Patent US2740347A successfully refreshed from Google Patents.
US2740347A
Expired / Lapsed
US
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Systems for ventilating tunnels and the like
Assignee: Individual
•
Filing: 1951-04-16
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Granted: 1956-04-03
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Expires: 1971-04-16
Abstract
No abstract record available.
Inventors
- 👤 William J Caldwell
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-05 05:09
CPC Classifications
E; E21; E21F; E21F1/00; E21F1/003
Claims Analysis
Total Claims: 0
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References Cited (Backward Citations)
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US671264A
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US975248A
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US1185453A
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US1280254A
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US1418980A
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GB341460A
Cited
US2131725A
Cited
US2032692A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1959-04-03 | 1959-10-03 | 1960-04-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1963-04-03 | 1963-10-03 | 1964-04-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1967-04-03 | 1967-10-03 | 1968-04-03 | $7700.00 | Window Closed / Lapsed |