IRRIGATION SPRINKLER SYSTEM CONTROL EMPLOYING PILOT OPERATED, PRESSURE ACTUATED AND SEQUENCED VALVE ASSEMBLIES

• US 3,747,620 A
• Filed: 02/01/1972
• Issued: 07/24/1973
• Est. Priority Date: 02/01/1972
• Status: Expired due to Term

• Current Assignee: Carl L.C. Kah Jr
• Original Assignee: Carl L.C. Kah Jr
• Inventors: Kah, Carl L. C. Jr.
• Primary Examiner(s): Schwadron, Martin P.
• Assistant Examiner(s): Zobkiw, David J.
• Application Number:
  US05/222,600
• Time in Patent Office: 539 Days
• Field of Search: 137/119,624.12,624.13,624.14,624.15,624.18,624.19,624.20 239/66
• US Class Current: 137/119.03
• CPC Class Codes: A01G 25/162 Sequential operation
• CPC Class Codes: Y02A 40/22 Improving land use; Improving water use or availability; Controlling erosion
• CPC Class Codes: Y10T 137/268 Responsive to pressure or flow interruption
• CPC Class Codes: Y10T 137/86397 With independent valve controller
• CPC Class Codes: Y10T 137/86445 Plural, sequential, valve actuations
• CPC Class Codes: Y10T 137/86461 Variable cycle

Abstract

The disclosure introduces a number of new concepts in the operation and control of pressure actuated and sequenced valve assemblies which include pressure cycling, selective reset, tracking of sprinkler section operation and cyclic pressure level control. Each of the pressure actuated and sequenced valve assemblies herein disclosed includes pressure cycling and/or reset capabilities operable as a direct function of line pressure changes and as an indirect function of a remote electrical control system which may be selectively employed to control such pressure changes. Alternatively, the direct function control may be based on time. One aspect of the invention is concerned with the constructional details of various pressure actuated and sequenced valve assembly configurations employing pilot valves and sequencing control elements for controlling the opening and closing movement of a main flow control valve while a second aspect of the invention relates to the control of those line pressure variations to which the pilot valves and sequencing control elements are responsive. The sequencing control elements in each of the line connected valve assemblies may be pressure cycled without opening the main valve by varying inlet line pressure at a level below that required to open the main valves and the sequencing control elements may be reset to a predetermined position by a further selective reduction in line pressure level. The remote electrical control system has a primary function of insuring that each cyclic line pressure change is of such magnitude and/or duration as to insure that each line connected valve assembly will be sequenced. The electrical control system further includes the capability of an automatic selection of a manually chosen one of the plurality of line connected sprinkler sections for individual and/or prolonged sprinkling as well as the additional features of pressure cycling and reset of all the line connected sequencing control elements which latter two functions may also be performed by a conventional hydraulic control adjacent the line pressure source when valve assemblies of the type herein disclosed, possessing these capabilities, are used.

Claims

1. A pressure actuated and sequenced valve assembly comprising;

a main valve for controlling fluid flow therethrough, a main valve actuator for opening and closing said main valve;

first passage means for constantly imposing pressure forces on one side of said main valve actuator, second passage means for imposing pressure forces on the other side of said main valve actuator, third passage means for venting the other side of the main valve actuator, a pilot valve biased to close said third passage means, means responsive to pressure variations for opening and closing said pilot valve, the last named means including a sequencing means for controlling the opening movement of said pilot valve and fluid pressure actuating means for indexing said sequencing means and opening said pilot valve, fourth passage means for communicating a pressure to said fluid pressure actuating means, said sequencing Means including a plurality of indexing elements, ratcheting means mounted for intermittent driving engagement with said indexing elements and drivingly interrelated with said fluid pressure actuating means for translating pressure changes into indexing movement of said sequencing means.

2. A valve assembly as set forth in claim 1 wherein said fluid pressure actuating means includes two separate pressure responsive means, one pressure responsive means being connected to said sequencing means and the other pressure responsive means being connected to said pilot valve.

3. A valve assembly as set forth in claim 1 wherein the flow passage area of said second passage means is small in comparison to that of said first passage means.

4. A valve assembly as set forth in claim 1 including a lost motion connection between said pilot valve and said fluid pressure actuating means whereby said sequencing means may be actuated by said fluid pressure actuating means without opening said pilot valve for pressure indexing the sequencing means.

5. A valve assembly as set forth in claim 1 including means for biasing said pilot valve to a closed position and means interacting between the biasing means and said sequencing means for automatically varying said bias as a function of the indexed position of said sequencing means whereby the pilot valve may be pressure operated to an open position.

6. A valve assembly as set forth in claim 1 wherein said pilot valve is a double acting pilot valve mounted for movement between the position closing said third passage means and a position closing said second passage means.

7. A valve assembly as set forth in claim 6 including means engageable by said sequencing means for engaging said pilot valve to open said third passage means and close said second passage means.

8. A valve assembly as set forth in claim 1 including means for resetting said sequencing means to a selected reference position.

9. A valve assembly as set forth in claim 8 wherein said resetting means is responsive to a pressure outside of said pressure variations.

10. A valve assembly as set forth in claim 9 wherein said resetting means is responsive to a reduced pressure from said pressure variations.

11. A valve assembly as set forth in claim 9 wherein said resetting means is also responsive to a time delay means so that said outside pressure will not reset said sequencing means for a predetermined time period.

12. A valve assembly as set forth in claim 8 wherein said resetting means includes means biasing said sequencing means in opposition to the direction of said indexing movement, and means for selectively restraining said resetting movement.

13. A valve assembly as set forth in claim 12 including means responsive to a pressure outside of said pressure variations for selectively restraining said resetting movement.

14. A valve assembly as set forth in claim 12 including means responsive to time and a pressure outside of said pressure variations for selectively restraining said resetting movement.

15. A valve assembly as set forth in claim 8 wherein said main valve is connected in line with at least two distinct pressure sources for selectively supplying line pressure variations for pressure indexing the sequencing means and for opening the main valve, and means for reducing pressure for resetting said sequencing means.

16. A valve assembly as set forth in claim 1 wherein said main valve is connected in line with at least two distinct pressure sources for selectively supplying pressure variations for pressure indexing the sequencing means and for opening the main valve.

17. A valve assembly as set forth in claim 1 wherein said third passage means terminates within the fluid flow line downstream of said main valve.

18. A valve assembly as set forth in claim 17 wherein said third passage means terminates in a venturi throat for providing a greater pressure sink therefor upon opening of said main valve.

19. A valve assembly as set fortH in claim 1 wherein said sequencing means includes reciprocal actuator rod means mounted for camming engagement with said ratcheting means for effecting the driving interrelation between said fluid pressure actuating means and said ratcheting means.

20. A pressure actuated and sequenced valve assembly comprising;

a line connected main valve for controlling fluid flow therethrough, a main valve actuator for opening and closing said main valve, sequencing control means for controlling the movement of said actuator in response to pressure variations, means for directing pressure variations to said control means, said control means including a pilot valve and an indexable member mounted for indexing movement through a plurality of main valve closed positions and at least one main valve open position, and said control means further including means for indexing said indexable member through any or all of said positions without opening said valve.

21. A valve assembly as set forth in claim 20 wherein said pressure variations are formed in said line.

22. A pressure actuated and sequenced valve assembly, comprising;

a valve for controlling fluid flow therethrough, sequencing control means including indexable means for controlling the opening and closing movement of said valve in response to pressure variations, and means for resetting said indexable means to a predetermined point in its indexing cycle as a function of a pressure level outside the range of said pressure variations.

23. A valve assembly as set forth in claim 22 wherein said resetting means resets as a function of time along with the pressure level.

24. A pressure actuated and sequenced valve assembly comprising;

a valve, a valve actuator, first passage means for communicating actuating pressure forces to said valve actuator, an indexable member, means responsive to a first pressure range variation for indexing said member and to a higher pressure level for opening said valve, the last named means including fluid pressure actuating means, second passage means for communicating pressure variations to said actuating means, and sequencing selection means carried by said indexable member for controlling the opening movement of said valve.

25. A valve assembly as set forth in claim 24 including means for resetting said indexable member in response to pressure levels below said first pressure range.

26. The valve assembly of claim 24 wherein said fluid pressure actuating means comprises a single actuator for indexing said member and opening said valve.

27. The valve assembly of claim 26 including means for resetting said indexable member in response to pressure levels below said first pressure range.

28. The valve assembly of claim 24 including spring means opposing the actuating movement of said actuating means defining said first pressure range and further defining a second pressure range including said higher pressure level, and the bias of said spring means changing abruptly at the juncture of said pressure ranges.

29. The valve assembly of claim 28 wherein said spring means further define a third pressure range below said first pressure range, means for moving said indexable member for resetting movement in opposition to the indexing movement, means restraining said resetting movement, and means responsive to pressure levels within said third pressure range for releasing said restraining means whereby said indexable member may be reset.

30. The valve assembly of claim 29 wherein said indexable member includes means for selective positioning of reset stop means whereby the indexable member may be reset to a predetermined base position by reduced pressure levels within said third range.

31. The valve assembly of claim 29 wherein said spring means comprise three concentric springs.

32. The valve assembly of claim 24 wherein said indexable member includes a plurality of indexable positions and said sequencing selection means comprise pin means selectively positionable at any of said inDexable positions.

33. A pressure actuated and sequenced valve assembly comprising;

a main valve, a main valve actuator, first passage means for communicating actuating pressure forces to opposite sides of said main valve actuator, second passage means including a pilot valve for selectively venting one side of said main valve actuator, an indexable member, means responsive to a first pressure range variation for indexing said member and to a higher pressure level for opening said pilot valve, the last named means including fluid pressure actuating means, third passage means for communicating pressure variations to said actuating means, and sequencing selection means carried by said indexable member for controlling the opening movement of said pilot valve.

34. A valve assembly as set forth in claim 33 including means for resetting said indexable member in response to pressure levels below said first pressure range.

35. The valve assembly of claim 33 including means biasing said pilot valve to close said second passage means and said sequencing selection means being movable into engagement with said biasing means for reducing the bias on said pilot valve.

36. The valve assembly of claim 33 wherein said fluid pressure actuating means comprises a single actuator for indexing said member and opening said pilot valve.

37. The valve assembly of claim 36 including a pilot valve actuator assembly connected to said single actuator, a lost motion connection between the last named assembly and said pilot valve for taking up limited relative movement therebetween as induced therein by said first pressure range variations applied to said actuator whereby the valve assembly may be pressure cycled without opening the pilot valve.

38. The valve assembly of claim 37 wherein said sequencing selection means includes means for restraining or permitting movement of said pilot valve actuator assembly under the influence of said higher pressure level within or beyond the range of said limited relative movement.

39. A pressure actuated valve assembly comprising;

a main valve, a main valve actuator, inlet passage means for communicating inlet line pressure forces to opposite sides of said main valve actuator, a dump passage including a pilot valve for selectively venting one side of said main valve actuator, means responsive to pressure variations for opening and closing said pilot valve, said last named means including actuating means, line connected venturi passage means, and said dump passage terminating in the throat area of said venturi passage means for inducing a greater pressure drop across said main valve actuator when said one side thereof is vented.

40. A pressure actuated and sequenced flow control valve, comprising;

a valve, valve actuator means including a fluid pressure actuator for opening and closing said valve, passage means for communicating a pressure to one side of said fluid pressure actuator, an indexable member, sequencing means responsive to a first pressure range variation for indexing said member and to a higher pressure level for opening said valve, said sequencing means including driving ratchet means mounted for movement into and out of driving engagement with said member and a lost motion connection between said valve and valve actuator means for permitting limited relative movement therebetween in response to pressure variations within said first pressure range, and first and second distinct biasing means respectively opposing movement of said valve actuator means within said first pressure range and to said higher pressure level.

41. A line connected pressure actuated and sequenced valve assembly including a main valve, a main valve actuator, a sequencing control assembly, a pilot valve assembly, and actuator means for the last named assemblies, the improvement comprising;

passage means for communicating operating pressure forces to opposite sides of said main valve actuator and to said actuator means;

a passage for selectively veNting one side of said main valve actuator;

means mounting said pilot valve assembly for movement between first and second extreme positions respectively opening and closing said passage;

said sequencing control assembly including an indexable member and ratchet means mounted for intermittent driving engagement with said member;

sequence control means carried by said member for controlling the movement of said pilot valve assembly to said first extreme position;

means biasing said pilot valve assembly in the direction of said second extreme position; and

said actuator means for said sequencing control and pilot valve assemblies comprising fluid pressure actuator means in communication with operating pressure forces.

42. The line connected valve assembly of claim 41 wherein said sequencing control assembly includes biasing means restraining driving engagement between said ratchet means and said indexable member, said biasing means restraining driving engagement between said ratchet means and indexable member being yieldable under a first pressure level applied at said actuator means, and said means biasing said pilot valve assembly in the direction of said second extreme position being yieldable under a second higher pressure level applied at said actuator means, and means for selectively imposing said first and second pressure levels whereby the valve assembly may be pressure cycled and actuated, respectively.

43. The line connected valve assembly of claim 42 including means biasing said indexable member in a direction opposite to the driving engagement thereof by said ratchet means, holding means for restraining the movement of said indexable member in the last named direction, means responsive to a third pressure less than said first pressure for releasing said holding means, and means for reducing said pressure below said first pressure level whereby said indexable member may be reset.

44. A pressure actuated and sequenced valve assembly including distinct, differentially loaded biasing means for the establishment of a first distinct pressure range within which the valve assembly may be sequenced while precluding actuation of the same and a second distinct pressure range within which said valve assembly may be actuated, comprising;

a valve;

an indexable member for controlling the opening movement of said valve;

means responsive to pressure variations for opening and closing said valve and sequencing said member;

the last named means comprising fluid pressure actuating means, passage means for communicating pressure to said actuating means, and drive means responsive to movement of said actuating means for sequencing said member and opening said valve;

said drive means being responsive to first pressure level variations within a first pressure range for sequencing said member and second pressure level variations within a second pressure range for sequencing said member and opening said valve;

first biasing means opposing the sequencing of said member within said first pressure range; and

second biasing means opposing the opening of said valve within said second pressure range whereby selective pressure variations within said first range will sequence said member without opening said valve.

45. The valve assembly of claim 44 wherein said first and second biasing means comprise first and second differentially biased spring assemblies, and said second spring assembly having a greater bias than said first spring assembly.

46. The valve assembly of claim 44 wherein said drive means includes an actuator having a first range of movement in response to pressure variations within said first pressure range applied at said actuating means and a second range of movement in response to pressure variations within said second pressure range, means for withholding the bias of said second biasing means from said actuator during said first range of movement thereof;

and means for applying the bias of said second biasing means to said actuator during said second range of movement wHereby the additive biasing forces of the two biasing means must be overcome to open the valve.

47. The valve assembly of claim 44 including reset biasing means opposing the sequencing movement of said member;

means for blocking reset movement of said member;

reset stop means for arresting movement of said member in the reset direction; and

means responsive to a reduced line pressure level below said first pressure range for releasing the reset blocking means whereby said member may be reset to a predetermined base portion.

48. The valve assembly of claim 47 wherein said means responsive to a reduced line pressure level includes a third biasing means.

49. A unit controller adapted to be connected between a main flow line and a main valve having a main valve actuator for converting the same into a pressure actuated and sequenced valve assembly comprising;

a unit housing, flow passage means including a dump line in said housing for selective communication of one side of the main valve actuator with inlet line pressure or said dump line, a pilot valve having a lost motion connection with a pilot valve actuator means for controlling said selective communication, sequencing control means including an indexable member and driving ratchet means therefor for moving said pilot valve actuator means, said indexable member including a plurality of indexable positions limiting the movement of said ratchet means to a stroke length less than the lost motion connection and at least one position permitting a stroke length travel of said ratchet means exceeding that of the lost motion connection, and means for limiting said stroke length when said indexable member is in said one position whereby the same may be pressure cycled without opening the main valve.

50. A unit controller adapted to be connected to a main valve actuator for converting the same into a pressure actuated and sequenced valve assembly comprising;

a unit housing, a valve for controlling fluid pressure on one side of the main valve actuator, a sequencing control means including an indexable member for controlling the movement of said valve in response to pressure variations, said indexable member being mounted for indexing movement through a plurality of valve closed positions and at least one valve open position; and

said control means further including means for indexing said indexable member through any or all of said positions without opening said valve.

51. A unit controller as set forth in claim 50 including means for resetting said indexable member in response to pressure levels below said pressure variations.

52. A unit controller as set forth in claim 51 wherein the last named means includes reset spring means for biasing the indexable member in one direction;

said sequencing control means further including drive means for indexing said member in the other direction in response to cyclic pressure variations, holding means restraining movement of said member in said one direction; and

means for releasing said holding means.

53. A unit controller adapted to be connected between a main flow line and a main valve having a main valve actuator for converting the same into a pressure actuated and sequenced valve assembly, comprising;

a unit housing, flow passage means including a dump line in said housing for selective communication of one side of the main valve actuator with inlet line pressure or said dump line, a pilot valve for controlling said selective communication, sequencing control means including a reciprocal fluid pressure actuator for opening said pilot valve and biasing means for closing the same, a lost motion connection between said last named actuator and pilot valve defining a range of limited relative movement therebetween, said sequencing control means further including means for selectively limiting the reciprocal movement of said last named actuator to a stroke length less than said range of limited movement, said last named means including an indexable member having a plurality of indExable positions for limiting said stroke length and at least one indexable position permitting an actuator stroke length exceeding that of the lost motion connection, and means for indexing said member in response to reciprocal movement of said last named actuator.

54. In combination with line connected pressure actuated and sequenced valve assembly means;

a control system for controlling line system pressure to said valve assembly means;

said control system comprising;

a selectively energizable line pressure controller;

a power source for energizing said controller;

a control circuit for controlling the energization of said controller by said power source in response to line system pressure changes;

said control circuit including energizable switch means in circuit between said power source and controller;

power means for energizing said switch means; and

line pressure responsive switching means in circuit between said power means and said energizable switch means.

55. The combination of claim 54 wherein said line pressure controller comprises a pressurization control relay and said energizable switch means includes a latching circuit.

56. The combination of claim 55 wherein said line pressure responsive switching means includes separate high and low pressure switches;

and said power means comprises a first electrical source in circuit with said high pressure switch and a second electrical source in circuit with said low pressure switch.

57. The combination of claim 56 wherein said control circuit includes first and second circuit means for alternately energizing said latching circuit by said first and second electrical sources;

a relay operated switch series connected in said first circuit means with the high pressure switch; and

means responsive to current flow in said second circuit means for actuating said relay operated switch in said first circuit means.

58. The combination of claim 57 including switch means operated by said latching circuit for opening and closing said second circuit means in response to the alternate energization of said latching circuit by said first and second electrical sources.

59. The combination of claim 58 including electrical means for tracking the line pressure changes induced by said line pressure controller.

60. The combination of claim 58 including remote control switch means for making and breaking said second circuit means.

61. In combination with line connected pressure actuated and sequenced valve assembly means;

a control system for controlling line system pressure to said valve assembly means;

said control system comprising;

electrically operated line pressure source control means;

first control circuit means Including first and second energizable switch means for controlling the energization of said source control means;

second control circuit means including energizable switch means for controlling the energization of said first switch means;

third control circuit means for controlling the energization of said second switch means;

electrical power means for said circuit means; and

fluid pressure responsive switching means in said second control circuit means.

62. The combination of claim 62 wherein said second control circuit means includes a first subcircuit responsive to the energization of one energizable switch means in said second control circuit means for energizing said first energizable switch means.

63. The combination of claim 63 wherein said fluid pressure responsive switching means includes separate high and low pressure switches;

said second control circuit means including a second subcircuit responsive to the energization of another energizable switch means in said second circuit for energizing said one energizable switch means.

64. The combination of claim 63 including a stepping relay intermittently energizable by said power means as a function of the energization of said one energizable switch means.

65. The combination of claim 62 wherein said second control circUit includes parallel subcircuits;

and said pressure responsive switching means including separate high and low pressure switches controlling respective ones of said subcircuits.

66. The combination of claim 66 including second electrically operated line pressure source control means and fourth control circuit means for controlling the same;

reset pressure responsive switching means in circuit with said fourth control circuit means; and

electrical power means for said fourth control circuit means.

67. In combination with line connected pressure actuated and sequenced valve assembly means;

a control system for controlling line system pressure to said valve assembly means;

Said control system comprising;

a selectively energizable line pressure controller;

a power source for energizing said controller;

a control circuit for controlling the energization of said controller by said power source as a function of time;

said control circuit including energizable switch means in circuit between said power source and controller;

power means for energizing said switch means; and

time responsive switching means in circuit between said power means and said energizable switch means.

68. The combination of claim 68 wherein said line pressure controller comprises a pressurization control relay and said energizable switch means includes a latching circuit.

69. The combination of claim 69 wherein said time responsive switching means includes separate high and low pressure switches;

and said power means comprising a first electrical source in circuit with said high pressure switch and a second electrical source in circuit with said low pressure switch.

70. The combination of claim 70 wherein said control circuit includes first and second circuit means for alternately energizing said latching circuit by said first and second electrical sources, a relay operated switch series connected in said first circuit means with the high pressure switch;

and means responsive to current flow in said second circuit means for actuating said relay operated switch in said first circuit means.

71. The combination of claim 71 including switch means operated by said latching circuit for opening and closing said second circuit means in response to the alternate energization of said latching circuit by said first and second electrical sources.

72. The combination of claim 67 including electrical means for tracking the line pressure changes induced by said line pressure source control means.

73. In combination with line connected pressure actuated and sequenced valve assembly means;

a control system for controlling line system pressure to said valve assembly means;

said control system comprising;

electrically operated line pressure source control means;

first control circuit means including first and second energizable switch means for controlling the energization of said source control means;

second control circuit means including energizable switch means for controlling the energization of said first switch means;

third control circuit means for controlling the energization of said second switch means;

electrical power means for said circuit means; and

time responsive switching means in said second control circuit means.

74. The combination of claim 74 wherein said second control circuit means includes a first sub-circuit responsive to the energization of one energizable switch means in said second control circuit means for energizing said first energizable switch means.

75. The combination of claim 75 wherein said time responsive switching means includes separate high and low pressure switches;

said second control circuit means including second sub-circuit responsive to the energization of another energizable switch means in said second circuit means for energizing said one energizable switch means.

76. The combination of claim 75 including a stepping relay intermittently energizable by said power means as a function of the energization of said one energizable switch means.

77. The combination of claim 74 wherein said second control circuit means includes parallel sub-circuits;

and said time responsive switching means including separate high and low pressure switches controlling respective ones of said sub-circuits.

78. The combination of claim 78 including second electrically operated line pressure source control means and fourth control circuit means for controlling the same;

reset time responsive switching means in circuit with said fourth control circuit means; and

electrical power means for said fourth control circuit means.

79. An irrigation system, comprising a plurality of line connected fluid distributors;

line connected fluid pressure means for supplying said distributors;

a plurality of line connected pressure actuated and sequenced valve assemblies for controlling fluid flow to said distributors as a function of line pressure variations;

each said valve assembly including;

a main flow control valve for controlling flow between said line and at least one of said distributors and an indexable member for controlling the opening movement of said main valve, line pressure actuated means for indexing said member and opening said main valve, biasing means defining distinct line pressure ranges for pressure cycling said valve assembly and for opening the main valve, said biasing means comprising first biasing means opposing the line pressure actuated means for indexing said member and second biasing means opposing the line pressure actuated means for opening the main valve; and

means controlling said fluid pressure means for selectively transmitting line pressure variations within one of said pressure ranges to each said valve assembly for sequencing the same and within another of said pressure ranges for opening the main valve of at least one of said valve assemblies.

80. The irrigation system of claim 80 wherein each said valve assembly further includes;

reset stop means associated with the indexable member for defining a basic start position, reset biasing means opposing the indexing of said member and biasing the same toward said start position, holding means responsive to pressure levels within said pressure ranges for restraining movement of said member toward the start position; and

line connected means for reducing line pressure below said pressure ranges for releasing the holding means in each said valve assembly and resetting the same to a basic start position.

81. An irrigation system, comprising;

a plurality of line connected fluid distributors;

a line connected fluid pressure source for supplying said distributors;

a plurality of line connected pressure actuated and sequenced valve assemblies for controlling fluid flow to said distributors as a function of pressure variations;

each said valve assembly including;

a main flow control valve for controlling flow between said line and at least one of said distributors and an indexable member for controlling the opening movement of said main valve, pressure actuated means for indexing said member and opening said main valve, return biasing means opposing the pressure actuated means for indexing said member and opening said main valve;

means including electrical control means for initiating cyclic pressure variations at said fluid pressure source for alternately increasing and decreasing pressure to index said member of each valve assembly under the alternate influence of increasing pressure and the return biasing means;

said electrical control means including first circuit means for initiating pressure increases and second circuit means for initiating pressure decreases; and

means for alternately making and breaking said circuits as a function of irrigation system parameters whereby an alternate pressure variation may not be initiated until all the line connected valve assemblies have been sequenced under the influence of the previous pressure variation.

82. An irrigation system as set forth in claim 82 wherein the pressure variations are line pressure variations.

83. An irrigation system as defined in claim 82 wherein said electrical control means include additional circuit means for precluding the making of said second circuit means;

and manual switch means in said additional circuit means for activating the same.

84. An irrigation system as defined in claim 84 wherein said manual switch means includes a manual selection switch for at least one of each said valve assembly;

and said additional circuit means including a stepping circuit for stepping circuit closures into and out of circuit with each manual selection switch whereby the fluid distributors associated with each valve assembly may be manually selected for extended irrigation.

85. An irrigation system as defined in claim 82 wherein said last named means include line connected pressure responsive switching means.

86. An irrigation system as defined in claim 82 wherein said last named means include timing means.

87. An irrigation system as defined in claim 82 including a second fluid pressure source for alternately increasing and decreasing line pressure within a line pressure range distinct from a range of fluid pressure variations derived from the first named fluid pressure source;

said biasing means including distinct spring assemblies; and

one of said spring assemblies being preloaded to yield within one of said pressure ranges and another being preloaded to yield within the other pressure range.