Patent US3491538A successfully refreshed from Google Patents.
US3491538A
Expired / Lapsed
US
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Air balanced oil well pumping system
Assignee: DRILTROL
•
Filing: 1968-03-04
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Granted: 1970-01-27
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Expires: 1988-03-04
Abstract
No abstract record available.
Inventors
- 👤 Robert G Pearson
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-09 07:09
CPC Classifications
F; F04; F04B; F04B47/00; F04B47/12; Y; Y10; Y10S; Y10S417/00; Y10S417/904; Y10T; Y10T137/00; Y10T137/2931; Y10T137/3115; Y10T137/3127; Y10T137/313
Claims Analysis
Total Claims: 0
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References Cited (Backward Citations)
US2470252A
Cited
US2481623A
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US2489412A
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US2665551A
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US2729942A
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US2780063A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1973-01-26 | 1973-07-28 | 1974-01-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1977-01-26 | 1977-07-28 | 1978-01-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1981-01-26 | 1981-07-28 | 1982-01-27 | $7700.00 | Window Closed / Lapsed |