Patent Description:
The invention relates to standstill seals, and more particularly, to pressure-driven standstill seals that are applicable for sealing against high pressure differentials.

Many rotating shaft seal approaches are known for limiting the escape of a process fluid through a housing that is penetrated by a rotating shaft. One example is a rotating face mechanical seal, which provides a non-contact seal with minimal process fluid leakage, even in the case of highly pressurized gas process fluids. In some cases, grooves or other features are included on at least one face of a rotating face mechanical seal that serve to repel process fluid from the seal when the shaft is rotating.

In many cases, for example when sealing a gas that is toxic or otherwise dangerous to personnel and to the environment, it is desirable to also form a tight seal with a shaft even when the shaft is not rotating. Many rotating shaft seals are inefficient for forming a seal under these "standstill" conditions. Instead, a separate standstill seal can be provided that is withdrawn from the shaft when the shaft is rotating, and pressed against the shaft to form a seal when the shaft is not rotating. Process fluid is thereby prevented from reaching the environment under standstill conditions, either by preventing the process fluid from reaching the rotating shaft seal, or preventing the process fluid from reaching the external environment if it leaks past the rotating shaft seal. Often, a controller is implemented both to control the starting and stopping of the shaft rotation and to control the opening and closing of the standstill shaft seal.

With reference to <FIG> one approach is to provide a solid, rigid sealing annulus <NUM> that surrounds the shaft <NUM> and can be pressed axially into contact with a radial structure <NUM> that is sealed to the shaft <NUM> via a supporting structure <NUM>. In the example of <FIG>, the sealing annulus <NUM> is pneumatically driven against the radial structure <NUM> when the shaft <NUM> is not rotating, and is withdrawn from the shaft <NUM> by a spring <NUM> when the shaft is rotating. In similar examples, the sealing annulus <NUM> is driven by a bi-directional pneumatic piston or by mechanical mechanism such as a solenoid. Typically, the standstill shaft seal is activated and deactivated by a controller (not shown), which may be but is not necessarily the same controller that also controls the rotational starting and stopping of the shaft.

While this approach is durable, and is able to seal high pressure process fluids such as high-pressure gasses, nevertheless this approach is intrinsically complex and expensive to manufacture.

With reference to <FIG> and <FIG>, another approach is to surround the shaft <NUM> with a hollow, elastomeric tube <NUM> that is constrained by a housing <NUM> and is in fluid communication via an inflation inlet <NUM> with an inflation source (not shown), for example a source of pressurized nitrogen gas. The cross-section of the tube <NUM> is shaped such that it normally does not extend beyond the housing <NUM> to the shaft <NUM>. However, when the interior <NUM> of the tube <NUM> is pressurized by the inflation source, it expands radially inward beyond the housing <NUM> and forms a seal both with the housing <NUM> and with the shaft <NUM>. <FIG> illustrates the standstill shaft seal when it is open, and <FIG> illustrates the seal when it is closed.

The approach of <FIG> and <FIG> is simple, and relatively easy to manufacture. However, it can be difficult to provide complex cross-sectional shaping to the tube <NUM>, because it is typically extruded rather than cast.

With reference to <FIG> and <FIG>, in a similar approach a shaped elastomeric band <NUM> is snapped onto a supporting form <NUM> and installed within the housing <NUM>. The supporting form <NUM> is penetrated by the inflation inlet <NUM>, which is directed to a rear surface of the band <NUM>. With reference to <FIG>, when no pressure is applied via the inflation inlet <NUM>, the elastomeric band <NUM> remains flat against the supporting form <NUM>, and does not extend beyond the housing <NUM>. However, with reference to <FIG>, when pressure is applied via the inflation inlet <NUM>, a pocket of fluid is formed between the band <NUM> and the supporting form <NUM>, such that the band <NUM> is extended radially inward out of the housing <NUM> and is pressed against the shaft <NUM>, forming a seal.

While these approaches can be effective under some circumstances, they are apt to fail when attempting to form a seal against a high-pressure fluid, such as a gas that is pressurized to <NUM> Bar or <NUM> Bar. With reference to <FIG>, if the seal is closed, and a very high pressure is applied by the process fluid upstream of the seal, with no corresponding pressure downstream of the seal, the elastomeric seal <NUM> can be distorted and even extruded <NUM> into the gap between the shaft <NUM> and the housing <NUM>, such that the band <NUM> may not fully withdraw from the shaft <NUM> when the pressure applied via the inflation inlet <NUM> is withdrawn. In such cases, it may be necessary to resort to a rigid, mechanical approach such as is illustrated in <FIG>.

Document <CIT> discloses a remotely actuated emergency shaft seal. Document <CIT> discloses a shaft seal. Document <CIT> discloses a double-acting inflatable seal. Document <CIT> discloses a bulkhead sealing device for ship.

What is needed, therefore, is a standstill shaft seal that is simple in design, relatively low cost to produce, and able to form a seal that reliably withstands high pressure process fluids.

The present invention is a fluid pressure driven standstill shaft seal according to appended claims that is simple in design, relatively low cost to produce, and able to form a seal that reliably withstands high pressure process fluids, such as process gasses pressurized to <NUM> Bar or higher.

The disclosed seal comprises a flexible band that is installed within an annular housing and surrounds a rotatable shaft. The flexible band comprises a thick, substantially rectangular central region flanked by thinner side regions on either side thereof. The thinner side regions of the flexible band provide radial or axial flexibility to the central region, such that the thick central region is able to be extended through an annular opening in the housing and then retracted therefrom. The thickness of the central region enables it to resist being distorted or extruded when it is pressed against the shaft and subject to a high fluid pressure differential. Pressurized control fluid is applied behind the central region via a control fluid inlet to close the standstill seal.

The pressurized control fluid that is applied behind the flexible band is controlled by a controller, which in embodiments also controls the rotation of the shaft. While the shaft is rotating, no pressure is applied behind the central region of the flexible band, such that it remains partially or fully within the annular housing and does not contact the shaft. When the shaft is not rotating (i.e. is in a standstill condition), fluid pressure is applied by the controller behind the central region of the flexible band via the control fluid inlet. As a result, the central region of the flexible band is pushed through the annular opening in the housing, and is pressed against the shaft, or against an intermediate structure that is sealed to the shaft, forming a standstill seal therewith. In radial embodiments the change in diameter of the central region is only a small percentage of the full diameter of the flexible band, such that the central region is easily able to accommodate the circumferential compression that is required as the central region is pressed radially inward toward the shaft.

In some embodiments, the source of the control fluid is independent of the process, and can be, for example, a source of pressurized nitrogen gas, pressurized air, or a pressurized liquid. In other embodiments, the control fluid is the process fluid. In some of these embodiments, a pressure boosting device is used to increase the pressure of the process fluid that is applied behind the flexible band.

In various embodiments, the flexible band is made from a material such as an elastomer that has sufficient elasticity to reliably spring back to its original shape when it is no longer distorted by applied fluid pressure, such that when the applied fluid pressure is removed, the central region is fully withdrawn from the shaft due to the elasticity of the elastomer. In other embodiments, the flexible band is made from a material that is flexible and durable, but has less elasticity, such as PTFE, such that the flexible band may not have sufficient elasticity to reliably withdraw the central region from the shaft when the control fluid pressure is withdrawn. Some of these embodiments include a pair of annular, toothed springs, each of which has a solid annular region that is clamped in place within the housing, and a toothed annular region that is beneath at least a portion of the side regions of the flexible band. The toothed springs provide added return force that ensures full withdrawal of the central region from the shaft.

Embodiments further include a pair of rigid annular rings on either side of the thick central region which completely eliminate the possibility that any of the thick region might be extruded into the gap between the housing and the shaft when the standstill seal is engaged. The annular rings can be attached to the central region of the flexible band or they can be fixed to the housing and extend into the gap between the shaft and the housing.

The standstill seal of the present invention can be implemented together with at least one rotating shaft seal, such as a rotating face mechanical seal. The standstill seal can be implemented upstream or downstream of the rotating shaft seal. Or, if a plurality of rotating shaft seals are included, then the standstill seal can be implemented between the rotating shaft seals. In some embodiments, a plurality of the disclosed standstill seals are deployed, for example one upstream of the rotating shaft seal and one downstream of the rotating shaft seal.

While the disclosed standstill seal is sometimes described herein as acting radially inward, it will be clear to those of skill in the art that in other embodiments the stationary seal is axial. For example, in embodiments the central region of the flexible band is pressed axially against a radially extending face that is fixed and sealed by an intermediate support structure to the rotating shaft.

The present invention is a standstill seal configured to form a seal with a rotatable shaft so as to prevent leakage of a process fluid past the standstill seal when the shaft is not rotating. The standstill seal includes a flexible band surrounding the shaft, the flexible band comprising a relatively thicker central region from which relatively thinner side regions extend longitudinally in the direction of sealing of the central region with the shaft, or with an intermediate structure that is sealed to the shaft, when seen in an axial cross-sectional view, the central region being substantially rectangular in cross section, a housing configured to house the flexible band, a pair of cover plates underlying the side regions of the flexible band and configured to prevent the side regions from being deflected past the cover plates, a gap being provided between the cover plates through which the central region of the flexible band can be extended, a control fluid inlet configured to provide fluid communication between a source of pressurized control fluid and a rear surface of the flexible band, and a controller.

The standstill seal is configured, when the controller applies the pressurized control fluid to the control fluid inlet, to extend the central region of the flexible band through the gap such that it makes contact and forms a seal with the shaft, or with an intermediate structure that is sealed to the shaft. The standstill seal is also configured, when the controller ceases to apply the pressurized control fluid to the flexible band, to withdraw the central region of the flexible band away from the shaft or intermediate structure.

In embodiments, the standstill seal is configured to apply the central region of the flexible band radially inward against the shaft or against the intermediate structure.

In any of the above embodiments, the standstill seal can be configured to apply the central region of the flexible band axially against the intermediate structure.

Any of the above embodiments can further include a pair of rigid annular support rings configured to support sides of the central region of the flexible band when the central region is extended through the gap between the cover plates.

In any of the above embodiments, the standstill seal can be configured to apply the central region of the flexible band radially inward against the shaft or the intermediate structure, and the annular support rings can include ring gaps that enable the annular support rings to compress radially when the central region is extended radially inward against the shaft or the intermediate structure. In some of these embodiments, the annular support rings are fixed to the central region of the flexible band. And in any of these embodiments, the annular support rings can extend from the housing.

In any of the above embodiments, the flexible band can include sufficient elasticity to cause the central region to be withdrawn from the shaft or intermediate structure when the controller ceases to apply the pressurized control fluid to the flexible band.

Any of the above embodiments can further include a spring that is configured to assist the withdrawal of the central region of the flexible band from the shaft or intermediate structure when the controller ceases to apply the pressurized control fluid to the flexible band.

In some of these embodiments, the standstill seal is configured to apply the central region of the flexible band radially inward against the shaft or the intermediate structure.

In some of these embodiments, the spring comprises a pair of spaced apart annular bands having solid annular portions from which teeth extend axially toward each other beneath the side regions of the flexible band, an axial gap being provided between the teeth through which the central region of the flexible band can be extended to contact the shaft or the intermediate structure, the teeth being bent radially inward as the central region of the flexible band is pushed toward the shaft. In some of these embodiments, the standstill seal further comprises a pair of rigid annular support rings that extend radially inward from the springs, the rigid annular support rings being configured to support sides of the central region of the flexible band when the central region is applied radially inward against the shaft or the intermediate structure.

In other of these embodiments, the standstill seal comprises a pair of rigid annular support rings that support opposing sides of the central region of the flexible band when the central region is extended through the gap between the cover plates, the support rings including circumferential gaps enabling radially inward compression of the support rings, and the springs are compression springs applied to the gaps in the support rings.

In other embodiments that include a spring that is configured to assist the withdrawal of the central region of the flexible band from the shaft or intermediate structure when the controller ceases to apply the pressurized control fluid to the flexible band, the standstill seal is configured to apply the central region of the flexible band axially against the intermediate structure, and the spring comprises a pair of radially concentric annular disks having solid annular portions from which teeth extend radially inward and outward toward each other beneath the side regions of the flexible band, a radial gap being provided between the radially inward and radially outward teeth through which the central region of the flexible band can be extended to contact the intermediate structure, the teeth being bent axially as the central region of the flexible ban dis pushed toward the shaft.

In any of the above embodiments, the side regions of the flexible band can include portions that are curved in longitudinal cross section, thereby enabling extension of the side regions when the central region is extended through the gap.

In any of the above embodiments, the standstill seal can be unitary with a rotating shaft seal that is configured to form a seal with the shaft when the shaft is rotating. In some of these embodiments, the standstill seal is configured to form a seal with the shaft or intermediate structure upstream of the rotating shaft seal, while in other of these embodiments the standstill seal is configured to form a seal with the shaft or intermediate structure downstream of the rotating shaft seal.

In any of the above embodiments, the control fluid can be a gas, or the control fluid can be the process fluid.

And in any of the above embodiments, the controller can be configured to start and stop the rotation of the shaft, as well as controlling the application of the pressurized control fluid to the flexible band.

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.

The present invention is a fluid pressure driven standstill shaft seal that is simple in design, relatively low cost to produce, and able to form a seal that reliably withstands high pressure process fluids, such as process gasses pressurized to <NUM> Bar or higher.

With reference to the cross-sectional illustration of <FIG>, the disclosed standstill seal comprises a flexible band <NUM> that is installed within an annular housing <NUM> and covered by a pair of annular cover plates <NUM>. The flexible band <NUM>, the housing <NUM>, and the cover plates <NUM> all surround a rotatable shaft <NUM>. The flexible band <NUM> comprises a thick, substantially rectangular central region <NUM> flanked by thinner side regions <NUM> on either side thereof. In the embodiment of <FIG>, the thinner side regions <NUM> of the flexible band <NUM> provide radial flexibility to the central region <NUM>, such that the thick central region <NUM> is able to be extended radially inward through an axial gap <NUM> between the cover plates <NUM> and then retracted therefrom. The thickness of the central region <NUM> enables it to withstand high axial pressure differentials when it is pressed against the shaft <NUM>, so that it is not distorted or extruded when the standstill seal is closed.

A pressurized control fluid, such as pressurized nitrogen gas, a pressurized liquid, or pressurized process fluid, is applied behind the central region <NUM> via a control fluid inlet <NUM> to close the standstill seal. The pressurized control fluid can be controlled by a controller (not shown), which in embodiments also controls the rotation of the shaft <NUM>. While the shaft <NUM> is rotating, as is illustrated in <FIG>, no pressure is applied behind the central region of the flexible band <NUM>, such that it remains partially or fully within the annular housing <NUM> and cover plates <NUM>, and does not contact the shaft <NUM>.

With reference to <FIG>, when the shaft <NUM> is not rotating (i.e. is in a standstill condition), pressurized control fluid is applied by the controller behind the central region <NUM> of the flexible band <NUM> via the control fluid inlet <NUM>. As a result, in the illustrated embodiment, a gap <NUM> filled with the pressurized control fluid is formed behind the central region <NUM> of the flexible band <NUM>, causing the central region <NUM> of the flexible band <NUM> to be pushed radially inward through the axial gap <NUM> between the annular cover plates and pressed against the shaft <NUM>, forming a standstill seal therewith. In other embodiments, the thick central region <NUM> is pressed axially against an intermediate structure that is sealed to the shaft <NUM>, as is discussed in more detail below with reference to <FIG>.

In the radial embodiment of <FIG> and <FIG>, the change in diameter of the central region <NUM>, when deployed, is only a small percentage of the full diameter of the flexible band <NUM>, such that the central region <NUM> is easily able to accommodate the circumferential compression that is required as the central region <NUM> is pressed radially inward toward the shaft <NUM>.

In the embodiment of <FIG> and <FIG>, the flexible band <NUM> is made from an elastomer or other material that has sufficient elasticity to reliably spring back to its original shape when it is no longer distorted by applied fluid pressure. In the embodiment of <FIG>, the flexible band <NUM> is made from a material such as PTFE that is flexible and durable, but has less elasticity, and may not be able, by itself, to reliably withdraw the central region <NUM> from the shaft <NUM> when the control fluid pressure is withdrawn.

Accordingly, the embodiment of <FIG> and <FIG> includes a pair of opposing annular toothed springs <NUM> that provide added radial return force to the side regions <NUM> of the flexible band <NUM>, ensuring full withdrawal of the central region <NUM> from the shaft <NUM> when the control fluid pressure behind the flexible band <NUM> is withdrawn. In the illustrated embodiment, the sides <NUM> of the flexible band <NUM> are configured so as to be substantially axial when control fluid pressure is not being applied, so that they can rest upon the axially directed teeth <NUM> of the spring <NUM>. The flexible band is secured within the housing <NUM> by two O-rings <NUM>.

The curved shaping of the side regions <NUM> of the flexible band <NUM> in the embodiment of <FIG> provides the additional length that is needed when the standstill seal is closed, as is shown in <FIG>. <FIG> is a perspective view from the side of one of the springs <NUM> of <FIG> and <FIG>. It can be seen that the spring <NUM> includes a solid annular portion <NUM> and a ring of axial teeth <NUM> that can be bent radially inward as the central region <NUM> of the flexible band <NUM> is pushed toward the shaft <NUM>.

<FIG> illustrates an embodiment that is similar to <FIG>, except that the "springs" <NUM> are elastomeric tubes that surround the shaft <NUM> within the housing <NUM> beneath the sides <NUM> of the flexible band <NUM>. When the central region <NUM> is deployed, the hollow tubes <NUM> are flattened, and when the control fluid pressure is released, the elasticity of the hollow tubes <NUM> assist in returning the central region <NUM> to its previous position within the housing <NUM>.

With reference to <FIG>, embodiments further include a pair of rigid, annular support rings <NUM> that are pressed against either side of the thick central region <NUM> to further support the central region <NUM> and completely eliminate the possibility that any of the thick central region <NUM> might be extruded <NUM> between the annular cover plates <NUM> and the shaft <NUM> when the standstill seal is engaged. Of course, the space between the two cover plates <NUM> is made large enough in these embodiments to accommodate the thicknesses of the support rings <NUM>, as well as the thickness of the central region <NUM> of the flexible band <NUM>.

With reference to <FIG>, in the illustrated embodiment the annular support rings <NUM> include gaps <NUM>, such that they do not extend a full <NUM> degrees about the shaft <NUM>. The gaps <NUM> enable the support rings <NUM> to compress radially inward together with the central region <NUM> of the flexible band <NUM>. In <FIG>, a support ring <NUM> is shown in cross section in its uncompressed state, while in <FIG> the support ring <NUM> is shown in its compressed state. <FIG> shows the relationship between the support ring <NUM> of <FIG> and the central region <NUM> of the flexible band <NUM>.

With reference to <FIG>, in similar embodiments, the support rings <NUM> are integral with the springs <NUM> that assist in reopening the standstill seal when the control fluid is depressurized.

In the embodiment of <FIG> and <FIG>, a compressible spring <NUM> is used to assist the opening of the standstill seal when the control fluid is depressurized, rather than toothed springs <NUM>. <FIG> is a cross sectional view similar to <FIG>, while <FIG> is a close-up view of the gap region of a support ring <NUM> showing the location and action of the spring <NUM>. Instead of applying a "lifting" force to the side regions <NUM> of the flexible band <NUM>, the compression spring <NUM> of <FIG> applies a circumferentially expanding force to the support rings <NUM>, thereby assisting in the retraction of the central region <NUM> of the flexible band <NUM> from the shaft <NUM>.

With reference to <FIG>, in other embodiments the support rings <NUM> are fixed to the cover plates <NUM>, and extend into the gap <NUM> between the shaft <NUM> and the cover plates <NUM>.

With reference to <FIG>, the standstill seal of the present invention can be implemented together with at least one rotating shaft seal. In the embodiment of <FIG>, the standstill seal is implemented upstream of an end face mechanical seal that includes a rotating seal face <NUM> that is sealed to the shaft by an intermediate support structure <NUM>, and a static seal face <NUM> that is sealed to the housing <NUM> and is pushed toward the rotating seal face <NUM> by a spring <NUM>. In the illustrated embodiment, the central region <NUM> of the flexible band <NUM> is configured to form a seal against the intermediate support structure <NUM> when the shaft <NUM> is not rotating, rather than forming a seal directly with the shaft <NUM>. It will be noted that the illustrated embodiment integrates the standstill seal with the end face mechanical seal into a single unit.

In some embodiments, the source of the control fluid is independent of the process, and can be, for example, a source of pressurized nitrogen gas or pressurized air, or a source of a pressurized liquid. In the embodiment of <FIG>, the control fluid is the process fluid. In the illustrated embodiment, process fluid is drawn from a pressurized side <NUM> of the seals, and is passed through a pressure boosting device <NUM> that increases the pressure of the process fluid before it is applied to the rear of the flexible band <NUM>. A valve <NUM> that controls the flow of the process fluid into the pressure boosting device <NUM> is actuated by a controller <NUM> that, in embodiments, also controls the stopping and starting of the rotation of the shaft <NUM>.

In similar embodiments, the standstill seal is implemented downstream of the rotating shaft seal. Or, if a plurality of rotating shaft seals are included, the standstill seal can be implemented between the rotating shaft seals. In some embodiments, a plurality of the disclosed standstill seals are deployed, for example one upstream of a rotating shaft seal and one downstream of the rotating shaft seal.

While the disclosed stationary seal is sometimes described herein as acting radially inward, it will be clear to those of skill in the art that in other embodiments the stationary seal is axial rather than radial. For example, with reference to <FIG>, in embodiments the central region <NUM> of the flexible band <NUM> is pressed axially against a radially extending face <NUM> that is sealed by an intermediate support structure <NUM> to the rotating shaft <NUM>. In the illustrated embodiment, the side regions <NUM> of the flexible band <NUM> extend radially rather than axially, and with reference to <FIG> the springs 300a, 300b are concentric rather than opposing, with the teeth of the outer spring 300a directed radially inward and the teeth of the inner spring 300b directed radially outward, with a gap <NUM> provided therebetween through which the central region <NUM> of the flexible band <NUM> can be deployed.

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 standstill seal configured to form a seal with a rotatable shaft (<NUM>) so as to prevent leakage of a process fluid past the standstill seal when the shaft is not rotating, the standstill seal comprising:
a flexible band (<NUM>) surrounding the shaft, the flexible band comprising a relatively thicker central region (<NUM>) from which relatively thinner side regions (<NUM>) extend longitudinally in the direction of sealing of the central region (<NUM>) with the shaft (<NUM>), or with an intermediate structure that is sealed to the shaft, when seen in an axial cross-sectional view, the central region (<NUM>) being substantially rectangular in longitudinal cross section;
a housing (<NUM>) configured to house the flexible band;
a pair of cover plates (<NUM>) underlying the side regions of the flexible band and configured to prevent the side regions from being deflected past the cover plates, a gap (<NUM>) being provided between the cover plates through which the central region (<NUM>) of the flexible band can be extended;
a control fluid inlet (<NUM>) configured to provide fluid communication between a source of pressurized control fluid and a rear surface of the flexible band; and
a controller;
the standstill seal being configured, when the controller applies the pressurized control fluid to the control fluid inlet (<NUM>), to press the rear surface of the flexible band (<NUM>) toward the gap (<NUM>), thereby extending the central region (<NUM>) of the flexible band through the gap, such that it makes contact and forms a seal with the shaft (<NUM>), or with the intermediate structure that is sealed to the shaft, whereby flexibility of the flexible band (<NUM>) is provided by the side regions (<NUM>);
the standstill seal being configured, when the controller ceases to apply the pressurized control fluid to the control fluid inlet (<NUM>), to withdraw the central region (<NUM>) of the flexible band away from the shaft (<NUM>) or intermediate structure.