United States Patent 5,503,407: Windback Seal Scope, Claims, Expiration, and Patent Landscape

U.S. Patent No. 5,503,407 is a mechanical-engineering patent, not a drug patent. Its claims cover a windback device used around a rotating shaft to return lubricant to a sump and protect a segmented shaft seal from lubricant fouling. The patent issued on April 2, 1996, and its ordinary 17-year U.S. term expired on April 2, 2013. It therefore presents no current U.S. infringement risk based on the issued claims. [1][2]

What does U.S. Patent 5,503,407 protect?

The patent protects a windback assembly integrated with a rotating shaft, lubricant sump, housing, and segmented seal. The core technical concept is a spiral thread formed on the inside of an annular member. As the shaft rotates, the thread moves lubricant back toward the sump.

The claimed improvement is a radial opening, or multiple openings, positioned between the end of the spiral thread and the flange supporting the segmented seal. The openings allow lubricant and pressure to pass from the sump-side region through the annular member. This pressure equalization is intended to stop lubricant from traveling beyond the thread terminus and fouling the seal segments.

The invention has two principal claim categories:

Claim category	Claims	Protected subject matter
Stand-alone windback assembly	1-3	Annular windback member, spiral thread, radial opening, flange, and segmented seal
Rotating-machine combination	4-5	Shaft, housing, sump, gaseous chamber, windback structure, and primary and secondary segmented sealing surfaces

The claims are directed to mechanical structure and operating relationships. They do not cover a chemical compound, pharmaceutical formulation, biological product, therapeutic method, or manufacturing process for a drug.

What are the key limitations of independent claim 1?

Claim 1 is an apparatus claim directed to a “windback means” used with a rotating shaft. Its principal limitations are:

The shaft has a portion positioned in a lubricant-containing sump.
The windback device is an elongated annular member surrounding the shaft.
The annular member has axially spaced ends and inner and outer surfaces.
A flange extends radially outward from one end of the annular member.
The flange contains openings for securing the device to a stationary housing.
The inner surface has a spiral thread beginning at the sump-facing end.
The spiral thread terminates before reaching the flange.
At least one radial opening extends completely through the annular wall.
The radial opening is located axially between the thread terminus and the flange.
A segmented seal is mounted on the flange adjacent to the flange-side end.
The opening is arranged to prevent lubricant from reaching and fouling the seal segments.

The most important claim boundary is the location of the radial opening. A radial passage located within the threaded region, or beyond the flange toward the seal, would not satisfy the express “between the terminus of said thread and said flange” limitation.

The claim also requires a segmented seal mounted on the flange. A windback device without that claimed seal relationship would not literally satisfy claim 1, although it could still fall within the scope of other patents.

How broad are claims 2 and 3?

Claims 2 and 3 narrow claim 1 by specifying multiple openings.

Claim	Added limitation
Claim 2	Multiple circumferentially spaced radial openings, each positioned between the flange and thread terminus
Claim 3	Multiple openings spaced equidistantly around the circumference at the relevant axial position

Claim 2 is broader than claim 3. Claim 2 requires circumferential spacing but does not expressly require equal spacing. Claim 3 requires the stronger geometric condition of equidistant spacing.

A device with one radial opening may fall within claim 1 but not claims 2 or 3. A device with four equally spaced openings at the specified axial position may fall within all three claims, assuming the remaining limitations are present.

What does claim 4 add to the patent scope?

Claim 4 is a combination claim. It requires a rotating machine having:

an elongated annular housing;
a shaft rotating within the housing;
two adjacent internal chambers;
one chamber containing lubricant;
another chamber containing a gaseous medium;
a windback structure located in the sump;
a flange fixed and sealed to the housing;
a spiral thread on the inner annular surface;
a segmented seal ring surrounding the shaft;
biasing of the seal segments against the shaft;
a secondary sealing surface on each segment;
biasing of the secondary surface against the flange; and
at least one radial opening between the spiral-thread terminus and the flange.

Claim 4 is narrower in system context than claim 1 but potentially stronger against a complete machine incorporating every specified relationship. It does not merely claim a windback component. It claims the cooperation of the shaft, sump, gaseous chamber, flange, windback thread, primary shaft seal, secondary flange seal, and pressure-equalizing opening.

The secondary sealing surface is a significant limitation. A segmented seal that contacts only the shaft, but not the flange, would not satisfy that portion of claim 4.

What does claim 5 cover?

Claim 5 narrows claim 4 to a machine having multiple circumferentially spaced radial openings at essentially the same axial position.

Unlike claim 3, claim 5 uses “essentially the same axial location” in the machine combination. That language may tolerate limited manufacturing or design variation, but the openings must remain grouped in the axial region between the thread terminus and the flange.

What is the likely claim-construction dispute?

The principal construction issues would concern the following terms:

“Windback means”

The term identifies a device that returns lubricant toward the sump. Because the claims recite substantial structural detail, the scope is not limited to a generic means-function interpretation. The annular body, flange, spiral thread, opening, and seal relationship are expressly required.

“Terminating short of said flange”

The spiral thread must end before the flange. A thread that continues onto the flange or reaches the flange may fall outside the literal claim scope.

“Radial opening”

The opening must extend through the annular member from the inner surface to the outer surface. A blind recess, axial groove, or passage that does not fully penetrate the wall would not meet the express limitation.

“Between the terminus of said thread and said flange”

The opening must be located in the axial gap between the end of the spiral thread and the flange. Its circumferential position is less important than its axial position.

“Segmented seal”

The claims require a seal made of separate segments. A unitary elastomeric ring or continuous lip seal would not literally satisfy the segmented-seal limitation.

“To prevent lubricant from fouling”

This language describes the intended operation of the structural arrangement. The stronger infringement analysis would focus on whether the accused device has the claimed opening, thread termination, flange, and segmented seal, rather than on subjective evidence of actual fouling.

When did U.S. Patent 5,503,407 lose exclusivity?

The patent issued on April 2, 1996. Because it was filed under the pre-Uruguay Round patent-term regime, its ordinary U.S. term was 17 years from grant. On that basis, the patent expired on April 2, 2013. [1][2]

Event	Date
U.S. patent grant	April 2, 1996
Ordinary statutory term	17 years from grant
Expected expiration	April 2, 2013
Current enforceability	Expired

The expiration date eliminates prospective U.S. patent infringement liability under the issued claims. Patent expiration does not eliminate the historical relevance of the patent as prior art or as a possible source of technical disclosure.

What is the current litigation and Paragraph IV status?

No Paragraph IV certification, FDA Orange Book listing, or Hatch-Waxman litigation applies because the patent does not claim a drug or drug product.

The patent’s claims concern rotating machinery and sealing hardware. They are outside the Orange Book framework, which covers patents submitted for approved drug products. The patent also cannot create biosimilar or generic-drug entry barriers.

A historical infringement action, if one existed, would not create current exclusionary rights after expiration. The six-year damages limitation under 35 U.S.C. § 286 would also constrain any historical damages analysis. [3]

What manufacturing and design barriers does the patent disclose?

The patent identifies a specific design problem: lubricant carried along a rotating shaft can pass the windback thread and contaminate a segmented seal. The claimed solution requires coordinated manufacturing of:

an annular sleeve or ring;
an internal spiral thread;
a flange for stationary mounting;
one or more through-wall radial openings;
a segmented shaft seal;
a secondary flange-contact seal surface; and
biasing structures for the seal segments.

The technical barrier is not the mere presence of a spiral groove. The claimed arrangement depends on the relative axial placement of the thread terminus, radial opening, flange, and seal. A competing design could avoid the expired claims by using a different pressure-management architecture, such as:

a continuous seal without segmented elements;
an axial or tangential pressure passage rather than a radial through-opening;
a radial opening positioned within the threaded region;
a windback thread that extends to a different sealing structure;
a separate pressure-relief chamber; or
a seal mounted independently of the windback flange.

These alternatives may raise infringement or validity questions under other patents, but they would not automatically satisfy claims 1-5.

How strong was the patent estate?

The issued patent has a concentrated claim set. It contains five claims, but only two independent claims:

Metric	Assessment
Independent claims	2
Dependent claims	3
Primary technology	Mechanical shaft sealing and lubricant management
Core inventive feature	Radial pressure-equalization opening between thread terminus and flange
Claim breadth	Moderate for the specified architecture; narrow outside it
Current enforcement value	None after expiration
Prior-art value	Potentially relevant to later windback and shaft-seal designs

Claims 1 and 4 provide separate enforcement theories. Claim 1 focuses on the windback assembly. Claim 4 requires the complete rotating-machine environment. Claims 2, 3, and 5 add opening-count and spacing limitations but do not materially expand the estate.

The estate is therefore technically focused rather than platform-like. It does not cover all lubricant-return systems, all shaft seals, or all rotating machines.

How does this patent compare with drug patents and Orange Book patents?

Issue	U.S. Patent 5,503,407	Drug patent
Subject matter	Mechanical windback and shaft seal	Active ingredient, formulation, method, or drug product
FDA approval required	No	Yes for regulated drug products
Orange Book listing	No	Possible for qualifying drug patents
Paragraph IV certification	No	Yes for ANDA challenges
Generic entry risk	Not applicable	Relevant
Biosimilar risk	Not applicable	Relevant to biologics
Patent term	Pre-1995 grant-based term	Usually 20 years from earliest nonprovisional filing
Commercial exposure	Machinery sales and licensing	Drug sales, launch timing, and market exclusivity

Any commercial analysis should therefore focus on industrial equipment, rotating machinery, compressor or turbine systems, mechanical-seal suppliers, and historical licensing or procurement records, not pharmaceutical revenue.

What is the geographic coverage?

The patent’s enforceable rights were limited to the United States. Foreign counterparts, if any, would have had separate prosecution histories, claim scope, expiration dates, and legal status. The U.S. patent number alone does not establish protection in Europe, Japan, China, Canada, or other jurisdictions.

Because the U.S. patent expired in 2013, current U.S. freedom to operate is not restricted by claims 1-5. Any current geographic risk would have to arise from later patents, foreign rights, trade secrets, contractual restrictions, or proprietary equipment designs.

Key Takeaways

U.S. Patent 5,503,407 is a mechanical windback and segmented-shaft-seal patent, not a drug patent.
The central claim feature is a radial through-opening located between the end of an internal spiral thread and a seal-supporting flange.
Claims 1-3 cover the windback assembly; claims 4-5 cover a rotating machine incorporating the assembly and segmented secondary sealing surfaces.
The patent issued April 2, 1996, and its ordinary term expired April 2, 2013.
The patent has no Orange Book, Paragraph IV, generic-drug, biosimilar, or FDA exclusivity relevance.
Current U.S. infringement risk from the issued claims is absent because the patent is expired.
The patent remains relevant as technical prior art and as a reference point for later shaft-seal and lubricant-management patents.

FAQs

Does U.S. Patent 5,503,407 cover a mechanical seal by itself?

No. The claims require a specific relationship between a windback annular member, internal spiral thread, radial opening, flange, and segmented seal. A conventional mechanical seal without those elements is outside the literal claim structure.

Could a device infringe if it has no radial pressure-equalization opening?

It would not literally satisfy the central opening limitation in claims 1-5. An equivalent-elements analysis would depend on the particular device and applicable legal standards, but the patent is expired in any event.

Is the patent relevant to compressor and turbine manufacturers?

Yes, as a technical disclosure concerning lubricant control around rotating shafts, sumps, gaseous chambers, and segmented shaft seals. It does not create current U.S. exclusionary rights.

Can the patent block importation of a windback seal into the United States?

No, because the patent expired in 2013. Importation risk would have to arise from another unexpired U.S. patent or a different legal right.

Does patent expiration remove the disclosure from the prior-art record?

No. Expiration ends enforceable patent rights but does not remove the patent from the prior-art record. The disclosure may remain relevant to novelty, obviousness, and design-history analyses.

References

U.S. Patent No. 5,503,407, “Windback means,” issued Apr. 2, 1996. Google Patents. https://patents.google.com/patent/US5503407A/en
United States Patent and Trademark Office. (2024). Patent term calculator and patent term information. https://www.uspto.gov/patents/laws/patent-term-calculator
35 U.S.C. §§ 154, 271, 282, 284, 286. Cornell Law School, Legal Information Institute. https://www.law.cornell.edu/uscode/text/35

Details for Patent: 5,503,407

Summary for Patent: 5,503,407