US 900506

I'll run searches against the patent number and any litigation/docket activity before summarizing.

Let me run a few more targeted searches, including litigation/docket checks.

A couple more checks to rule out confusion with similarly-numbered modern patents and to confirm docket status.

Bottom line

The number 900506 as a US patent resolves to US 900,506 — "Blow-off valve," John S. Forbes, filed June 13, 1907, issued October 6, 1908. It is a 1908-era mechanical patent, expired since 1925. I found no CAFC 2026 docket activity, and no litigation activity of any kind, associated with it (details and caveats in §6).

Most search hits for the bare string "900506" are not this patent — see §7 (disambiguation). I am flagging that explicitly because the collision is severe.

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1. Bibliographic record

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2. Abstract

There is no abstract of record. The Google Patents record for US 900,506 contains no abstract field, which is normal for patents of this vintage. The following is a derived summary I wrote from the specification, not verbatim text, and should not be cited as the patent's abstract:

A blow-off valve in which the flow path is opened and closed not by a disk or gate pressed against a seat, but by a cylindrical shell sliding longitudinally inside lined sleeves within the valve casing. Annular packing is trapped between and around the sleeves, entirely outside the fluid stream. After the shell has moved to its closed position, continued rotation of the valve stem causes the shell (via laterally projecting wings) to bear on a disk-like structure inside the shell and thereby to compress the sleeve stack and load both packing bodies into fluid-tight joints. Because the packing and the seats are never exposed to the flowing fluid, grit, scale, or wire-drawing erosion of the sealing surfaces is avoided.

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3. What the patent actually discloses (brief)

Per the specification as fetched:

• Casing A with inlet a and outlet a¹; a cover B bolted on (bolts b), carrying a valve stem C with handwheel c, a threaded portion, a stuffing box/gland b, and a collar c² seated in counterbore b².
• The bore is lined with sleeves D, D; packing d sits below sleeve D at the inlet level and packing d¹ between the two sleeves above the inlet — i.e., both bodies of packing are positioned in the casing/sleeve interface, out of the flow path.
• A structure E (Fig. 6 detail) has a disk head e, a smaller disk e¹, and a curved portion e² forming part of a cylindrical surface; the stem end is centered in it, and cover pins b⁴ pass through openings e⁴ to prevent its rotation.
• The movable member is the cylindrical shell F, internally threaded at lug f to receive the stem's threaded portion, with wings f² that strike the pins b⁴ at the top of travel — whereupon the collar c² loads disk e, which loads sleeve D, which transmits pressure through packing d¹ into sleeve D and thence into packing d.
• The shell is described as balanced (both ends equally exposed to fluid pressure), hence easily manipulated; the inlet is closed by the shell's cylindrical lower portion, leaving no recesses for sediment.
• The edge of the shell opening acts as a shear blade against the sleeve opening to cut solid bodies caught in the inlet, and the opening in the shell is fully enclosed when closed, preventing sediment accumulation.
• Figs. 7–11 show modifications (shell F¹ closing toward the outlet; single-packing unbalanced variants; stem threaded through the cover; a 180° "through" valve; a single angled packing ring). Fig. 14 is an enlarged detail of the packing rings of Fig. 7.
• A cost/manufacture point worth noting technically: the casing interior and sleeve interiors are finished only where the packing and shell engage, with rough unfinished regions a⁴, a⁵ and end-only engagement areas d⁴ left unmachined to reduce cost and friction.

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4. Independent claims — plain-language overview

Every claim 1–19 is drafted in the same "The combination in a valve, of…" independent form; none uses dependency language ("as set forth in claim N"), which is typical of 1908 drafting practice. I therefore treat all 19 as independent claims.

Caveat: the claim text in the fetched record is OCR-degraded (e.g., "aiul," "packin)r," "casin"). The preamble of claim 7 and of claim 10 is partly missing, and claim 19 is truncated mid-sentence. My numbering is inferred from sequence and may be off by one where the OCR merged lines around the claims that begin "The combination in a valve…".

1. Sliding-shell valve, generic. Casing with a cylindrical bore having side and end openings; a shell whose opening can be aligned with the side opening; means to move the shell; plus a structure on the side-opening side. (Claim 1's preamble is partly lost in OCR; the visible tail reads "…and having an opening capable of being brought opposite the side opening thereof, means for moving the shell, and a structure side opening.")
2. Shell outside a fixed disk structure. Casing bore with side and end openings; a disk-shaped structure mounted in the casing on one side of the side opening; a shell that slides longitudinally outside that disk structure; means to move it open/closed.
3. Self-tightening packing, generic. Casing with inlet/outlet; sliding shell; packing around the shell preventing leakage between inlet and outlet; and a tightening device actuated by continued operation of the shell-moving means after the shell reaches closed position.
4. Two packing bodies, self-tightening. As claim 3 but packing bodies on both sides of the opening, tightened by a device actuated by the shell-moving means.
5. Sleeve + packing + pressure transmission. Casing with inlet/outlet; a sleeve; packing confined between one sleeve end and the casing, located between inlet and outlet; a shell; and means causing the shell-moving means to press on the sleeve to load the packing against leakage around the shell.
6. Two-body packing via sleeve stack. Casing; shell cutting off flow; sleeves outside the shell; one packing body between the sleeves and a second between a sleeve and the casing; moving means operative on the sleeves to tighten the packing after closing.
7. Pressure-transmission variant (OCR preamble partly missing). Combines the claim-6 architecture with a device actuated by the moving means that presses one sleeve to force both packing bodies into intimate engagement with adjacent structures to prevent leakage.
8. Threaded shell + cover + stem. Cover on one casing end; valve stem through the cover with a threaded portion; a longitudinally movable shell with a threaded lug engaging the stem; an end opening and a side opening in the shell positioned so the valve closes as the shell moves toward the cover.
9. Rotatable stem with limited longitudinal travel. Casing; shell opened/closed within it; packing around the shell between inlet and outlet; a rotatable valve stem with limited longitudinal movement operatively connected to the shell; and means acted on by the stem for tightening to prevent leakage past the shell between the two openings.
10. Pin-trip packing load (OCR preamble partly missing). Involves a collar on the stem, a pin or pins on the cover positioned to engage the shell structure when the valve is closed, and a sleeve acted on by the collar after the pins engage the shell, compressing the packing to prevent leakage.
11. Disk inside the shell on the far side of the side opening. Casing with one opening in its side; stem supported at one casing end; shell driven by the stem to cut off flow; a disk-like structure fitting inside the shell on the side of the side opening distant from the other opening; and a supporting structure for that disk forming a recess with the casing interior to receive the shell.
12. Twin disks joined by a sleeve section as rod guide. Casing; cylindrical shell; two disk-like structures connected by a sleeve section, mounted in one casing end; a cover; a valve rod engaging the shell and guided by those disk-like structures; the sleeve forming a shell-receiving recess with the casing interior.
13. The fully specified commercial form (the most detailed claim). Cover with projecting pin(s); lining sleeves; two packing bodies (between adjacent sleeve ends, and between a sleeve and the casing); a disk-like structure clamped between cover and sleeve with openings for the pins; a shell with a port alignable with a casing opening; a stem through the cover and disk structure with a threaded portion engaging a threaded part of the shell; a collar on the stem bearing on the disk structure; and wings on the shell to strike the cover pins under predetermined conditions.
14. Anti-rotation sleeve + actuation through the shell. Casing; a sleeve with means preventing it from turning; packing engaged by one sleeve end; a movable shell within the sleeve; means to move the shell longitudinally; and a device actuated from that means through the shell to press the sleeve and compress the packing when closed.
15. Internal guide / debris exclusion (side + end opening valve). Shell moved by a rod to bring a shell surface opposite the side opening to close it; with structure inside the shell serving as a guide for the end of the rod and preventing solid material from reaching the part of the shell remote from the end opening.
16. Internal disk barrier. Same side/end-opening valve, with a disk mounted in the shell on the side of the casing opening distant from the end opening.
17. Structure inside but independent of the shell. Casing; cylindrical shell; valve rod; and a structure placed within, but independent of, the shell that receives the rod's inner end and confines material to that part of the shell between inlet and outlet.
18. Finished/unfinished sleeve interiors. Casing; lining sleeve(s); cylindrical shell controlling inlet-to-outlet flow; means to move it; where the sleeve interior has both finished and unfinished portions — the finished areas of limited extent positioned to be engaged by the shell, the unfinished areas remote from the shell and forming empty spaces separate from the fluid passage.
19. Truncated in the record. Only the preamble is legible: "The combination in a valve, of a casing having an inlet and an outlet, a longi…". I cannot state its scope with confidence.

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5. Forward citations (not prior art)

The modern "Cited By" list (third-party citations, not examiner citations from 1908) is: US 4,175,909 A (Bullough Limited, 1979, valve means for a hydraulic motor); US 2004/0186202 A1 / US 7,235,602 B2 (3M Espe, polymerizable epoxy-silane dental preparations — facially unrelated); US 2016/0169401 A1 (MAC Valves, stepper-motor-operated balanced flow control valve). The 1908 patent cites no prior-art references of record.

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6. USPTO / CAFC 2026 docket check

• No litigation or appeal activity found for US 900,506. No district court case, no IPR/PGR, and no CAFC 2026 docket referenced to this patent appeared in any search.
• This is expected and essentially foregone: the patent's anticipated expiration was October 6, 1925, and its status is Expired – Lifetime, so it cannot support a live infringement action in 2026.
• Confidence caveat, stated plainly: I searched via general web search, not a direct PACER, CAFC docket, or USPTO PatentCenter docket query. My failure to find a docket is therefore absence of evidence, not a certified finding of no docket. I did not independently confirm the PatentCenter "no proceedings" status.
• Docket-style hits for a bare "'506" that surfaced in my searches belong to modern litigation involving entirely different patents (specifically, a Netlist v. Samsung matter referencing a "'506 Patent"). I could not verify from the retrieved material which U.S. patent number that shorthand denotes, and I will not guess. It is not US 900,506.

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7. Disambiguation — identifier collisions (important)

The string "900506" is heavily overloaded, and nearly all web hits are unrelated:

• FR‑900506 — a compound code (tacrolimus), not a patent number. It appears in EP 0 184 162 A2/B1, US 4,894,366, US 4,916,138, US 5,830,717, etc. ("FR‑900506 substance," "FR‑900525," "FR‑900520"). This is a Fujisawa fermentation-product designation and has nothing to do with US 900,506.
• "'506 Patent" shorthand in modern litigation (see §6).
• I attempted to check whether a modern US 9,005,506 exists — i.e., a seven-digit 2015-era patent that could be visually confused with US 900,506 — but that search was cut off before returning results. I therefore cannot confirm or deny the existence of a separate US 9,005,506. If your interest is in a recent patent, please confirm the punctuation (US 9,005,506 vs. US 900,506), because the two are different identifiers and I have reported only the latter.

Per the operating rule, I have not auto-corrected any identifier: everything above is keyed to the literal number 900506, which resolves to US 900,506.

I'll research litigation involving US patent 900506.

Let me run additional targeted searches to confirm.

Let me verify whether any patent numbered 9,005,506 exists and check litigation databases directly.

No Litigation Found for US Patent 900,506

I searched litigation-focused sources (including the Unified Patents litigation portal, CAFC opinions/orders, PACER-adjacent court records surfaced via CourtListener, and general patent-litigation reporting) for the specific patent number 900506. No litigation, IPR, PGR, or other PTAB proceeding involving US Patent No. 900,506 was found.

Why this result is expected

Before answering, it is worth confirming which patent 900506 is, since the number is easy to confuse:

Source: https://patents.google.com/patent/[US900506](/patent/US900506)/en

Because the patent expired more than a century ago (the term ran from 1908 to 1925), there is no live patent right capable of being asserted, which is consistent with the absence of any recorded infringement action. Google Patents' citation data for this patent shows only three later "Cited By" references (none of which are litigation):

• US 4,175,909 A — Bullough Limited (1979)
• US 2004/0186202 A1 — Thomas Klettke (2004)
• US 2016/0169401 A1 — Mac Valves, Inc. (2016)

None of these are litigation involving the '506 patent; they are simply documents that cite it as prior art.

Important caveat — do not confuse this with other "506" patents

My searches surfaced several lawsuits referencing a "'506 patent." These involve different patents and must not be attributed to US 900,506:

• U.S. Patent No. 10,860,506 (Netlist, Inc.) — asserted in Netlist, Inc. v. Samsung Elecs. Co., No. 2:21-cv-00463-JRG (E.D. Tex.) and Netlist, Inc. v. Micron Tech., Inc., No. 2:22-cv-00293-JRG (E.D. Tex.), among others. This is a memory-module patent, unrelated to Forbes' 1908 valve.
• "FR-900506" — this is a compound/substance designation (tacrolimus, FK-506) appearing in pharmaceutical patents such as US 4,894,366 and EP 0184162. It is a chemical identifier, not a patent number.

Bottom line

No known litigation exists for US Patent No. 900,506. The patent is a 1908 blower/valve patent that expired in 1925, and no court case, PTAB proceeding, or litigation record could be found identifying it. If you are actually looking for litigation on a modern patent that happens to end in "506" (e.g., US 10,860,506), let me know and I can research that number specifically.

Confidence note: I could not locate any authoritative litigation database entry affirmatively listing US 900,506 as litigated. Given the patent's 1925 expiry, the practical likelihood of any litigation is effectively nil, but I am stating this as an absence of evidence rather than a positive confirmation that no pre-1925 suit ever existed — very old litigation records from the early 20th century are not comprehensively indexed in the modern databases I searched.

Proceedings overview

Total AIA trial proceedings on US 900506: zero (0). There is nothing to break down by status — no IPRs, no PGRs, no CBMs, no institution denials, no settlements, no Federal Circuit appeals. This is not a "the patent is hardened" signal; it is a "there is nothing left to attack" signal, because US 900506 is US Patent 900,506 — "Blow-off valve," John S. Forbes, filed 1907-06-13, granted 1908-10-06, expired 1925-10-06. The structured ODP block in this prompt reports no AIA trial proceedings, and my independent web searches surfaced no PTAB, ITC, or Federal Circuit activity on this patent. The bottom-line defensive posture for a defendant is therefore unusual: no PTAB defense is needed, because the patent cannot be asserted at all — it has been in the public domain for over a century. If you received a demand letter citing "US 900506," the assertion is either a clerical error pointing at a different patent number or a scam; see the number-confusion note below before you draft anything.

No per-proceeding entries

I will not manufacture proceeding numbers, panels, or claim-level outcomes. There is no FWD to quote, no institution decision to characterize, and no CAFC docket to link. Any IPR/PGR/CBM identification number I produced here would be fabricated, and an invention in this posture is the one thing a PTAB analysis must not do.

Why the answer is structural, not just empirical

Three independent reasons, each grounded in the patent's own front page (https://patents.google.com/patent/US900506/en):

• Expiry. Google Patents records the anticipated expiration as 1925-10-06 (the pre-1995 17-year term from the 1908-10-06 grant). Infringement of an expired patent is legally impossible; the only residual value would be pre-expiry damages, which are time-barred by any measure (35 U.S.C. § 286's six-year lookback).
• PGR is statutorily unavailable. 35 U.S.C. § 321 applies only to patents whose claims have an effective filing date on or after 2013-03-16. Every claim of the '506 has an effective filing date of 1907-06-13. No PGR can ever be filed.
• CBM is unavailable. The transitional covered-business-method program, now sunset, was limited to patents claiming a method or apparatus for performing data processing or other operations used in the practice, administration, or management of a financial product or service. A 1908 boiler blow-off valve (F16K3/22, F16K3/24 — sliding cylindrical-shell valve members) is not a covered business method by any reading.

The only theoretically available vehicle would be an IPR under § 311, which reaches any unexpired or expired patent. Practically, no rational petitioner files one: there is no exclusionary right to clear, no litigation to support, and the Board would apply Phillips construction to expired claims. The absence of filings here is not the "well-asserted patents eventually attract IPRs" signal — it is the "commercially dead since the Wilson administration" signal.

Strategic summary

Claim status. All claims of US 900506 (independent claims 1, 5, 8, 11, 13, 15, 16, 17, 18, 19 and their dependents, as printed) were never tested in any AIA trial — no claim was canceled, none was confirmed, and none was the subject of an estoppel-generating final written decision. The claims as issued are best described as untested but universally unenforceable on expiry grounds. When a patent has no IPR history, the standard caveat is "you can't rely on validity having been tested"; here that caveat is irrelevant because the invalidity question has been mooted by the passage of time, not by a panel.

Estoppel landscape. There is no § 315(e)(2) estoppel of any kind attaching to this patent, because there has been no IPR petitioner, no FWD, and no privity chain. For a defendant currently facing assertion, this cuts in your favor in a different way than usual: you are not looking for available prior-art grounds, because your strongest position is not invalidity at all. It is that the asserted patent expired 1925-10-06 and cannot be infringed. Notably, if a plaintiff tried to breathe life into this number, the pre-1910 claim style and the 1907 specification (e.g., the fluid-tight joint formed by compressing packing rings d and d1 between sleeves D and D1) would present severe § 112 and § 103 problems — but you should not need them.

Pattern signals. None. The "Cited By" list on the Google Patents page (US4175909A, US20040186202A1, US7235602B2, US20160169401A1) consists of modern, unrelated patents citing the 1908 Forbes disclosure as historical background — not assertion activity. No defensive aggregator (Unified Patents, RPX, etc.) appears anywhere in the chain; aggregators file on live asserted patents, and there is nothing to aggregate here. There is no repeat petitioner, no patent owner appellate history, and no PTAB appeal. Legal status is "Expired – Lifetime," and the assignee is listed as "Individual."

Look-alike number check (do this before responding to any demand letter). The certainty of "zero proceedings" rests on the number meaning what the source text says it means. A 1908 patent and a modern seven-digit patent can be conflated easily, and the search results show several unrelated, live-or-recently-litigated "506" patents. If your letter may actually reference one of these, the answer changes completely:

Neither search result for the look-alikes gave me a verified claim-level outcome, so I am not characterizing them beyond what the snippets state. I flag them solely so you resolve the citation ambiguity before relying on the "no proceedings" finding.

Recommended next steps

1. Confirm the number in the demand letter character-by-character. If it reads "900,506" or "US 900506," respond that the patent expired 1925-10-06, attach the Google Patents bibliographic page (https://patents.google.com/patent/US900506/en) showing the "Expired – Lifetime" status and 1925-10-06 anticipated expiration, and demand the basis of any assertion. If it reads "9,005,506," "7,214,506," or "10,726,506," run the PTAB analysis on that number instead — the look-alike rows above are your starting points.
2. Do not file a defensive IPR or seek a DJ of invalidity as a first move. There is no live right to clear, and a § 315(a)(1) DJ filing would needlessly complicate the picture. The expiry defense is dispositive and cheap.
3. Treat unsolicited "license" offers on US 900506 as a fraud indicator. A 1908 boiler blow-off valve that lapsed in 1925 is a classic vehicle for bogus patent-demand schemes; the absence of any PTAB, litigation, or assignment record is consistent with that.
4. Verify on the record, not on my summary, if money is at stake. I could not query PTAB E2E/PTAB Center directly; I relied on the ODP structured block supplied in this prompt as the canonical list and on web search as a check. A direct PTAB E2E search on application 378,759 / patent 900506 is a two-minute confirmation, and USPTO's Patent Assignment Search will confirm the "Individual" assignee and absence of transfers. If it returns nothing — as I expect — you have your answer in writing.

I'll research the ownership chain for US 900,506. Let me start with targeted searches on the assignment record and the inventor's commercial context.

Let me try a few more angles to see if any ownership or corporate context surfaces.

Let me verify the coverage window of the USPTO assignment database itself — that's critical for a 1908 patent — and check the inventor's portfolio.

Ownership Analysis — US Patent 900,506

Critical framing note before the sections below: this patent granted in 1908 and expired in 1925. The USPTO's online Patent Assignment Search — the primary source specified for this task — begins with August 1980 recordations. The patent's entire enforceable life, and the first 55 years of post-expiry history, fall before the online database's coverage window. That is a coverage limitation of the tool, not a finding about the patent, and it governs every section below.

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Inventors

The specification and claims are signed by John S. Forbes with two witnesses, Wm. E. Smith and Jos. H. Klein (https://patents.google.com/patent/[US900506](/patent/US900506)/en). Witnesses to an inventor's signature in this era were commonly neighbors, shop colleagues, or the attorney's staff — they are not correspondents of record and carry no assignment significance. No attorney or agent of record is visible in the OCR text of the front page; I cannot confirm whether an attorney field was present but lost to OCR.

Portfolio pattern (third-party aggregator data — treat as indicative, not authoritative): GoodIP lists "FORBES JOHN S" as holding 15 US patent applications/publications, the earliest published in 1900, including US 900,506 and a much later US 2,144,754, "Valve." Source: https://goodip.io/iq/assignee/forbes-john-s

If that attribution is correct, Forbes had a roughly 39-year inventing career spanning 1900 to the late 1930s, repeatedly in the valve art, and consistently filed as an individual rather than through a corporate assignee. That pattern is the opposite of the "all inventors departing the original assignee within 12 months of filing" fire-sale precursor described in the task prompt — it reads as a career independent/consulting inventor, not an employee-inventor whose rights were consolidated by an employer. I flag this as moderate confidence only, since I could not corroborate the GoodIP dataset against the patent faces directly.

Original assignee

Original Assignee: Individual. Google Patents records the assignee for US 900,506 as "Individual" for both original and current assignee, with the express disclaimer that "the listed assignees may be inaccurate" and that no legal analysis has been performed (https://patents.google.com/patent/US900506/en).

In plain terms: there was no corporate assignee at issue. The patent was granted to John S. Forbes personally. Consequently:

• Product embodying the claims: None attributable. The device is a boiler blow-off valve — a balanced cylindrical-shell valve in which the sliding shell is protected from the fluid stream, with packing compressed by continued rotation of the handwheel after closure (claims 3, 4, 5, 10, 14). This is a commercial-industrial valve type of the steam-boiler era. Whether Forbes licensed it, sold valves, or simply held the patent as an individual cannot be determined from any source I could reach.
• Primary line of business: Not determinable. No company name appears on the patent, in the specification, or in any indexed source.
• Current status: Not applicable — no entity to be operating, acquired, dissolved, or bankrupt. The patent itself is Expired – Lifetime, with anticipated expiration 1925-10-06 (17 years from the 1908-10-06 grant).

Assignment timeline

The USPTO Assignment Center has no online records for US Patent 900,506.

The USPTO's own guidance states the searchable database "contains all recorded Patent Assignment information back to August 1980" (USPTO, Assignment Database Webinar, https://www.uspto.gov/sites/default/files/documents/Assignment%20Database%20Webinar_20150120.pdf). MPEP 301.01 confirms the historical database "is maintained separate and apart from the database of assignments affecting title recorded since 1980," and practitioner guidance notes pre-1980 records "may not be available through the online Patent Assignment Search," requiring direct contact with the Assignment Recordation Branch or a Patent and Trademark Resource Center (https://blueironip.com/ufaqs/how-are-historical-patent-assignment-records-maintained/).

Because US 900,506 expired in 1925 — 55 years before coverage begins — no reel/frame, conveyance type, assignor, assignee, or correspondent of record can be retrieved for this patent from the specified primary source. I am not going to invent reel/frame numbers to fill this section.

Per the protocol for this section, I stop here — with three caveats that should travel with any downstream use of this file:

1. "No online records" ≠ "never assigned." A 1908–1925-era transfer, if it happened, would have been recorded on microfilm and would be retrievable only by ordering copies from the USPTO Assignment Recordation Branch for a fee, or by on-site research. The patent face saying "Individual" reflects the state of title at grant, not necessarily at expiry.
2. Google Patents shows no assignment event in the legal-events timeline — only priority to US 378,759, filing 1907-06-13, grant 1908-10-06, and anticipated expiration 1925-10-06. Google Patents does not separately ingest pre-1980 assignment microfilm for patents of this vintage, so this is consistent with, not independent of, the coverage gap.
3. The three "Cited By" documents (US 4,175,909 to Bullough Ltd.; US 2004/0186202 A1 to Thomas Klettke; US 2016/0169401 A1 to Mac Valves, Inc.) are later patents citing '506 as prior art. They are not assignments and create no ownership link in either direction.

Timeline diagram

The chain below is built from the patent's legal events (Google Patents), not from assignment records, because no assignment records exist online. It is shown for orientation only.

timeline
    title Ownership of US 900506
    1907 : Filed by John S Forbes as individual
    1908 : Patent granted to Forbes
    1925 : Patent term expired
    1980 : USPTO online assignment records begin

NPE / troll-pattern signals

Each signal is assessed against the record available. The honest baseline here is that seven of the eight signals depend on post-issuance assignment activity that cannot be observed, and the eighth depends on litigation that (per the prior litigation analysis) does not exist for this patent number.

Verdict

Insufficient data — no assignment records exist for this patent in the designated primary source.

US Patent 900,506 was granted on 1908-10-06 to John S. Forbes as an individual and expired 1925-10-06, 55 years before the USPTO Assignment Center's coverage begins in August 1980; no reel/frame, conveyance, assignee, or correspondent of record is therefore retrievable, and I decline to fabricate any. The only defensible ownership statement from the available record is that the patent left the inventor's hands — if it ever did — before the modern assignment database existed, and there is no litigation, no asserted patent, and no live right, the patent having lapsed 101 years ago. The NPE/privateering framework is not merely unsupported here; it is chronologically inapplicable, since the modern NPE business model post-dates this patent's expiry by roughly six decades.

Verification links:

• USPTO Assignment Center (search by patent number 900506): https://assignmentcenter.uspto.gov/
• USPTO Patent Assignment Search: https://assignment.uspto.gov/patent/index.html
• Google Patents legal events for US 900506: https://patents.google.com/patent/US900506/en
• For the pre-1980 historical database, contact the USPTO Assignment Recordation Branch or a Patent and Trademark Resource Center directly (MPEP 301.01).

Residual uncertainty (stated plainly): I cannot exclude the possibility that John S. Forbes assigned US 900,506 to a valve manufacturer sometime between 1908 and 1925. Confirming or refuting that would require ordering the microfilmed pre-1980 assignment records from the USPTO — a paid, offline step outside what I could execute here. If a corporate assignee is later identified, the practical consequence is nil: any such entity's rights expired in 1925 and the patent is unenforceable against anyone.

I'll verify the citation record for US 900,506 and gather details on each reference.

Prior Art Analysis — US Patent No. 900,506

0. Scope confirmation (no number substitution)

Per the strict rule, I am analyzing US 900,506 (US900506A) exactly as numbered — "Blow-off valve," John S. Forbes, Philadelphia, PA; App. No. 378,759 filed June 13, 1907; granted October 6, 1908; expired October 6, 1925. Source: https://patents.google.com/patent/[US900506](/patent/US900506)/en

This analysis does not concern and must not be confused with similarly numbered modern patents (e.g., US 9,005,506, US 10,860,506), which are unrelated. (Cross-reference the litigation section, which already flagged those.)

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1. What the citation record for 900506 actually contains — an important correction

The task assumes there is a set of "patent citations for 900506." I have to flag a factual problem before answering:

US 900,506 cites no prior art on its face. The Google Patents record for this patent has no "Patent Citations" (backward-citation) section at all. That is expected for US patents of this vintage: for pre‑1930 US grants, citation data was never entered into the database because the printed patent itself typically did not include a "References Cited" listing, and 19th/early‑20th‑century examiner citation records are not fully digitized.

What the record does contain is:

• a "Cited By" (forward-citation) list — documents that cite 900506 as prior art; and
• a "Similar Documents" machine-similarity list — not legal citations of any kind.

So I will (a) analyze the forward citations and explain why they are legally incapable of anticipating, then (b) identify the actually relevant pre‑1907 art, which is what a § 102 analysis of this patent would have to reach.

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2. Forward citations ("Cited By") — cannot serve as § 102 prior art

These are the only documents Google Patents lists as citing US 900,506. All four post‑date the 1907 filing by 68–109 years. Under 35 U.S.C. § 102 (pre-AIA, which would govern a 1907 filing) a reference must pre-date the applicant's invention/§ 102(b) critical date. None of these can anticipate any claim.

§ 102 potential against US 900,506: none, for any claim (1–19). All are decades too late.

⚠️ Anomaly worth flagging (not auto-corrected): it is technically inexplicable why a 2007 3M dental-composite patent (US 7,235,602 B2) would cite a 1908 steam-boiler valve. Google Patents displays US900506A (en) | 1907-06-13 | 1908-10-06 | John S Forbes | Blow-off valve inside US7235602B2's "Citations (32)" list (https://patents.google.com/patent/US7235602B2/en). This is most likely a citation-data artifact/mis-mapping rather than a genuine technical citation, but I am reporting it literally rather than correcting it.

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3. Most relevant prior art for US 900,506

Because the patent's own record carries no backward citations, the relevant field art must be assembled from the pre‑1907 documents in the "Similar Documents" list (all drawn from F16K3/22–3/24, "sliding valves with cylindrical valve members" — the exact subclass).

Below, "Critical date" = June 13, 1907 (constructive reduction to practice; presumptive invention date on or before filing).

3.1 The closest reference (same field, same problem statement)

US 862,143 A — John B. Duffy, "Blow-off cock for steam-boilers," Indian Orchard, MA.

• Filed: November 24, 1906 (Ser. No. 344,847). Granted: August 6, 1907.
• URL: https://patents.google.com/patent/[US862143A](/patent/US862143A)/en
• Description (verified from full text): A turning-plug blow-off cock for steam boilers. The plug carries packing strips (23) in dovetail retaining grooves, oppositely disposed from the port openings, so the packing surrounds the inlet/outlet when closed. The operating mechanism lifts the plug off its seat when the valve is opened, expressly to (i) avoid sticking/grinding and (ii) "prevent the inner edges of the inlet and outlet of the valve seat… from cutting or destroying the packing strips on the plug." A petcock drains sediment below the plug.
• § 102 assessment:
  • The problem addressed is identical to Forbes' stated object (protect packing/joint surfaces from grit, scale, and cutting) — see Forbes' "Definitions" section: "the surfaces forming the seat or joint are liable to become scratched or scored by grit or scale passing over them."
  • However, Duffy's packing is on the moving plug and rotates, whereas Forbes' packing surrounds a sliding cylindrical shell and is compressed by continued tightening of the stem after closure. Duffy has no shell, no lining sleeve, no packing-compression-on-closing mechanism.
  • Anticipation: none of claims 1–19 is anticipated. Duffy is a § 103-class reference at best (and even § 103 is weak given the wholly different closure principle — rotating plug vs. sliding cylindrical shell). It is highly probative of the state of the art / problem, not of claim content.
  • Date nuance: its grant date (Aug. 6, 1907) is after the June 13, 1907 filing, so under the statute then in force (R.S. § 4886, "patented… before his invention") it is not prior art. It would only qualify as a pre-AIA § 102(e) reference (prior art as of its Nov. 24, 1906 filing date) if Forbes' invention date post-dates Nov. 24, 1906 — possible but not established.

3.2 Structural references in the same classification

3.3 Same-field documents that are NOT prior art (post-date 900506) — context only

These emerged in searching and are not citable against 900506, but they confirm Forbes' field and show his concept was carried forward:

• US 937,096 A — John V. Schmid, "Blow-off valve," filed May 29, 1908 (≈11 months after the '506 filing), granted Oct. 19, 1909. Claims a reciprocating plunger in a smooth bore with cooperating parts that adjust packing "entirely independent of the means for reciprocating the plunger but… simultaneously therewith," and protection of operating parts from scale/sediment. This is functionally the closest disclosure to Forbes' claims 3–7/14 — but it post-dates the '506 filing and cannot be prior art to it. https://patentimages.storage.googleapis.com/f1/c7/5f/d3cabbcf000622/[US937096](/patent/US937096).pdf
• US 1,525,113 A — David Robert Yarnall (Yarnall-Waring Co.), "Blow-off valve," filed Aug. 22, 1922 (continuation-in-spirit of Yarnall's US 1,103,120, granted July 14, 1914). Claims a sleeve travelling with the plug, packing 17/18 on opposite sides of a central apertured lining member 19, with the upper packing compressed by a collar 22. Structurally the nearest later analogue to Forbes' claims 5–7 — but it post-dates 900506 by 15 years. https://patentimages.storage.googleapis.com/45/92/bd/a35c911dabcbb9/US1525113.pdf

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4. Claim-by-claim § 102 bottom line

Conclusion: on the available record, no reference anticipates any of claims 1–19 of US 900,506. The absence of any examiner-cited art, combined with the very specific closing-driven packing-tightening mechanism, is consistent with the patent having issued over the art of its day.

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5. Confidence and limitations (stated explicitly)

• High confidence: US 900,506 is a 1907/1908 Forbes blow-off valve; there is no backward "Patent Citations" section in the Google Patents record; its three forward citations (US 4,175,909 A; US 2004/0186202 A1 / US 7,235,602 B2; US 2016/0169401 A1) all post-date it and cannot anticipate.
• Moderate confidence: my claim-by-claim anticipation assessment of the pre-1907 "Similar Documents." I retrieved full or substantial text for US 862,143, US 269,111, and US 704,522, but only metadata/titles for US 744,441, US 678,014, US 400,128, and US 167,092. US 400,128 A in particular I could not characterize — its title ("shepherd") appears to be an OCR/assignee artifact and should be re-pulled from the PDF before being relied upon.
• Not verified: whether the 1907 USPTO file wrapper (if extant) contains examiner citations. Pre‑1930 US file wrappers are not comprehensively digitized; Google Patents' absence of a Citations section is not proof that no art was cited during prosecution, only that none is in the database.
• I did not retrieve the USPTO Patent Center/Patent Public Search record directly (tool steps were exhausted); the analysis above rests on the authoritative Google Patents full text supplied plus the verification searches performed. The USPTO's own record for this patent should be checked at https://patentcenter.uspto.gov and https://ppubs.uspto.gov to confirm the absence of a References Cited listing.

Bottom line: For US 900,506, the "citations" on record are forward citations that are legally incapable of anticipation; the most technically relevant prior art is US 862,143 A (Duffy, blow-off cock for steam boilers, filed 1906‑11‑24, granted 1907‑08‑06) — same field, same stated problem, but a rotating-plug closure with none of Forbes' shell/packing-tightening structure, and even then only arguably prior art under a § 102(e)-type analysis dependent on Forbes' actual invention date. No reference in the available record anticipates any of claims 1–19.

I'll ground this analysis in the actual prior-art references listed on the patent page, then assess combinability.

Obviousness Analysis — US 900,506 (Forbes, "Blow-off valve")

0. Scope and sources used

I used the reference lists appearing on the patent's page at https://patents.google.com/patent/[US900506](/patent/US900506)/en — the "Cited By" list and the "Similar Documents" list — which together constitute the prior-art section of that record. I verified the substance and critical dates of the five pre-1907 references by retrieving their own pages/PDFs (links below).

Threshold problem: US 900,506 was filed June 13, 1907 and granted Oct. 6, 1908. Only references with a publication date before June 13, 1907 (strictly, before June 13, 1906 for a §102(b)-equivalent statutory bar) can be used in a §103 combination against it.

So the entire usable prior-art set is Reimann '111, Shepherd '128, Merrill '014, Douglas '522, Underwood '441 (plus, unverified, '092 and possibly '143). Everything cited on the page under "Cited By," and 18 of the 25 "Similar Documents," cannot be used in a §103 combination. That is a material limitation on the strength of any obviousness case built only from this page.

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1. Framing caveat before the merits

35 U.S.C. § 103 did not exist when this patent issued. It was created by the Patent Act of 1952 and applies to patents "issued before" only insofar as they remained in force. US 900,506 expired Oct. 6, 1925 (per the page's legal-status field). Its validity would in fact have been judged under R.S. §§ 4886/4920 and the judge-made "invention" requirement (Hotchkiss v. Greenwood, 52 U.S. 248 (1851)), applied in the era's terms as the "combination vs. mere aggregation" doctrine. As the Third Circuit put it in Rainear v. Western Tube Co., 158 F. 433, 434 (3d Cir. 1908) — a case decided four months after '506 issued — the question was whether one skilled in the art, "in the face of these facts long and well known," would have made the combination.

Applying modern §103/KSR (KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007)) therefore tends to make '506 look more vulnerable than it would have looked in 1908, because the modern standard is more permissive than Hotchkiss/"flash of creative genius." Read the conclusions below with that skew in mind. I flag it rather than hide it.

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2. Claim set as I read it (and where the text is broken)

The OCR of the claim sequence on the page is intact for claims 2–6, 8, 11–18. Claims 1, 7, 10 and 19 are truncated or garbled and I will not reconstruct them:

• Claim 1 reads: "…a shell … in the casing and having an opening capable of being brought opposite the side opening thereof, means for moving the shell, and a structure side opening, substantially as described." The element following "a structure" is lost. I cannot say whether claim 1 requires an internal disk/sleeve structure, so I treat claim 1 as indeterminate.
• Claim 7: "…tl ti device actuated by said means for pressing upon one of said sleeves to force the two bodies of packing into intimate engagement…" The antecedent is lost.
• Claim 10: requires "a pin or pins on the cover," a "collar," and "a sleeve acted on by said collar after the pins have engaged the shell structure."
• Claim 19: truncated at "a longi—".

For analysis I group the readable claims:

• Group I — sliding ported shell in a ported cylindrical bore (claims 1*, 2, 15, 16, 17)
• Group II — packing around the shell, tightened by continued operation of the shell-moving means (claims 3, 4, 5, 6, 7*, 9, 14)
• Group III — internal disk/support structure guiding the rod and confining flow (claims 11, 12, 13, 15, 16, 17)
• Group IV — screw-threaded stem driving a threaded lug on the shell (claims 8, 10*, 13)
• Group V — sleeve interiors with finished and unfinished portions (claim 18)

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3. Combination A — Group I and Group IV: Douglas '522 + Reimann '111

What each reference discloses

Douglas, US 704,522 (verified, https://patents.google.com/patent/[US704522A](/patent/US704522A)/en): a valve chamber of circular form and equal diameter throughout; a hollow plug or valve that "practically fills the entire chamber" with ports i, k in its bottom and side that register with an inlet port f and outlet port g in the chamber; a stem l passing through a removable cap d; a spring holding the valve to its seat. Douglas expressly states the result: "said valve completely fills the said chamber no appreciable quantity of liquid … can enter between the valve and wall of the chamber, and therefore no leakage can take place above the valve, which enables me to dispense with the use of packing."

Forbes' claim 1/2/15/16/17 movable member is a "cylindrical shell … having an opening capable of being brought opposite the side opening" of a "cylindrical bore." Douglas is the same machine, differing essentially in that his shell rotates rather than slides longitudinally.

Reimann, US 269,111 (verified, https://patents.google.com/patent/[US269111](/patent/US269111)): a casing whose vertical portion has a plain interior; a thimble B fitting snugly within it, "provided upon each side with an opening coinciding, when the thimble is in place, with the space in the horizontal portion which is provided for the passage of the steam"; a plug/finger D travelling longitudinally on a left-handed internal thread engaged by screw-stem F; a guide-ring C whose vertical projections c fit recesses in the thimble's upper edge so the ring "is incapable of a revolving movement," and whose horizontal projections c' seat in the plug's recess d'd "so that it is accurately guided in its vertical movement." Reimann's screw-nut b' draws the thimble "tightly into the casing and holding it securely against vertical movement."

The combination

Take Douglas' ported hollow cylindrical shell in a ported cylindrical chamber and drive it axially with Reimann's screw-stem + anti-rotation guide. Every element of Group I is then present:

Motivation to combine (the KSR "identified, predictable solutions" rationale, which is also the 1908-era rationale):

1. Both references address the same problem Forbes states — leakage past a valve whose seating surfaces are exposed to the fluid (Douglas: "no leakage can take place above the valve"; Forbes: seats "liable to become scratched or scored by grit or scale").
2. Reimann states the same design goal Forbes does, in the same words: a valve "which shall be steam and air tight, and which also shall have a capacity for the renewal of those special parts which are exposed to wear without the renewal of the remaining parts."
3. Converting a rotary shell drive to an axial one by means of a screw-and-guide is the most predictable of mechanical substitutions, and the art already contained the exact mechanism: Reimann's threaded plug travelling in a guide ring.
4. Forbes himself concedes in the specification that the stated object "is accomplished by the use of packing arranged to form a joint between the interior surface of the valve-casing or body and a sliding cylindrical shell" — i.e., the asserted point of novelty is the linearisation of a ported cylindrical valve plus a packed joint, not a new mechanism.

Conclusion: Claims 2, 15, 16, 17 and 8 are, on this record, obvious over Douglas + Reimann. Claim 8 (stem threaded through the cover, shell with a threaded lug, opening in the end and side of the shell closing when the shell moves toward the cover) is met almost verbatim by Reimann's threaded plug D driven by stem F through cap E — Forbes' threaded lug on the shell is Reimann's internally threaded plug, and the "opening in the end and the side" is Douglas' two ports. Claim 1 I cannot conclude on, because its text is broken (see §2).

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4. Combination B — Group II: Reimann '111 + Underwood '441 (+ Merrill '014 for the sleeve/casing joint)

This is the strongest §103 attack in the record, because Forbes' headline feature — packing that is compressed by the continued over-travel of the shell-moving means after the valve has closed — has direct, explicit analogues.

Underwood, US 744,441 (verified, https://patents.google.com/patent/[US744441A](/patent/US744441A)/en): "the object of this invention is to provide a bib or valve wherein the same will be self-stuffing, thereby obviating the necessity of providing a stuffing means such as have heretofore been used." The mechanism: cap 4 screwed on the extension 3; the operating screw itself (cap/stem assembly) compresses the soft-metal body 10 against the neck 3 of the valve body. Underwood: "When the part 10 is worn away to such an extent that it has no frictional contact with the neck of the valve-body, the compression of the part 4 against said part 10 will compress the same, thereby forcing it outwardly against said neck of the valve-body, thus insuring a water-tight joint." That is the same problem (wear → leakage), the same solution (over-travel of the operating screw takes up the slack and compresses a body of packing), and the same functional relationship Forbes claims in claims 3, 4, 5, 6, 9 ("a device actuated by said means for tightening the packing," "means for causing said shell moving means to exert pressure on the sleeve to cause the packing to prevent leakage around the shell").

Reimann '111 supplies (a) the sleeve held in the casing and drawn tight against it by a screw (screw-nut b', "for the purpose of drawing the thimble tightly into the casing and holding it securely against vertical movement"), and (b) the sleeve prevented from turning (guide-ring C projections in the thimble's edge) — the "means for preventing turning of the sleeve" of claim 14. Reimann also discloses the operative chain Forbes claims in claim 14: turning the stem → moving a member under anti-rotation guidance → the coupling between the moving member and the sleeve (Reimann's recess/ring/keyway geometry is the mirror image of Forbes' lugs f7 riding in grooves d10).

Merrill, US 678,014 (verified, https://patents.google.com/patent/[US678014A](/patent/US678014A)/en) supplies the sleeve/casing packing joint itself: a short pipe-section B in an opening 2 of casing A, with an annular flange 3 bolted to the casing "making a water-tight joint," a thickened flange portion c giving "a surface that will not wear away so rapidly," and flanges d fitting the casing opening. Merrill also supplies the motivation: the invention is "intended particularly for use in gates controlling the flow of water in which is contained a great deal of sediment and where the wear upon the valve and valve-seat is consequently very great and where it is necessary from time to time to grind down or remove either of the contacting faces of these two parts to prevent leakage."

The combination

Teach the sleeve-and-packing joint of Merrill/Reimann to the Douglas/Reimann ported sliding shell of Combination A, and place a second packing ring between two sleeves as Reimann's nut b' arrangement permits. Tighten both by coupling the shell's end-of-travel to a downward thrust on the upper sleeve (Forbes' pins b4/wings f2 or lugs f7, claims 10/13/14) — which is Underwood's screw-compresses-packing mechanism relocated from the stem stuffing to the shell/sleeve joint.

Motivation:

1. Underwood expressly frames self-stuffing through the operating screw as substituting for a separate stuffing means — the exact advantage Forbes asserts ("there being also provided means whereby the part serving as the movable element of the valve causes a body or bodies of packing to be so acted on as to prevent leakage through the valve after said part has been brought to its closed position").
2. Reimann shows the sleeve-in-casing joint drawn tight by the same screw-thread that operates the valve — the identical mechanical expedient.
3. Merrill shows the field (sediment-laden water gates) already recognised the problem Forbes opens with, and already solved it by replaceable, thickened, bolted-in seat/sleeve surfaces.

Conclusion: Claims 3, 4, 5, 6, 9 and 14 are obvious over the combination of Reimann + Underwood, with Merrill supplying the packing-joint structure. Claim 5 specifically ("a body of packing confined between one end of said sleeve and the casing … and means for causing said shell moving means to exert pressure on the sleeve to cause the packing to prevent leakage") is essentially Underwood's principle with Reimann's sleeve. Claim 14 (anti-rotation of the sleeve + compression "actuated from said means through said shell") is Reimann's guide-ring/nut structure plus Forbes' own lugs-and-grooves, and the only genuinely Forbes-specific element — routing the compressive force "through said shell" — is a design choice with no stated unexpected result.

Counterargument to note (this is where the era's law cuts the other way): Under the pre-1952 doctrine quoted in the page's neighbouring case law — "the assemblage of old devices, 'without securing some new and useful result as the joint product of the combination, — something more than a mere aggregation of old results,' — is not such invention" (Adams v. Stamping Co., 141 U.S. 539, quoted in J. L. Mott Iron Works, 110 F. 776) — a defendant could argue claims 4/6 are a mere aggregation of two independent packing rings. Forbes' answer, and a real one, is that his tightening device acts on both rings jointly through a chain of co-acting parts, which is the classic "combination" test (Pickering v. McCullough, 104 U.S. 310). This argument favours the patent with respect to claims 4/6/7 and is the most plausible non-obviousness holding available on this record.

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5. Combination C — Group III: Reimann '111 + Underwood '441

Claims 11, 12, 13, 15, 16, 17 require a disk-like structure inside/outside the shell, receiving the inner end of the valve rod and "confining material" to a part of the shell.

• Reimann discloses a closed-bottom thimble mounted in the casing with side openings coincident with the flow passage, in which the movable member works, and a cap with a bearing shoulder receiving the stem — i.e., a structure inside the flow casing that both guides the moving member and shields part of the casing interior from the flow. That is structurally the Fig. 9 form of '506 (sleeve E2 with a closed upper end, an opening e in line with the inlet a, the stem guided in the sleeve's end section) and half of claim 12's "two disk-like structures having a section of a sleeve connecting them."
• Underwood discloses "the interior of this stem 5 is hollow, and a valve-stem 6 is closely fitted therein" — a rod whose inner end is received inside a hollow member that is itself inside the valve body. That is the "structure placed within but independent of the shell to receive the inner end of the valve rod" of claim 17.

Motivation: both references are directed to guiding the inner end of the actuating member against lateral deflection under flow pressure and to keeping the fluid away from the working surfaces. Reimann's stated object of enabling renewal of only the worn parts, and Underwood's stated object of eliminating an external stuffing means, are the exact advantages Forbes claims for his internal disk structure ("its movable element completely protected from the injurious action of any solid bodies," "means within the shell constructed to serve as a guide for the end of the shell operating rod for preventing passage of solid material").

Conclusion: Claims 15, 16, 17 are obvious. Claim 12 is close but depends on exactly two disk-like structures joined by a sleeve section; Reimann's thimble + guide-ring + cap assembly is a reasonable but not exact correspondence — I would call this probably obvious, with lower confidence. Claim 13 stacks a large number of specific structural features (cover pins, two bodies of packing, disk with pin openings, collar on stem, wings on shell); I have not found a reference in this set disclosing the pin-and-wing interlock (pins on the cover passing through openings in the disk and engaged by wings on the shell), and I would not call claim 13 obvious on this record. It is the claim most likely to survive.

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6. Combination D — Claim 18 (finished/unfinished sleeve surfaces)

Claim 18 requires the sleeve interior to have finished portions "of limited extent … placed to be engaged by the shell" and unfinished portions "distant from the shell" that "provide empty spaces separate from the passage for the flow of fluid."

Merrill '014 gets closest — separate bolted-in section and ring, with flanges d fitting the casing opening, and an explicit cost-of-repair rationale — and restricting precision machining to functional surfaces is ordinary shop practice. But none of the five references is directed to the stated problem (reducing machining cost by leaving casing and sleeve interiors rough and oversized), and none discloses the resulting empty annular spaces separated from the flow passage, which is a structural limitation with a stated functional consequence (less friction on the shell, lower cost). Under a Graham v. John Deere analysis this claim looks weakly supported by the available art; I would not call it obvious on this record, though a broader search of 1890s–1900s valve-casting practice might change that.

Claim 19 cannot be assessed — its text is truncated on the page.

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7. Overall conclusion

The single most damaging reference in the set is Douglas, US 704,522, because it already discloses the core structural idea — a hollow cylindrical valve member with ports registerable with ports in a cylindrical chamber, filling that chamber, operated by a stem through a cap, expressly for the purpose of eliminating leakage between the valve and the chamber wall. The second most damaging is Reimann, US 269,111, which supplies the screw-driven, anti-rotation-guided longitudinal motion and the screw-tightened sleeve-and-packing joint. Underwood, US 744,441 supplies the packing-compressed-by-operating-screw idea that Forbes presents as a principal object.

8. Confidence and limitations (stated plainly)

• I verified the disclosure, filing date and grant date of Reimann '111, Shepherd '128, Merrill '014, Douglas '522 and Underwood '441 from their own records. I did not retrieve the text of US 167,092 (1875) or US 862,143 (1907); the latter is facially later than the '506 filing date, and its use would require proof that its own application predates Forbes' invention date.
• This is an analysis confined to the prior-art lists on the '506 page, not an examiner-grade search. A full pre-1907 search of the piston/plunger-valve and balanced blow-off valve art would very likely add references and strengthen Combinations A, C and D materially — particularly against claims 13 and 18, which I could not defeat on this record.
• The §103 framework is anachronistic for a patent that expired in 1925 (§103 dates from 1952); the 1908-era "invention" standard was stricter than KSR, so this analysis probably overstates the patent's vulnerability.
• No secondary-consideration evidence (commercial success, long-felt need, copying) appears on the page; the page's only litigation-related content is the absence of litigation noted in the earlier section of this analysis.