Method and apparatus for reducing the precipitation rate of an irrigation sprinkler

A method and apparatus for reducing the effective precipitation rate of an irrigation sprinkler during an irrigation cycle without disrupting the supply of pressurized water from the source opening and closing the inlet to the sprinkler riser at timed intervals through the use of a flow stop valve assembly disposed at the base of the riser, and which includes a lost motion piston and cylinder assembly and first and second flow control devices which control the time the flow stop valve is in the open and closed conditions during the irrigation cycle.

FIELD OF THE INVENTION

This invention relates to irrigation sprinklers, and more particularly to a new and improved method and apparatus for reducing the effective precipitation rate of a fixed spray type sprinkler, particularly of the pop-up type.

BACKGROUND OF THE INVENTION

Probably the most common method of irrigating landscape areas of vegetation is by the use of sprinklers. In a typical irrigation system various types of sprinklers are used to distribute water over a desired area. In general, sprinkler devices are divided into two types, namely rotating stream type and fixed spray pattern type. The stream type sprinkler, commonly referred to as a rotor, trajects a stream of water outwardly from a nozzle, which is rotating slowly over a predetermined arc or complete circle. The spray type sprinkler sprays water from a stationary nozzle, the pattern of coverage being determined by the geometric shape of the discharge passage of the nozzle.

For reasons well known to those involved in the design of irrigation systems, the precipitation rate of the rotor type sprinklers is much lower than the precipitation rate of the fixed nozzle type sprinkler. For proper irrigation of plant life and conservation of water it is extremely important to have a uniform or prescribed amount of water delivered by the irrigation system to a specific area. Because of the difference in precipitation rates of the two types of sprinklers, heretofore it has been necessary to operate the rotor type of sprinkler for a longer time than the spray type sprinkler. In order to accomplish this, it has been necessary to have the two types of sprinklers operated separately whereby each type could be operated for a suitable time to supply the desired total precipitation to the irrigated area. Prior to this invention many attempts have been made to reduce the precipitation rates of spray type sprinklers. Most, if not all of such attempts have been concentrated on the design of the nozzles in order to reduce the rate of flow of water.

SUMMARY OF THE INVENTION

The method and apparatus for producing the low precipitation rate sprinkler of this invention provides a fixed pattern type sprinkler with attainable precipitation rates equivalent to the precipitation rates of rotary stream sprinklers. This makes it possible to operate rotary and spray type sprinklers on the same supply circuit and for the same length of time thereby reducing the cost and simplifying the operating of the irrigation system. The detailed descriptions following will describe the invention as applied to presently conventional spray type sprinklers. This invention provides a means of reducing the effective time of operation of the sprinkler while using conventional flow rate nozzles. The reduction of sprinkling time is accomplished by interrupting the flow of water to the sprinkler nozzle. This is most obviously accomplished by turning the water supply to the nozzle on and off in timed durations of several seconds. For example, if the water is permitted to flow through the nozzle for a period of 5 seconds and then prevented from flow for 20 seconds, the effective precipitation rate is reduced to one fifth of the normal rate of precipitation for the specific nozzle being used. The method for accomplishing this operation will be described in detail following.

A second advantage of the invention is to provide more uniform distribution of water over the covered area. The distribution of water from fixed pattern spray nozzles is inherently non-uniform having the most water concentrated in an annular area an appreciable distance from the nozzle. The uniformity of distribution of water is improved due to the radial propagation and decay of the spray stream as the flow is started and stopped.

More specifically, in accordance with the method of the present invention for reducing the effective precipitation rate of an irrigation sprinkler during an irrigation cycle, the method includes the steps of initiating an irrigation cycle to supply a constant source of pressurized water into the casing of the sprinkler, and sequentially blocking and then unblocking the flow of water within said casing from said source to said nozzle without disrupting the supply of pressurized water to said casing, thereby to sequentially cycle the flow of water from said source to said nozzle without interrupting the irrigation cycle.

Typically, the apparatus of the present invention will be used in an irrigation sprinkler of the type comprising a casing having a water inlet connection at the bottom for coupling the sprinkler with a pressurized source of water and a cap at the top end, and an extensible tubular riser having a water directing bore disposed within the case for movement between a retracted inoperative position within the casing and an extended operative position projecting through the cap out of the casing, the riser including a spray nozzle at its upper end and an entrance end disposed within the casing below the cap, the riser serving to direct water from the source to the nozzle for irrigating an area extending outwardly from the sprinkler. In accordance with the apparatus of the invention, a flow stop valve assembly is coupled to the entrance end of the riser within the casing, and includs a valve head adapted to move between an open and a closed position, respectively unblocking and blocking the entrance end of the riser, and a lost motion piston and cylinder assembly coupled to said valve head for moving said valve head between said open and closed positions, said lost motion piston and cylinder assembly including a piston cyclically moveable within a cylinder between an upper and a lower position for effecting closing and opening, respectively, of said valve head. A water flow path is provided extending between said cylinder below said piston and said bore of said riser above said valve head, and a first flow control device is disposed in said water flow path for limiting the rate of flow of water through said water flow path when said piston is moving downwardly within said cylinder. A second flow control device is disposed in said flow path for limiting the rate of flow of water through said water flow path when said piston is moving upwardly within said cylinder, whereby the time during which said valve head is in said closed position is controlled by said first flow control device, and the time during which said valve head is in the open position is controlled by said second flow control device.

Other features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

As shown in the exemplary drawings, the present invention is embodied in a spray type sprinkler100, herein of the pop-up sprinkler of generally conventional type, and which is intended to water a fixed area around the sprinkler. In this instance, the sprinkler100includes a cylindrical casing103adapted to be buried in the ground, and having a water supply inlet101at the bottom for attachment to a source of pressurized water, and a cover99overlying the top of the casing. Disposed for reciprocation between an extended upper operating position, as shown inFIG. 1, and a lower inoperative position retracted inside the casing103, is a hollow tubular riser102having an internal bore126, extending between a lower end disposed within the casing and an upper end adapted to project above the casing and cover, and having a spray nozzle98removably attached thereto.

A conventional retract spring97, herein a coil spring, is disposed around the riser102within the casing103, and has one end abutting the underside of the cover99and the other end abutting an enlarged upwardly facing radial surface96surrounding the lower end of the riser. The retract spring97operates to bias the riser102to the inoperative, retracted position within the casing103when no water pressure is supplied to the sprinkler, and to compress to the position shown inFIG. 1when water pressure is admitted to the sprinkler casing inlet101, and the riser is extended to the upper, operative position.

When in normal use, pressurized water enters the inlet101and flows through the riser102to the upper end where it is ejected outwardly away from the sprinkler100through the nozzle98in a fan-shaped spray pattern and at a precipitation rate determined by the spray nozzle and water supply pressure utilized. Depending on the type of nozzle98installed on the riser102, the spray pattern can be any shape, typically from a full circle to a small pie-shaped part circle, such as a quarter circle pattern. When the supply of pressurized water is shut off, the retract spring97moves the riser102downwardly to the retracted inoperative position inside the casing103. It should be noted that each time the supply of pressurized water is admitted to the casing103, the rise in internal pressure causes the riser102to extend upwardly to the operative position, and as water pressure builds within the riser, water ejected though the nozzle98results in a spray pattern that initially extends radially outwardly from adjacent the sprinkler100to the maximum distance away from the sprinkler for the specific nozzle and supply pressure utilized. On shutting off the supply of pressure to the casing inlet101, the water pressure decreases so that as the riser102retracts to the inoperative position within the casing103and, the spray pattern decays from the maximum radial distance back to the area adjacent the sprinkler. Thus, with each cycle of sprinkler operation, the area around the sprinkler100is watered from adjacent the sprinkler out to the maximum radial distance of throw of the nozzle. In accordance with the present invention, a water flow interrupter assembly, generally designated by reference numeral95, is disposed within the water supply passage to the nozzle, herein secured to the lower portion of the riser102and moveable therewith, and which functions to periodically shut-off the supply of pressurized water to the nozzle for a predetermined period of time without interrupting the supply of water from the source to the inlet101of the sprinkler100. The flow interrupter assembly95operates in a highly effective and efficient manner to permit controlled reduction in the effective precipitation rate of the sprinkler100, and allows the use of any size nozzle98and nozzle pattern without effecting the overall lowered precipitation rate of the sprinkler. Moreover, the flow interrupter95is relatively simple in construction, reliable in use and economical to manufacture, yet can be utilized with virtually any spray type sprinkler where it is desirable to reduce and control the precipitation rate during an irrigation cycle without having to turn the supply of pressurized water from the source on and off.

Toward the foregoing ends, as can be seen inFIG. 2, the flow interrupter assembly95includes a generally cylindrical housing structure94secured to the lower end portion of the riser102so as to form a lower extension of the riser. The interrupter housing94, which has an outer diameter less than the inner diameter of the sprinkler case103so that water entering the sprinkler inlet101can freely flow around the interrupter housing, houses a timing valve assembly, generally designated93, a first flow control mechanism, generally designated92, and a second flow control mechanism, generally designated91, which together operate to periodically admit and shut off water to the riser102and nozzle98in a timed and controlled manner during each irrigation cycle.

In general, and as will become more apparent hereinafter, the timing valve assembly93functions to control the flow of water from the sprinkler inlet101into the bore126of the riser102by utilizing a flow stop valve116operated by a lost motion piston and cylinder assembly90. The first flow control mechanism92cooperates with the timing valve assembly to control the length of time that water is prevented from flowing from the source inlet101into the riser102. The second flow control mechanism91controls the length of time the flow of water to the riser is permitted, such that during a given irrigation cycle, water is periodically and cyclically admitted to the riser102for a preset period of time, and is then stopped for a second preset period of time, thereby reducing the effective sprinkler precipitation rate as compared to a continuous and uninterrupted flow of water to the nozzle98during the irrigation cycle.

With reference toFIG. 2which illustrates the sprinkler100in a non-spraying mode, it will be seen that water admitted into the sprinkler inlet101(not shown inFIG. 2) flows into the case103around the riser102and housing94of the flow interrupter assembly95. Due to the pressure of the water within the case103acting on the lower end of the interrupter housing94, the riser102and attached interrupter housing is caused to extend against the bias of the retract spring97, to the raised operational position. However, as can be seen inFIG. 2, the flow stop valve116prevents any water flow from within the case103from entering the riser102, thus prohibiting water from being ejected from the nozzle98. Thus, notwithstanding that the riser102has extended to the operative position, no water can be sprayed until the flow stop valve116has first opened to permit water from the source to flow into the riser.FIG. 4illustrates the fully open condition with the flow stop valve116moved away from the sealing position so that water can flow from the source into the riser102for spraying from the nozzle98.

More specifically as best seen inFIG. 2, the interrupter housing94herein includes an upper housing or cover section portion104and a lower housing section105, each having a generally cylindrical shape. Herein, the upper housing section104includes an upper cylindrical end portion89that surrounds and provides an internal surface to which the lower open-ended portion of the riser102is secured. Below the cylindrical end section89, the upper housing104defines a first enlarged open passageway88extending vertically from the lower end of the upper housing to the inlet end of the riser102for permitting water to flow into the riser from the source. Adjacent the first passageway88, a second generally vertical passageway87, herein of smaller size, is formed between the lower end of the upper housing104and the inlet end of the riser102, and through which a controlled flow of water into and out of the riser takes place, as will be explained in more detail below. In this instance, disposed between the lower end of the riser102and the upper end of the upper housing104is a disc-shaped filter plate119having a first opening86formed to be concentric with the first enlarged passageway88, and a second opening85disposed to overlie the second passageway87. The filter plate119herein forms a mounting structure for a disc-shaped filter screen131disposed to filter water flowing through the second opening85and passageway87, and a metering orifice plate132which functions as the second flow control mechanism91, as will become more apparent hereinafter.

The lower section105of the interrupter housing94herein is formed to have a closed bottom wall84and an upwardly projecting cylindrical side wall83to the top of which the upper housing section104is secured. Formed within in the lower section105of the interrupter housing94is a first enlarged upwardly open cylindrical chamber107forming a cylinder of the piston and cylinder assembly90, and the centerline of which is aligned with the centerline of the first passageway88through the upper housing section104. To allow pressurized water from the source flowing around the interrupter housing94to flow into the housing to the riser102from the sprinkler inlet101, one or more laterally directed ports128are formed in the upper end of the lower housing section105, and which connect with a cylindrical cavity127disposed between the underside of the upper housing section104and the upper open end of the cylinder107.

The flow stop valve116is disposed for reciprocation within the cylinder107and includes a flow-stop valve head135having a resilient seal washer134attached thereto disposed to seat against and seal the inlet to the first passageway88, and a downwardly projecting valve stem113slideably supported by the lost motion piston and valve assembly90. In this instance, as best seen inFIG. 3, the lost motion piston and valve assembly90includes a generally cylindrical piston body106having an upper end cap111formed with a central aperture82through which the valve stem113of the flow stop valve116projects and is guided. Centrally disposed within the piston body106is a upwardly open bore110having a closed bottom81into which the stem113of the valve116projects and is movable between an upper and lower position. As can best be seen inFIGS. 2 through 4, a compressible spring136, herein a coil spring, is disposed around the valve stem113, one end of which abuts the under side of the end cap111and the other end of which abuts an enlarged radial surface80of nut114threaded to the lower end of the valve stem.

The piston body106is also formed with a cylindrical, donut-shaped recess79extending upwardly from the bottom of the piston body radially outwardly of the closed bore110and having a closed upper end78, and within which is disposed a second compression spring109, herein a coil spring. The second spring109extends between the bottom of the cylinder107the closed upper end78of the cylindrical recess79to bias the piston body106upwardly. The combination of the compression spring136acting on the valve stem113and the compression spring109acting on the piston body106cooperate to form the lost motion connection for operating the flow stop valve116by permitting the piston body to be moved downwardly within the cylinder107without moving the flow stop valve until the valve stem spring136has been fully compressed against the cover end cap111, as best seen in FIG.3.

Importantly, for purposes of interconnecting the inside of the cylinder107below the piston body106to the inside of the riser102, the housing94is provided with a flow port124extending laterally from the bottom of the cylinder107to an upwardly directed flow passage123extending along the side of the cylinder107to the second passageway87, whereby water can flow through the port124and flow passage123between the cylinder107and the riser102through the first and second flow control mechanisms,92and91, respectively. Thus, when the piston assembly90is moved downwardly within the cylinder107, water within the cylinder below the piston assembly is forced from the cylinder to the riser102through the port124and the flow passage123.

Herein, the first flow control mechanism92controls the rate at which water can flow from the cylinder107into the riser102, while the second flow control mechanism91functions to control the rate at which water can flow from the riser back into the cylinder. More specifically, the first flow control mechanism92controls the rate at which water can be forced out of the cylinder107as the piston assembly90is moved downwardly by providing a restriction to the flow of water between the cylinder and the riser102. In this instance, the restriction is provided by employing as the first flow control mechanism92, a conventional pressure compensating drip irrigation emitter herein designated120, such as of the type illustrated and described in U.S. Pat. No. 5,820,029 owned by Rain Bird Corporation, the disclosure of which is incorporated herein by this reference, and which is disposed to have an inlet77for receiving water from the cylinder107and an outlet76directing water to the second passageway87. This flow control device restricts the flow of water by employing a pressure responsive diaphragm overlying a tortuous path groove such that the inlet pressure of water entering the emitter causes the diaphragm to restrict the groove cross-sectional size and thereby limit the flow of water at the outlet76to a preset amount, regardless of inlet pressure. Notably, the pressure compensating emitter120is a “one-way” device such that water flow in an opposite direction, that is from the outlet76to the inlet77toward the cylinder107, is not restricted by the internal diaphragm, but rather is free flowing, the only restriction being that provided by the cross-sectional size of the emitter inlet and outlet openings.

As can be seen in the sequence of positions of the timing valve assembly93shown inFIGS. 2 through 4, with the flow stop valve116blocking flow to the riser102and the piston assembly90in the position shown inFIG. 2, the pressure of water admitted from the source though the inlet101of the casing103and port128acts on piston assembly90in a downward direction. Once the force from water pressure has exceeded the force of the spring136, the piston assembly90will move downwardly into the cylinder107, forcing water within the cylinder below the piston to flow through the port124and first flow control device92, herein the emitter unit. To effect a lost motion connection between the piston assembly90and the flow stop valve head135, the valve spring136disposed around the valve stem113is selected to require less force for total compression than the upwardly acting force from water pressure on the lower face of the valve head135so that as the piston body moves downwardly in the cylinder107, the valve head remains in the flow stop position, and the valve spring136compresses within its cavity, as shown in FIG.3. Upon reaching full compression of the valve spring136, as shown inFIG. 3, the continued downward movement of the piston body106results in the valve head135being pulled downwardly by the end cap111acting on the top of the compressed spring and radial surface80of nut114. Notably, once the valve head135has initially opened to permit flow from the chamber127through the first passageway88into the riser102, the upward force from water pressure on its lower face is released, and the valve spring136will extend and snap the valve head downwardly to the fully retracted position within the cavity110to permit unrestricted flow of supply water into the riser102, as seen in FIG.4.

Once the valve head135has snapped to the fully open position and water is permitted to flow unrestricted to the riser102, the fluid pressure above the flow control devices91and92will build to a level substantially equal to the pressure above the piston assembly90, thereby eliminating the fluid pressure differential across the piston body106. The piston spring109will then begin to move the piston body upwardly within the cylinder107, thereby reducing the pressure below the piston body and drawing water downwardly from the riser102through the flow control devices91and92and flow passage123into the cylinder. The second flow control device91, which in this instance is formed by a simple circular orifice133in the orifice plate132, restricts the rate of flow of water downwardly into the cylinder, thereby controlling the time required for the piston assembly90to move to the fully upward position within the cylinder and close inlet of the first passageway88to the riser102and effect a shut off of water to the nozzle98.

More specifically, the orifice plate132is formed with an orifice133dimensioned to control the flow of water from the riser102toward the cylinder107so as to require the desired time for the water to flow into the cylinder, permitting piston assembly90and valve head135to move upward from the force of spring109as it extends, and stop valve116to seat against the inlet to the first passageway88and stop the flow to the nozzle98. Similarly, the first flow control device92is selected to permit a flow rate that will restrict the outflow of water from the cylinder107such that the lost motion piston assembly90will not open the valve head135for a selected period of time after closure. Notably, since the first flow control device92employs a pressure compensating emitter unit, the time interval required for opening the valve head135is independent of the pressure of the incoming supply water. Similarly, since closure of the valve head135is effected solely by the spring109and flow rate of the orifice plate132, the pressure of the water within the sprinkler housing103and riser102does not have any effect on the rate of closure and time the flow stop valve116remains open. Thus, by controlling the flow rates of the first and second flow control devices92and91, respectively, and appropriate selection of the spring109for the size of piston and cylinder assembly90, the sprinkler100can be designed to operate in such a manner as to reduce the precipitation rate over a wide range to a desired level through cycling of the water flow to the riser102.

By way of example, in a model constructed by employing a pressure compensating emitter manufactured by Rain Bird Corporation, under its model Number XB-05 having a one-half gallon per hour flow rate for the first flow control device92, and an orifice plate132having an orifice133of approximately one sixteenth of an inch in diameter for the second flow control device91, with a one half inch diameter piston106having a stroke of approximately one half inch, a ratio of “on” to “off” of one to three was obtained. That is, with the set parameters, the flow of water to the riser102was permitted for approximately one second, and the flow was stopped for approximately three seconds. Thus, the precipitation rate of the sprinkler100was reduced to one quarter of its normal level with out the present invention.

FIGS. 5 through 8illustrate another embodiment of the present invention wherein the first and second flow control devices92′ and91′, respectively, are disposed to both lie along the centerline of the piston and cylinder assembly90′, as opposed to side-by-side as in the embodiment of FIG.2. In this instance, as shown by the arrows inFIG. 5, water from the sprinkler inlet is directed around the piston and cylinder housing94′ through a plurality of circumferentially disposed channels60extending axially around the housing94′ from the bottom end84′ of the housing to a cylindrical cavity127′ above the piston body106′ whereby water from the source can communicate with the cylindrical cavity and act on the piston and valve assembly90′. This construction lends itself to a more compact unit capable of use in a smaller diameter sprinkler casing103′.

As best seen inFIGS. 5 and 8, the first flow control device92′ is attached to and forms the bottom of the cylindrical center bore110′ of piston body106′. Herein, as best seen inFIGS. 5 and 8, the first flow control device92′ is formed by a disc shaped body71having an upwardly closed tortuous path groove70formed in its lower face, and which has an outer annular chamber50leading to an inlet69through which water can enter the groove70. At the center of the body71is an upwardly opening outlet68which leads to an upwardly directed central passage203formed through the center of the piston stem113′. Underlying the disc shaped body71is a free floating rubber diaphragm67, the disc shaped body and the diaphragm being retained in place by a cup-shaped cover66having a peripheral skirt portion65secured around the lower end of the piston body106′, and a horizontally disposed cap portion64including several upstanding ribs63disposed to hold the diaphragm away from the cap portion.

As should be understood to those having some knowledge of flow control devices employing pressure responsive diaphragms pressing against low restricting grooves such as used in the drip irrigation field, the diaphragm67herein has a diameter sufficient to permit water to flow around its periphery and enter inlet69. To permit water from the cylinder110′ to flow through the first flow control device92′, the cap portion64is provided with several through holes62so that water can enter the cover66and flow into the annular chamber50and inlet69of the disc shaped body71. Notably, as is the case with the emitter used in the first embodiment, water pressure within the cylinder110′ caused by the downward movement of the piston body106′ acts on the diaphragm67to press it into the groove70and restrict the cross-sectional size of the groove to thereby form a pressure compensating flow control device. During reverse flow through the flow control92′, however, the ribs63hold the diaphragm67away from the holes62to permit unrestricted flow of water from the chamber203back into the cylinder107.

The second flow control device91′ herein is formed as a metering or restrictive passageway132′ extending centrally from the bottom of the valve stem113″ of the flow stop valve116′ to a centrally disposed flow passage123′ leading upwardly through the valve head135′ to the riser bore126′. In this instance, the restrictive passageway132′ has a cross-sectional diameter sufficient to limit the downward flow of water from the riser bore126′ to the desired level, just as the orifice133of the first embodiment limits flow through the orifice plate132. Like the embodiment ofFIG. 2, the water flowing from the riser126′ downwardly through the flow passage123′ and restrictive passageway133′ is filtered by a filter screen131′, herein disposed in the valve head135′ at the entrance end of the flow passage.

In operation of the embodiment ofFIGS. 5-8, with the flow stop valve116′ in the closed position as shown inFIG. 5, upon initiation of an irrigation cycle, water pressure from the source is admitted to the sprinkler casing inlet101(not shown inFIGS. 5-8) and flows through the plurality of channels60into the chamber127′, thereby applying water pressure to the top of the piston body106′. The application of water pressure to the piston body106′ causes the piston body to move downwardly in the cylinder107′ against the bias of the spring109′, the rate of movement being controlled by the rate at which water from under the piston body can flow through the first flow control device92′ to the riser126′. As the piston body106′ moves downwardly, like the embodiment ofFIG. 2, the lost motion connection between the flow stop valve stem113′ and the piston body allows the piston body to move downwardly as seen inFIG. 6before the flow stop valve116′ is opened to allow unrestricted water flow from the source into the riser. In this instance, the flow stop valve116′ as shown as having valve head135′ that projects into the opening88′ to the riser bore126′, the valve having a pair of integral diameter sealing disks52attached to the valve stem113′ below the valve head and which seal the opening88′ from the chamber127′ when the flow stop valve is in the closed position, as shown in FIG.5.

Herein, as pressure within the chamber127′ initially forces the piston assembly90′ downwardly, like the embodiment ofFIG. 2, the piston body106, moves downwardly while the valve head135′ and stem113′ remain stationary in the flow shut-off mode and valve spring109′ compresses. Upon reaching the limits of the lost motion connection, the valve stem113′ is pulled downwardly with the piston body106′ pulling the valve head135′ downwardly out of sealing engagement with the inlet to the passageway88′ leading to the riser bore126′. Once the valve head135′ begins to open, water pressure and the valve stem spring136′ snaps the valve head to the fully open position shown in FIG.7.

Following the opening of the flow stop valve116′, the water pressure sensed by the piston body106′ both at it upper face and at its lower face inside the cylinder107′ is substantially the same since water pressure inside the riser126′ communicates with the inside of the cylinder through the passage123′ and restrictive passageway132′. Since the pressure across the piston body106′ is substantially the same, the piston body begins to move upwardly within the cylinder107′ under the force of the cylinder spring109′. The rate of upward movement of the piston body106′ is controlled by the rate at which water can flow from the riser126′ through the restrictive passageway132′ so that a finite and controlled time is required for the piston and valve assembly90′ to return to the position shown inFIG. 5with the flow of water to the riser126′ shut off. As previously noted in connection with the embodiment ofFIG. 2, through proper selection of the size of the elements of the piston and valve assembly90′, including the cylinder and valve springs109′ and136′, together with the flow rates of the first and second flow control devices,92′ and91′, respectively, the cycle time for maintaining the flow stop valve116′ in the opened and the closed positions can be accurately controlled during an irrigation cycle, thereby allowing the precipitation rate of the overall sprinkler10to be reduced to a desired level relative to the same sprinkler operating on a continuous basis.

From the foregoing, it should be apparent that the present invention provides a new and improved method of reducing the precipitation rate of a spray type irrigation sprinkler without affecting the supply of water during an irrigation cycle. Moreover, the apparatus of the present invention is relatively simple in design and reliable in use , and provides a very accurate means for reducing the precipitation rate of a sprinkler to virtually any desired level. In this connection, while the first flow control device has been described herein in connection with the use of a conventional pressure compensating drip emitter type device, those skilled in the art will appreciate that other types of flow control devices may be suitable for use in performing the flow control function described herein. Further, while the second flow control device has been described herein as having the form of a controlled size orifice or passage, it should be apparent that other forms of flow control could be substituted for the presently preferred structure disclosed herein with out departing from the spirit and scope of the present invention. Similarly, it will be appreciated that various other modifications and changes can be made without departing from the spirit and scope of the present invention.