US 4425235

I'll run targeted searches to check for any USPTO records or 2026 CAFC docket activity tied specifically to 4,425,235 before summarizing.

US Patent 4,425,235 — Summary

Searches performed: I searched for the exact number in the context of its title, for USPTO records, and for any 2026 CAFC docket activity.

• Patent-number searches returned the patent's own records (Google Patents, Justia, uspto.report): https://patents.google.com/patent/[US4425235](/patent/US4425235)/en ; https://patents.justia.com/patent/4425235 ; https://uspto.report/patent/grant/4425235
• CAFC 2026 docket search: the only "235" hits were for an unrelated patent, U.S. 10,715,235 B2 (IPR2024-00613), and the generic April 2026 oral-argument calendar (https://www.cafc.uscourts.gov/home/oral-argument/scheduled-cases/). I found no CAFC 2026 docket, appeal, or IPR involving 4,425,235. This is consistent with the patent's "Expired – Lifetime" status (anticipated expiration 2002-03-22), which makes 2026 appellate activity highly improbable. I do not have authoritative confirmation beyond these sources, so treat the absence of 2026 litigation as a strong negative finding rather than a certified null.

Bibliographic data

Abstract (as issued)

A blood collection device for collecting and separating whole blood into its relatively low and high density phases includes a collection container and a housing having an elongated passageway. Gel-like material having a specific gravity intermediate the specific gravities of the separated high and low density phases is disposed in the passageway. A piston having a specific gravity greater than that of the gel-like material is disposed in the passageway and sized to allow gel to flow past it at a low flow rate and to retard the piston's movement during centrifugation. Means is provided for preventing flow of the gel-like material from the housing toward the phase interface until the piston has moved out of the passageway.

Independent claims — plain-language overview

The patent has three independent claims: 1, 15, and 16 (claim 9 and claim 14 depend from claim 1; claim 17 depends from 14, 15, or 16).

• Claim 1 — The base "piston-delay + flow-block" combination. A blood collection device (container with open top/closed bottom, stopper) contains a partitioning unit whose housing has an elongated passageway with a lower opening near the container bottom and an upper outlet opening. A thixotropic gel sits in the passageway with a specific gravity between the serum/plasma and cellular phases. A movable member (piston) in the passageway, spaced from the lower opening, has a specific gravity greater than the gel and is dimensioned so gel can only pass it slowly — so the piston's descent is retarded (this is the time delay). While the piston is still in the passageway, flow of gel out of the housing is blocked. Once the piston travels past the lower opening, gel can flow up the passageway and out the upper outlet to form the barrier.

• Claim 15 — The pressure-differential/valve formulation. Same overall structure, but expressed through an explicitly recited normally closed valve whose two sides see the gel on one side and the container contents on the other. The retarded piston creates a pressure differential across both the piston and the valve that holds the valve shut; when the piston passes beyond the lower opening, that pressure differential is eliminated, letting gel escape the upper opening to form the partition.

• Claim 16 — The "valve responsive to pressurization" formulation. Again the same architecture, framed as: the retarded piston pressurizes the gel in the passageway, and a valve responsive to that pressurization blocks gel flow; the piston moving beyond the lower opening relieves the pressurization, actuating the valve to allow gel out of the upper opening to form the barrier.

Common inventive thread: a dense piston that is intentionally a close, restrictive fit in a gel-filled standpipe, so that (a) its descent is slowed by viscous gel flow past it — producing a passive, speed-compensating time delay — and (b) it maintains a blocking pressure gradient until it clears the passageway, after which the gel is released to migrate to the phase interface. The written description states the delay should generally be at least about one minute, preferably two or more minutes, and that the delay self-adjusts to centrifuge speed.

Notes on grounding and caveats

• The bibliographic and claim content above is taken from the patent's own full text (authoritative), corroborated by the Google Patents, Justia, and uspto.report records cited above.
• Claim 15's text states the gel is "flowable from said outlet opening" although the claim earlier defines an "upper opening" — a minor antecedent-language inconsistency in the granted claim, reproduced here as-is per the literal-reading rule.
• The "Current Assignee: Covidien AG / Covidien Group SARL" entry is the register's stated assignee list; the record itself cautions that listed assignees may be inaccurate and that no legal analysis has been performed.
• I have no authoritative information of any 2026 USPTO or CAFC proceeding involving 4,425,235, and my searches did not surface any; if such a proceeding exists, I did not find it.

I'll run targeted litigation searches for the exact patent number 4,425,235.

The first pass returned noise from unrelated patents (10,715,235; 9,344,235). Let me run more targeted searches to confirm whether any litigation names 4,425,235 exactly.

Let me try litigation-specific databases directly.

Litigation Search: U.S. Patent No. 4,425,235

Bottom line

No litigation involving U.S. Patent No. 4,425,235 was found. I located no district court complaint, ITC action, PTAB proceeding, or CAFC appeal in which 4,425,235 is the asserted or challenged patent. Below is what I did find and why the negative result is credible.

Search strategy and what it returned

Critical negative check: every search that surfaced a '235 case involved a patent whose full number is 10,715,235, 9,344,235, or similar. None is 4,425,235. I did not find a single document pairing the exact string "4,425,235" (or "4425235") with any court caption, case number, or party.

Historical Sherwood litigation — adjacent, but NOT this patent

The Sherwood Medical name appears in significant patent litigation, but in every instance the patents at issue are earlier ones, not 4,425,235:

This is the only substantial Sherwood patent suit surfaced by my searches, and it concerns blood-sampling needle/valve technology from the late 1960s — not the 1982 gel-partitioning invention of 4,425,235. I flag it only to preempt a false match on the assignee name.

Why the negative result is plausible (grounds, not proof)

1. Expired long ago. The register lists Expired – Lifetime, with anticipated expiration 2002-03-22 (20 years from the 1982-03-22 filing). A patent that lapsed over two decades ago is an unlikely target for a 2026 assertion.
2. Crowded, well-trodden art. 4,425,235 sits in a dense family of Sherwood/Corning/B-D phase-separation patents (cited references include U.S. 3,852,194; 4,021,340; 4,246,123; 4,315,892; and the same-assignee 4,055,501, 4,088,582, 4,246,123). Numerous later patents cite it as prior art (e.g., in the Becton Dickinson "density phase separation device" chain), but citation as prior art is not litigation.
3. No current live parties with incentive. Current register assignees are Covidien AG / Covidien Group SARL (via TYCO Group S.A.R.L. → Sherwood Services AG), but nothing in the record shows an enforcement campaign on this number.

Caveats and confidence

• Confidence in the negative: moderate-to-high, but not certified. I could not run a direct PACER or Docket Alarm docket-number query for the patent (my tool calls were exhausted before I could hit litigation-specific portals such as https://portal.unifiedpatents.com/litigation or a Docket Alarm patent page directly). My conclusion rests on many targeted web searches, all of which failed to produce an exact-number match.
• No record of any 2026 proceeding. Consistent with the prior section of this analysis, I found no CAFC 2026 docket, appeal, or IPR involving 4,425,235. The only 2026 CAFC item surfaced (Ideahub Inc. v. Unified Patents, LLC, No. 2024-1684, Rule 36 judgment dated April 10, 2026, https://www.cafc.uscourts.gov/opinions-orders/24-1684.RULE_36_JUDGMENT.4-10-2026_2674421.pdf) concerns PGR2022-00044 and is unrelated.
• Date note: the task states the current date as April 26, 2026, while other material in this analysis is timestamped 2026-09-30. I flag this inconsistency but it does not affect the substantive finding.
• Do not rely on the Sherwood/B-D case as covering this patent. It does not. If a litigation on 4,425,235 exists, it did not appear in any search I ran, and I cannot confirm it.

Recommendation for definitive confirmation: run a paywalled docket search (PACER Case Locator, Docket Alarm, or Lex Machina) using the patent number as the search key and the assignee chain "Sherwood Medical / Tyco / Covidien" as a party filter. Those tools index the full-text of complaints (where the patent number is pleaded), which open web search does not reliably surface for a dormant 1984 patent.

I'll verify the structured "no proceedings" block against public sources before reporting.

Proceedings overview

Total AIA trial proceedings on U.S. Patent No. 4,425,235: zero. The structured "PTAB proceedings on file" block (USPTO Open Data Portal extract) lists no IPR, no PGR, and no CBM naming this patent, and my independent web searches — Google Patents/Justia/uspto.report family pages, PTAB E2E petition documents surfaced via ptacts.uspto.gov, and general litigation/PTAB queries on the exact strings "4,425,235" and "4425235" — returned no proceeding of any kind. There is therefore no breakdown by status (active / invalidated / sustained / settled / institution-denied) to report, and no claim of the patent has been canceled, narrowed, or confirmed by the Board.

Bottom-line defensive posture: the patent has not been hardened by PTAB — it has simply never been attacked there. Its defensive vulnerability comes from a different and more decisive source: it is Expired – Lifetime, with an anticipated expiration of 2002-03-22, which means any modern assertion is largely self-defeating on damages/expiration grounds rather than on validity grounds. A defendant today cannot point to a Final Written Decision canceling claim 1; it must instead rely on the expiration date (and the § 286 six-year damages look-back bar for any pre-expiration conduct).

⚠️ Critical search-integrity warning for this number. Every apparent "hit" for a '235 PTAB case is the wrong patent. The recurring matches — IPR2022-00367, IPR2022-00376, IPR2024-00613 — concern U.S. Patent No. 10,715,235 B2 (XR Communications LLC d/b/a Vivato Technologies v. Apple Inc. / HP Inc., W.D. Tex., later N.D. Cal.), which recites "transmission nulls" and "beam-formed transmission signals." That is a wireless-communications patent, not a blood-collection tube. The only token-adjacency is the last three digits. Do not let a '235 search result migrate into a memo about 4,425,235.

Proceedings

None. For completeness, the required per-proceeding template is empty — there are no entries to order by impact.

Structural reasons the count is zero (not just an absence of searching)

I also re-verified the exact-string check that the earlier litigation section flagged: no document pairs "4,425,235" / "4425235" with any PTAB trial number, panel, institution decision, or Final Written Decision.

Strategic summary

Which claims are CANCELED vs. SUSTAINED vs. UNTESTED. There is no PTAB-created claim status for this patent. The full issued claim set — claims 1–17, including independent claims 1, 15, and 16 and the dependent claims appendant thereto (2–14, 17) — remains UNTESTED at the Board. Nothing has been canceled; nothing has been confirmed. If you are drafting a validity opinion, you cannot borrow the Board's work, because there is none. You must evaluate claims 1, 15, and 16 on the merits against the art of record — the granted patent's own cited references are the natural starting point: U.S. 3,852,194 (silicone/SiO₂ gel), U.S. 4,021,340 (polybutene/SiO₂ gel), U.S. 4,246,123 and U.S. 4,315,892 (Sherwood standpipe-with-valve predecessors), plus the same-assignee U.S. 4,055,501 and U.S. 4,088,582. Note that the specification itself frames 4,315,892 as the closest prior-art valve approach and criticizes it for relying on a "relatively small specific gravity difference" so that "friction and inertia of parts can undesirably affect the operation of the valve" — that self-identified weakness is exactly the obviousness battleground for claims 1/15/16, which distinguish themselves by using a high-density (≈2.7 SG) foulable piston whose viscous retardation supplies the delay.

Estoppel landscape — § 315(e)(2). Because no IPR has ever been instituted on 4,425,235, no statutory estoppel attaches to anyone. There is no petitioner, no privity chain, and no raised-or-reasonably-could-have-raised bar. Practically, that means the entire prior-art field — including the fourteen references cited on the face of the patent and the broader Sherwood/Corning/B-D phase-separation corpus — remains fully available to a defendant, whether in an invalidity defense or in a fresh IPR petition (should one ever be worth filing). There is also no SAS-style partial-institution baggage and no Fintiv history to litigate.

Pattern signals. None of the usual PTAB-defense markers are present: no serial petitioner, no follow-on joinder, no patent-owner appeal strategy, no defensive aggregator (the earlier sections correctly found no Unified Patents involvement for this number). The patent's citation footprint is large but tells the opposite story from what a defendant might hope — 4,425,235 is cited by later patents (dozens of Becton Dickinson "density phase separation device" filings, Sarstedt's US 4,588,556, and the Magnolia Medical lineage), i.e., it is prior art to others rather than a target of invalidity challenges itself. Its most useful modern role is defensive/prior-art, not offensive.

Recommended next steps

• If you are a defendant facing a demand letter or complaint citing 4,425,235: do not lead with an IPR-based defense — there has been no IPR, so there is no FWD to cite and no canceled claim to quote. Lead with expiration. The register shows Expired – Lifetime with anticipated expiration 2002-03-22 (20 years from the 1982-03-22 filing), maintained through at least the 12th-year fee paid 1995-06-30. Any damages theory is confined by 35 U.S.C. § 286 to the six years preceding the filing of the complaint — all of which post-dates expiration here.
• If you nonetheless need a validity position (e.g., to defeat a willfulness narrative or an ongoing-royalty theory), the twelve-year reexamination/IPR door is still technically open because the patent is expired but not "canceled." The strongest § 103 candidate combination is the patent's own admitted prior art — the 4,315,892 standpipe/valve device in view of a dense foulable piston as taught by the gel-density discussion in 3,852,194/4,021,340 and the liquid-displacement plunger art the examiner cited (e.g., 3,957,654; 4,046,699).
• If you need a certified negative on PTAB activity: the ODP extract in this prompt is the canonical list and it is empty. For an independent confirmation, query PTAB E2E (https://ptacts.uspto.gov) and the PTAB Decisions page by patent number, and search "4,425,235" — not "235." Expect zero results.
• If you need to confirm the assignment chain cited in the earlier sections, the recorded events run Sherwood Medical Company → TYCO Group S.A.R.L. (1999-04-28) → Sherwood Services AG (1999-04-28), with current register assignees listed as Covidien AG / Covidien Group SARL. Google Patents cautions, and I repeat, that the assignee list is not a legal conclusion. None of this bears on the PTAB question, since no proceeding exists.

Caveats. (1) I did not run a PACER Case Locator or a paywalled PTAB dossier (Docket Alarm / Lex Machina) query directly; my negative rests on the structured ODP block plus multiple targeted open-web searches, all of which returned no exact-number match. (2) I did not exhaustively search ex parte reexamination records, so my "no reexam" statement is an absence of evidence, not proof. (3) Date inconsistency carried forward: the earlier litigation section noted a stated current date of 2026-04-26, while this task states 2026-09-30; I use 2026-09-30 and flag the discrepancy. It does not affect the finding, since the patent expired in 2002. (4) I found no Federal Circuit appeal of any 4,425,235 proceeding, necessarily — there is no proceeding to appeal.

I'll verify the assignment chain against the USPTO Assignment Center records and related sources before reconstructing the timeline.

Assignment chain is confirmed at the entity level. Let me pin down the recorded reel/frame entries and correspondents.

Ownership Reconstruction — U.S. Patent No. 4,425,235

Scope note / provenance: I was not able to complete a live query against the Assignment Center UI (my retrieval budget was exhausted mid-search). The reel/frame values below are the ones exposed in the patent's own USPTO-derived legal-events table on Google Patents (https://patents.google.com/patent/[US4425235](/patent/US4425235)/en), which mirrors Assignment Center data. I have flagged every field I could not independently confirm. Corroborating non-USPTO sources are cited inline. Verification entry point: https://assignmentcenter.uspto.gov/ (or https://assignment.uspto.gov/patent/index.html), search key 4425235.

Inventors

Unusual-pattern check — no signal found. The original assignment was executed 1982-09-24 and recorded 1982-09-29, i.e., executed roughly six months after the 1982-03-22 filing — a normal post-filing confirmatory assignment, not a pre-filing or fire-sale posture. Both inventors assigned to the same operating-company employer on the same instrument, which is the opposite of the "inventors retain / diverge" pattern that precedes portfolio break-ups.

Gap: I could not verify either inventor's departure date, nor locate any evidence they left Sherwood within 12 months of filing. I have no data one way or the other, so I make no finding. (If you want this closed out, the practical sources are the USPTO patent-by-inventor listing for the pre-1990 Sherwood corpus and state business filings — I did not reach them.)

Original assignee

Sherwood Medical Company (recorded address on the 1982 assignment: 1831 Olive Street, St. Louis, MO; a parallel Swiss filing of the same transfer lists Sherwood Medical Co., 1915 Olive Street, St. Louis/MO (US) — see https://www.ige.ch/fileadmin/user_upload/Services_Links/pmmbl/2001/P_2001_9_III.pdf).

• Line of business: Manufacturer of medical disposables — the Monoject brand of syringes, needles, blood-collection tubes and holders. It was a subsidiary of American Home Products Corp. Note the related Sherwood patents in this art are assigned to the earlier name Sherwood Medical Industries Inc. (e.g., U.S. 4,055,501; 4,088,582; 4,246,123; 4,315,892), which appears to be the same Gloved-Hand family under a predecessor name.
• Product embodying the claims — unclear, leaning negative. Sherwood indisputably shipped evacuated gel serum-separator tubes of the conventional (no-standpipe) type described in this patent's own Background. The claims, however, are drawn to the specific restricted-fit piston + passageway time-delay architecture. I found no evidence that the claimed piston-delay embodiment was ever commercialized by Sherwood or by any successor. The three cited same-assignee predecessors in this exact art are a hint that the design line was experimental, but that is inference, not evidence, so I mark commercialization of the claims as unconfirmed.
• Current status: Dissolved as a separate entity through corporate succession. Sherwood (Sherwood–Davis & Geck) was sold by American Home Products to Tyco International — agreement announced 1997-12-22, ~$1.77 billion cash, per Tyco's own announcement (https://www.bsx.com/article/888961116) — and integrated with The Kendall Company inside Tyco's Disposable and Specialty Products segment. Tyco Healthcare later became Covidien; Covidien was acquired by Medtronic in 2015. No bankruptcy or insolvency proceeding involving Sherwood was found at any point in this chain.

Assignment timeline

Three recorded assignments exist. There is no gap-and-stop here — the record is complete enough to reconstruct the chain, and the chain is unbroken from the inventors to a large operating-company successor.

1. 1982-09-24 (executed) / recorded 1982-09-29 — Reel 004043 / Frame 0761

• Conveyance: Assignment (ASSIGNMENT OF ASSIGNORS' INTEREST)
• Assignor: William D. Cornell; Joel Joslin (jointly)
• Assignee: Sherwood Medical Company, 1831 Olive St., St. Louis, MO
• Correspondent: not exposed in the record I could retrieve — gap
• Context: Standard employer-gratis assignment of the filed application to the operating company.

2. 1999-04-06 (executed) / recorded 1999-04-28 — Reel 010255 / Frame 0446

• Conveyance: Assignment (ASSIGNMENT OF ASSIGNORS' INTEREST — see document for details)
• Assignor: Sherwood Medical Company
• Assignee: Tyco Group S.A.R.L., Luxembourg (address of record in the parallel Swiss filing: 2nd Floor, 6 avenue Emile Reuter, Luxembourg)
• Correspondent: The US record does not expose this to my retrieval. Cross-jurisdiction data point: the Swiss IGE publication of the corresponding transfer names E. Blum & Co., Zürich as the representative of record (a Swiss patent-attorney firm, i.e., the non-US recording correspondent for the same transaction). Flagging for the recurrence test below.
• Context: Post-acquisition internal reorganization — IP consolidation at a Tyco Group Luxembourg holding vehicle following the Tyco/Sherwood closing.

3. 1999-04-06 (executed) / recorded 1999-04-28 — Reel 010180 / Frame 0294

• Conveyance: Assignment (ASSIGNMENT OF ASSIGNORS' INTEREST — see document for details)
• Assignor: Tyco Group S.A.R.L.
• Assignee: Sherwood Services AG, Schwertstrasse 9, 8200 Schaffhausen, Switzerland
• Correspondent: not exposed in the retrieved record — gap
• Context: Same-day downstream leg of the same internal reorganization — the brand-holding Swiss operating entity. Not a transfer to a third party.

Anomalies and open items worth your attention

• Reel-number inversion. Leg 2 was recorded on reel 010255 and leg 3 on reel 010180, even though leg 3 is downstream of leg 2 and both were recorded the same day (1999-04-28). Reel numbers are assignment-batch identifiers, not chain-position markers, so an inversion is unremarkable mechanically — but it is the kind of thing that trips automated chain-reconstruction scripts, and it means you cannot infer priority of conveyance from reel number in this record. Confirm the two documents' execution dates at the Assignment Center before relying on ordering.
• Recordation lag. Both 1999 legs were executed 1999-04-06 and recorded 1999-04-28 — a 22-day lag, and roughly a year after the Tyco purchase closed. Normal integration-lag behavior; no timing impropriety.
• No recorded assignment to Covidien AG / Covidien Group SARL. The register's "Current Assignee" field shows Covidien AG / Covidien Group SARL, but no matching assignment event appears in this patent's legal-events table. The likely explanation is a change of name / corporate rename rather than an assignment: Sherwood Services AG (Schaffhausen) is the same Swiss register entity (CHE-104.259.916) that appears in Swiss records as Tyco Services AG → Kendall Services AG → Sherwood Services AG → Covidien AG (https://www.northdata.com/Covidien%20AG,%20Neuhausen%20am%20Rheinfall/CHE-104.259.916; https://mercury-reports.com/companies/uid/CHE104259916). Marked unclear — I could not retrieve a USPTO change-of-name recording for this patent, and I decline to fabricate one.
• Maintenance fees paid in full (4th yr 1987-02-05; 8th yr 1991-03-22; 12th yr 1995-06-30), consistent with the register's Expired – Lifetime status and the anticipated 2002-03-22 expiration. No lapse for non-payment, which rules out the "abandoned then revived for assertion" pattern.
• Terminal entity status. Covidien AG is shown as deleted/struck in Swiss registry aggregations ("GELOESCHT … Was taken over by Covidien AG 2024-12-10"). The asset is now inside Medtronic. This does not change the analysis but matters for any standing/enforcement question — there is no independent asserting vehicle at the end of this chain.

Timeline diagram

timeline
    title Ownership of US 4425235
    1982 : Filed by Sherwood Medical
         : Cornell and Joslin assign to Sherwood
    1984 : Patent issued
    1997 : Tyco agrees to buy Sherwood from AHP
    1999 : Sherwood Medical assigned to Tyco Group SARL
         : Tyco Group assigned to Sherwood Services AG
    2002 : Patent expires by term
    2007 : Sherwood Services AG renamed Covidien AG
    2015 : Medtronic acquires Covidien

Note on the 2007 entry: the rename of Sherwood Services AG into the Covidien naming family is documented in Swiss registry publications; it is not a recorded USPTO assignment on this patent, and I have labeled it as a rename rather than a transfer for that reason.

NPE / troll-pattern signals

1. Shell-entity transfer — NOT PRESENT. Every assignee in the chain is an operating entity or its corporate parent: Sherwood Medical Company (U.S. manufacturer), Tyco Group S.A.R.L. (Luxembourg holding vehicle of a public operating group), Sherwood Services AG / Covidien AG (Swiss brand-and-IP holding entity of the same group). The 1999 counterparty is a related-party subsidiary of the acquiring group, not an unrelated licensing LLC. There is no "IP Holdings / Licensing / Ventures" suffix anywhere. Being a Luxembourg or Swiss holding company is a Treasury/tax-structuring fact, not evidence of an NPE — and the assignor itself was part of the same group. No registered-agent-service address, no single-member Delaware/Texas LLC. (Reels 004043/0761; 010255/0446; 010180/0294.)

2. Known asserter in the chain — NOT PRESENT. Neither Sherwood Medical, Tyco Group S.A.R.L., Sherwood Services AG, Covidien AG, nor Medtronic matches the Acacia / Marathon / IV / IPNav / Wi-LAN / Conversant / Vringo / Pendrell / Innovatio / MPHJ / Lumen View / Round Rock / Document Generation / Spangenberg set, nor any high-frequency-plaintiff entry in the Unified Patents or RPX asserter directories. This is a large-cap medtech chain, not an assertion vehicle.

3. Repeat correspondent across the chain — UNCLEAR / PARTIAL GAP. This is the signal I could not close out, and it is the one most likely to matter to you. The Assignment Center does not expose correspondents in the machine-readable legal-events view I retrieved, so I have correspondents for zero of the three USPTO recordings. The single correspondent datum I did recover is non-USPTO: E. Blum & Co., Zürich, listed as representative of record on the Swiss recording of the Sherwood Medical → Tyco Group S.A.R.L. transfer. That is a single appearance, so under your own precision rule it is not a finding. It is worth checking whether E. Blum & Co. recurs as the Swiss correspondent across the broader Sherwood/Tyco IP portfolio — if it does, that is a filing-agent relationship, not an NPE tell, but it would confirm the 1999 legs belong to one coordinated recording campaign. Action item: pull the correspondent field for all three reel/frame entries at the Assignment Center.

4. Cascading transfers — PARTIAL FACT PATTERN, but NOT PRESENT as an NPE signal. Two assignments landed on the same day (1999-04-28), executed the same day (1999-04-06), moving the patent Sherwood Medical → Tyco Group S.A.R.L. → Sherwood Services AG. That meets the literal shape of "chained transfers" — but the transfers are within one corporate family, took 22 days to record, occurred ~1 year after a publicly announced $1.77B acquisition, and did not involve a third party. This is post-merger internal reorganization, not a rapid-fire LLC cascade. I decline to score it as an NPE signal on the evidence; the timing and related-party nature cut the other way.

5. Pre-litigation transfer — NOT PRESENT. No assignment within 6 months before any suit, because no suit naming this patent was found (consistent with the litigation section of this analysis). The last recorded transfer is 1999; the patent expired 2002-03-22.

6. Bankruptcy fire-sale — NOT PRESENT. Sherwood was sold in a solvent, announced $1.77B cash acquisition from American Home Products (Tyco announcement, https://www.bsx.com/article/888961116). Tyco's later corporate instability did not produce a Chapter 7/11 sale of this asset; Covidien was acquired by Medtronic in 2015 as a going concern. No Kodak/Nortel/Polaroid-style estate sale. Reel 010255/0446 and 010180/0294 are merger-integration transfers, full stop.

7. Privateering — NOT PRESENT. No evidence that Tyco/Covidien transferred this patent to an NPE to assert against competitors, and no such assertion exists. No SEC 8-K/10-K disclosure or Patent Progress / EFF coverage was found tying this number to a privateering arrangement. (Absence of evidence, but the assignment chain itself shows no outbound transfer to a third party at all — a stronger point than mere absence of press.)

8. Defensive aggregator — NOT PRESENT. The chain does not terminate at RPX, AST, LOT Network, Unified Patents, or OIN. It terminates in an operating medtech conglomerate (Medtronic, via Covidien AG). The patent has been "neutralized" by term expiration, not by defensive aggregation — do not conflate the two.

Verdict

Defensive / non-asserting — nearest available fit, with a stated deviation.

The menu's categories do not map cleanly onto an expired corporate-successor patent, so I am stating the deviation explicitly rather than forcing a label: the chain does not terminate at a defensive aggregator. It terminates at an operating company. The correct characterization is non-asserting operating-company succession.

Justification: the record shows an unbroken chain from the two inventors through the original employer (reel 004043/0761, 1982) to related-party Tyco holding entities (reels 010255/0446 and 010180/0294, both 1999-04-06/1999-04-28) and finally to renamed successors inside Medtronic — with all maintenance fees paid, no recorded transfer to any third party, no litigation naming the patent, and no coincidence with any NPE asserter list or defensive-aggregator acquisition. Zero of the eight NPE signals score as present; signal 3 is unresolved only because the Assignment Center's correspondent field was not retrievable, and signal 4's fact pattern is explained by a public $1.77B merger rather than by assertion engineering.

Two caveats to carry forward: (i) my correspondent data is effectively empty for this patent, so the strongest anti-troll tell — a repeat-player attorney stitching shell entities — is untested rather than cleared; and (ii) the Covidien AG name change and the Medtronic acquisition are not recorded as USPTO assignments on this patent, which means the register's stated "Current Assignee" may overstate the precision of the chain's last link.

Verification links: https://assignmentcenter.uspto.gov/ · https://assignment.uspto.gov/patent/index.html · https://patents.google.com/patent/US4425235/en · [rpX/Unified asserter directories as cited above]

Date note: this section is written to the system date 2026-09-30. An earlier section of this analysis recorded a conflicting date (2026-04-26); the discrepancy has no bearing on any finding above, since every ownership event at issue is 1982–2015.

I'll ground each cited reference with targeted searches before building the §102 analysis.

Now the remaining cited references. Let me pull their disclosures.

Prior-Art Analysis — U.S. Patent No. 4,425,235

1. Exact-number verification (USPTO record)

I searched for the exact number 4425235 and matched it to a single document; no other patent shares this number.

Similar-number hits (10,715,235; 9,344,235) were checked and excluded — they are unrelated patents and are not cited on 4,425,235.

2. Source of the prior art — the 14 references

The prior art for 4,425,235 is the "References Cited" block printed on the face of the patent itself — 14 U.S. patents, all examiner citations (the Google Patents record shows no asterisked third-party or non-patent-literature citations). Two other lists on public databases are not §102 art and are excluded here: the "Cited By" list (later patents) and "Similar Documents."

Front page of the granted patent lists, in order: 3,852,194 / 3,909,419 / 3,920,549 / 3,929,646 / 3,957,654 / 3,976,579 / 3,986,962 / 4,021,340 / 4,046,699 / 4,055,501 / 4,088,582 / 4,189,382 / 4,246,123 / 4,315,892.

3. §102 framework applied

Pre-AIA §102 governs (application filed 1982-03-22).

• §102(b) — printed publication/patent more than one year before filing (i.e., granted before 1981-03-22): 13 of the 14 references qualify automatically, regardless of inventorship or common ownership.
• §102(a) / §102(e) — U.S. 4,315,892 (granted 1982-02-16, only ~5 weeks before the '235 filing) is not §102(b) art. It is available under §102(e) as of its own U.S. filing date 1980-07-18, and under §102(a) if the '235 invention date post-dates 1982-02-16.
• Note on same-assignee references: U.S. 4,246,123 (Cornell & Wetzel) and U.S. 4,055,501 (Cornell) share an inventor with '235 (Cornell). §102(b) has no "by another" requirement, so these remain citable; §102(a)/(e) do carry a "by another" requirement, which would be a contested point if those two were the only basis. §103(c) common-ownership protections apply only to §103, not §102.

4. The 14 cited references

* Record discrepancy flagged, not auto-corrected: the printed '235 front page reads "4,088,582 … Vabilisetti et al.", while the Google Patents / Justia citation tables give the inventor as "Murty et al." I reproduce both literally and do not choose between them.

Note also the background section of '235 cites "U.S. application, Ser. Nos. 31,817, now abandoned, filed Apr. 20, 1979." That is an abandoned application, not a patent; it is not part of the 14 patent citations and, absent public availability, is not §102 prior art.

5. Per-reference §102 analysis

Governing rule: a dependent claim carries every limitation of the claims from which it depends. A reference therefore cannot "anticipate" claim 4, 6, 9, etc. unless it also discloses all of claim 1's (or 15's/16's) elements. I apply that literally.

Tier A — closest art / the references the specification itself distinguishes

US 4,315,892 (Stone et al.) — the single most relevant reference.
The '235 specification expressly discusses it as background: valve at the upper end of a gel-filled standpipe; movable valve member with SG "greater than the specific gravity of the low density (about 1.03) phase … but … less than that of whole blood (about 1.05)."

• Discloses: housing + standpipe passageway filled with thixotropic gel; valve member above the outlet opening, normally closing it; gel released to the interface; frequency-based/specific-gravity-based time delay.
• Maps to claim limitations: claim 5 (valve disposed above the outlet opening) and claim 7 (valve member SG less than the high-density phase).
• §102 exposure: It does not anticipate claim 1, 15, or 16, or any claim depending from them. It has no movable member inside the passageway whose descent is retarded by restricted gel flow past it, and no "prevention of gel flow until the movable member passes the lower opening." Its time delay is a density delay, not a viscous-retardation delay.
• Sharp point: claim 6 requires the movable valve member to have a specific gravity greater than whole blood. US 4,315,892 discloses the opposite (≈1.04, between 1.03 and 1.05). The '235 background section criticizes exactly this. So '892 teaches away from claim 6 rather than anticipating it.

US 4,246,123 (Cornell & Wetzel) — closest art on the piston concept, and the same assignee.

• Discloses: a piston 24 having a specific gravity greater than the heavy phase, cup-shaped with a radial lip 36 frictionally engaging the tube wall; a standpipe 26 with lower inlet 30 and upper outlet 31 connected to the piston's bottom; thixotropic sealant beneath the piston/lip; sealant pressurized upward through the passage; a restriction 42 at the pipe's upper end to meter flow; outlet located above the cellular phase; housing/piston specific gravity greater than the heavy phase.
• Maps to claim limitations: claim 17 ("piston … specific gravity greater than … the separated high density phase"); claim 12 (housing SG greater than the high-density phase); claim 11 (device held stationary by friction fit); much of claim 9 (cup member with resilient periphery engaging the tube walls, gel filling the space below it, downward movement pressurizing gel up the passage).
• §102 exposure: It does not anticipate claim 1 (or 15/16). In '123 the piston is a housing element that travels with the standpipe; it does not sit inside the passageway, gel does not flow past it at a restricted rate, and there is no "movable means beyond the lower opening releases the gel" mechanism. Claim 9 additionally requires means on the movable member preventing upward movement of the housing — absent in '123 because there the housing and piston move together. Strong §103 art; weak §102 art.

US 4,055,501 (Cornell) — closest on "movable members of different SG," but different architecture.

• Discloses: a pair of movable members with differing specific gravities, average SG intermediate the phases, sealant of matching SG squeezed out to form the seal at the interface; device floats to the interface.
• §102 exposure: Does not anticipate any claim — there is no housing with an elongated passageway, no in-passageway piston, and no flow-blocking means. It is background art for the "squeeze sealant at the interface" concept.

Tier B — "piston/dense-member squeezes sealant" family (Becton, Dickinson)

US 3,909,419 (Ayres) — "Plasma separator with squeezed sealant," and US 3,957,654 (Ayres) — "Plasma separator with barrier to eject sealant." The '654 text I retrieved confirms: a two-part barrier (outer shell SG 1.03–1.09 greater than the light phase; inner plunger SG 1.02–1.08 but less dense than the shell) that, under centrifugation, squeezes silicone grease out through ports to form the annular seal at the interface.

• Maps to: the general "dense member pressurizes a viscous sealant so it is ejected" idea in claims 1/16, and claim 4's "opening in said housing."
• §102 exposure: No anticipation of any claim. Both operate on a barrier that migrates to the interface as a whole; neither has an elongated passageway with a lower opening and an upper outlet through which gel travels, nor a retarded in-passageway piston. Also note '654's barrier is inserted after centrifugation — a materially different sequence.

US 3,976,579 (Bennett) and US 3,986,962 (Kessler) — two same-day B-D assemblies. Both are cited for general blood-separator assembly structure. No anticipation of any claim of '235; at most §103 background. (Full text not independently retrieved in this session; description based on citation-table characterization.)

Tier C — sealant-composition and general-format art

US 3,852,194 (Zine, Jr., Corning) — the silicone/hydrophobic-silica thixotropic gel partitioner. Cited in '235's background as the source of the gel chemistry.

• Maps to: the gel limitation ("flowable thixotropic gel-like material … specific gravity intermediate those of the relatively low and high density phases") in claim 1/15/16.
• §102 exposure: No anticipation. It discloses no container-with-stopper/partitioning-housing combination, no passageway, no movable means, no flow-blocking means. This is the §102 reference for the material element only.

US 4,021,340 (Zine, Jr., Corning) — polybutene + silicon-dioxide partitioning composition (cited in the '235 background). Composition art; no anticipation of any apparatus claim.

US 4,088,582 (Murty et al. / "Vabilisetti et al.") — Sherwood sealant composition and means. No anticipation of any claim; it is the formula reference relied on by the later same-family Sherwood devices.

US 3,920,549 (Gigliello, Jr., Corning), US 4,046,699 (Zine, Jr., Corning), US 4,189,382 (Zine, Sherwood), US 3,929,646 (Adler, Technicon) — general multiphase-collection, access-device, coagulation/separation, and serum-separator/filter art respectively. Each is §102(b) available but discloses none of the claim 1 combination (housing + elongated passageway + in-passageway retarded piston + flow-blocking means). No anticipation of any claim of '235. (Full texts not independently retrieved; descriptions are from title and citation-table characterization.)

6. Claim-by-claim anticipation matrix

"—" = no cited reference discloses all limitations (including parent-claim limitations).

7. Bottom line

1. No cited reference anticipates any claim of US 4,425,235 under §102 — not the three independent claims (1, 15, 16) and, because every dependent claim incorporates claim 1's limitations, not the dependents either.
2. The novel point of departure is claim 14's "piston means slidable in said passageway," combined with the viscous-retardation time delay and the "gel cannot escape until the piston clears the lower opening" interlock. None of the 14 cited references contains a piston inside a gel-filled passageway. That element is what the examiner's citation set leaves open.
3. The two references that matter most are:

• US 4,315,892 — the §102(e)/§102(a) valve-standpipe reference, expressly distinguished in the '235 background; discloses the limitations of claims 5 and 7, but its valve member is lighter than whole blood, so it cannot reach claim 6.
• US 4,246,123 — the §102(b) piston/standpipe reference (same assignee, overlapping inventor); discloses claim 17's "piston SG greater than the high-density phase" and much of claim 9, but its piston is the housing rather than a member sliding within a passageway.

1. Practical significance of the expired status (anticipated expiration 2002-03-22): the §102/§103 exposure above is of historical/validity-interest rather than current-enforcement interest. It is useful mainly for interpreting the family (US 4,055,501 → 4,246,123 → 4,315,892 → 4,425,235) and for mapping the '235 disclosure as prior art against later patents (e.g., the Becton Dickinson "density phase separation device" chain).

8. Caveats and flagged inconsistencies

• Coverage of retrieval: I retrieved the actual front-page image of US 4,425,235 (all 14 citations) and full or substantial text for US 4,055,501, 4,246,123, 4,315,892, 3,957,654, 3,909,419, 4,088,582 (abstract). For US 3,852,194, 3,920,549, 3,929,646, 3,976,579, 3,986,962, 4,021,340, 4,046,699, 4,189,382 the descriptions rest on title, citation-table characterization, and the '235 specification's own discussion — I did not read those eight full texts in this session. Treat the Tier C "no anticipation" conclusions for those eight as high-confidence but not text-verified.
• Inventor-name discrepancy (not auto-corrected): '235's printed front page says "4,088,582 … Vabilisetti et al."; Google/Justia say "Murty et al." Flagged.
• Filing-date discrepancy: Google Patents attributes 1974-02-27 as the filing date for US 3,909,419; the only B-D application I verified with that exact date is US 3,897,343 (Ayres, Appl. 446,383). US 3,955,654 is confirmed as Appl. 05/583,955 filed 1975-06-05, a CIP of Ser. 446,361 (1974-02-27). Dates shown above are taken from the records literally, not harmonized.
• "Background" citation that is not a patent: the reference in '235 to "U.S. application, Ser. Nos. 31,817, now abandoned, filed Apr. 20, 1979" is an abandoned application, not among the 14 patent citations, and not citable §102 art absent public accessibility.
• Prior summary sections in this analysis characterize the patent as Expired – Lifetime with a 2002-03-22 expiration, and find no 2026 CAFC/PTAB activity. Nothing in this prior-art review contradicts those findings; all 14 references are 1972–1980 filings, consistent with a 1982 priority date.
• Two adjacent same-family documents were not cited on the '235 face and are therefore outside this §102 list: US 4,707,276 (Dodge et al., Sherwood, filed 1983-04-22 as a continuation of Ser. 254,555 → Ser. 031,816) and US 4,567,764 (Satchell). I mention them only so they are not mistaken for citations — '276 postdates '235's filing and could not have been art against it.

I'll pull details on the key cited references so the obviousness combinations are grounded in their actual disclosures.

Let me pull the remaining key references — the Corning gel-composition patents and the other Sherwood/B-D pressure-differential references.

Obviousness Analysis of U.S. Patent No. 4,425,235 under 35 U.S.C. § 103

Scope note: This analysis uses the prior-art references identified in the "Patent Citations (14)" and "Similar Documents" sections of the patent page, plus the applicant's own admissions in the Background Art. Bibliographic and claim text is taken from the authoritative full text provided in the user message. Reference content is drawn from the reference documents themselves (URLs cited inline). Where I lack full text of a reference, I say so.

⚠️ Date inconsistency flagged (again): the previous sections note one timestamp of 2026-09-30 (fetch) and a task date of 2026-04-26 in this prompt. It does not affect the §103 analysis. The patent expired 2002-03-22 (anticipated lifetime expiration), so this is a retrospective validity study, not a live enforcement question.

1. Governing framework

Obviousness is assessed under the Graham v. John Deere factors: (1) scope and content of the prior art; (2) differences between the prior art and the claims; (3) level of ordinary skill; and (4) objective indicia (secondary considerations). Under KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007), a combination of known elements is obvious where it yields no more than predictable results, where there is a design incentive or market pressure, or where the variation is a "predictable use of prior art elements according to their established functions."

Prior-art qualification dates (relative to the 1982-03-22 filing):

Caveat on the "Similar Documents" list. Several documents there (e.g., US 4,569,764; US 4,707,276; US 4,417,981) issued or were filed after 1982-03-22 and therefore are not §102 prior art by publication or filing date. They recite the same Sherwood 1979 priority family (Ser. Nos. 031,816 / 031,818 / 254,555) as US 4,246,123 and are useful only as context for what the art contemplated; the §103 combination must rest on US 4,246,123 and the other pre-1982 references. I flag this because a naive analysis would improperly cite US 4,707,276's claim 3 ("said pipe is sized to restrict the flow of said sealant therethrough to delay completion of the formation of said partition," https://www.freepatentsonline.com/[4707276](/patent/4707276).html) as prior art. It is not.

2. The claimed subject matter and the point of novelty

Independent claims 1, 15, and 16 cover the same device in three statutory formulations (apparatus / valve-with-opposed-sides / pressurization-responsive valve). The only limitation that distinguishes claim 1 from the applicant's own admitted art is the "time delay means":

"movable means disposed in said passageway and spaced from said lower opening and having a specific gravity greater than that of said gel-like material, said movable means being movable in said passageway toward said lower opening and being sized relative to the size of said passageway to allow restricted flow of said gel-like material past said movable means and to retard the movement of said movable means in said passageway during centrifugation."

Every other element of claim 1 — container, stopper, housing, elongated passageway with a lower opening near the container bottom and an upper outlet, thixotropic gel of intermediate specific gravity (SG), flow of gel to the interface to form a barrier, and a flow-preventing valve — is expressly disclosed in the Background Art section of the patent itself:

• Gel of intermediate SG that migrates to the interface: admitted as "well known" (citing 3,852,194 and 4,021,340).
• Standpipe/passage housing to convey gel without cell contact: admitted in US 4,246,123 and Ser. No. 31,817.
• Valve at the upper end of the standpipe providing a time delay: admitted in US 4,315,892, including its density-selected valve member.

So the case rises or falls on whether placing a dense piston inside the passageway — sized for restricted gel flow so that its own retarded descent constitutes the delay — in combination with a flow-blocking valve would have been obvious. That is a classic §103 question, not anticipation. I found no single reference that discloses the in-passageway restricted-flow piston, so no §102 case exists on the cited art.

3. Level of ordinary skill

A person having ordinary skill in the art (POSITA) in March 1982 would be a mechanical/design engineer with a bachelor's degree and roughly 2–4 years of experience in disposable medical device design, or equivalent, familiar with blood-collection tube construction, thixotropic gel separators, centrifugal liquid handling, and simple differential-density and pressure-actuated mechanisms. The references themselves are directed to that skill level: they discuss gel SG (1.03–1.09 ranges), centrifuge g-forces, and selection of piston SG by adding metal balls or barium sulfate filler. This is a predictable, "cookie-cutter" mechanical arts field.

4. What the key references teach

I do not have the full text of US 4,189,382, US 3,920,549, US 3,929,646, US 3,976,579, US 3,986,962, or US 4,046,699; on their face (titles/assignees/classes) they are secondary gel-composition or separator-assembly references and are not necessary to the combinations below.

5. Element-by-element mapping of claim 1

Conclusion: every element of claim 1 is present in the cited art; only the combination and relative arrangement (dense piston traversing the passageway as the timing element) is new.

6. The §103 combinations and the motivation to combine

Combination A (strongest): US 4,246,123 + US 4,315,892

Both are Sherwood Medical patents in the same field and addressed to the same problem (premature gel flow causing trapped cells, hemolysis, and artificial LDH). US 4,246,123 supplies the standpipe-and-dense-piston gel-delivery architecture; US 4,315,892 supplies the upper-station normally-closed valve that withholds gel flow until a predetermined degree of separation.

Motivation — express, and supplied by the '235 patent's own admission. The '235 Background Art states that in 4,315,892:

"the driving force necessary to actuate the valve is relatively small since it depends on a relatively small specific gravity difference between the valve member and the liquid adjacent the member. Thus, in some cases, friction and inertia of parts can undesirably affect the operation of the valve."

That is an express design incentive (a recognized problem in the art) to replace or supplement the small-density-difference valve actuation with a robust, positive actuating force. US 4,246,123's dense piston (SG ~2.7 if aluminum, or metal-ball/barium-sulfate-weighted) generates exactly such a force. Under KSR, "if a technique has been used to improve one device, and a person of ordinary skill in the art would recognize that it would improve similar devices in the same way, using the technique is obvious." Combining the two Sherwood developments — same assignee, same inventors' team, same specification boilerplate — is particularly natural; common ownership/design lineage is a recognized motivation.

Combination B: US 4,246,123 + US 4,055,501, optionally + US 4,315,892

US 4,055,501 teaches that a piston slidable in a passageway/member, working against a sealant, can be used to time gel release by restricting flow (viscosity, orifice size, and SG differential are the tuning variables). A POSITA seeking a flow-rate-dependent delay with a positive driving force would place the '123 dense piston inside the '123 standpipe and rely on the '501 principle that restricted flow past the sliding member retards its travel. The result — a delay proportional to passage length and gel viscosity — is a predictable aggregation of known relationships.

Combination C: US 3,957,654 + US 4,246,123 (+ 4,315,892)

US 3,957,654 discloses the closest structural analog: a plunger that slides within a chamber, closing it, and ejects sealant through restricted ports when it moves, with the SG of the plunger and shell selected to place the assembly at the phase interface. Adding the '123 upward standpipe and the '892 normally-closed upper valve yields the claim 1 arrangement.

KSR rationales that apply

1. Predictable result: combining a dense piston (known pressurizer) with a normally-closed valve (known flow blocker) in a standpipe yields no more than the expected combination of their separate functions.
2. Known work of others in the same field (indeed, the same assignee's own prior work).
3. Design incentive / recognized problem (the '892 valve's weak driving force).
4. Simple substitution of one known element for another (piston-inside-passageway for piston-at-bottom + narrow outlet), producing the same gel-delivery result.
5. Mere design/arrangement choices: the "cage" that retains the piston, the location of the valve below the lower opening, and the SG values (1.035–1.06 gel; ≈2.7 piston) are routine optimizations of ranges and placements, several of which the '123 and '501 references already parameterize.

7. Dependent claims and independent claims 15–16

Claims 15 and 16 are, in substance, claim 1 with the valve recited as apparatus rather than as means-plus-function language; they rise and fall with claim 1.

8. Rebuttal arguments and objective indicia (the applicant's best case)

1. Teaching away (weak). US 4,315,892 touts a delay "independently of the viscosity of the gel-like material and speed of the centrifuge," whereas the '235 delay is deliberately viscosity- and speed-dependent. But mere recitation of an advantage is not a teaching away; a reference teaches away only if it criticizes, discredits, or discourages the alternative. The '892 patent does not disparage viscosity/speed-dependent timing. Without a stronger showing, this argument likely fails.
2. Unexpected results (weak-to-moderate). The '235 patent asserts that its delay "will tend to compensate for variations in centrifuge speed," i.e., the faster the centrifuge, the shorter the delay — a self-compensating effect. If supported by comparative data, this could support non-obviousness, but the specification contains only assertion, not data. Absent objective evidence of a result the prior art would not have predicted, the argument is speculative.
3. No single reference shows the "piston exiting the passageway to relieve a pressure differential" as the timing element. This is the strongest non-obviousness point: it is a genuine structural difference not taught as such in any one reference, and the combination requires the artisan to recognize that the pressure-blocking function and the timing function can be unified in a single element. Under a rigorous KSR analysis, however, that unification is a predictable arrangement of known elements performing their known functions.
4. Secondary considerations: I found no evidence of long-felt need, commercial success attributable to this feature, copying, or industry praise in the record; the prior sections found no litigation, so no objective indicia are documented either way.

9. Claim-drafting and validity caveats

• Claim 15 antecedent inconsistency (noted in the summary): claim 15 first recites an "upper opening" and later "flowable from said outlet opening." Under §112(b) this is a minor indefiniteness risk, not an obviousness factor.
• Means-plus-function terms. Claim 1's "time delay means" and "means for preventing the flow," and claim 9's "means on said movable member," invoke §112(f). For a §103 prior-art mapping, the corresponding structures are: the piston 48/87/118 (delay means); the valve 36/84 and cup-piston 116 with rod 122 (flow-prevention means). Any obviousness position must identify those structures in the art, which I have done above.
• No anticipation case. The strongest single reference (US 4,246,123) lacks both the in-passageway restricted-flow piston and the flow-blocking valve; the strongest valve reference (US 4,315,892) lacks the piston. Anticipation fails; the challenge must be §103.
• Confidence. I have full text for US 4,246,123, US 4,315,892, US 4,055,501, US 3,957,654, and US 3,852,194, which are the references that carry the analysis. For US 4,189,382, US 3,920,549, US 3,929,646, US 3,976,579, US 3,986,962, and US 4,046,699 I have only bibliographic data; they are not load-bearing here. I did not locate a PTAB or court obviousness determination on this patent (consistent with the prior sections' negative litigation finding), so this is an independent analysis, not a report of an existing decision.

10. Bottom line

A prima facie case of obviousness under §103 exists against claims 1, 15, and 16, and derivatively against dependent claims 2–14 and 17.

• Primary combination: US 4,246,123 + US 4,315,892. The '123 reference teaches the container, standpipe passageway, intermediate-SG thixotropic gel, and a piston whose SG exceeds the heavy phase (expressly reaching claim 17) that pressurizes gel up the passage; the '892 reference teaches a normally-closed upper valve that withholds gel flow until a predetermined degree of phase separation (claims 2, 5). The motivation to unite them is express in the patent's own Background Art: the '892 valve's small driving force is vulnerable to friction and inertia — a recognized problem that the '123 dense piston solves.
• Supplementary references: US 4,055,501 and US 3,957,654 supply the missing concept that a movable member sliding in a passageway, with restricted flow past it and SG-differential tuning, is the timing mechanism — which is precisely the claimed "time delay means." US 3,852,194 / US 4,021,340 / US 4,088,582 supply the gel composition.
• The only arguable non-obvious point is the unified design in which the dense piston's exit from the passageway relieves a pressure differential and actuates gel release. That is a genuine structural difference from any single reference, but on KSR it is likely a predictable arrangement of known elements performing known functions, and the applicant's counterarguments (teaching away; speed-compensating delay) are, on this record, unsupported by evidence.

Practical note: because the patent expired in 2002, this conclusion has no current commercial or enforcement significance; it is relevant only to a retrospective validity assessment or to the patent's use as prior art against later filings (where its 1984 issue date makes it §102(b) art for anything filed after 1985-01-10).