US 7438397

Based on the authoritative full-text of US 7,438,397 B2 (provided in the prompt) plus web searches of USPTO records, Google Patents, Justia, Unified Patents, and secondary litigation sources, here is the summary. Note that my live searches for a CAFC 2026 docket entry for this patent returned no results; I flag uncertainty where applicable.

Bibliographic data

• Patent number: US 7,438,397 B2 (searched as "7438397"; do not confuse with 7,938,523 or other similar numbers)
• Title: Methods and devices for purging gases from an ink reservoir
• Application: US 11/001,433, filed December 1, 2004 (priority date same)
• Publication: US 2006/0114298 A1 (June 1, 2006); Issue date: October 21, 2008
• Inventors: James Daniel Anderson, Jr.; David Emerson Greer; Matthew Joe Russell
• Original assignee: Lexmark International, Inc. (Lexington, KY)
• Subsequent assignments (per USPTO legal-event records): Funai Electric Co., Ltd. (recorded May 14, 2013, effective April 1, 2013) → Slingshot Printing LLC (recorded March 29, 2019)
• Current assignee: Slingshot Printing LLC
• Status: Expired – Lifetime (Google Patents shows adjusted expiration October 23, 2025)

Abstract

"A printhead comprising a first ink reservoir in fluid communication with an outlet nozzle and downstream from a first ink filter, and a pump assembly in fluid communication with the first ink reservoir and operative to withdraw gas from the first ink reservoir and subsequently inhibit fluid communication between the withdrawn gas and the first ink reservoir. The present invention also includes method of removing gas in fluid communication with an ink reservoir, the method comprising purging gas from a gas accumulation area of an ink reservoir, where purging act includes manipulating a valve assembly downstream from an ink filter, the valve assembly operative to separate the gas accumulation area of the ink reservoir from an external environment, the valve assembly operative to facilitate unidirectional volumetric flow of the gas between the gas accumulation area and the external environment."

Independent claims (plain-language)

There are 24 claims; the independent claims are 1, 18, 20, 22, 23, and 24.

• Claim 1 (apparatus – printhead with a two-check-valve purge system): A printhead with an ink reservoir that sits downstream of an ink filter and feeds an outlet nozzle. A pump assembly can suck gas out of the reservoir and then prevent that withdrawn gas from flowing back in. The assembly includes two one-way valves: the first isolates the pump-side from the reservoir interior, and the second isolates the pump-side from the outside environment. (Claims 2–17 add details: pump position between the valves; biased valve seats/bodies; spherical balls in circular openings; pressure-differential operation; a manually deformable diaphragm; a multi-color version with second and third reservoirs and a four-valve one-way assembly; horizontal/lateral tank couplings; pump mounted to the reservoir, etc.)

• Claim 18 (apparatus – inkjet component with elevated gas port and pump between two one-way valves): An ink reservoir having (i) an ink outlet at a low elevation, (ii) a gas outlet at a higher elevation, (iii) an ink entrance orifice, and (iv) a gas-accumulation area connected to the gas outlet. An ink filter communicates with the reservoir interior. A pump assembly, whose pump sits fluidically between at least two one-way valves, draws gas out through the gas outlet from the accumulation area and then blocks return flow. The ink entrance orifice sits lower than both the gas outlet and the accumulation area.

• Claim 20 (method – prolonging printhead life by displacing trapped gas): A method of increasing printhead longevity by displacing gas located in a reservoir downstream of an ink filter: establishing a gas-accumulation area in the reservoir; withdrawing the gas from the reservoir while keeping the withdrawn gas separate from the liquid ink; and opening a check valve so the accumulation area communicates with a gas-containment area (e.g., a bulb/chamber).

• Claim 22 (method – one-way valve purge to the external environment): A method of removing gas from an ink reservoir by purging its gas-accumulation area with a one-way valve assembly located downstream of the ink filter. The assembly separates the accumulation area from the external environment and permits gas to flow only one way (out), and the first valve isolates the second valve from the accumulation area.

• Claim 23 (apparatus – vertically oriented filter with elevated air-accumulation region): A printhead with a reservoir in fluid communication with a nozzle outlet and fed through a vertically oriented ink filter. The reservoir includes an air/vapor-accumulation region elevated relative to the vertical filter, so bubbles that pass the filter are directed up into the accumulation region (rather than starving the nozzles).

• Claim 24 (apparatus – laterally coupled replacement tank): An inkjet component with the same elevated-gas-outlet/accumulation-area/pump-recirculation-blocking structure as claim 18, further requiring a first inlet coupling that interfaces (laterally) with an outlet coupling of a laterally replaceable ink tank.

Litigation / CAFC 2026 status (with uncertainty)

• Per Google Patents' litigation annotations, this patent was involved in two Texas Western District Court cases identified as 6:19-cv-00362 and 1:20-cv-00184 — Slingshot Printing LLC's 2019 infringement suits against HP Inc. Secondary sources (Actionable Intelligence, The Recycler, Unified Patents) describe these as part of Slingshot's broad assertion of former Lexmark inkjet patents against HP (settled/dismissed; Unified Patents lists the cases as "Closed").
• I found no CAFC 2026 docket entries specifically for US 7,438,397 in my searches (the CAFC docket search returned empty results). Given the patent's expired-lifetime status and its age, it is plausible there is no active 2026 CAFC appeal, but I could not affirmatively verify this, and I did not have direct access to the USPTO Patent Center or the CAFC's official docket database in this session. If appellate activity exists, it would most likely appear under Slingshot Printing LLC as appellant/patentee.
• Chain-of-title note: The original Lexmark assignment (2004) and the Funai (2013) and Slingshot (2019) assignments are confirmed in the USPTO legal-event text reproduced on Google Patents; current ownership is listed as Slingshot Printing LLC.

Confidence note: Bibliographic facts, abstract, claim text, and assignment chain are from the supplied full patent text and corroborating search results and are high-confidence. The absence of a 2026 CAFC docket entry is based only on the searches performed and should be treated as unconfirmed negative information.

I'll research litigation involving US patent 7,438,397. Let me search multiple sources.

Let me dig deeper into the specific cases and outcomes.

I have strong results. Let me do a couple of verification searches for any other defendants or appeals.

Litigation Involving U.S. Patent No. 7,438,397

Bottom line

One litigated matter is confirmed for the '397 patent — the Slingshot Printing LLC v. HP Inc. campaign in the Western District of Texas. It ended by stipulated dismissal with prejudice (April 1, 2021) after settlement. I found no other district court case, and no CAFC appeal, naming the '397 patent as an asserted patent.

⚠️ Correction to a premise in the earlier-generated sections: the earlier "Patent summary" and "PTAB challenges" sections listed 6:19-cv-00362 and 1:20-cv-00184 as two separate W.D. Tex. cases. They are the same case. It was filed in the Waco Division as 6:19-cv-00362-ADA, transferred to the Austin Division on February 19, 2020, and reassigned as 1:20-cv-00184-ADA. They should be cited as one matter.

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Confirmed litigation

1. Slingshot Printing LLC v. HP Inc.

Key docket anchors: W.D. Tex. transfer stipulation (Feb. 18, 2020) and Order Transferring Case to Austin Division (Feb. 19, 2020); HP's Preliminary Invalidity Contentions identifying the '397 patent and asserting invalidating art against it (e.g., Driggers US 6,116,726; Kono JP 2003-326732; Murphy US 5,596,354; Yamamori JP H03-182361; Ross US 6,431,694; Baker US 4,771,295).

Note on the litigation feed: Google Patents' annotations link the '397 patent to both numbers precisely because of the reassignment — consistent with the above, not evidence of two suits.

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Related but NOT asserting the '397 patent

These are the same plaintiff/campaign but asserted different patents; they are not litigation "involving the '397 patent" and should not be listed as such:

• Sibling W.D. Tex. cases against HP filed the same day (June 11, 2019): 6:19-cv-00363-ADA, 6:19-cv-00364-ADA, 6:19-cv-00549-ADA (→ 1:20-cv-00186-ADA, 1:20-cv-00187-ADA, 1:20-cv-00189-ADA, etc.), plus 6:20-cv-00048. These asserted other Lexmark-origin patents (e.g., '587, '563, '246, '575, '012, '341, '864, '823, '629, '299). All resolved by the same 2021 HP settlement/dismissal wave.
• Slingshot Printing LLC v. Canon U.S.A., Inc. et al., No. 2:22-cv-01852 (E.D.N.Y.) (filed April 1, 2022) — asserted patents such as 7,195,341; 7,290,864; 7,410,246; 7,484,823; 7,559,629. The '397 patent is not among them. The related PTAB/CAFC activity (Canon IPRs, and the Federal Circuit affirmances in 2026 at Nos. 24-1956 and 25-1033/25-1034) concerns those other patents, not the '397 patent.

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Appeals

• No Federal Circuit appeal specific to U.S. 7,438,397 was found. The active CAFC docket Slingshot Printing LLC v. Canon U.S.A., Inc. (Fed. Cir. 2026, CourtListener docket 73288909) concerns different Slingshot patents. Because the '397 case settled and was dismissed with prejudice in 2021 with no merits judgment, there was nothing on the '397 patent to appeal.

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Method / sourcing notes

• Searched literally for 7438397 / 7,438,397 (no similar-number substitution). Sources: Unified Patents litigation portal (caselist and case pages for 6:19-cv-00362 and 1:20-cv-00184), Justia Dockets, Patexia, Docket Alarm (PTAB exhibits of the W.D. Tex. pleadings), The Recycler, Actionable Intelligence, PTACTS/USPTO petition exhibits quoting HP's invalidity contentions and Slingshot's mandatory notices, and CourtListener for the CAFC docket.
• I did not have direct PACER access; case status is taken from the docket text reproduced in the above secondary sources and corroborated across at least two of them for each material fact.
• Facts I could not independently verify from an authoritative source in this session: the exact pleading by which the '397 patent first entered the HP case (original vs. amended complaint), and the existence of any non-public settlement terms. If certainty is required for a filing, pull the W.D. Tex. docket for 6:19-cv-00362 / 1:20-cv-00184 and the April 1, 2021 dismissal order directly from PACER.

Proceedings overview

Total AIA trial proceedings on file: 0 — no IPR, PGR, or CBM petitions have ever been filed against US 7438397, and none are pending. The USPTO ODP API returns no proceedings for this patent, and my web sweeps surfaced no IPR/PGR/CBM directed to the '397 patent itself (the many PTAB cases involving current assignee Slingshot Printing LLC — e.g., HP's IPR2020-01084 series and Canon's IPR2022-01414/01415/01416, IPR2023-00312/00313 — all target other Lexmark-origin patents such as 6,394,593, 7,014,299, 7,938,523, 7,484,823, and 7,594,708, not this one). Bottom line for a defendant: this patent has never been through an AIA trial, so there is no PTAB estoppel, no canceled claims, and no FWD to rely on — but the stronger defensive fact is chronological: the patent's adjusted term expired on 2025-10-23 and its USPTO status is Expired - Lifetime, so as of today (2026-09-08) it is only capable of supporting damages for pre-expiration conduct, not ongoing relief.

Because no proceedings exist, there are no per-proceeding sections to report below. What follows is the cross-proceeding (here, litigation-level) picture and what the absence of PTAB activity means.

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Strategic summary

Claim status: all 24 claims UNTESTED at the PTAB — but the patent is EXPIRED

Every claim of US 7438397 (claims 1–24) is UNTESTED in any AIA trial proceeding. No claim has been canceled, and none has been sustained, because the Board has never been asked to review the patent. That is not a sign of strength — it is a function of the patent's assertion history and life cycle:

• The patent issued 2008-10-21 from a 2004-12-01 filing, and Google Patents lists it as Expired - Lifetime with an adjusted expiration of 2025-10-23 (maintenance fees were paid through the 12th year in 2020, but the 20-year term has now run).
• The patent was litigated. The Google Patents litigation feed ties it to two Texas Western District Court cases, 6:19-cv-00362 and 1:20-cv-00184, and HP's own PTAB filings confirm the '397 patent was among the "Patents-in-Suit" in Slingshot Printing LLC v. HP Inc., No. 1:20-cv-00184-ADA (W.D. Tex.), alongside the '707 and '523 patents (see HP proposed claim constructions, Ex. 1008 in IPR2020-01084, which lists asserted claims of the '397 patent including claim 20).
• That W.D. Tex. case did not end in a merits judgment. The docket shows a Joint Motion to Stay and Notice of Settlement (2021-02-02), a Stipulation of Dismissal (2021-03-23), and an Order of Dismissal with prejudice entered 2021-04-01. HP's contemporaneous wave of IPRs against other Slingshot patents (IPR2020-01084 through -01090 and IPR2020-01659) was likewise Terminated-Settled in March 2021. Settlement, not adjudication, resolved the '397 patent's only known enforcement campaign.

Estoppel landscape — a blank slate, which cuts both ways

Because no IPR was ever instituted on this patent, § 315(e)(2) estoppel binds no one. HP, Canon, or any future petitioner is free to raise any § 102/§ 103 ground — including art that was fully litigated or settled in district court — because "reasonably could have raised" estoppel only attaches to grounds actually raised or that could have been raised in an instituted AIA proceeding. That said, the practical value of that freedom is limited: with the patent expired, the only remaining exposure is pre-2025-10-23 damages (subject to the six-year § 286 look-back from when suit is filed), and a would-be petitioner must weigh the cost of an IPR against the modest remaining damages tail. The § 315(b) one-year bar would also be measured from service of any new complaint, so a defendant sued today still has the full one-year window.

Pattern signals

• No repeat-petitioner pattern on this patent — the only known challengers (HP in 2020–2021; Canon on sibling patents in 2022–2024) never targeted the '397 patent, presumably because the 2021 settlement and dismissal neutralized it and the patent's term was winding down.
• The Patent Owner is a known, aggressive litigant: Slingshot Printing LLC (a Funai/Lexmark inkjet spinoff that took assignment in 2019) has litigated its portfolio in W.D. Tex. and E.D.N.Y. against HP and Canon and has lost on the merits at the PTAB on closely related printhead patents — the Federal Circuit affirmed PTAB obviousness findings against Slingshot in Slingshot Printing LLC v. Canon U.S.A., Inc., Nos. 24-1956 (2026-04-23, '341 patent) and 25-1033/25-1034 (2026-07-16, '823 and '708 patents). That pattern tells you Slingshot's portfolio is being actively challenged and is vulnerable on obviousness grounds — the '397 patent just aged out before it became a target.
• No defensive aggregator (e.g., Unified Patents) appears in this patent's chain; the listed assignments run Lexmark → Funai (2013) → Slingshot (2019), and Unified Patents appears only as the source of the litigation-data feed.

Recommended next steps

1. Lead with expiration, not IPR. If you are a defendant receiving a demand letter today citing US 7438397, the first line of defense is that the patent expired 2025-10-23 (USPTO status: Expired - Lifetime). No injunction is possible, and liability is capped at proven past damages for infringing acts before that date, subject to 35 U.S.C. § 286's six-year damages bar. Verify the expiration date and terminal-disclaimer/adjustment history in USPTO Patent Center before litigating anything else.
2. There is no PTAB play to run — say so plainly. The USPTO ODP data shows zero AIA proceedings on this patent, and web research confirms none were filed. Do not file an IPR on an expired patent for strategic theater; if the plaintiff only seeks pre-expiration damages, a validity challenge belongs in district court (where no § 315(e) estoppel risk exists and where HP's and Canon's prior-art wins against sibling Slingshot printhead patents — e.g., Torgerson/Bruce, Benjamin/Giere673, Imanaka/Hamafuku/Whitman — give you a ready-made invalidity blueprint).
3. If you are in litigation on a sibling patent, mine the Slingshot loss record. The Federal Circuit affirmance in Slingshot Printing LLC v. Canon U.S.A., Inc., Nos. 24-1956 and 25-1033/25-1034 (CourtListener links above) confirms the PTAB and CAFC treat this Slingshot/Lexmark printhead portfolio as obvious over the inkjet prior art. Any assertion of the '397 patent by the same owner should be met with the same art.
4. Watch the related litigations for re-assertion. The '397 patent was dismissed with prejudice in Slingshot v. HP, 1:20-cv-00184-ADA on 2021-04-01 — if HP is your client, that dismissal (and the accompanying settlement) may already bar or estop re-assertion against HP or its privies; confirm the settlement's scope. For non-HP defendants, the dismissal does not bind the patent owner, but the expiry date is universal.

Caveat on sourcing: The "no PTAB activity" conclusion rests on the canonical USPTO ODP block in this prompt plus targeted web searches; if you require absolute certainty before making representations to a court, run the patent number through the USPTO PTAB E2E/PTACTS public search and Patent Center directly. I did not locate any proceeding number to verify, and per the operating rules I have not invented one.

Inventors

All three inventors were Lexmark employees at filing (2004-12-01) and assigned their interests to Lexmark the same day — a routine employer assignment. No evidence of the "all inventors depart within 12 months" pattern that sometimes precedes a portfolio sale; I could not find departure data and will not speculate.

Original assignee

Lexmark International, Inc. (Lexington, Kentucky) is the entity named on the issued patent. Lexmark was an IBM spinoff (1991) and a major manufacturer of inkjet and laser printers, printheads, and ink cartridges. Lexmark did ship products embodying this technology — the "chiclet"/on-carrier ink reservoir printheads described in the specification were used in Lexmark inkjet cartridges and printheads of the mid-2000s. Current status: Lexmark exited the inkjet hardware business, sold its inkjet technology portfolio to Funai Electric (2013), and was acquired/taken private by the Apex Technology (Ninestar) consortium in 2016; the printer company itself remains operating but no longer owns this patent.

Assignment timeline

The USPTO Assignment Center / Google Patents legal-event record shows three recorded assignments for US 7,438,397. The reel/frame numbers and dates below come from the recorded legal events; I could not retrieve the correspondent-of-record names from the sources available to me (the Assignment Center database was not directly queryable in this session), so correspondents are marked unknown rather than guessed.

• 2004-12-01 (executed) / recorded 2004-12-01 — Reel 016058/0183

  • Conveyance: Assignment (inventor → employer, filed with the application)
  • Assignor: James Daniel Anderson, Jr.; David Emerson Greer; Matthew Joe Russell
  • Assignee: Lexmark International, Inc.
  • Correspondent: not retrievable from available sources
  • Context: Original assignment of rights from the three inventors to Lexmark at filing — standard employment assignment, not a monetization event.

• 2013-04-01 (effective) / recorded 2013-05-14 — Reel 030416/0001

  • Conveyance: Assignment
  • Assignor: Lexmark International, Inc.; Lexmark International Technology, S.A.
  • Assignee: Funai Electric Co., Ltd.
  • Correspondent: not retrievable from available sources
  • Context: Portfolio divestiture — Funai announced (~April 2013) acquisition of Lexmark's inkjet-related technology and assets for ~$100M, covering 1,500+ US/foreign patent assets; this patent rode along as part of that inkjet business exit.

• 2019-03-29 (executed) / recorded 2019-03-29 — Reel 048745/0551

  • Conveyance: Assignment
  • Assignor: Funai Electric Co., Ltd.
  • Assignee: Slingshot Printing LLC
  • Correspondent: not retrievable from available sources
  • Context: Transfer-to-asserter — Funai moved 100+ US inkjet patent assets to the newly formed NPE Slingshot Printing LLC, which began suing HP within ~10 weeks (see signals below).

No security agreements, mergers, changes of name, releases, or corrections appear in the recorded chain. The chain is complete and current: Slingshot Printing LLC is the last recorded assignee.

Timeline diagram

timeline
    title Ownership of US 7438397
    2004 : Filed by inventors
         : Assigned to Lexmark International
    2008 : Patent issued
    2013 : Assigned to Funai Electric
    2019 : Assigned to Slingshot Printing
         : HP sued in W D Tex
    2025 : Patent expired

NPE / troll-pattern signals

1. Shell-entity transfer — present. Reel 048745/0551 (2019-03-29) moved 100+ patents from Funai, an operating OEM that made printers/cartridges, to Slingshot Printing LLC, which has no products in commerce. The "shell" inference is supported by concrete evidence, not just the name: RPX contemporaneously described Slingshot as a "recently formed NPE" that "received more than 100 US assets from Funai," and Unified Patents' portal tags Slingshot as "NPE (Patent Assertion Entity)" in its litigation and IPR dockets (e.g., IPR2022-01416).

2. Known asserter in the chain — present. Slingshot Printing LLC is a high-frequency plaintiff on former Lexmark/Funai inkjet patents, classified as an NPE by Unified Patents and tracked by RPX. Its targets are printer OEMs — HP Inc. (W.D. Tex. 6:19-cv-00362 et seq., filed 2019-06-11; later cases through 2020) and Canon (E.D.N.Y. 2:22-cv-01852, 2022, plus multiple IPRs). Google Patents' litigation metadata ties this specific patent (7,438,397) to W.D. Tex. cases 6:19-cv-00362 and 1:20-cv-00184 in that Slingshot campaign.

3. Repeat correspondent across the chain — unclear. The correspondent-of-record names on reels 016058/0183, 030416/0001, and 048745/0551 were not retrievable from the sources available in this session, so I cannot test for a recurring attorney. (Slingshot's litigation/IPR counsel of record is Fitch Even Tabin & Flannery LLP / MoloLamken LLP, but that is litigation counsel, not the assignment correspondent.) No finding either way.

4. Cascading transfers — not present in the classic sense. There is no rapid <24-month churn through chained LLCs: only three assignments over 15 years (2004, 2013, 2019). The structure is instead a deliberate two-hop operating-company → operating-company → NPE progression ending in a single transfer-to-asserter.

5. Pre-litigation transfer — present. The Funai → Slingshot assignment (reel 048745/0551) was recorded 2019-03-29; Slingshot's first infringement complaints against HP were filed in the Western District of Texas on 2019-06-11 — approximately 74 days later, well inside the 6-month window. The chain was arranged immediately before assertion.

6. Bankruptcy fire-sale — not present. Neither transfer to Funai (2013) nor to Slingshot (2019) was a bankruptcy sale. Lexmark divested its inkjet line as a going-concern business decision (~$100M sale, ~April 2013) and was later acquired by Apex/Ninestar (2016); Funai's own later financial collapse post-dates the Slingshot transfer and is irrelevant to it.

7. Privateering — present. Funai (an operating manufacturer of inkjet printers/cartridges, including under the KODAK brand) handed 100+ patents to NPE Slingshot, which then sued Funai's inkjet competitors HP and Canon. RPX reported that "assignment records suggest that Funai might hold an economic interest in Slingshot's litigation," and HP later moved to drag Funai into the W.D. Tex. litigation — the classic operating-company-financed assertion (privateering) pattern.

8. Defensive aggregator (anti-NPE) — not present. The chain terminates at Slingshot Printing LLC, an assertion entity; there is no RPX, AST, LOT, Unified Patents, or OIN interest. (Separately, the patent's adjusted term expired 2025-10-23 per the USPTO status record, so its enforcement life has ended regardless.)

Verdict

NPE — high confidence

The chain ends at Slingshot Printing LLC, an entity Unified Patents and RPX classify as a patent-assertion NPE that has sued HP and Canon on former Lexmark inkjet patents (strong signal: known asserter + shell-entity transfer, reel 048745/0551, recorded 2019-03-29). The Funai → Slingshot assignment was recorded ~74 days before Slingshot's first W.D. Tex. complaints of 2019-06-11 (pre-litigation transfer), and RPX-reported assignment records suggest Funai retained an economic interest in the litigation (privateering). Verification: search US 7438397 at https://assignmentcenter.uspto.gov/ (records on reels 016058/0183, 030416/0001, and 048745/0551).

USPTO Prior-Art Analysis: US Patent 7,438,397 B2

1. Patent identification (verified)

• Patent No.: US 7,438,397 B2 (searched literally as 7438397 / 7,438,397; no similar-number results were substituted)
• Title: "Methods and devices for purging gases from an ink reservoir"
• Inventors: James Daniel Anderson, Jr.; David Emerson Greer; Matthew Joe Russell
• Assignee (original): Lexmark International, Inc.
• Application No.: US 11/001,433 — Filed: December 1, 2004
• Granted: October 21, 2008
• Status: Expired – Lifetime (adjusted expiration Oct. 23, 2025); now assigned to Slingshot Printing LLC
• The USPTO/Google Patents record (https://patents.google.com/patent/US7438397/en) and the USPTO PDF (https://patentimages.storage.googleapis.com/7c/5b/d9/3b231c057f0ea8/US7438397.pdf) confirm the above.

2. Statutory framework applied

Because the application was filed December 1, 2004 (pre‑AIA), pre‑AIA 35 U.S.C. § 102 governs:

• § 102(a): the invention was known, used, patented, or described in a printed publication before the invention date (taken as Dec. 1, 2004 for this analysis).
• § 102(b): patented or described in a printed publication more than one year before the U.S. filing date, i.e., on or before Dec. 1, 2003 — the strongest category for the older references below.
• § 102(e): described in a U.S. patent application by another filed before Dec. 1, 2004, even if published after that date.
• The '397 patent's own pre-grant publication (US 2006/0114298 A1) is not prior art (it is the same application).

3. Claim "legend" (for the mapping below)

• C1 (indep.): printhead; reservoir downstream of ink filter; pump assembly withdraws gas and then inhibits re-communication of the withdrawn gas with the reservoir; pump + one-way valve assembly concurrently in communication with reservoir interior and external environment; first one-way valve isolates second from reservoir; second one-way valve isolates first from external environment.
• C2–C6: pump interposed between the two one-way valves (C2); biased valve seats/bodies (C3); circular seats/spherical balls (C4); pressure-differential opening (C5); manually deformable diaphragm (C6).
• C7–C13: multi-color (2nd/3rd reservoir) variants; four-valve assembly; four pressure differentials; diaphragm (C13).
• C14, C15, C19: horizontal/lateral (side-saddle) tank-to-reservoir couplings.
• C16–C17: repositionable manually deformable diaphragm (C16); pump assembly mounted to reservoir (C17).
• C18 (indep.): ink reservoir with ink-exit orifice at lower elevation, gaseous-exit orifice at higher elevation, ink-entrance orifice, gas-accumulation area; pump fluidically interposed between at least two one-way valves; entrance orifice partly lower than gaseous-exit orifice/accumulation area.
• C20/C21 (indep. method): displacing gas downstream of filter; accumulation area; opening check valve into gas-containment area; pumping gas to an area not in fluid communication with reservoir.
• C22 (indep. method): purging gas-accumulation area via a one-way valve assembly; first valve isolates second valve from the accumulation area.
• C23 (indep.): printhead reservoir downstream of a vertically oriented ink filter; elevated air-accumulation region directing bubbles upward.
• C24 (indep.): C18-type component plus laterally coupled replacement ink tank.

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4. Per-citation analysis (patent-citations appearing on the face of '397)

The record lists 36 patent citations. Full citation, dates, description, and potential § 102 claim coverage follow. "Potential" means the reference appears to disclose all elements of the claim; where a limitation is likely missing I flag it, and the reference would then be § 103 art rather than a § 102 anticipation.

A. Strongest / closest art

1. US 6,270,211 B1 — "Bubble elimination and filter tower structure" — Lexmark International (Ward, Powers, Russell, Long). Filed Jul. 7, 1999; issued Aug. 7, 2001 (§ 102(b)).
Filter tower between an ink cartridge and pen; filter cavity; upper gas-accumulation area; gas-outlet needle valve and ink-inlet valve; on cartridge installation gas is displaced from the accumulation area into a bellows chamber.
Potential § 102: C18 (accumulation area + gas exit above filter), C20/C21 (displacing gas via accumulation area; check-valve into a containment area = bellows; pumping to a non-ink area), and elements of C1. Notably, one '397 inventor (M. Russell) is a co-inventor, but the 2001 publication still counts as § 102(b) prior art. Caveat: '211 vents gas into a bellows as a consequence of cartridge installation/ink back-pressure rather than through a pump interposed between two one-way valves — that arrangement (C1/C2/C22 full combination) is likely not disclosed in a single reference.

2. US 6,457,821 B1 — "Filter carrier for protecting a filter from being blocked by air bubbles in an inkjet printhead" — Hewlett-Packard. Filed Mar. 13, 2001; issued Oct. 1, 2002 (§ 102(b)).
Addresses the exact problem stated in '397's Background (bubbles collecting under a horizontal filter) by orienting/mounting the filter so bubbles are not trapped.
Potential § 102: C23 (vertically oriented/arranged filter with bubbles directed away); combination aspects of C18's geometry. Caveat: the reference likely lacks the pump/one-way-valve purge stack of C1/C18/C22.

3. US 6,257,715 B1 — "Ink jet printer with ink conduit gas exhaust facility and method" — Hewlett-Packard. Filed Mar. 7, 2000; issued Jul. 10, 2001 (§ 102(b)).
Gas exhaust/vent facility on the ink conduit downstream of supply, removing entrapped air from the ink path.
Potential § 102: C1, C18 and C22 in structure (gas exit at elevated location, exhaust to atmosphere) if it shows the two-valve isolation arrangement; otherwise strong § 103 anchor. Caveat: two-series-one-way-valve "pump interposed" isolation is not confirmed from the face of the reference.

4. US 6,318,851 B1 / US 6,761,445 B2 — "Method and system for purging air from a print mechanism" — Hewlett-Packard. Filed Apr. 7, 1999; issued Nov. 20, 2001 / Jul. 13, 2004 (§ 102(b) for the '851; '445 is a continuation).
Purging air from a print mechanism/printhead.
Potential § 102: method claims C20–C22. Caveat: most HP purging systems of this era purge with ink through the nozzles rather than withdrawing gas through a dedicated gaseous-exit orifice to the external environment, so full anticipation of C22's two-valve isolation is doubtful; these are better § 103 references.

5. US 2005/0168520 A1 — "Removing gas from a printhead" — Lexmark (Mantooth). Filed Jan. 30, 2004; published Aug. 4, 2005 (§ 102(e) — filed before Dec. 1, 2004).
Lexmark's own earlier-filed application directed to removing gas from a printhead (same problem statement as '397). Because it was filed ~10 months before '397 and published after, it is § 102(e) prior art, not § 102(b).
Potential § 102: C1 and C18 combinations (reservoir + gas-withdrawal pump assembly) if it discloses the two-one-way-valve isolation, and C20/C22 methods. This is one of the two or three most threatening references and warrants a full element-by-element comparison in any validity analysis.

6. US 7,118,206 B1 — "Gas bubble removal from ink-jet dispensing devices" — 3D Systems. Filed Mar. 19, 2004; issued Oct. 10, 2006 (§ 102(e)).
Filed before '397; discloses gas-bubble removal from ink-jet dispensing devices (valves/pump removing entrapped gas).
Potential § 102: C1, C18, C20, C22 depending on the valve stack disclosed; same caveat about the specific two-one-way-valve, pump-interposed isolation of C1/C22.

7. US 5,847,734 A — "Air purge system for an ink-jet printer" — Pawlowski, Jr. Filed Dec. 4, 1995; issued Dec. 8, 1998 (§ 102(b)).
Remote reservoir + variable-volume chamber pump + one-way valve; positive-pressure ink flushes air out of the supply line and pen; check valve releases air as the path fills.
Potential § 102: C20 (withdrawing/displacing gas; check valve; containment) in part. Caveat: '734 purges by flushing with ink and venting, not by pumping gas out of an elevated accumulation area through a two-valve one-way stack to the external environment; so C1/C18/C22's "gas-only withdrawal + subsequent isolation" combination is probably not fully met — a strong § 103 combination reference.

8. US 5,812,168 A — "Air purging of a pressure regulated free-ink ink-jet pen" — Hewlett-Packard. Filed Oct. 31, 1994; issued Sep. 22, 1998 (§ 102(b)).
Air-purge apparatus for regulator-based free-ink pens, purging accumulated air from the printhead body.
Potential § 102: C20/C22 method elements; structural overlap with C1's "withdraw gas and inhibit re-entry" concept. Caveat: purge typically occurs at a service station through the regulator/nozzles, not a reservoir-mounted one-way valve stack.

9. US 5,677,718 A — "Drop-on-demand ink jet print head having improved purging performance" — Tektronix. Filed Jun. 4, 1992; issued Oct. 14, 1997 (§ 102(b)).
Improved purging for drop-on-demand heads.
Potential § 102: method claims C20/C22; limited structural overlap.

10. US 5,426,459 A — "Combined filter/aircheck valve for thermal ink-jet pen" — Hewlett-Packard. Filed Dec. 22, 1992; issued Jun. 20, 1995 (§ 102(b)).
Filter combined with an air-check valve in a pen to vent air.
Potential § 102: C23-type structure (filter + air vent); C20. Caveat: lacks pump and dual one-way valve stack of C1/C18.

11. US 5,870,126 A — "Ink jet printer having bubble purge mechanism" — Hitachi Koki. Filed Jan. 20, 1995; issued Feb. 9, 1999 (§ 102(b)).
Bubble-purge mechanism in an ink-jet printer.
Potential § 102: method claims C20–C22; structural overlap moderate.

B. Delivery-system, valve, diaphragm and cartridge-coupling art (mostly § 103 combination anchors; § 102 only if the specific claim limitation set is coincidentally present)

12. US 6,698,870 B2 — "Ball check valve for bulk ink supply system" — HP. Filed Jul. 25, 2002; issued Mar. 2, 2004 (§ 102(b)).
Potential § 102: C3/C4 and C11 ball-in-seat valve structure (spherical body received in seat). Not the purge-combination claims.

13. US 2002/0057972 A1 — "Overmolded elastomeric diaphragm pump for pressurization in inkjet printing systems" — HP (Barinaga). Filed Sep. 15, 2000; published May 16, 2002 (§ 102(b)).
Potential § 102: C6/C13/C16 (diaphragm pump, deformable; could be manually deformable). Not the reservoir-purge combination.

14. US 6,296,345 B1 / US 6,471,334 B2 / US 6,499,826 B1 — "Method and apparatus for horizontally loading/unloading an ink-jet print cartridge from a carriage" and "Horizontally loadable carriage" — HP. Filed Jan. 5, 2000; issued Oct. 2, 2001 / Oct. 29, 2002 / Dec. 31, 2002 (§ 102(b)).
Potential § 102: C14/C15/C19/C24 (horizontal/lateral interface of tank outlet coupling with reservoir inlet coupling). No purge-valve disclosure.

15. US 5,936,650 A — "Ink delivery system for ink-jet pens" — HP. Filed May 24, 1995; issued Aug. 10, 1999 (§ 102(b)).
Potential § 102: background structure only; § 103 with purge art.

16. US 5,844,577 A — "Back pressure regulator ink-jet pen" — HP. Filed Oct. 31, 1994; issued Dec. 1, 1998 (§ 102(b)).
Potential § 102: none standing alone for the gas-purge claims; § 103 with air-purge references.

17. US 6,257,714 B1 — "Method and apparatus for removing air from an inkjet print cartridge" — HP. Earliest priority listed Oct. 27, 1995; issued Jul. 10, 2001 (§ 102(b)).
Potential § 102: C20/C22 methods if it shows gas withdrawal from a filter-downstream region; otherwise § 103 with '168/'734.

18. US 6,650,080 B2 — "Re-circulating fluid delivery system" — HP. Filed Apr. 30, 2002; issued Nov. 25, 2003 (§ 102(b)).
Potential § 102: none alone for C1/C18/C22; § 103 (recirculation to remove bubbles).

19. US 6,739,706 B2 — "Off axis inkjet printing system and method" — HP. Filed Apr. 19, 2002; issued May 25, 2004 (§ 102(b)).
Potential § 102: none alone; § 103.

20. US 6,752,493 B2 — "Fluid delivery techniques with improved reliability" — HP. Filed Apr. 30, 2002; issued Jun. 22, 2004 (§ 102(b)).
Potential § 102: none alone; § 103 (air handling in fluid delivery).

21. US 6,773,097 B2 — "Ink delivery techniques using multiple ink supplies" — HP. Filed Aug. 29, 2001; issued Aug. 10, 2004 (§ 102(b)).
Potential § 102: none alone for multi-reservoir purge claims C7–C13 (no concurrent single valve stack); § 103.

22. US 6,874,872 B2 — "Monitoring and controlling ink pressurization in a modular ink delivery system" — HP. Earliest priority Jul. 15, 1996; issued Apr. 5, 2005 (§ 102(e) by virtue of 1996 filing; published after the Dec. 1, 2003 § 102(b) bar date).
Potential § 102: none alone; § 103.

23. US 2004/0020552 A1 — "Method for filling a printing ink reservoir and device for carrying out said method" — Ruffer. Filed Oct. 11, 2000; published Feb. 5, 2004 (§ 102(b)).
Potential § 102: none alone; filling/gas-venting method, § 103 with C20/C22.

24. US 2005/0084952 A1 — "Small volume chambers" — HP (Bass). Filed Dec. 24, 2001; published Apr. 21, 2005 (§ 102(e)).
Potential § 102: none alone for the claimed purge stack; § 103.

25. US 6,481,837 B1 — "Ink delivery system" — Askren. Filed Aug. 1, 2001; issued Nov. 19, 2002 (§ 102(b)).
Potential § 102: none alone; § 103.

C. Peripheral / cumulative art (older; low anticipation potential; § 103 context)

26. US 4,149,172 A — "Ink supply system for piezoelectrically operated printing jets" — Siemens. Priority Dec. 20, 1974; issued Apr. 10, 1979 (§ 102(b)).
Early ink-supply system. Potential § 102: none for the claimed combinations.

27. US 5,126,767 A — "Ink tank with dual-member sealing closure" — Canon. Priority Feb. 9, 1984; issued Jun. 30, 1992 (§ 102(b)).
Sealing closure for ink tank. Potential § 102: none for purge claims.

28. US 5,500,664 A — "Ink jet recording apparatus and detachably mountable ink jet cartridge" — Canon. Priority Jan. 25, 1991; issued Mar. 19, 1996 (§ 102(b)).
Potential § 102: none alone; § 103 (detachable cartridge interface, relevant to C14/C15/C19 coupling concept generally).

29. US 5,621,445 A — "Apparatus for refilling ink cartridges" — HP. Priority Aug. 27, 1991; issued Apr. 15, 1997 (§ 102(b)).
Refill/venting. Potential § 102: none alone.

30. US 5,949,459 A — "Method and apparatus for securing an ink container" — HP. Filed Jun. 4, 1997; issued Sep. 7, 1999 (§ 102(b)).
Potential § 102: none for purge claims.

31. US 6,079,808 A — "Ink jet recording apparatus" — Seiko Epson. Filed Aug. 5, 1996; issued Jun. 27, 2000 (§ 102(b)).
Potential § 102: none alone; purge methods possibly relevant to C20/C22.

32. US 6,209,997 B1 — "Impulse fluid jet apparatus with depriming protection" — Illinois Tool Works. Filed Mar. 25, 1997; issued Apr. 3, 2001 (§ 102(b)).
Potential § 102: none alone.

33. US 2006/0114298 A1 — Lexmark (Anderson; Greer; Russell) — the '397 application's own pre-grant publication (Dec. 1, 2004; published Jun. 1, 2006).
Not prior art under § 102 (same application / same inventive entity). It is listed only as a publication of the same patent family.

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5. Bottom line — most relevant prior art for § 102 anticipation

Ranked by likely threat to the independent claims:

6. Candid limitations of this analysis

• I performed the requested USPTO/patent-record verification for 7,438,397 and searched a subset of the cited references in depth (US 6,270,211; US 5,847,734; US 2005/0168520 A1 partially). For the remaining references I relied on the bibliographic data printed on the face of '397 (as reproduced in the authoritative Google Patents record) plus the references' known abstracts. Element-by-element anticipation cannot be confirmed without reading the full text of each cited reference.
• A § 102 anticipation finding requires each and every claim element in a single reference. My mapping identifies where that is plausible; where I noted a missing limitation (e.g., no pump-interposed dual one-way valve stack, no gas-only withdrawal), the reference should be treated as § 103 combination art rather than an anticipating reference.
• The most valuable next step for a validity/invalidity position would be a full-text comparison of US 6,270,211 B1 and US 2005/0168520 A1 against claims 1, 18, 20, and 22, because those two references (one § 102(b), one § 102(e)) come closest to the claimed gas-accumulation-area + purge-valve combination.

I'll research the key prior art references to ground the obviousness analysis in their actual disclosures.

Let me research additional key references that could be combined.

Obviousness Analysis — U.S. Patent No. 7,438,397 B2 ("Methods and devices for purging gases from an ink reservoir")

1. Scope of analysis and governing law

Because the application was filed December 1, 2004, the analysis is governed by pre-AIA 35 U.S.C. § 103 and the framework of Graham v. John Deere Co., 383 U.S. 1 (1966), as informed by KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007). Under KSR, a claimed combination is obvious when the prior art, taken as a whole, would have suggested the combination to a person of ordinary skill in the art (POSITA), including where the combination is merely the predictable union of known elements each performing its known function.

Field of art / POSITA: An engineer or designer with, e.g., a B.S./M.S. in mechanical or chemical engineering and 2–4 years' experience in inkjet printhead fluidics, ink-delivery architecture, filter towers, and purge/venting systems, familiar with the patent literature of Lexmark, Hewlett-Packard, Canon, Epson, and Tektronix in IPC classes B41J2/175 and B41J2/19.

Claim landscape. The independent claims are 1, 18, 20, 22, 23, and 24:

• Claim 1 – printhead: reservoir downstream of an ink filter + pump assembly that withdraws gas and then isolates the withdrawn gas, implemented as a pump plus a one-way valve assembly having first and second one-way valves, with the first valve isolating the second from the reservoir interior and the second isolating the first from the external environment.
• Claim 18 – component: reservoir with an ink exit orifice at a first elevation, a gaseous exit orifice at a higher second elevation, an ink entrance orifice, a gas accumulation area, an ink filter, and a pump assembly whose pump is fluidicly interposed between at least two one-way valves.
• Claims 20 & 22 – methods: displacing gas downstream of a filter using a gas accumulation area, opening a check valve, pumping withdrawn gas to an area not in fluid communication with the reservoir (20); purging through a one-way valve assembly with the first valve isolating the second from the gas accumulation area (22).
• Claim 23 – reservoir downstream of a vertically oriented ink filter with an elevated air-accumulation region.
• Claim 24 – like claim 18 plus a laterally coupled replacement ink tank.

Key dependent limitations: pump fluidicly interposed between the two valves (2); biased valve bodies/seats (3); spherical bodies/circular openings (4); pressure-differential opening (5, 12); manually deformable diaphragm (6, 13, 16); second and third color reservoirs (7–13); four-valve multi-color manifold (8–13); horizontally interfaced inlet couplings (14, 15); pump mounted to the reservoir (17); lateral tank coupling (19).

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2. Central inventive concept and the closest prior art

The specification frames the problem exactly as the prior art did: "accumulation of air within the ink filter tower … block[s] ink from reaching the nozzles; i.e., starving the chip" and "result[s] in premature printhead failure." The solution has two prongs: (i) geometric – a vertically oriented filter and an elevated gas-accumulation area so bubbles gravitate away from the ink path, and (ii) valved pump – a manually actuated pump with one-way valves that draws gas out of the accumulation area and vents it externally without permitting backflow or ink loss.

Every prong is addressed by the cited art:

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3. Primary obviousness combination for claims 1, 18, 20, 22 and 23

Combination A: US 6,270,211 B1 + US 6,318,851 B1 (or US 6,257,715 B1 / US 5,812,168 A), optionally + US 5,425,459 A.

Element-by-element mapping (claim 1):

For claims 20 and 22 (methods), the same combination supplies every step: displacing gas downstream of a filter (211/851/8520), implementing a gas-accumulation area (211/851), withdrawing gas by opening a check valve into a containment area (211 bellows; 734/718 purge systems), pumping the withdrawn gas to an area not in fluid communication with the reservoir (851 blow-off vent; 715 gas-release facility), and arranging first/second one-way valves so the first isolates the second from the accumulation area (734/718 purge valves; 870 ball-check series).

Why a POSITA would combine them — motivation:

1. Same problem, same assignee, same inventors. The '397 specification's own Background repeats the problem solved by '211 (air in the filter tower after cartridge exchange; starvation; premature failure). '211 is a Lexmark patent sharing inventor Matthew J. Russell with '397, so the '397 team demonstrably knew of the filter-tower/gas-accumulation approach. The '397 "improvement" is not a new problem but a re-packaging of known solutions.
2. Complementary, not conflicting, disclosures. '211 teaches where gas collects and a cartridge-installation-activated bellows to remove it; '851 teaches pressure-based venting of a filter-equipped local container with upward bubble routing and a blow-off vent. A POSITA seeking a low-cost, user-actuable purge for a chiclet-style on-carrier tower would simply substitute the manual squeeze-bulb pump of the purge art ('734, '718, '714) or the '851 venting scheme for '211's cartridge-installation-activated bellows — a textbook KSR "known technique … applied to a known device ready for improvement."
3. Predictable result. Two one-way valves flanking a deformable chamber is the classic "priming bulb" configuration (intake check + exhaust check). Using it to withdraw gas from an elevated accumulation region and vent it externally, while the valves prevent ink loss and gas re-entry, is a predictable design choice — not a new principle.
4. Express suggestion in the art. '851 expressly collects bubbles gravitating upward and expels them through a vent; '211 expressly forms a "gas accumulation area" at the top of the filter cavity and connects it to a gas-removal valve. Combining "top-of-tower accumulation" with "valved venting" is the union of two references that point at each other's missing half.

Claim 23 (vertical filter + elevated accumulation region). The vertical-filter idea is itself addressed in the art: '851's air-escape paths on both sides of the filter collect upward-gravitating bubbles; '459/HP filter art places filters in planes arranged to avoid bubble blockage; '821 (filter carrier) exists specifically to stop air bubbles from blocking a filter. Placing the accumulation region above a vertically oriented filter is the direct teaching of '211 (gas accumulation area in the upper portion of the filter cavity) read with '851 (bubbles "gravitating upward"). A POSITA would find claim 23 obvious over '211 alone or '211 + '851.

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4. Secondary combinations for the dependent and remaining claims

4.1 Multi-color, four-valve claims 7–13

'715 expressly describes "several conduits in parallel, with separate gas release facilities for each tube" for multi-color printing; '977 (ink delivery using multiple ink supplies) and '706 (off-axis system) likewise show multiple reservoirs/channels. Adding a third reservoir and duplicating the inlet check-valve per channel (as '397 itself depicts: three towers, three check balls, one shared outlet check ball) is an obvious scaling of the Combination A purge. The four-valve arrangement is the natural manifold: one shared exhaust valve (fourth) plus one inlet valve per color (first, second, third), all interposed by a single pump — a standard plumbing layout.

4.2 Manually deformable diaphragm pump (claims 6, 13, 16)

'211 already uses a deformable bellows; '715 uses a diaphragm pump; Barinaga '2002/0057972 A1 expressly teaches an overmolded elastomeric diaphragm pump for inkjet pressurization; '397's own bulb is a manually deformable diaphragm. Substituting a finger-actuated deformable diaphragm for '211's cartridge-actuated bellows is an obvious interchange of equivalent actuators.

4.3 Spherical-body / circular-seat check valves (claims 4, 11)

'870 (HP, "Ball check valve for bulk ink supply system") and the ball-and-seat purge seals used throughout the cited purge art ('734, '718) make spherical valve bodies seated in circular openings a routine choice. The '397 specification itself describes "check balls" biased against tapered orifices — precisely the structure of the prior purge bulbs.

4.4 Horizontal/lateral coupling claims 14, 15, 19, 24

HP's US 6,296,345 B1 and US 6,499,826 B1 ("method and apparatus for horizontally loading and unloading an ink-jet print cartridge from a carriage"; "horizontally loadable carriage") are cited on the face of the '397 patent and squarely teach horizontally interfaced couplings between a printhead/carriage and a laterally inserted ink supply. Combining a horizontal-loading interface (345/826, or Canon '664/'767's detachable cartridge interface) with the Combination A reservoir/purge structure yields claims 14, 15, 19 and 24. The motivation is ergonomic and space-driven — a POSITA designing an on-carrier "chiclet" system with refillable tanks would look directly to HP's horizontal-loading carriage art, which is cited by the Examiner.

4.5 Pump mounted to the reservoir (claim 17)

'211 mounts its bellows/valve structure directly on the filtration-and-air-removal device between cartridge and pen; '397's own Figure 4 shows the purge bulb/housing captured under the printhead lid on the body. Mounting a purge pump on the reservoir/body it serves is the conventional arrangement shown in '211 and in the purge art.

4.6 § 102(e) published applications (supporting the whole case)

US 2005/0168520 A1 (filed Jan. 30, 2004) and US 7,118,206 B1 (filed Mar. 19, 2004) both predate the '397 filing date (Dec. 1, 2004) and are § 102(e) prior art even though published/granted later. '8520 teaches removing gas trapped downstream of the ink supply by inducing ink flow (venturi) to displace gas — an alternative mechanism that would have suggested gas removal downstream of a filter to a POSITA. '8206 teaches gas-bubble removal in ink-jet dispensing devices generally. Either can be used as a secondary reference confirming the motivation to purge downstream gas.

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5. Graham-factor synthesis and likely outcome

• Scope and content of the prior art: Extensive. Multiple references in the same IPC subclasses address air/gas accumulation in ink-filter towers and downstream reservoirs, with geometric (elevated accumulation, vertical filters, bubble-routing conduits) and valved-pump (bellows, blow-off vents, ball check valves, diaphragm pumps) solutions.
• Differences between claims and prior art: The principal differences are (i) the specific two-series-one-way-valve gas purge manifold claimed in claims 1 and 18, and (ii) the elevation relationships of claim 18 and the vertical filter + elevated accumulation region of claim 23. Both differences are aggregations of known elements (biased check valves flanking a deformable pump chamber; routing gas to the highest point of a reservoir above the inlet) whose benefits — preventing backflow and ink ingestion — were well understood.
• Level of ordinary skill: Moderate; a POSITA would routinely consult the Lexmark/HP/Canon/Epson/Tektronix purge-and-filter literature.
• Obviousness conclusion: Independent claims 1, 18, 20, 22, 23 and 24 are the most vulnerable. Claim 1 reads closely onto the combination of Lexmark's own '211 filter-tower gas-accumulation structure with the valved purge/vent schemes of '851/'715/'734/'718. Claims 18 and 23 are essentially "route the gas pocket to the top of the reservoir above the filter/entrance and vent it" — the express teaching of '211 and '851. The dependent mechanical details (claims 2–6, 16, 17) are conventional ball-check/diaphragm implementations evidenced by '870 and Barinaga. The strongest positions for the patentee are the specific four-valve multi-color manifold (claims 8–13) and the combination of elevation constraints in claim 18, which may require stitching three or more references together — but even these are plausibly obvious under KSR given the express multi-color parallel-channel teaching of '715 and the manifold logic of the art.

Caveats. This analysis rests on the bibliographic data, abstracts, and partial disclosure text available for the cited references (particularly '211, '851, '715, '459, and '8520, whose full texts I verified in relevant part). For a complete validity opinion, each combination should be checked against the full-text PDFs of '734, '718, '714, '168, '870, and '821, and claim charts should be prepared element-by-element. Additionally, the Google Patents record shows the '397 patent has been asserted in the Western District of Texas (6:19-cv-00362 and 1:20-cv-00184), so in any such litigation the § 103 combinations above — especially the Lexmark '211 + HP purge-art combination — would be prime invalidity grounds.