US3886765A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Compressor-expander having thermal isolation and adjustment features
Assignee: Rovac Corp
•
Filing: 1974-07-29
•
Granted: 1975-06-03
•
Expires: 1994-07-29
Abstract
Abstract A compressor-expander for use in air conditioning which includes a housing having a chamber of oval profile divided into a compression side and an expansion side and containing a cylindrical rotor having a plurality of outwardly biased vanes forming compartments which progressively decrease and then increase in volume as the rotor rotates. The housing has compression side inlet and outlet ports and expansion side inlet and outlet ports, with the heat exchanger being connected between the compression side outlet port and the expansion side inlet port so that an incoming charge of air is first compressed, flows at constant pressure through the heat exchanger where the heat of compression is removed and then expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state. To improve thermal efficiency, a flexible liner of thin cross section covers the wall of the chamber, a layer of insulation being interposed under the lining to inhibit flow of heat from the compression side to the expansion side. Means are provided for peripherally shifting the liner, if desired, to change the phase of the port positions. In one embodiment, the liner is in the form of a continuous strip supported upon insulated pedestals formed in the wall of the chamber and with diametrically opposed means being provided for applying peripheral shifting movement in opposite directions. In another embodiment, the liner has ends terminating in interdigitated fingers having a limited amount of endwise clearance so that when traction is applied to one of the ends of the liner for adjustment purposes, the effect is to reduce the diametrical dimension of the liner and thus unseat it from the wall of the chamber. When bottoming occurs at the fingers, the liner is bodily shifted to the new position. In a final aspect of the invention, the liner is in the form of a plurality of strips each of which carries a portion of the port openings and with the strips being individually shiftable to vary the relative positions of the ports.
Inventors
- 👤 Thomas C Edwards
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-25 03:46
CPC Classifications
F; F04; F04C; F04C28/00; F04C28/10; F04C28/14; F01; F01C; F01C1/00; F01C1/30; F01C1/34; F01C1/344; F01C1/3446; F01C21/00; F01C21/06; F01C21/10; F01C21/104; F01C21/106; F25; F25B; F25B9/00; F25B9/002; F25B9/004; F05; F05C; F05C2225/00; F05C2225/04
Claims Analysis
Total Claims: 31
Claim 1
Independent Claim
247 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile having a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of radially movable and outwardly biased vanes extending into engagement with the end plates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port when the rotor is rotated: (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of compression is absorbed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner being of thin cross section for limited heat conductivity and having a layer of insulation between it and the outer wall for preventing flow of heat through the housing from the compression side to the expansion side.
Claim 2
Dependent Claim
247 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile having a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of radially movable and outwardly biased vanes extending into engagement with the end plates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port when the rotor is rotated: (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of compression is absorbed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner being of thin cross section for limited heat conductivity and having a layer of insulation between it and the outer wall for preventing flow of heat through the housing from the compression side to the expansion side.
Claim 3
Dependent Claim
247 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile having a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of radially movable and outwardly biased vanes extending into engagement with the end plates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port when the rotor is rotated: (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of compression is absorbed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner being of thin cross section for limited heat conductivity and having a layer of insulation between it and the outer wall for preventing flow of heat through the housing from the compression side to the expansion side.
Claim 4
Dependent Claim
247 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile having a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of radially movable and outwardly biased vanes extending into engagement with the end plates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port when the rotor is rotated: (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of compression is absorbed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner being of thin cross section for limited heat conductivity and having a layer of insulation between it and the outer wall for preventing flow of heat through the housing from the compression side to the expansion side.
Claim 5
Dependent Claim
39 words
The combination as claimed in claim 1 in which the outer wall of the chambeR is formed with pedestals of limited cross section for suporting the liner in oval configuration, the spaces between the pedestals being occupied by insulation.
Claim 6
Dependent Claim
17 words
The combination as claimed in claim 2 in which the insulating material between the pedestals is air.
Claim 7
Dependent Claim
24 words
The combination as claimed in claim 2 in which each of the pedestals is topped with a thin layer of insulation of predetermined thickness.
Claim 8
Dependent Claim
236 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port when the rotor is rotated: (a) is compressed with increase in temperature due to the heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of the compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner having externally accessible means for shifting the same peripherally in opposite directions by a slight amount thereby to change the effective phase positions of the ports.
Claim 9
Dependent Claim
236 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port when the rotor is rotated: (a) is compressed with increase in temperature due to the heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of the compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner having externally accessible means for shifting the same peripherally in opposite directions by a slight amount thereby to change the effective phase positions of the ports.
Claim 10
Dependent Claim
39 words
The combination as claimed in claim 5 in which the shifting means includes teeth on the outside surface of the liner and a manually operated gear for meshing with the teeth for shifting of the liner in opposite directions.
Claim 11
Dependent Claim
39 words
The combination as claimed in claim 5 in which teeth are provided on the outside surface of the liner at substantially diametrical positions, a pair of gears respectively meshing with the teeth, and means for coupling the gears together.
Claim 12
Dependent Claim
80 words
The combination as claimed in claim 5 in which the liner is provided with a first set of teeth at a position between the compression side inlet port and the expansion side outlet port and a second set of teeth between the compression side outlet port and the expansion side inlet port, a pair of gears for respectively meshing with the sets of teeth, and means for rotating the gears for imparting equal amounts of peripheral displacement to the liner.
Claim 13
Dependent Claim
83 words
The combination as claimed in claim 5 in which first and second sets of teeth are provided on the outer surface of the liner adjacent respective edges of the liner and in which the externally accessible shifting means is in the form of a shaft journalled in the housing and positioned along side of the liner, the shaft having gears respectively aligned with the sets of teeth for shifting the liner peripherally in opposite directions free of generation of any unbalanced cocking forces.
Claim 14
Dependent Claim
57 words
The combination as claimed in claim 5 in which the liner is in the form of an endless loop having engagement means on the outside of the liner at diametrically spaced positions and first and second shifting means penetrating the housing and coupled to the engagement means for imparting equal amounts of shifting movement to the liner.
Claim 15
Dependent Claim
311 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlEt ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates to form compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a strip of oval profile covering the outer wall of the chamber and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where the heat of compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner being of thin cross section for limited heat conductivity and having an isolation layer of predetermined thickness between the liner and the wall, the isolation layer being made of a material having good thermal insulating properties for preventing flow of heat through the housing from the compression side to the expansion side as well as having self-lubricating properties, the liner in addition having externally accessible means for manually shifting the same peripherally in opposite directions by a slight amount thereby to change the effective phase position of the ports.
Claim 16
Dependent Claim
311 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means defining compression side inlet and outlet ports as well as expansion side inlet and outlEt ports, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates to form compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a strip of oval profile covering the outer wall of the chamber and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where the heat of compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, the liner being of thin cross section for limited heat conductivity and having an isolation layer of predetermined thickness between the liner and the wall, the isolation layer being made of a material having good thermal insulating properties for preventing flow of heat through the housing from the compression side to the expansion side as well as having self-lubricating properties, the liner in addition having externally accessible means for manually shifting the same peripherally in opposite directions by a slight amount thereby to change the effective phase position of the ports.
Claim 17
Dependent Claim
16 words
The combination as claimed in claim 11 in which the isolating layer is formed of teflon.
Claim 18
Dependent Claim
54 words
The combination as claimed in claim 11 in which the outer wall of the chamber is undercut to provide peripherally spaced pedestals, each of the pedestals being capped by an isolating layer of predetermined thickness formed of a material which combines thermal insulation with self-lubricating properties to facilitate the peripheral shifting of the liner.
Claim 19
Dependent Claim
285 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means in the housing defining compression side inlet and outlet ports, as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates to form compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where the heat of compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, means for bodily shifting the liner peripherally in opposite directions by a slight amount thereby to change the effective phase position of the ports, the liner being formed of a thin strip of metal having interdigitated ends which are fitted together to provide a joint having smooth transition with sufficient peripheral clearance and sufficient outward springing to insure seating of the liner on the wall.
Claim 20
Dependent Claim
285 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means in the housing defining compression side inlet and outlet ports, as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates to form compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where the heat of compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, means for bodily shifting the liner peripherally in opposite directions by a slight amount thereby to change the effective phase position of the ports, the liner being formed of a thin strip of metal having interdigitated ends which are fitted together to provide a joint having smooth transition with sufficient peripheral clearance and sufficient outward springing to insure seating of the liner on the wall.
Claim 21
Dependent Claim
303 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journAlled therein, means in the housing defining compression side inlet and outlet ports, as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates to form compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, means for bodily shifting the liner peripherally in opposite directions by a slight amount thereby to change the effective phase position of the ports, the liner being formed of a straight strip of flexible material having interdigitated ends which are fitted together and which have end-to-end clearance with means for relatively moving the ends toward one another to slightly reduce the length, hence the diametrical dimension, so that the liner is lifted free of the wall of the chamber to facilitate the shifting movement.
Claim 22
Dependent Claim
303 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journAlled therein, means in the housing defining compression side inlet and outlet ports, as well as expansion side inlet and outlet ports, a heat exchanger interposed between the compression side outlet port and expansion side inlet port, the rotor having a plurality of outwardly biased vanes extending into engagement with the end plates to form compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a flexible strip of oval profile covering the outer wall and having port openings in respective communication with the ports in the housing so that a charge of air drawn in between adjacent vanes at the compression side inlet port (a) is compressed with increase in temperature due to heat of compression, (b) flows at substantially constant pressure through the heat exchanger where heat of compression is removed and then (c) expands in the expansion side to produce a sharp drop in temperature for discharge in the cold state through the expansion side outlet port, means for bodily shifting the liner peripherally in opposite directions by a slight amount thereby to change the effective phase position of the ports, the liner being formed of a straight strip of flexible material having interdigitated ends which are fitted together and which have end-to-end clearance with means for relatively moving the ends toward one another to slightly reduce the length, hence the diametrical dimension, so that the liner is lifted free of the wall of the chamber to facilitate the shifting movement.
Claim 23
Dependent Claim
43 words
The combination as claimed in claim 15 in which a layer of lubricating material is interposed between the liner and the wall for the purpose of lubricating the shifting movement at those portions of the liner which remain in contact with the wall.
Claim 24
Dependent Claim
74 words
The combination as claimed in claim 15 in which the ends of the liner are formed into interdigitated fingers which are fitted together with end-to-end clearance, the fingers having abutments adjacent the tips thereof, and means for engaging associated abutments to produce a reduction in the end-to-end clearance with consequent reduction in the diametrical dimension so that the liner is lifted free of the wall followed by shifting movement thereof to a new position.
Claim 25
Dependent Claim
132 words
The combination as claimed in claim 15 in which the ends of the liner are formed into interdigitated fingers having first and second set of abutments at the respective tips thereof and providing limited end-to-end clearance, and an adjusting member penetrating the housing for alternatively engaging one of the sets of abutments to apply pressure thereto in the peripheral direction for (a) taking up the end-to-end clearance thereby to reduce the diametrical dimension so that the liner is lifted free of the wall accompanied by interdigitated bottoming of the fingers, and (b) upon continued movement effecting bodily shifting of the liner to a new position for adjustment of the phase position of the ports, following which the adjusting means is backed off to restore seated contact between the liner and the wall.
Claim 26
Dependent Claim
93 words
The combination as claimed in claim 15 in which the first and second ends of the liner have fingers which are interdigitated and lie closely side by side with limited clearance at the ends of the fingers and in which means are provided for alternatively applying traction to the respective ends of the liner with the result that the end clearance is taken up for slightly reducing the diametrical dimension of a liner thereby to lift it clear of the wall followed by bodily shifting of the liner to a new phase position.
Claim 27
Dependent Claim
75 words
The combination as claimed in claim 15 in which abutments are provided on the respective ends of the liner for applying traction thereto and in which a unitary adjusting member is provided having means for imparting shifting movement in opposite directions for alternatively engaging the abutments for unseating the liner from the wall of the housing and for subsequently imparting bodily shifting movEment to the liner for adjusting the same to a new phase position.
Claim 28
Dependent Claim
188 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side, and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means in the housing defining a compression side inlet port, compression side outlet port, expansion side inlet port, and expansion side outlet port, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of vanes extending into engagement with the end plates and outwardly biased so that adjacent vanes define compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a plurality of thin flexible strips of oval profile merging smoothly edge to edge and extending between the end plates, the strips each having port openings communicating with a portion of the ports in the housing and at least a portion of the strips being peripherally adjustable to vary the relative phase positions of the ports.
Claim 29
Dependent Claim
188 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side, and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means in the housing defining a compression side inlet port, compression side outlet port, expansion side inlet port, and expansion side outlet port, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of vanes extending into engagement with the end plates and outwardly biased so that adjacent vanes define compartments which are progressively decreased and then increased in volume as the rotor rotates, a liner in the form of a plurality of thin flexible strips of oval profile merging smoothly edge to edge and extending between the end plates, the strips each having port openings communicating with a portion of the ports in the housing and at least a portion of the strips being peripherally adjustable to vary the relative phase positions of the ports.
Claim 30
Dependent Claim
183 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means in the housing defining a compression side inlet port, compression side outlet port, expansion side inlet port, and expansion side outlet port, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of vanes extending into engagement with the end plates and outwardly biased to form compartments which are progessively decreased and then increased in volume as the rotor rotates, a liner in the form of a pair of thin flexible strips of oval profile merging smoothly edge to edge for covering the outer wall, the strips each having port openings communicating with a portion of the ports in the housing and at least one of the strips being peripherally adjustable to vary the relative phase positions of the ports.
Claim 31
Dependent Claim
183 words
In a compressor-expander for use in air conditioning, the combination comprising a housing defining a chamber having an outer wall of oval profile divided into a compression side and an expansion side and enclosed by end plates, a cylindrical rotor extending between the end plates and having a shaft journalled therein, means in the housing defining a compression side inlet port, compression side outlet port, expansion side inlet port, and expansion side outlet port, a heat exchanger interposed between the compression side outlet port and the expansion side inlet port, the rotor having a plurality of vanes extending into engagement with the end plates and outwardly biased to form compartments which are progessively decreased and then increased in volume as the rotor rotates, a liner in the form of a pair of thin flexible strips of oval profile merging smoothly edge to edge for covering the outer wall, the strips each having port openings communicating with a portion of the ports in the housing and at least one of the strips being peripherally adjustable to vary the relative phase positions of the ports.
References Cited (Backward Citations)
US3686893A
Cited
US3752605A
Cited
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1978-06-02 | 1978-12-02 | 1979-06-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1982-06-02 | 1982-12-02 | 1983-06-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1986-06-02 | 1986-12-02 | 1987-06-03 | $7700.00 | Window Closed / Lapsed |