Abstract:
An apparatus for changing a length of a pipe, the pipe including first and second pipe portions each having an interior, includes a cylinder having a first end wall and an open end, the cylinder being connectable to the first pipe portion. The apparatus also includes a piston having a second end wall, the piston being receivable in slidable and sealable engagement with the cylinder, the piston being connectable to the second pipe portion, wherein the cylinder and the second end wall define a chamber physically isolated from the interiors of the first and second pipe portions, the chamber being adapted to receive a control fluid for displacing the piston relative to the cylinder to vary a distance between the first and second pipe portions while permitting fluid communication between the first and second pipe portions, the chamber including a cushioning region in communication with the chamber.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of Invention 
         [0002]    This invention relates generally to adjusting the length of a pipe, and more particularly, to an apparatus for adjusting the height of a sprinkler head riser. 
         [0003]    2. Description of Related Art 
         [0004]    In golf courses, lawns, and other grass covered areas, frequent watering is required to maintain the area in an esthetically pleasing and healthy condition. It is well known in the art that a network of distributed pipes and sprinkler head attachments may be provided underneath the surface of the ground to provide the required watering. Such an underground system is not visible when not in use, and does not require set up for each watering, but merely requires activation. 
         [0005]    In the field of golf course design, in-ground sprinkler heads and their associated network of piping are common. The use of in-ground sprinkler systems in golf courses, however, presents unique design requirements due to the nature of the game of golf which is played around such sprinkler heads. 
         [0006]    For example, the top surface of the sprinkler head should preferably be as level with the surrounding ground as possible. Should the sprinkler head extend above the surface of the surrounding ground, it may pose a hindrance or obstruction to any golf ball which may come into contact or close proximity to the sprinkler head. Conversely, should the sprinkler head be at a position below the surface of the surrounding ground, the sprinkler head may create a depression in the playing surface of the golf course with the result that golf balls tend to roll into such a depression. Therefore, should the top surface of the sprinkler head assembly not be flush with the surrounding ground, the sprinkler may serve to reduce the enjoyment of the golf players, due to the above-mentioned hindrances, thereby reducing the desirability of the course. 
         [0007]    Also, a frequent activity of golf course maintenance is to distribute sand or other soil material across the top surface of the golf course. This addition of soil to the golf course may serve to reduce the height of the top surface of the sprinkler head relative to the surrounding ground as the additional soil is added. Therefore, it is frequently necessary to increase the height of the sprinkler head relative to the distribution piping network so as to maintain the top surface of the sprinkler head flush with the surrounding ground. In some arrangements, this activity may require excavation of the sprinklers so as to adjust the height of the sprinkler head relative to the water supply lines. This is commonly accomplished by adjusting the angle of a conventional swing joint. It will be appreciated that such an activity of excavating and adjusting the height of each individual sprinkler head on a golf course is a time consuming and expensive activity. This periodic excavation of the sprinkler heads, also serves to render the immediate vicinity around the sprinkler head unplayable for a certain period of time while the necessary adjustments are being made. 
         [0008]    In addition, any grassy surface such as a golf course is required to be cut periodically through the use of a mower. On a property such as a golf course, such a mower may be a large piece of equipment having a substantial weight. During the process of mowing the golf course, the wheels of such a mower may ride over top of a sprinkler in the ground. This will transfer the large weight of mower to the sprinkler head and any equipment under it for a short period of time. The weight from mowers, or from other equipment or other heavy objects, may cause damage (such as a crack or another source of a leak, for example) to the sprinkler head, or to a pipe for supplying water to the sprinkler head. This damage may require repair, and may cause water to leak and be wasted. Also, leaking water may cause damage to surrounding terrain. 
         [0009]    Many previous arrangements require the sprinkler head riser assembly to be excavated to access the adjusting means which is buried. In addition, many previous attempts have relied upon threading or ridges between a pair of telescoping bodies to adjust a height of a sprinkler head. These attempts have relied on a fixed structure to extend the riser assembly and resist the compressive forces of the mower. Disadvantageously, such mechanisms may become damaged and jammed should the applied weight of the mower become too great. In addition, such mechanisms have a tendency to become jammed by the inclusion of dirt and other contaminants. 
         [0010]    Other previous attempts have relied upon a biasing element securing a connection between two telescoping members. These mechanisms rely on a frictional or non-returning engagement between the biasing element and the telescoping members to secure relative position between them. These mechanisms have the disadvantage of not enabling the height of the sprinkler head to return to a set position after been forcibly compressed, for example, by the weight of a mower. 
       SUMMARY OF THE INVENTION 
       [0011]    In accordance with one aspect, there is provided an apparatus for changing a length of a pipe, the pipe including first and second pipe portions each having an interior. The apparatus includes a cylinder having a first end wall and an open end, the cylinder being connectable to the first pipe portion. The apparatus also includes a piston having a second end wall, the piston being receivable in slidable and sealable engagement with the cylinder, the piston being connectable to the second pipe portion, wherein the cylinder and the second end wall define a chamber physically isolated from the interiors of the first and second pipe portions, the chamber being adapted to receive a control fluid for displacing the piston relative to the cylinder to vary a distance between the first and second pipe portions while permitting fluid communication between the first and second pipe portions, the chamber including a cushioning region in communication with the chamber. 
         [0012]    The cushioning region may include at least one groove formed in at least one wall of the chamber to increase the volume of the chamber. 
         [0013]    The cushioning region may include an annular recess in the second end wall. 
         [0014]    Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    In drawings which illustrate embodiments of the invention, 
           [0016]      FIG. 1  is a side view of an in-ground sprinkler head installation according to a first embodiment of the invention. 
           [0017]      FIG. 2  is a cross-sectional view of a sprinkler head riser apparatus according to a first embodiment of the invention. 
           [0018]      FIG. 3  is a cross sectional view of the cylinder portion of the sprinkler head riser apparatus of  FIG. 2 . 
           [0019]      FIG. 4  is a cross sectional view of the piston portion of the sprinkler head riser apparatus of  FIG. 2 . 
           [0020]      FIG. 5  is a cross sectional view of the guard ring of the sprinkler head riser apparatus of  FIG. 2 . 
           [0021]      FIG. 6  is a cross-sectional view of a sprinkler head riser apparatus according to a second embodiment of the invention. 
           [0022]      FIG. 7  is a cross sectional view of the cylinder portion of the sprinkler head riser apparatus of  FIG. 6 . 
           [0023]      FIG. 8  is a cross sectional view of the piston portion of the sprinkler head riser apparatus of  FIG. 6 . 
           [0024]      FIG. 9  is a cross sectional view of the guard ring of the sprinkler head riser apparatus of  FIG. 6 . 
           [0025]      FIG. 10  is a cross-sectional view of a sprinkler head riser apparatus according to a third embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
       [0026]    Referring to  FIG. 1 , an in-ground sprinkler system including an adjustable sprinkler head riser assembly  14  according to a first embodiment of the present invention is shown generally at  10 . The in-ground sprinkler system comprises a sprinkler head assembly  12 , an sprinkler head riser assembly  14 , a swing joint  16  and a water supply pipe  18 . The sprinkler head assembly  12 , swing joint  16  and water supply pipe  18  are conventional in the art. 
         [0027]    The swing joint  16  comprises a tubular body having first and second pivotable joints that enables the height of the sprinkler head to be adjusted during installation by pivoting the swing arm assembly about the pivot connected to the water supply main. The adjustable sprinkler head riser assembly  14  may be threadably attached to the swing joint  16 . The sprinkler head assembly  12  may be threadably attached to the sprinkler head riser assembly. Accordingly, the swing joint  16  and sprinkler head riser assembly  14  form a continuous water conduit path between the water supply pipe  18  and the sprinkler head assembly  12 . 
         [0028]    In a conventional in-ground sprinkler system, the height of the sprinkler head may be adjusted at the time of installation by means of the swing joint  16 . According to the present invention, the height of the sprinkler head may additionally be adjusted after installation by means of the adjustable sprinkler head riser assembly  14 . It will be appreciated that although the current embodiment of the present invention includes a swing joint  16 , such an assembly may not be necessary and the sprinkler head riser assembly  14  may be connected directly to the water supply pipe  18 . 
         [0029]    Referring to  FIG. 2 , a cross-sectional view of an assembled adjustable sprinkler head riser assembly  14  in accordance with the first embodiment of the invention is shown. The sprinkler head riser assembly  14  comprises a substantially elongate extendible tubular body having first and second opposite ends  20  and  22  respectively. The sprinkler head riser assembly  14  comprises a cylinder portion  30 , a piston portion  80 , and a guard ring  120 . 
         [0030]    Referring to  FIG. 3 , a detail cross-sectional view of the cylinder portion of the first embodiment is shown generally at  30 . The cylinder portion  30  is comprised of an elongated cylindrical first pipe portion  32  surrounded by an outer tubular shell  34 . An end wall  36  connects shell  34  to pipe portion  32 . The first pipe portion  32  comprises an elongated cylindrical body having an axis  38  and includes the first end  20  of the sprinkler head riser assembly  14 . The first pipe portion  32  also includes an outer surface  42 , an inner surface  40  forming a bore  41  therethrough, and external threading  44  at the first end  20 . It will be appreciated that although external threading  44  is shown in the attached figures, other methods also be used to connect the sprinkler head riser assembly  14  to the sprinkler head assembly  12 . Such alternative connection means may include but are not limited to, connecting the sprinkler head riser assembly to the sprinkler head assembly by means of glue, solder, or a compression fitting. In addition internal threading on the cylinder portion may connect to external threading on the sprinkler head assembly. The first pipe portion  32  may also include one or more internal grooves  46  in the inner surface  40  at a second end  48  each adapted to receive an O-ring  50 . 
         [0031]    The shell  34  comprises an elongated cylindrical body co-axially aligned with the first pipe portion  32  about axis  38 . The shell  34  includes an inner surface  52  and an outer surface  54 . The outer surface  54  may include external threading  56  and a set screw hole  58 . 
         [0032]    The end wall  36  comprises an annular disc having a substantially planar shape between first and second radii defining inner and outer edges  60  and  62 , respectively. End wall  36  may be perpendicular to the axis  38  and includes an inner surface  64  and an outer surface  66 . The end wall is connected at its inner edge to the first pipe portion  32  and at its outer edge to the shell  34 . The outer surface  42  of the pipe portion  32 , the inner surface  52  of the shell  34  and the inner surface  64  of the end wall  36  define an annular cavity  68  having an open lower end  70 . The end wall  36  may also include a bore  72  therethrough so as to permit the introduction of a control fluid into the cavity  68 . The bore  72  may be threaded to accept a correspondingly threaded first fluid control supply tube ( 140  in  FIG. 1 ). 
         [0033]    Referring to  FIG. 4 , a cross-sectional view of the piston portion  80  of the first embodiment is shown. The piston body comprises a second pipe portion  82  surrounded by an annular piston  84 . The second pipe portion  82  comprises an elongate tubular body having a free first end  86 . The opposite end of the second pipe portion merges with the piston  84  to define the second end  22  of the sprinkler head riser assembly  14 . The second pipe portion  82  includes an outer surface  94  and an inner surface  96  defining a bore  98  therethrough. Bore  98  adjacent second end  22  may include internal threading  88 . It will be appreciated that although internal threading  88  is shown in the attached figures, other methods may also be used to connect the sprinkler head riser assembly to the swing joint  16  or water supply pipe  18 . Such alternative connection means may include but are not limited to, connecting the sprinkler head riser assembly to the sprinkler head assembly by means of glue, solder, or a compression fitting. In addition external threading on the piston portion may connect to internal threading on the sprinkler head assembly. 
         [0034]    The piston  84  comprises a piston head  100  and a connecting portion  102 . The piston head  100  comprises an annular body aligned with axis  38 . The piston head  100  has an annular outer surface  104 , an annular inner surface  106 , and a generally disk-shaped end surface  108 . The outer surface  104  may include a circular groove  110  adapted to receive an outer O-ring  112 . The piston head  100  is connected to the second end  22  by piston connecting portion  102 . Piston connecting portion  102  consists of an elongated tubular body extending between the piston head  100  and the second end  22 . Piston connecting portion  102  also includes an outer cylindrical surface  118  having a central axis co-axial with axis  38 . Preferably, the end surface  108  is not flat, but rather defines at least one recess and/or at least one projection, for defining a cushioning region. In the illustrated embodiment, the end surface  108  defines an annular recess  134  (which may also be termed an “annular groove”). 
         [0035]    Referring to  FIG. 5 , a cross-sectional view of the guard ring  120  of the first embodiment is shown. The guard ring  120  comprises an annular ring  122  having an axis common with axis  38 , and an internal lower flange  124 . The internal flange has an inner edge  126  which defines an opening  128 . The opening  128  has a radius matched to the radius of the outer cylindrical surface  118  of the piston connecting portion  102 . The guard ring  120  also includes internal threading  130  operable to engage the threading  56  on the cylinder body, and a set screw hole  132 . 
         [0036]    As shown in  FIG. 2 , piston portion  80  is received within cylinder portion  30  such that the piston  84  is received in slidable and sealable engagement within the cavity  68 , and the second pipe portion  82  is received within the first pipe portion  32 . All parts are co-axially aligned with common axis  38 . The piston  84  is received within the cavity  68  such that outer surface  104  slidably engages with inner surface  52  of the shell  34  and the inner surface  106  slidably engages with outer surface  42  of the first pipe portion  32 . O-ring  112  preferably serves to seal the connection between the piston and the cylinder. As assembled in this manner, a first sealed control chamber  74  is formed between the cylinder and the piston head  100 . Specifically, inner surface  52  of shell  34 , outer surface  42  of the first pipe portion  32 , inner surface  64  of end wall  36 , and end surface  108  of the piston head  100  form the first sealed control chamber  74 . The first sealed control chamber  74  has a volume, which changes as the piston  84  is displaced within the cylinder along axis  38 . 
         [0037]    Guard ring  120  may then be secured to the external threading  56  on the shell  34  so as to enclose the bottom end of the cylinder. When the guard ring  120  is secured to the shell, the opening  128  of the guard ring may closely engage upon the outer cylindrical surface  118  of the piston connecting portion  102  so as to prevent the fouling of the riser apparatus by its surrounding soil, water and other contaminants. The guard ring  120  may also be secured to the shell by means of a set screw being passed through set screw hole  132  of the guard ring and set screw hole  58  of the shell. In addition, it will be appreciated that set screw hole  58  or an additional hole in the shell may be used as a relief port to the cylinder when the sprinkler head riser assembly is extended. The set screw hole may be contained within the guard ring  120  or may optionally include an expellable plug that may be displaced under a predetermined pressure in the cylinder so as to relieve the pressure in the cylinder. 
         [0038]    It will be appreciated that the cylinder and piston arrangement as described above is not necessarily limited to an annular arrangement. Other cylinder and piston arrangements may be used in addition to those specifically discussed above to achieve the same result. Specifically, the cylinder and piston may have a circular shape and be disposed adjacent to the first and second pipe portions  32  and  82  respectively. In such an arrangement, the adjacent cylinder may be connected to the first pipe portion  32  and the enclosed piston connected to the second pipe portion  82 . In addition, the apparatus may comprise a plurality of cylinders and associated pistons disposed around the first and second pipe portions. Such a plurality of cylinders and pistons may be arranged in an irregular or regular-radial peripheral array pattern around the first and second pipe portions  32  and  82  respectively. It will also be appreciated that in other embodiments, the first and second pipe portions  32  and  82  respectively need not be in axial alignment. 
         [0039]    The sprinkler head riser assembly  14  according to the first embodiment may be installed as part of an underground sprinkler system as shown in  FIG. 1 . The underground sprinkler system may comprise a water supply pipe  18 , a swing joint  16 , and a sprinkler head assembly  12 . Water is supplied to the system by the water supply pipe  18 . This water is passed through the swing joint  16  and into the bore  98  at the second end  22  of the sprinkler head riser assembly  14 . The water then passes through the bore  41  to the first end  20  and thereafter into the sprinkler head assembly  12 . 
         [0040]    Referring to  FIGS. 1 and 2 , a first control fluid supply tube  140  may be connected to the bore  72  in the sprinkler head riser apparatus. The first control fluid supply tube  140  comprises an elongated tube connectable to bore  72  to communicate the first sealed control chamber  74  with a control fluid source. The first control fluid supply tube includes a free end  144  disposed adjacent to the top surface  146  of the sprinkler head. The first control fluid supply tube may be free floating or secured to the sprinkler head assembly for the majority of its length. The first control fluid supply tube may also be incorporated into the sprinkler head assembly. 
         [0041]    In operation, a user may connect a fluid source and pump (not shown) to the free end  144  of the first control fluid supply tube  140  as shown in  FIG. 1 . The pump is operable to supply a control fluid under pressure to the first control fluid supply tube  140 . The first control fluid supply tube  140  then supplies the fluid through its second end  142  which is connected to the bore  72  in the sprinkler head riser assembly. 
         [0042]    In such a manner, the user may increase or decrease the amount of control fluid in the first sealed control chamber  74 . Varying the amount of control fluid within the first sealed control chamber  74  will serve to displace the piston  84  relative to the cylinder  30 . As the piston  84  is displaced relative to the cylinder  30 , the distance between the first and second ends  20  and  22 , respectively, of the sprinkler head riser assembly  14  is varied. 
         [0043]    The control fluid may include but is not limited to hydraulic fluid, water or any other suitable fluid. It will be preferable to use a control fluid that is an environmentally safe, viscous fluid. Examples of such fluids may include vegetable and grain based oils and greases as well as environmentally safe anti-freeze solutions. In addition, water may be used as a control fluid in locations where there is no risk of freezing. 
         [0044]    Alternatively, a compressible control fluid, such as air, for example, may be desirable so that forces exerted on the top surface  146  of the sprinkler head by a mower wheel, or by any other heavy object, may be absorbed by compression of the compressible control fluid in the first sealed control chamber  74 . It will be appreciated that the control fluid in the first sealed control chamber  74  may also include a combination of fluids, such as air and water, for example. 
         [0045]    Accordingly, the height of the top surface  146  of the sprinkler head assembly may be adjusted relative to the water supply pipe  18  from which it is supplied. In this way, the user may adjust the height of the sprinkler head relative to the surrounding ground to account for changes in settling soil as well as the addition of additional soil over time to maintain the top surface  146  of the sprinkler head at a desired height. 
         [0046]    When force exerted by a mower wheel, or by any other heavy object, is absorbed by compression of a compressible control fluid in the first sealed control chamber  74 , a resulting transmitted force exerted by the adjustable sprinkler head riser assembly  14  on the water supply pipe  18  may be reduced or eliminated, and thus risk of damage to the water supply pipe  18  from mower wheels or other heavy objects may advantageously be reduced. Furthermore, when force is absorbed by compression of the control fluid in the first sealed control chamber  74 , the swing joint  16  may not be required to absorb such forces. Instead, the adjustable sprinkler head riser assembly  14  may be coupled directly to the water supply pipe  18 , for example, which may advantageously reduce cost of the system  10 . 
         [0047]    Preferably, the control fluid that is introduced into the first sealed control chamber  74  can enter a cushioning region that is defined by the end surface  108  and in communication with the first sealed control chamber  74 , such as the annular recess  134 , for example. Therefore, when the control fluid in the first sealed control chamber  74  includes a compressible control fluid, and when a mower wheel or another heavy object exerts a force on the top surface  146  of the sprinkler head, for example, the annular recess  134  (or any other cushioning region that is defined by the end surface  108 ) may receive a portion of the control fluid in the first sealed control chamber  74 . Thus, the annular recess  134  may advantageously enable a greater absorption of a force that is exerted on the top surface  146  of the sprinkler head by a mower wheel, or by any other heavy object, for example. 
         [0048]    It will be appreciated that the end surface  108  may define a cushioning region other than the annular recess  134 , and may also define a plurality of cushioning regions. For example, the end surface  108  may define one or more bores, grooves, channels, and/or other cavities of various configurations. Alternatively, the end surface  108  may define one or more projections to define a cushioning region when the one or more projections abut a portion of the inner surface  64 . More generally, any non-flat end surface  108  may define one or more cushioning regions for receiving control fluid in the first sealed control chamber  74 , to enable a greater absorption of a force exerted on the top surface  146  of the sprinkler head by the control fluid. Furthermore, in alternative embodiments, a cushioning region may additionally or alternatively be defined elsewhere in the first sealed control chamber  74 , such as by the inner surface  64 , for example. 
         [0049]    It will further be appreciated that although as described above, the sprinkler head riser assembly  14  and the sprinkler head assembly  12  are described as separate components, the sprinkler head riser apparatus may be formed including the sprinkler head assembly. According to such an embodiment, the sprinkler head will be formed as continuous with the first pipe portion. In such an alternative embodiment, the fluid may be supplied to the first sealed control chamber  74  through a supply tube internal to the sprinkler head. In some such alternative embodiments the end wall  36  may be disposed close to the to surface of the sprinkler head and therefore the fluid source and pump may be connected directly to the bore  72 . 
       Second Embodiment 
       [0050]    Referring to  FIG. 6 , a cross-sectional view of an assembled adjustable sprinkler head riser apparatus in accordance with a second embodiment of the invention is shown generally at  200 . The sprinkler head riser apparatus  200  includes a cylinder portion  210 , a piston portion  240 , and a guard ring  280 . 
         [0051]    Referring to  FIG. 7 , a detail cross-sectional view of the cylinder portion of the second embodiment is shown generally at  210 . The cylinder portion  210  includes an elongated cylindrical first pipe portion  212  surrounded by an outer tubular shell  218 . An end wall  220  connects the outer tubular shell  218  to the first pipe portion  212 . The first pipe portion  212  includes an outer surface  214  and an inner surface  216 , defining a bore  217  therethrough. The first pipe portion  212  also includes external threading  222  operably configured for coupling the cylinder portion  210  to the sprinkler head assembly  12  ( FIG. 1 ). However, it will be appreciated that other methods, such as glue, solder, a compression fitting, or internal threading, may be used for coupling the cylinder portion  210  to the sprinkler head assembly  12 . 
         [0052]    The first pipe portion  212  includes one or more grooves  224  in the outer surface  214 , each operably configured to receive an O-ring  226 . It has been found that in some manufacturing processes, it is easier to create the grooves  224  in the outer surface  214  of the first pipe portion  212  than it is to create internal grooves  46  in the inner surface  40  of the first pipe portion  32  of the first embodiment. It has also been found that in some manufacturing processes, it is easier to create the grooves  224  in the outer surface  214  of the first pipe portion  212  if the grooves  224  are made on a portion of the first pipe portion  212  that extends farther from the end wall  220  than the outer tubular shell  218 , as shown in  FIG. 7 . 
         [0053]    The outer tubular shell  218  includes an elongated cylindrical body having an inner surface  228 , an outer surface  230 , and external threading  232 . In the second embodiment, the outer tubular shell  218  does not include a set screw hole  58 . The end wall  220  includes an inner surface  221  and a bore  236 , and is substantially similar to the end wall  36  of the first embodiment. The outer surface  214  of the first pipe portion  212 , the inner surface  228  of the outer tubular shell  218 , and the inner surface  221  of the end wall  220  define a cavity  234 . 
         [0054]    Referring to  FIG. 8 , a cross-sectional view of the piston portion of the second embodiment is shown generally at  240 . The piston portion  240  includes a second pipe portion  242  coupled to an annular piston  250 . The second pipe portion  240  includes an inner surface  244  defining a bore  248  therethrough. The inner surface  244  includes internal threading  246  operably configured for coupling the piston portion  240  to the swing joint  16  or to the water supply pipe  18  ( FIG. 1 ). It will be appreciated that other methods, such as glue, solder, a compression fitting, or external threading, may be used for coupling the piston portion  240  to the swing joint  16  or to the water supply pipe  18 . 
         [0055]    In the second embodiment, the second pipe portion  242  does not extend substantially along the length of the annular piston  250 . It has been found that in some manufacturing processes, manufacturing the piston portion  240  is easier than manufacturing a piston portion wherein the second pipe portion extends substantially along the length of the annular piston. 
         [0056]    In the second embodiment, the annular piston  250  includes an annular outer surface  251 , an annular inner surface  252 , and a piston head  254 . The piston head  254  includes an annular outer surface  256  and a generally disk-shaped end surface  258 . The outer surface  256  includes a circular groove  260  operably configured for receiving an outer O-ring  262 , and the inner surface  252  includes a circular groove  264  operably configured for receiving an inner O-ring  266 . However, in other embodiments, the circular grooves  260  and  264  and the O-rings  262  and  266  may be omitted. In particular, the circular groove  264  and the O-ring  266  may be omitted because sealing between the outer surface  214  and the annular inner surface  252  is provided by the O-ring  226  described above. 
         [0057]    Preferably, the end surface  258  is not flat, but rather defines at least one recess and/or at least one projection, for defining a cushioning region, as described above with respect to the end surface  108  of the first embodiment. In the illustrated embodiment, the end surface  258  defines an annular recess  299  (which may also be termed an “annular groove”), but the annular recess or groove  299  is illustrated by way of example only. As described above with respect to the end surface  108  of the first embodiment, any non-flat end surface  258 , or any other surface defining the first fluid chamber  297  shown in  FIG. 6 , may define one or more cushioning regions for receiving control fluid. 
         [0058]    Referring to  FIG. 9 , a cross-sectional view of the guard ring of the second embodiment is shown generally at  280 . The guard ring  280  includes an annular ring  282 , and an internal lower flange  284 . The internal lower flange  284  has an inner edge  286  that defines an opening  288  having a suitable radius for the annular piston  250  ( FIG. 8 ) to pass therethrough such that the annular outer surface  251  may be in slidable and sealable engagement with the inner edge  286 . The inner edge  286  includes a circular groove  290  operably configured for receiving an O-ring  292 . The guard ring  280  also includes internal threading  294  operably configured for engaging the external threading  232  of the cylinder portion  210  ( FIG. 7 ), but it will be appreciated that other methods, such as glue or solder, may be used for coupling the cylinder portion  210  to the guard ring  280 . In the second embodiment, the guard ring  280  does not include a set screw hole  132 . However, in the second embodiment, the guard ring  280  includes a bore  296  therethrough. 
         [0059]    Referring back to  FIG. 6 , the annular piston  250  of the piston portion  240  is received within the cavity  234  of the cylinder portion  210  such that the outer O-ring  262  and the annular outer surface  256  of the piston head  254  are in slidable and sealable engagement with the inner surface  228  of the outer tubular shell  218 , and the inner O-ring  266  and the annular inner surface  252  of the annular piston  250  are in slidable and sealable engagement with the O-ring  226  and the outer surface  214  of the first pipe portion  212 . Thus, a first sealed control fluid chamber  297  is formed between the piston head  254  and the end wall  220 , and the bores  217  and  248  form a continuous sealed water passage through the sprinkler head riser apparatus  200 . The guard ring  280  may be coupled to the cylinder portion  210  such that the annular outer surface  251  of the annular piston  250  is in slidable and sealable engagement with the O-ring  292  and the inner edge  286  of the internal lower flange  284  of the guard ring  280 . Although the first and second pipe portions  212  and  242  respectively are shown in axial alignment, it will be appreciated that the first and second pipe portions need not be in axial alignment. 
         [0060]    The result of this assembly, and the operation of the sprinkler head riser apparatus  200 , are substantially as described above with reference to the first embodiment. However, in the second embodiment, the annular piston  250 , the outer tubular shell  218 , and the guard ring  280  define a second sealed control fluid chamber  298 . A second fluid control supply tube (not shown) may be coupled to the bore  296 , so that a user may supply a control fluid under pressure to the second sealed control fluid chamber  298 . Thus, in the second embodiment, a user may supply a control fluid under pressure independently through the bores  236  and  296  to “double acting” control fluid chambers  297  and  298  respectively, thereby exerting complementary forces on the piston portion  240  relative to the cylinder portion  210 . 
       Third Embodiment 
       [0061]    Referring to  FIG. 10 , a sprinkler head riser apparatus in accordance with a third embodiment of the invention is shown generally at  300 . The sprinkler head riser apparatus  300  includes a cylinder portion  302 , a piston portion  304 , and a guard ring  310 . The piston portion  304  includes a piston head  306 , and the piston head  306  includes a disk-shaped lower surface  308 . The guard ring  310  includes an internal lower flange  312 . The sprinkler head riser apparatus  300  includes the elements of the first embodiment or the second embodiment, and further includes a spring  310  for urging the annular lower surface  308  away from the internal lower flange  312 . The spring  310  may advantageously resist a potential tendency for water pressure in the sealed water passage to urge the annular lower surface  308  towards the internal lower flange  312 . However, in other embodiments, the spring  310  may urge the annular lower surface  308  towards the internal lower flange  312 . 
         [0062]    Preferably, the piston head  306  has an end surface  316  that is not flat, but rather defines at least one recess and/or at least one projection, for defining a cushioning region, as described above with respect to the end surface  108  of the first embodiment. In the illustrated embodiment, the end surface  316  defines an annular recess  318  (which may also be termed an “annular groove”), but the annular recess or groove  318  is illustrated by way of example only. As described above with respect to the end surface  108  of the first embodiment, any non-flat end surface  316  or other surface may define one or more cushioning regions for receiving control fluid. 
         [0063]    While specific embodiments of the invention have been described and illustrated, such embodiments should be considered illustrative of the invention only and not as limiting the invention as construed in accordance with the accompanying claims.