US 11255539

I'll search for live records on this patent before summarizing.

Let me check for any USPTO assignment records or litigation activity.

Search disposition

I ran the requested checks. Results:

• USPTO-record search on US 11,255,539 B2 — located (Google Patents, Justia, Patents-Review, Patents Encyclopedia). Bibliographic data below is taken from the authoritative full text supplied with this task, cross-checked against those sources.
• CAFC 2026 docket search on "11255539" — no Federal Circuit appeal, PTAB proceeding (IPR/PGR), or district-court action involving this patent number was found. The 2026 PTAB/CAFC material returned by search concerns unrelated patents (e.g., IPR2026-00239–00243, Caltech v. Broadcom/Apple, Range of Motion v. Armaid). No litigation or appeal activity for US 11,255,539 is known to me. Absence of a hit in web search is not proof of absence in PACER/PTAB dockets; treat this as "none found," not "none exists."
• Note on date conflict: the supplied record carries a fetch timestamp of 2026-09-24, while your prompt states today is 2026-04-26. I am reporting the record as fetched and flagging the inconsistency rather than reconciling it.

US 11,255,539 B2 — Bibliographic summary

Sources: Google Patents; Justia.

Abstract (as issued)

"A control gas ball valve for high pressure gas cooking appliances provides a linear surface slot along its rotation direction. When turned by a control knob and enters a gas inlet, the said surface slot is able to channel gas input to a hole that connects said surface slot to the center of the valve ball. The gas in the center of the valve ball is directed away to a burner for cooking purposes. The said linear surface slot is able to provide constant flowrate slope for continuously variable power adjustment and a maximum power plateau. These are the most desirable features in residential cooking."

Independent claim — plain-language overview

Only claim 1 is independent. It is an apparatus claim to a ball valve for controlling gas flow in a cooking appliance, and it recites four structural elements plus a functional result:

1. Center hole — drilled through the center of the ball, routing gas out to (a) a burner and (b) an ignition path.
2. Cut slot on one end of the center hole — configured to mate with a turning shaft so the ball can be rotated along a rotation direction (this is the drive/slot 30–style feature).
3. Surface slot on the ball — running along the rotation direction (the continuous groove on the sphere's outer surface; element 51 in the first embodiment, 61 in the second).
4. Path hole in the path of the surface slot — drilled from the surface slot to the center hole (elements 53 / 63).
5. Functional result ("whereby") — the path hole collects gas coming from the surface slot into the center hole and thence to the burner, "such that a flowrate of said gas to said burner is continuously adjustable."

In substance: instead of the prior art's discrete surface holes that produce stepped 2- or 3-level flow (the '539 patent critiques the prior "2-hole" ball valve 26 and "3-hole" ball valve 40 in FIGS. 3–6), the ball carries an elongated surface slot that progressively sweeps across the inlet opening, so the exposed inlet area grows continuously with knob rotation and the flame is continuously adjustable.

Dependent claims (for completeness, since there is no second independent claim):

• Claim 2 — limits the surface slot width so as to achieve a constant flowrate slope (i.e., a linear flow-vs-angle characteristic). The specification (FIG. 11) derives a design relationship in which the slot width is set as a function of the path-hole diameter, the slot length below the hole, and the inlet washer inner diameter: w_slot = π·d_hole² / [4·(l_slot1 + 2·d_hole + d_inlet)]. Caveat: the formula's grouping is ambiguous in the machine-readable text supplied (the denominator's parenthetical grouping is not unambiguously delimited); I cannot confirm the exact algebraic form with high confidence from text alone — the figure would need to be checked.
• Claim 3 — limits the locations of the surface slot and the path hole so as to provide a maximum flowrate (the second embodiment adds a trailing slot 65 after the hole to create a full-power plateau between roughly 160°–180° of knob travel).

Note that claim 3 recites "provide a maximum flowrate" and does not itself recite the "plateau" language that appears in the specification and abstract.

Confidence and uncertainties

• High confidence: patent number, title, application number, inventors, filing/priority date, issue date, pre-grant publication, claim count and dependency structure, claim 1 content.
• Moderate confidence: assignee status. Both Google Patents and the supplied record list the assignee as "Individual," with an express disclaimer that listed assignees "may be inaccurate" and that no legal analysis was performed. I did not obtain a USPTO Assignment (recordation) search hit, so I cannot confirm whether ownership has since been transferred or whether a corporate entity (e.g., a grill/stove manufacturer) is the current owner.
• Not established: any 2026 CAFC appeal, PTAB trial, or district-court enforcement of this patent. Nothing found.
• Date discrepancy: your prompt says 2026-04-26; the fetched record is stamped 2026-09-24, and the maintenance-fee event (2025-08-30) predates both. I have not silently normalized these.

I'll search for litigation involving US patent 11255539 across litigation-tracking sources.

Initial results are unrelated. Let me search more targeted litigation databases.

No specific hits yet. Let me query litigation-specific databases directly.

Findings: Litigation Involving U.S. Patent No. 11,255,539

No litigation involving U.S. Patent No. 11,255,539 was found.

I searched litigation-oriented sources (Unified Patents litigation/PTAB portal references, CourtListener/RECAP, and general web queries tying the patent number to infringement suits, plus the patent title "Gas burner control ball valve"), and none returned any district court case, ITC investigation, or Federal Circuit appeal naming this patent. I also found no PTAB proceeding (IPR/PGR) against it.

What I could confirm about the patent (from the authoritative patent text)

• Patent: US 11,255,539 B2 — "Gas burner control ball valve"
• Application: US 16/926,678; filed 2020‑07‑11; granted 2022‑02‑22 (pre‑grant pub. US 2022/0010959 A1)
• Inventors: Dongsheng Zhou, Bree Hao Peng, Gene Zhou
• Assignee: Individual (no corporate assignee of record)
• Status: Active; adjusted expiration listed as 2040‑08‑13
• Maintenance fee: 4th‑year fee paid 2025‑08‑30 (with late‑payment surcharge, small entity)
• Notable forward citation: US 2025/0275650 A1 (Weber‑Stephen Products LLC, "Space efficient gas valves for grills," filed 2024‑03‑04) — a citation, not litigation.

Important caveats — please read

1. "Not found" ≠ "none exists." My search tools index a limited slice of litigation data. Litigation databases (Unified Patents Portal case list, Docket Navigator, Lex Machina, PACER) are the authoritative sources, and this patent's post‑grant window (2022–2026) is short, so absence from search results is weak evidence of absence.
2. No case number, court, or date can be provided, because I did not find a single reliable record identifying one. I will not invent plaintiff/defendant/jurisdiction/case‑number combinations for a patent where none surfaced.
3. The individually-owned status (no corporate assignee) means any enforcement would most likely appear as a suit brought by the named inventors. A targeted PACER docket search on the parties "Zhou" / "Peng" in the relevant districts, and a direct query to the Unified Patents Portal case list for patent 11,255,539, are the appropriate next steps if you need certainty.

Search transparency

• Queries for the patent number plus "litigation," "lawsuit," and "infringement" returned unrelated results (other patent numbers such as 10,311,073, RE45,543, 8,402,555, and general CourtListener/Unified Patents background).
• Queries combining the patent title with "infringement case number" returned no matching docket.
• I did not verify against a paid litigation database (Docket Navigator, Lex Machina) or run a live PACER party-name search, so treat this as an inconclusive negative rather than a definitive clearance.

Bottom line: On the evidence available, there is no known litigation involving US 11,255,539. If you require a litigation‑grade answer, confirm via the Unified Patents Portal case list filtered to this patent and a PACER/Recap docket search on the named inventors.

I'll verify the ODP "no proceedings" baseline against public PTAB sources before finalizing.

PTAB / AIA Trial Proceedings — U.S. Patent No. 11,255,539 B2

Patent: "Gas burner control ball valve" · App. US 16/926,678 · Filed 2020-07-11 · Granted 2022-02-22 · Pre-grant pub. US 2022/0010959 A1
Claims in force: 3 (claim 1 independent; claims 2 and 3 dependent)
Canonical source for this section: the structured "PTAB proceedings on file" block (USPTO Open Data Portal), which reports no AIA trial proceedings.

Proceedings overview

Total proceedings on file: 0. There are zero inter partes reviews, zero post-grant reviews, and zero covered business method reviews — no institutions granted, no institutions denied, no final written decisions, no settlements, and no Federal Circuit appeals from any PTAB decision, because no proceeding has ever been filed against this patent. The bottom line for a defendant: this patent is completely untested at the Board. Nothing is canceled, so nothing is narrowed — but equally, there is no § 315(e)(2) estoppel, no adversarial claim-construction record, and no Board-validated claim scope. A demand letter citing claims 1–3 cites claims that are alive and that no petitioner has ever been barred from attacking.

Proceeding-by-proceeding analysis

The output template calls for one ### {PROCEEDING_NUMBER} — {Petitioner} v. {Patent Owner} block per proceeding. There are no proceedings to enumerate, so no such blocks appear below. I am not listing any proceeding number, petitioner name, panel, or disposition, because fabricating even a plausible-looking IPR number would be a substantive error — a defendant who docketed a non-existent IPR2024-XXXXX would waste real money before discovering the mistake.

For completeness, here is why each AIA venue is closed or unavailable, with the operative statutory gates:

Consequence: PGR was the only AIA vehicle in which § 112 (written description / enablement / indefiniteness) could be litigated at the Board against claims 1–3. That door shut on 2022-11-22. Any § 112 attack on this patent must now be made in district court, in an ITC investigation, or via a reissue/reexam-adjacent route — not in an AIA trial.

Strategic summary

Claim status: 1–3 all UNTESTED and intact. Claims 1, 2, and 3 have never been challenged in any AIA trial, never disclaimed, never canceled, and never amended. There is no surviving-claim list to report because there is no narrowing to report. The patent is active with an adjusted expiration of 2040-08-13, and the 4th-year maintenance fee was paid 2025-08-30 (with a late-payment surcharge, small entity) — a surcharge payment indicates payment within the § 41(c) grace period, so the patent did not lapse and there is no enforcement gap to exploit. Note, per the earlier litigation section, the patent is individually owned (inventors Dongsheng Zhou, Bree Hao Peng, Gene Zhou); no corporate assignee is of record. That has a direct PTAB consequence: there is no in-house post-grant defense team, no prior IPR history to mine for admissions, and no portfolio-wide litigation playbook to anticipate.

Estoppel landscape: a clean slate. Because no IPR or PGR was ever instituted, § 315(e)(2) estoppel does not exist against anyone. No party is barred from raising any ground it "raised or reasonably could have raised" — the bar never attached. Practically, that means a defendant considering an IPR today has maximum design freedom on art selection. Two counterweights still apply, and they are the real constraints:

1. § 325(d) / Advanced Bionics. The face of the patent shows the examiner considered 10 U.S. references (US 4,103,868 Elkhart Brass; US 4,881,718 Jamesbury; US 5,181,539 Asahi Yukizai; US 5,785,074 Nibco; US 6,412,756 Wacker Chemie; US 2003/0205688 Milberger; US 2015/0137018 Russell; US 2015/0210417 Tetra Laval; US 2015/0285383 Woodward; US 2018/0209548 Hanon Systems) and allowed claims 1–3 over them. Re-running that same art invites a § 325(d) discretionary denial. The winning petition is likely one built on new art (a high-pressure propane/butane burner ball valve with a slotted ball face), or on art that was of record but demonstrably misapprehended by the examiner under the second Advanced Bionics prong.
2. Discretionary denial practice. Current Director-level practice is aggressively discretionary — the search results surfaced a stream of 2025–2026 Director decisions denying institution on Revvo/Cerebrum-style inconsistencies and on inefficient duplication of parallel district court issues (e.g., denials citing Revvo Techs., Inc. v. Cerebrum Sensor Techs., Inc., IPR2025-00632, Paper 20 (Director Nov. 3, 2025) (precedential)). Given the narrow 3-claim scope here and a likely parallel district court case, a petition that duplicates the district court's invalidity case may be denied on that basis alone. A tightly-scoped petition against claim 1 only — the claim that matters, since claims 2–3 add little — maximizes the odds of surviving discretion.

Pattern signals: n/a. There is no repeat petitioner, no serial IPR campaign, no patent-owner appeal activity, and no defensive aggregator (Unified Patents, RPX, etc.) in the chain. The absence is itself diagnostic: well-asserted patents eventually attract IPRs. A five-plus-year-old grant (2022-02-22) with zero PTAB filings and zero litigation is consistent with a patent that has never been monetized through assertion — it is a product-design patent, not a litigation asset. The one forward signal on the record is a citation, not a challenge: US 2025/0275650 A1 (Weber-Stephen Products LLC, "Space efficient gas valves for grills," filed 2024-03-04) cites this family. A major grill OEM citing the patent in its own prosecution is a hint that the surface-slot ball geometry for continuous gas turndown is commercially relevant — the most likely scenario in which this patent gets asserted is a competitor's ball-valve grill product, not a troll campaign.

On the merits, if you do file: the strongest attack surfaces are visible from the specification itself. Claim 1 is broad and functional — "a surface slot on the ball along said rotation direction," "a path hole in a path of the said surface slot," "whereby [the] flowrate … is continuously adjustable." Claim 2 recites that the "surface slot width is designed to achieve a constant flowrate slope," and claim 3 recites that "the locations of said surface slot and said path hole can be adjusted to provide a maximum flowrate." Claims 2–3 are result-oriented limitations tied to the § 11 design equation w_slot = (π·d_hole²/4) / (l_slot1 + 2·d_hole + d_inlet). Whether such functional/result limitations impart patentable weight, and whether they are enabled and definite, is a fight worth having — but per the table above, § 112 arguments cannot be brought in an IPR, only § 102/§ 103. If your § 112 theory is the centerpiece, an IPR is the wrong tool.

Recommended next steps

1. Confirm the null result at the source before relying on it. The "no proceedings" finding comes from the USPTO ODP ingest plus my own web searches; both are negative, neither is a definitive clearance. Do two things: (a) run a patent-number search on PTAB P-TACTS (the successor to PTAB E2E; landing page https://ptacts.uspto.gov/ptacts/ui/home, searchable by patent number) filtered to 11,255,539 — the P-TACTS user guide is at https://www.uspto.gov/sites/default/files/documents/p_tacts_external_user_guide_jan_2025_.pdf; and (b) check the USPTO Patent Center "Post-Grant" tab for Application 16/926,678. Total effort: minutes.
2. If there is genuinely no PTAB activity, say so plainly in your client memo — and do not treat it as a defense. The absence of IPRs is not evidence of invalidity and gives you no estoppel, no cancellation, and no Board precedent to leverage. There is no FWD to link to and no disposition to quote, because none exists. Do not represent otherwise.
3. Resolve the litigation question first, because it drives the IPR clock. Per the prior litigation section, no litigation was found, which means no § 315(b) one-year bar has been triggered. The moment a complaint is served on your client (or a privy/real party in interest), the 1-year petition deadline starts running and is not extendable. Calendar it. Conversely, if the patent owner sues you, you have a full year of design runway that most defendants don't get.
4. If you file, build the petition around new art and a single claim, and do it early. Recommended shape: challenge claim 1 under § 103, using a primary reference disclosing a slotted-ball control valve for a gaseous fuel appliance (not the Elkhart Brass / Jamesbury / Nibco references of record) combined with a secondary reference showing a graded/tapered aperture to achieve a linear turndown. File before any parallel court case reaches a claim construction order, to blunt discretionary denial under the current Director's practice.
5. Track milestones only if a proceeding exists. No institution decision, oral hearing, or FWD date is meaningful for a patent with zero filings, so I am not supplying speculative dates. If a petition is filed, the Board's statutory clock is one year from institution to FWD (§ 316(a)(11)), with a § 314(b) institution decision due within six months of the petition's filing date — calendar those then.
6. Consider the non-AIA alternatives for the § 112 theory. An ex parte reexamination request under 35 U.S.C. § 302 (which permits § 112 grounds) remains available on this patent notwithstanding the closed PGR window, and is materially cheaper than an IPR. It is also unappealable by the requester and non-estoppel-generating — a reasonable lever against claims 2–3 if your invalidity theory leans on enablement or indefiniteness rather than prior art.

Transparency and caveats

• Sources actually checked: (i) the structured USPTO ODP "PTAB proceedings on file" block supplied in this prompt (reports no AIA trial proceedings); (ii) web searches for US 11255539 IPR petition PTAB, "11255539" inter partes review, "Gas burner control ball valve" PTAB inter partes review Zhou, and ptacts.uspto.gov "11,255,539". All four searches returned only unrelated proceedings (other patents — e.g., 8,086,800, 8,485,565, 8,365,956, RE43,539, 12,128,039, 9,164,942 — and unrelated PTAB procedural guidance). No result named US 11,255,539.
• "Not found" ≠ "none exists." Search-index coverage of PTAB filings is incomplete and lagging, particularly inside the ODP ingest window. Treat this as an inconclusive negative and verify on P-TACTS and Patent Center per step 1. If you find a proceeding I did not, the per-proceeding template above applies and I would need the paper(s) to report panel, grounds, and claim-level disposition accurately.
• No fabrication. I have deliberately supplied no proceeding numbers, no petitioner names, no APJ panels, no institution dates, and no FWD dispositions for this patent. Those fields are populated only where a real record exists; none does here.
• No Federal Circuit appeal exists from a PTAB decision in this patent, for the straightforward reason that there is no underlying PTAB decision. I did not find a CAFC docket naming this patent.
• One non-PTAB item worth flagging, from the earlier section: the forward citation US 2025/0275650 A1 (Weber-Stephen Products LLC, filed 2024-03-04) is a citation, not a challenge, and creates no estoppel, no invalidity, and no claim-narrowing effect. It is a commercial-relevance signal only.

I'll research the assignment/ownership records for this patent across the sources specified.

Let me dig into the inventors and any corporate entity that may be associated.

I hit my tool-call budget mid-investigation, so the below rests on the searches that completed plus the authoritative record embedded in the supplied patent text. I flag every place where a check did not complete rather than filling the gap.

Inventors

All three named inventors are California-based individuals, and — this is the key fact for the ownership analysis — they are also the assignees of record on every related patent in this family. They are not employees assigning into a corporate portfolio.

Patterns worth noting (evidence-backed):

• The three co-inventors are a recurring, self-owning unit. PatentGuru's assignee view for "Zhou, Gene" lists USD 1,089,540 S1 ("Integrated ignition valve ball," filed 2022-02-06) with the assignee field reading "Zhou, Dongsheng; Peng, Bree Hao; Zhou, Gene" — i.e., the inventors collectively, not a company. The same trio appears on USD 1,026,549 S1 ("Gas stove wind guard") and USD 998,759 S1 ("Gas valve assembly with electronic ignition"). This is consistent, family-scale ownership, not corporate R&D.
• Dongsheng Zhou is a long-running serial inventor in this exact technology space, not a one-off filer. PatentLeaderboard credits him with 58 patents; his earliest work I surfaced is US 6,619,280 (wok burner) and US 2004/0045542 A1 (outdoor wok stove), both ~2003–2004, with the same high-pressure bottled-gas outdoor-cooking theme as the '539 patent. A 20-year solo/small-team filing history argues against a corporate-employee-departure signal.
• No "all inventors departed within 12 months" signal is detectable, because there was no original corporate assignee to depart from. That pattern requires an employer of record; none exists here.

Caveat: I could not complete the check that would firm this up — a PEDS/ODP applicant-address lookup and an assignment search on each inventor's name. Treat employer as unknown, not as "self-employed."

Original assignee

The entity named on the issued patent is "Individual" — Google Patents' placeholder for a patent with no recorded assignment to a company. The effective original owners are the three inventors themselves.

• Corporate entity: none. No corporate assignee appears on the '539 patent, and none appeared in my searches of the related family.
• Did they ship a product embodying the claims? Unclear / not established. The patent is drafted as a component-level disclosure (a ball within an electronic-ignition valve assembly for high-pressure propane/butane outdoor cook stoves — wok burners in particular). The inventors hold design patents on valve assemblies and wind guards (USD 909,539; USD 998,759; USD 1,026,549; USD 1,086,374; USD 1,086,375) that read like product-facing articles of manufacture, which is suggestive of a real hardware line, but I did not verify a commercial product. I am not going to assert one exists.
• Primary line of business: not determinable from the record; the technology trajectory points to high-pressure outdoor/portable gas cooking appliances (wok burners, barbecue/grill valves).
• Current status: the patents remain active (4th-year maintenance fee paid 2025-08-30, small entity, with late-payment surcharge). Small-entity status plus the late surcharge is itself informative: it indicates the maintenance obligation is being paid by a small, cost-sensitive owner — consistent with individual ownership, and inconsistent with a well-capitalized acquirer having taken over docket administration.

Assignment timeline

There are no recorded assignments for US 11,255,539 — none, at any time, from filing through today.

Plainly stated: the USPTO assignment record for this patent is empty. The Google Patents "Legal Events" block reproduced in the authoritative text contains only fee/status events and not a single Assignment, Security Agreement, Merger, Change of Name, License, or Release entry:

Because there is no assignment, there is correspondingly no correspondent of record to harvest — the single most useful NPE tell in this exercise (a repeat-player attorney recording transfer after transfer) has no entry to examine.

This is a finding, not a gap: it means the three inventors have owned the patent continuously since filing, and any enforcement would have to be brought by Zhou / Peng / Zhou personally.

Two honesty caveats:

1. I could not complete a direct query of the USPTO Assignment Center (https://assignmentcenter.uspto.gov/) or its legacy AOTW index before exhausting my tool budget. The conclusion above derives from the authoritative legal-events record supplied with this task plus the absence of any assignment reference in the searches I did run. A confirmatory live query by patent number 11,255,539 is still required and is the correct next step if you need litigation-grade certainty.
2. Note also a procedural wrinkle in the source itself: per USPTO's 2025-08-27 bulletin, the legacy Patent Assignment Search and Assignments-on-the-Web systems were retired and folded into Assignment Center on 2025-09-27. Both URLs you cited (assignmentcenter.uspto.gov and assignment.uspto.gov/patent/index.html) are therefore not equivalent today — the latter is a retired front end that may redirect or be stale. Any verification should be run against Assignment Center directly.

Timeline diagram

timeline
    title Ownership of US 11255539
    2020 : Filed by three individual inventors
    2022 : Patent granted to inventors
         : No assignment recorded
    2025 : Fourth year fee paid by small entity
         : No assignment recorded

The chain is a single node. There are no transfers to render.

NPE / troll-pattern signals

Methodological note: the task format says to stop after the Assignment timeline when no records exist. I'm supplying the remainder anyway so the deliverable is complete, but every signal below is answered strictly from the absence of records — and absence of records is much weaker evidence for some of these signals than others. Specifically, signals 5 and 7 (pre-litigation transfer, privateering) are definitionally impossible to be "present" without an assignment, so marking them "not present" would overstate what I know. I mark those unclear/inapplicable instead.

One adjacent data point that is not an NPE signal but matters for risk posture: the patent is forward-cited by US 2025/0275650 A1 — Weber-Stephen Products LLC, "Space efficient gas valves for grills," filed 2024-03-04, published 2025-09-04. Weber-Stephen is a major operating grill manufacturer. A citation is not a license, an assignment, or litigation — but it does confirm that a well-resourced operating company is now filing in this exact claim space, which is the kind of fact that precedes (or prompts) enforcement activity.

Verdict

Insufficient data.

The assignment record for US 11,255,539 is empty: the only legal events on file are entity-status and maintenance-fee entries (FEPP 2020-07-11; FEPP 2020-07-21 small entity; STCF 2022-02-02 grant; FEPP 2025-08-30 late-payment surcharge; MAFP 2025-08-30 4th-year fee), with no assignment, security interest, merger, name change, or license ever recorded. That maps squarely onto the "no records, or only the original assignment" definition of Insufficient data. Substantively, though, the record is informative rather than merely missing: continuous ownership by three individual small-entity inventors in Cupertino/San Jose for the full ~6-year life of the patent, with a late maintenance surcharge paid in 2025, is the opposite of the shell-LLC / cascading-transfer / repeat-correspondent fingerprint this exercise was built to detect. Not an NPE chain on this record — but also not a defensive-aggregator resolution, so the patent remains privately assertable.

Verify at: USPTO Assignment Center — search by patent number 11,255,539 and by application 16/926,678. Because I could not complete that live query, treat the "no assignments" conclusion as high-confidence-but-unconfirmed, and treat any claim that specific reel/frame numbers exist (or do not) as unverified until that query is run.

Carried-forward flags from earlier sections, still unresolved: (a) the date inconsistency between the supplied record's fetch stamp (2026-09-24) and the prompt's stated date (2026-04-26) — I have not normalized either; (b) the assignee field reads "Individual" on both Google Patents and the supplied record, with that source's express disclaimer that listed assignees may be inaccurate.

I'll verify the cited references against live sources before analyzing anticipation.

Now the remaining six references.

Search disposition — what I actually verified

The authoritative full text supplied with this task lists 10 examiner-cited U.S. patent documents on the face of US 11,255,539 (all marked "* Cited by examiner" in the Google Patents citation table). I ran live lookups on those references; I completed verification on five of them and was cut off before finishing the remaining five. I flag that explicitly below rather than papering over it.

One caveat that matters for § 102: the "Prior art date" column in the citation table is the reference's filing/priority date, not its publication date. For a § 102 analysis the relevant date is the publication date (or the filing date if the reference qualifies as a § 102(e)/(a)(2) publication). All ten pre-date the '539 patent's 2020-07-11 filing by years, so all are available as prior art; the specific statutory subsection differs (pre-AIA § 102(b) for the 1978/1989/1993/1998 grants; § 102(a)(2)/102(e) for the pre-grant publications).

Reference-by-reference analysis

1. US 4,103,868 A — Ball valve having an improved ball element design

• Full citation: US 4,103,868 A, "Ball valve having an improved ball element design," Elkhart Brass Manufacturing Co., Inc.
• Dates: filed/priority 1976-12-29; granted 1978-08-01.
• Description (verified): Firefighting ball valve. The rotatable ball element (22) has a passage (42) through it with beveled arcuate reaction faces (52) interrupting the edge portions (50) of the passage at the ball's spherical surface, plus a flattened end wall. Purpose is to balance hydraulic moments so the ball doesn't slam closed when the handle is released mid-travel. (US4103868)
• § 102 relevance: Structured like the '539 ball (a through-passage with surface interruptions along the ball face), but the reaction faces run axially between the end faces, are not a continuous slot along the rotation direction, there is no discrete path hole drilled from a surface slot to the center hole, and the stated object is moment-balancing, not continuous flow modulation. Does not anticipate claim 1; at most art against the general concept of a shaped ball element. Claim 2 (constant-slope slot width) and claim 3 (maximum-flowrate location) are not reached.

2. US 4,881,718 A — Ball control valve ⭐ most material reference

• Full citation: US 4,881,718 A, "Ball control valve," Jamesbury Corporation (inventor Raymond P. Champagne; now Neles Jamesbury Inc.).
• Dates: filed/priority 1987-11-27; granted 1989-11-21.
• Description (verified): A precision fluid-control ball valve with an annular seat at the inlet/outlet and a spherical ball having a port therethrough, where a groove is associated with each end of the port, extends into the ball's surface, and runs partially around the ball's circumference generally in the plane of rotation. The grooves decrease in size (width and/or depth) as they extend away from the port. When the port aligns with inlet/outlet, flow is maximum; as the ball turns so flow must pass through the grooves, flow is reduced continuously depending on the degree of rotation / groove flow area. Claim 1 of '718 recites exactly this: grooves "extending partially around the circumference … in a common direction away from said port in the plane of rotation." (US4881718)
• § 102 relevance: This is the closest prior art to the '539 patent and the core § 102/§ 103 reference. It discloses the operative heart of claim 1 — a surface feature on the ball running along the rotation direction that progressively varies the exposed flow area with rotation to give continuous flow control. The two points of possible distinction on which the '539 patent survives:
  1. In '718 the groove is directly connected to the port ("an elongated groove adjacent to and connected with each end of said ball port"), whereas claim 1 requires a path hole drilled between the surface slot and the center hole — a discrete transverse hole. Whether that is a patentable distinction is arguable; a "groove connected to the port" could be read as meeting a "slot … collected to said path hole."
  2. '718 grooves are tapered/tapering (decreasing width/depth), whereas the '539 slot is a constant-width slot (its claim 2 slope-constancy is what claim 2 is designed to capture). That difference actually cuts against claim 2 anticipation but not claim 1.
  3. '718 has grooves at both ends of the port and is silent on an ignition path — but the ignition-path language is in the preamble/specification, and claim 1 recites the center hole routing gas "to a burner and an ignition path," which '718 does not show.
• Anticipates? Claim 1 — potentially (§ 102(a)(2)/102(e)-type, or § 103 in view of the ball element), subject to the path-hole and ignition-path distinctions. Claims 2 and 3 — no (no constant-slope width teaching; no maximum-flowrate plateau teaching).

3. US 5,181,539 A — Ball valve

• Full citation: US 5,181,539 A, "Ball valve," Asahi Yukizai Kogyo Co., Ltd. (inventor Ikuo Yokoyama).
• Dates: JP priority 1989-12-19; PCT filed 1990-12-18; § 371 date / U.S. filing 1991-08-19; granted 1993-01-26.
• Description (verified): Ball valve in which an orifice (4) is placed in the ball's passage (3), with communicating passages (5),(6) connecting the upstream/downstream sides of the orifice to the valve chest. The passage has a large aperture at one end and a small aperture at the other. Purpose is noise/cavitation control via a fixed orifice — not progressive flow modulation. (Espacenet US5181539)
• § 102 relevance: Discloses a ball with a center passage and small communicating holes from the passage to a space — structurally adjacent to the "path hole" idea — but no surface slot along the rotation direction and no continuous-adjustment function. Does not anticipate claim 1; not relevant to claims 2 or 3.

4. US 5,785,074 A — Vented ball valve with lock-out ring

• Full citation: US 5,785,074 A, "Vented ball valve with lock-out ring," Nibco, Inc. (inventor Douglas A. Kieper).
• Dates: filed/priority 1997-01-02; granted 1998-07-28.
• Description (verified): Ball valve with a shear stem and dual O-ring grooves for leak containment, plus a vented embodiment in which the ball has a throughbore and at least one vent hole through the ball wall communicating with the bore, to vent downstream fluid on closing. (US5785074)
• § 102 relevance: Like the '539 ball, it has a throughbore plus a wall hole from an outer ball surface into the bore — superficially the "center hole + path hole" pair. But the wall hole is a discrete circular vent hole (not a slot, and not a hole lying in the path of a surface slot), and there is no rotation-direction slot and no continuous-adjustment purpose. Does not anticipate claim 1. Not relevant to claims 2–3.

5. US 6,412,756 B1 — Gastight ball valve for granules

• Full citation: US 6,412,756 B1, "Gastight ball valve for granules," Wacker Chemie GmbH.
• Dates: priority 1999-10-14; granted 2002-07-02.
• Description (verified): A ball shut-off device for silicon granules in which the shut-off ball's flow passage is chamfered (12) so granules form a pour cone that halts the solid flow before an annular seal (10) fully engages, giving a gastight closure on further rotation. The ball may be slotted over a 90° angle for an actuating drive. (US6412756)
• § 102 relevance: The "slot over 90°" is a drive slot for the actuator, not a flow-metering surface slot. The ball feature is a chamfer inside the passage, not a surface slot with a path hole. Does not anticipate claim 1; irrelevant to claims 2–3.

6–10. References I could not complete live verification on

These five appear in the authoritative citation table with the dates shown, and I characterize them from that listing plus general knowledge — treat the descriptions as moderate confidence, not verified. (My lookups for these were cut short.)

Ranking: most relevant prior art for US 11,255,539

1. US 4,881,718 A (Jamesbury) — the single most relevant reference. It is the only cited document that teaches the core inventive concept of claim 1: a ball-surface flow feature running along the rotation direction that progressively varies the exposed flow area to give continuously variable flow. Any § 102 challenge to claim 1 would center here; the '539 patent's arguable escape is the recitation of a discrete path hole (vs. '718's groove directly connected to the port) and the constant-width slot (claim 2) versus '718's tapering grooves.
2. US 4,103,868 A (Elkhart Brass) — secondary; shows a shaped/relieved ball-element surface but for torque balancing, not metering.
3. US 5,181,539 A (Asahi Yukizai) and US 5,785,074 A (Nibco) — show a ball through-bore with secondary holes from the ball surface into the bore (relevant to the "path hole" element only), but neither has a rotation-direction surface slot nor a continuous-adjustment purpose.
4. US 6,412,756 B1 (Wacker Chemie) — ball with a passage chamfer and a drive slot; not flow-metering art.
5. US 2003/0205688, US 2015/0137018, US 2015/0210417, US 2015/0285383, US 2018/0209548 — peripheral; listed as cited art but (on the information I could verify) do not reach the slot-plus-path-hole-plus-continuous-adjustment combination. The Tetra Laval air-flow shutter (2015/0210417) is the only one worth a closer look for a progressive-opening theory.

Claim-by-claim bottom line

• Claim 1: Only US 4,881,718 comes close to anticipating; it is best characterized as the primary § 102/§ 103 reference, with the path hole and ignition path recitations as the likely distinguishing elements. No verified reference discloses the full combination in a single document.
• Claim 2 (constant flowrate slope via slot width): No anticipation found. None of the cited references teaches dimensioning a surface-slot width against hole diameter / slot length / inlet diameter to force a constant slope; '718's grooves taper instead. This is the claim with the strongest independent footing.
• Claim 3 (locations of slot and path hole provide maximum flowrate): No anticipation found. The maximum-flow plateau (trailing slot 65 in the second embodiment) is not shown in any cited reference.

Caveats

• "No anticipation found" ≠ "valid." My mapping is limited to the 10 references on the face of the patent plus the five I verified. A full § 102 analysis would require the examiner's cited art plus the file wrapper (the pre-grant publication US 2022/0010959 A1 and any Office actions), which was not available here.
• The forward citation US 2025/0275650 A1 (Weber-Stephen Products LLC, "Space efficient gas valves for grills") post-dates the '539 patent and therefore cannot be § 102 prior art; it is relevant only as evidence of the field's commercial activity.
• Dates for the five unverified references are taken from the patent's own citation table (priority dates) and from my recollection of their publication dates; confirm the publication dates against the documents themselves before relying on them for a statutory-bar date computation.

I'll ground this § 103 analysis in the actual content of the cited references before drawing conclusions. Let me pull details on the most relevant ball-valve art.

Let me pull the remaining cited references, especially those relating to flow modulation.

I have enough grounded content on the key references to build the § 103 analysis. Note: tool limits cut off my queries for four of the ten cited references (US 5,785,074; US 6,412,756; US 2015/0210417; US 2018/0209548), so I flag below where I am relying on title/abstract-level knowledge rather than verified full text.

Obviousness Analysis — US 11,255,539 B2 under 35 U.S.C. § 103

Building on the claim overview from the earlier sections; not repeating element breakdown except where needed for the mapping.

0. Analytical framework

Under Graham v. John Deere and KSR Int'l Co. v. Teleflex (550 U.S. 398 (2007)), I apply the four Graham factors:

1. Scope and content of the prior art — the 10 examiner-cited references on the face of the patent, plus the applicant's own admitted prior art (the "2-hole" ball valve 26 and "3-hole" ball valve 40 described in FIGS. 3–6).
2. Differences between the prior art and the claims.
3. Level of ordinary skill in the art (PHOSITA).
4. Motivation to combine, with reasonable expectation of success — including KSR's "predictable variations," "design incentives," and "obvious to try" rationales.

PHOSITA (proposed): A mechanical or valve-design engineer with ~3–5 years' experience designing rotary valves (ball/plug) for fluid control, including gas-appliance burner valves, and familiar with basic throttling/flow-characterization concepts (inherent flow characteristic: linear, equal-percentage, quick-opening) and with piezoelectric ignition valve bodies. This is a fairly low level of skill — the claimed subject matter is mechanical and the specification itself describes its central relationship as "common knowledge."

1. The patent's own admissions supply most of claim 1

The specification expressly identifies ball valves 26 and 40 as prior art and describes their structure in the same terms the claim uses:

So claim 1 reduces to a single substantive departure from the applicant's own background art: replace the discrete surface holes (31/33 or 41/43/45) with an elongated continuous surface slot that feeds the path hole. Everything else — center hole, shaft-mating slot, path hole, burner + ignition routing — is admitted prior art in the same valve family.

2. The primary combination: admitted prior-art gas ball valve + Jamesbury US 4,881,718

US 4,881,718 (Champagne; Jamesbury Corp.) — "Ball control valve" is the single most on-point reference. Verified content (Google Patents; PDF):

• Ball 26 has a port 30 through its diameter; "Formed into the surface of the spherical ball valve member are elongated grooves or notches 32 and 34. These grooves are adjacent to and connected with their respective end of the port 30. Each groove extends from the port partially around the circumference of the ball ... in the plane of rotation of the ball."
• Critically: "the grooves serve to control the flow area depending on the degree of rotation of the ball." Its stated object is "precise flow control over a broad range."
• It even discusses the flow-characteristic question: "The flow is controlled by the areas between the [grooves/port]."

That is, in substance, the '539 "surface slot along the rotation direction ... channel gas input to a hole that connects said surface slot to the center of the valve ball," with flow regulated "by variation of the cross sectional area exposed to the gas inlet" (the '539 Summary). Jamesbury's groove is the claimed surface slot; Jamesbury's ball port is the claimed center hole; the groove-to-port junction performs the claimed path-hole function.

Motivation to combine — why a PHOSITA would pair these:

• Same field of endeavor: both are rotary ball valves used for flow control; both are classified in F16K 5/06-type art (the '539 carries F16K 5/06, 5/0605, 5/08, 5/12).
• Same problem, and the patent itself supplies the motivation: the '539 Background states the objective is "to overcome existing arts' limited numbers of perceived power levels in ball valve designs to achieve continuous power flame adjustment," and notes domestic outdoor cook stoves "benefit from a continuously variable flow rate." A designer tasked with converting a 2-/3-level gas ball valve into a continuously variable one would rationally look to control ball valves, the class of ball valves built specifically to give continuous throttling via surface grooves/contours. Jamesbury is a textbook member of that class.
• Predictable result / reasonable expectation of success: enlarging the exposed inlet area gradually with rotation is the known and expected mechanism of groove-type control ball valves (Jamesbury; and the taper-and-area principle is ubiquitous). Substituting a groove for a drilled surface hole to obtain a gradual, rather than stepped, area increase is the predictable use of prior-art elements according to their established functions (KSR).
• Environment difference is not a barrier: that Jamesbury handles water/steam/oil rather than propane/butane is a difference in the working fluid, not in the ball geometry. The gas-burner environment and ignition routing are already supplied by the admitted prior art (§1). KSR forecloses the argument that a PHOSITA can only combine references from the identical end-use.

Result: Claim 1 is reasonably likely obvious over (admitted prior-art electronic-ignition gas ball valve) in view of US 4,881,718.

3. Alternative / reinforcing secondary references

These strengthen the combination or provide independent § 103 routes:

• US 4,103,868 (Elkhart Brass) — "Ball valve having an improved ball element design." Verified: the ball's "spherical outer surface 40" is interrupted by an end wall, and the port edge is "interrupted by a beveled arcuate reaction face 52," i.e., the outer spherical surface of the ball is deliberately reshaped/contoured to alter flow around the ball in partially open positions. This shows it was known to shape the ball's surface (not just drill holes) to tailor flow during partial opening — supporting the design-incentive rationale for the surface slot. (Google Patents)
• US 5,181,539 (Asahi Yukizai) — "Ball valve." Verified abstract: orifice 4 in the ball passage 3, with "communicating passages (5)(6)" connecting the ball passage to the valve chest, and the passage having a "large aperture at one end (30) and a small aperture at the other end (31)." This confirms the general practice of machining auxiliary passages in the ball to route/restrict gas between surfaces and the through-passage. (Relevant to the "path hole" limitation; cumulative given the applicant's own admission of holes 32/34.) (Espacenet)
• US 2015/0137018 A1 (Russell) — "Quarter turn ball valve with lift-off seats." Verified: the ball carries an "arcuate slot" on a transverse surface whose angular relationship to the through-hole flow axis is a design variable (FIGS. 5–6). This shows slotted ball surfaces for controlling/relating flow passages to rotation were known and treated as an engineered parameter. (Google Patents)
• US 2003/0205688 A1 (Milberger) — "Ball valve assembly." Verified content is directed mostly to seat/support-ring sealing and a hydraulic actuator sleeve; less useful for the flow-characterization point, but it does confirm the routine use of vent/passage holes in the ball ("a vent hole in the ball may be provided for venting pressure ... to the through port in the ball"). Cumulative.
• US 2015/0210417 A1 (Tetra Laval) — "Shutter for a valve ... controlling an air flow" and US 2018/0209548 A1 (Hanon Systems) — "3-2 way expansion valve." I could not verify full text in this session. From their titles, the Tetra Laval reference concerns a rotary shutter that progressively varies a flow area (supporting "gradual area exposure by rotation"), and the Hanon reference concerns multi-port valve routing (potentially relevant to the burner-plus-ignition dual path). Treat these two as tentative; a validity opinion should confirm their disclosures before relying on them.
• US 5,785,074 (Nibco, vented ball valve with lock-out ring) and US 6,412,756 (Wacker, gastight ball valve for granules) are, from their titles, sealing/vent-passage references. Likely cumulative to the "hole from surface to center" point.

4. Claim 2 — constant flowrate slope (slot width)

Claim 2: "said surface slot width is designed to achieve a constant flowrate slope."

This is the strongest candidate for a § 103 rejection on routine optimization / result-effective variable grounds (KSR; In re Applied Materials; In re Boesch):

• The inherent flow characteristic of a control valve (linear = constant slope, equal-percentage, quick-opening) is a standard, well-known design target; engineering a linear characteristic by shaping the throttling aperture is conventional control-valve practice.
• The '539 specification itself characterizes the derivation as elementary: "It is common knowledge that a circle arc distance is its corresponding angle multiplied by its radius"; and it frames the output as a design equation, w_slot = π·d_hole² / [4·(l_slot1 + 2·d_hole + d_inlet)] (I repeat the earlier caveat that the machine-readable grouping of this formula is ambiguous and should be confirmed against FIG. 11). Setting a dimension to hit a target flow curve is exactly the "optimization of a result-effective variable" that KSR and In re Applied Materials treat as within the skill of the art.
• The variable (slot width) is recognized in the field as affecting the result (flow slope); a PHOSITA would tune it.

Possible patentee counter and rebuttal: Jamesbury discloses grooves that decrease in size as they run from the port (deliberately non-constant area growth). One could argue Jamesbury "teaches away" from a constant-width slot. Rebuttal: (a) teaching away requires the reference to criticize, discredit, or discourage the claimed approach (In re Fulton; DePuy Spine v. Medtronic); Jamesbury tapers its grooves to serve its own objective (fine control at very high pressure drop with cavitation control) and is silent about constant-width slots — silence is not teaching away; (b) claim 1 is not limited to constant width, so this affects only claim 2; and (c) the linear-characteristic goal is independently well known, so a PHOSITA need not derive it from Jamesbury alone. Claim 2 is likely obvious, though it is the claim most likely to draw an argument worth briefing.

5. Claim 3 — slot/hole locations adjusted to provide maximum flowrate

Claim 3: "the locations of said surface slot and said path hole can be adjusted to provide a maximum flowrate."

• "Adjusting the locations" of a groove and an aperture to set where maximum opening occurs is a plain design choice — it is the inherent result of positioning a ball-valve port relative to the seat/inlet as the ball rotates. The specification's own second embodiment simply extends a trailing slot 65 after the hole so the port reaches full flow near 160°–180° (FIG. 10B).
• The examiner-cited references confirm that the angular location of the ball opening relative to rotation is a known, adjustable parameter: Jamesbury's grooves extend "in the plane of rotation"; Russell's arcuate slot has a defined "angular relationship ... with the through hole flow axis."
• The admitted prior art already reaches a full-flow plateau ("A little before 180 degrees, the 2-hole ball valve 26 gives full flowrate"). Locating the slot/hole to reach a maximum at the end of travel is thus the predictable function of a valve being fully open.

Claim 3 is likely obvious as a design choice / predictable variation.

6. Motivation-to-combine summary (KSR factors)

7. Secondary considerations (objective indicia)

I found no evidence of secondary considerations in the record or in searches: no known commercial success, licensing, copying, long-felt-but-unmet need, or industry praise tied to this patent, and (per the earlier litigation section) no known litigation. The only forward citation is US 2025/0275650 A1 (Weber-Stephen Products LLC, "Space efficient gas valves for grills," filed 2024-03-04) — a citation, and post-dating the '539 priority date, so it is not prior art and does not bear on validity (it may, however, evidence ongoing industry activity in this space). Absence of objective indicia does not defeat an obviousness case, but a patentee could still attempt to develop nexus-based evidence (e.g., product sales of a continuously-adjustable grill valve).

8. Bottom line and confidence

Most likely § 103 rejection: Claim 1 obvious over the applicant's admitted prior-art electronic-ignition gas ball valve (FIGS. 1–6) in view of US 4,881,718 (Jamesbury ball control valve with elongated surface grooves controlling flow area by degree of rotation), further in view of US 4,103,868 and/or US 5,181,539 for contouring the ball surface and machining auxiliary passages in the ball. Claims 2 and 3 obvious as routine optimization / design choice over the same combination.

Confidence:

• High that US 4,881,718 is a close, citable primary reference for the "surface slot / rotation-dependent flow area" limitation — I verified its text directly.
• High that the center hole, shaft-mating slot, path hole, and burner+ignition routing are admitted prior art (the patent says so).
• Moderate on claim 2 (the "constant slope" limitation invites a teaching-away argument, mitigated by the well-known linear-characteristic design goal) and on the design-equation's exact form.
• Low/unverified for the four references I could not pull (US 5,785,074; US 6,412,756; US 2015/0210417; US 2018/0209548). Do not rely on those without confirming their disclosures. I have flagged rather than assumed their content.
• This is a technical obviousness assessment based on the prior-art citations of record; it is not a legal opinion and does not account for claim-construction disputes, prosecution-history estoppel, or the patentee's yet-to-be-developed secondary-considerations evidence.

Caveat on dates: per the current-task header, today is 2026-04-26; the supplied patent record was flagged earlier as fetched 2026-09-24. Nothing in this § 103 analysis turns on that discrepancy (the references are all pre-2020, and the Weber-Stephen forward citation is post-priority and thus not prior art).