland housing, the first and second packing seals (<NUM>, <NUM>) being separated from each other along the valve stem by a seal gap (<NUM>);
a seal pressurization port (<NUM>) configured to allow a seal pressurizing fluid to enter into the seal gap (<NUM>) and to be pressurized within the seal gap (<NUM>) to a desired gap pressure;
a pressurization fluid source (<NUM>);
a pressurizing fluid pressure regulating apparatus (<NUM>) and a pressurization fluid line (<NUM>) that provides fluid communication between the pressurization fluid source (<NUM>) and the seal pressurization port (<NUM>) of the valve;
a flow measuring device (<NUM>) configured to measure a flow rate of the pressurizing fluid into the seal gap (<NUM>), said pressurization fluid line (<NUM>) being unrestricted between the pressurizing fluid pressure regulating apparatus (<NUM>) and the seal pressurization port (<NUM>) of the valve.