Patent Publication Number: US-2019175968-A1

Title: Sprinkler head adapter

Description:
PRIORITY 
     The present application is an international application claiming the benefit of priority to U.S. Provisional Application No. 62/348,624 filed on Jun. 10, 2016, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Pipe fittings used in the installation of fire protection sprinklers are well known. Generally, fire protection sprinklers or sprinkler heads include a sprinkler frame body with an inlet end having an external pipe thread for forming a threaded pipe connection with a supply pipe of firefighting fluid, such as for example, water and an outlet end for discharging the fluid to address a fire. The pipe thread on most sprinklers are tapered pipe threads in accordance with an accepted pipe thread standard such as, for example, National Pipe Thread Taper (NPT)-ANSI/ASME B1.20.1,“Pipe Threads, General Purpose, Inch.” For proper sprinkler installation, it is necessary for the sprinkler and its external pipe thread to form a fluid tight seal. Moreover, for many sprinklers, the sprinkler must be properly oriented with respect to the supply piping. Many fire protection sprinklers include operational components which distribute the firefighting fluid. These components includes a deflector member that is spaced from the outlet of the sprinkler body to distribute the firefighting fluid in a spray pattern based upon the fluid discharge from the outlet. The deflector member may be supported by frame arms formed integrally with the sprinkler frame body. In order for the sprinkler to distribute the water in a desired manner, it is often necessary to orient the deflector member and/or the frame arms with respect to the supply pipe. One problem that may arise in orienting the sprinkler into position is that it can compromise the fluid tight engagement at the sprinkler thread connection. The sprinkler may be over-torqued, which can damage the sprinkler threads or the sprinkler and thereby compromise the fluid tight connection. Alternatively, the sprinkler can be under-torqued which can result in an improper seal at the threaded connection. 
     Prior sprinkler fittings have been described to address these problems. For example, U.S. Pat. No. 8,297,663 describes a fire sprinkler fitting to install a fire protection sprinkler. The described fitting includes an open end upstream end through which fluid can flow to a downstream end having an internal thread for receiving a fire sprinkler. The internal thread is described as NPT thread conforming to ASTM standard F1498 with “the pitch diameter is at the end to oversize.” The U.S. Pat. No. 8,297,663 Patent describes that in operation, the sprinkler can be rotated for up to 360° into its proper installed orientation after forming a fluid tight seal. To form the fluid tight seal, the sprinkler end engages and compresses a gasket within an internal “gasket retention area” of the fitting having a “flat gasket retention area base surface” upstream of the internal threads. According to the patent and its figures, the sprinkler compresses the gasket “so as to laterally distort the gasket inwardly.” It is believed that this distortion alters the flow characteristics through the fitting from the uncompressed to the compressed state of the gasket. This alteration in flow characteristics can negatively impact the expected flow and spray pattern characteristics from the sprinkler. 
     U.S. Pat. No. 8,297,663 describes that the sprinkler fitting can be constructed from a cross-linked polyethylene material; and U.S. Pat. No. 5,437,481 describes another sprinkler fitting in the form of a coupling made from polyvinyl chloride (PVC) or chlorinated polyvinyl chloride (CPVC). In the Background Section of U.S. Pat. 5,437,481, a problem is described with pipe fitting made of plastic and in particular, internal or female plastic threaded fittings. These plastic fitting experienced failure when metal threaded elements are threaded into the plastic female threaded fitting when excessive torque is applied. To address this problem, U.S. Pat. No. 5,437,481 describes a coupling having a metal connection portion in which a metallic internally threaded insert is disposed and disposed about the metal connection portion is a reinforcing collar. Other examples of fittings with metal reinforcements are described in U.S. Pat. 8,297,663 in which polyethylene fitting include metallic thread inserts and in U.S. Pat. 7,017,951 in which a PVC or CPVC pipe fitting includes a compression band disposed over an internally threaded attachment end of the pipe fitting. 
     DISCLOSURE OF INVENTION 
     There remains a need for a plastic sprinkler fitting that can form a sealed threaded engagement with a metal fire protection sprinkler without a metal insert or other reinforcement structure. Preferred embodiments of a sprinkler head adapter or sprinkler adapter and methods of assembly are provided for coupling a fire protection sprinkler to a firefighting fluid supply pipe. The preferred adapter includes a receptacle with an internal thread for engaging the fire protection sprinkler and a gasket chamber for housing a gasket to form a fluid tight seal with the sprinkler without negatively affecting the fluid flow characteristics of the sprinkler. 
     A preferred sprinkler adapter includes a housing having a first end for connection to a firefighting fluid supply pipe, a second end including an internal passageway extending from the first end to the second end. The internal passageway including a receptacle formed at the second end with an internal preferably straight pipe thread for a threaded engagement with a fire protection sprinkler. The internal passageway also preferably includes a gasket chamber between the first end and the internal straight thread. A gasket is disposed in the chamber with a central opening defining an area through which fluid can flow. The gasket chamber has a holding portion and an expansion portion. The holding portion defines a first volume in which the gasket is completely housed in an unloaded state of the gasket, and the expansion portion defines a preferred second volume or pocket for a displaced portion of the gasket in a loaded state of the gasket defined by the threaded engagement between the sprinkler and the internal thread. The housing is preferably constructed and configured as a self-supporting monolithic plastic about the internal thread of the receptacle to eliminate any need for a reinforcing collar, insert or other reinforcement structure. 
     In another preferred embodiment, a sprinkler adapter preferably includes a body having a first end portion, a second end portion with a through hole extending from the first end portion to the second end portion along a first central axis. The second end portion has an external thread with an enlarging bore defining a bottom surface formed about the through hole. The adapter also includes a cap having a first end portion, a second end portion, with a through hole extending from the first end portion to the second end portion along a second central axis. The first end portion of the cap has an enlarging bore with a bottom surface formed about the through bore of the cap and an internal thread that is engaged with the external thread of the body. The cap is coupled to the body to coaxially align the first and second central axes such that the bottom surface of the body is opposed to and spaced from the bottom surface of the cap to define bearing surfaces of a preferred gasket chamber. An annular gasket is disposed within the gasket chamber. The bottom surface of the cap is planar and perpendicular with respect to the coaxial axes to support the gasket and the bottom surface of the body includes a skewed portion that is skewed with respect to the bottom surface of the cap. 
     A method of coupling a sprinkler to a fluid supply pipe is also provided. The method includes coupling a plastic adapter to the fluid supply pipe and placing a sprinkler into contact with a first surface of an annular gasket housed in an initially unloaded state within an internal gasket chamber of the plastic adapter. The method further includes threading the sprinkler within the adapter to place the gasket in a loaded state with a second surface of the gasket against a bearing surface of the gasket chamber to form a fluid tight seal with an internal diameter or open area of the annular gasket being the same in the loaded state as in the unloaded state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention. 
         FIG. 1  is an exploded perspective view of a preferred sprinkler adapter assembly. 
         FIG. 2A  is a cross-sectional view of the preferred sprinkler adapter in the assembly of  FIG. 1  with a gasket in an unloaded state. 
         FIG. 2B  is a cross-sectional view of the preferred sprinkler adapter in the assembly of  FIG. 1  with a gasket in a loaded state. 
         FIG. 3  is detailed cross-sectional view of a preferred sprinkler adapter for use in the assembly of  FIG. 1   
         FIGS. 4A-4D  are cross-sectional views of alternate embodiments of a sprinkler adapter for use in the assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Shown in  FIG. 1  is an exploded perspective view of a an assembly having a preferred embodiment of a sprinkler adapter  10  for coupling a fire protection sprinkler  200  to a fluid supply line or pipe fitting  300 . Generally, the adapter  10  includes a housing  12  having a first end  14  and inlet  14   a  for connection to the firefighting fluid supply pipe fitting  300  and a second end  16  for connection to the fire protection sprinkler  200 . The first end  14  can be formed as either a female connector as shown, or a male connector  10   a,  as shown in  FIG. 4A , for connecting the adapter  10  to the fluid supply piping  300 . Referring to  FIG. 2A , the housing  12  is a substantially tubular member with an internal passageway  18  extending from the first end  14  to the second end  16  along a central axis A-A. As shown, the adapter  10  is a straight fitting and can be additionally formed as a reducer fitting. Alternatively, the adapter  10  can be formed as an elbow fitting  10   b  as seen, for example, in  FIG. 4B . The internal passageway  18  includes a receptacle  20  formed at the second end  16  with an internal thread  22  for a threaded engagement with the fire protection sprinkler  200 . In use, firefighting fluid flows from the inlet  14   a  at the first end  14  through the receptacle  20  at the second end  16  and to the inlet of the sprinkler  200 . The housing  12  is preferably formed from a plastic material, for example molded BLAZEMASTER® CPVC material from Lubrizol Corporation of Wickliffe, Ohio, and constructed to be self-supporting in its engagement with the fire protection sprinkler. The piping  300  is also preferably of a similar thermoplastic material. As used herein, “self-supporting” means that the housing  12  or its operative portion fully forms a coupled engagement with the sprinkler  200  without a separate support or other component such as, for example, an external metal collar, internal metal insert or other reinforcements structure to resist outward radial tension along the engagement between the sprinkler  200  and the internal thread  22  of the housing. Accordingly, the preferred self-supporting housing  12  is preferably a monolithic plastic about the internal thread  22  from the internal thread to the outer surface of the housing  12 . 
     The housing  12  and its internal passageway  18  includes a gasket chamber  24  preferably located between the first end  14  and the internal thread  22 . The gasket chamber  24  and the receptacle  20  are preferably aligned with one another and centered about the central axis A-A. A gasket  26  is disposed in the gasket chamber  24 . The gasket  26  is preferably an annular member having a central opening or hole through which fluid delivered to the first end  14  can flow. The gasket  26  has an unloaded state and a loaded state within the gasket chamber  24 . More specifically, without a sprinkler  200  in the receptacle  20  or fully engaged in the receptacle  20 , the gasket  26  is in its unloaded state in which the gasket is merely housed within the chamber. In the loaded state, the gasket  26  forms a fluid tight seal with the sprinkler  200  that is advanced into the receptacle  20  to press the gasket  26  against bearing surfaces of the gasket chamber  24 . In addition to providing a fluid tight seal between the gasket  26  and the sprinkler  200 , the loaded interaction between gasket chamber  24  and gasket  26  substantially maintains the discharge and/or rated flow characteristics of the sprinkler  200  as rated by the nominal K-factor of the sprinkler. “K-factor” is a discharge coefficient defined as an average flow of water in gallons per minute through the internal passageway divided by a square root of pressure of water fed into the inlet end of the internal passageway in pounds per square inch gauge: Q=K√P where P represents the pressure of water fed into the inlet end of the internal passageway through the body of the sprinkler, in pounds per square inch gauge (psig); Q represents the flow of water from the outlet end of the internal passageway through the body of the sprinkler, in gallons per minute (gpm); and K represents the nominal K-factor constant in units of gallons per minute divided by the square root of pressure expressed in psig. 
     Referring to  FIGS. 2A and 2B , the receptacle  20  formed at the second end  16  of the housing  12  is preferably formed with an internal straight thread  22 . Generally, the external thread  202  of the sprinkler  200  is of a tapered form, for example, NPT thread. By using female or internal straight threads  22  for receipt of the male or external tapered sprinkler thread  202  of the sprinkler  200 , a proper fluid tight seal can be formed upon a preferably squared contact between the sprinkler  200  and the gasket  26 . Moreover, the straight threads  22  of the adapter facilitate the self-supporting engagement with the sprinkler  200 . Because the female straight thread  22  does not correspondingly taper with the tapering thread  202  of the sprinkler  200 , the dissimilar threaded engagement between the two is limited and does not generate the same outward radial forces as is generated in complimentary engaged tapered threads. Thus, the adapter  10  does not need any additional reinforcement in or about the housing, such as for example, a metal reinforcement insert or an metal collar disposed about the second end  16  of the housing. 
     In addition to the preferred internal straight thread formation  22  of the receptacle  20 , the housing  12  includes a preferred minimum wall thickness WT at the second end  16  of the housing to facilitate the self-supporting function of the adapter. In a preferred embodiment, where the internal thread  22  defines an internal diameter ID of ½ inch (0.5 in.), the second end  16  of the housing  12  defines a preferred minimum width or diameter DW that ranges from 1.4-1.5 inches to define a preferred wall thickness of 0.45-0.5 in. Accordingly, a preferred ratio of housing width-to-receptacle internal diameter (DW:ID) along the receptacle  20  ranges from 2.8:1 to 3:1. The internal diameter ID of the internal straight thread  22  can be defined by any one of the pitch diameter, minor diameter or major diameter of the internal thread  22  provided the straight thread engages the tapered thread of the sprinkler  200 . The internal straight thread can be for example, ½-14 NPS Thread. Although the preferred straight-to-tapered thread engagement with the sprinkler  200  is limited, use of the preferred straight internal thread  22  permits the sprinkler  200  to be infinitely rotatable about the axis A-A within the receptacle  20  while fully loading the gasket  26 . Accordingly, the sprinkler  200  can be rotationally oriented in any desired position to correspondingly orient its deflector or other deflecting structure to effect proper or desired fluid distribution from the sprinkler  200  over the area being protected while maintaining a fluid tight seal with the internally disposed gasket  26 . To further facilitate the engagement between the adapter  10  and the sprinkler  200 , the outer or external surface of the adapter  10  of the receptacle  20  includes a tool engagement surface formed radially about the internal thread  22  for engaging a wrench or other tool for threading about the sprinkler  200 . Given the self-supporting structure of the adapter, the adapter is unitarily plastic in the radial direction from the internal thread  22  to the tool engagement surface. 
     Respectively shown in  FIGS. 2A and 2B  is the adapter  10  with the gasket  26  in the unloaded and loaded states. Referring specifically to  FIG. 2A , the gasket chamber  24  generally has two regions: (i) a holding portion  24   a  and (ii) an expansion portion  24   b.  The holding portion  24   a  preferably defines a first volume in which the gasket is completely housed in the unloaded state of the gasket  26 . Preferably, the volume defined by the holding portion  24   a  is substantially cylindrical for holding the annular shaped gasket  26 . The expansion portion  24   b  of the gasket chamber  24 , defines a second volume for housing a displaced portion of the gasket  26  in the loaded state of the gasket  26 . The expansion portion  24   b  preferably defines an annular void or gap located above or axially adjacent the unloaded gasket  26  for receipt of the displaced gasket portion in a loaded state of the gasket  26 . 
     As seen in the cross-sectional view of  FIG. 3 , the expansion portion  24   b  is more preferably defined as a triangular or wedged-shaped void circumscribed about the central axis A-A. The gasket chamber  24  and its portions  24   a,    24   b  is defined by various gasket bearing surfaces. The housing  12  and its gasket chamber  24  includes a first gasket bearing surface  28 , a second gasket bearing surface  30  spaced from the first bearing surface and an internal wall  32  extending between the first and second bearing surfaces  28 ,  30 . The second gasket bearing surface  30  is preferably a planar surface extending perpendicular to the central axis A-A. The second gasket bearing surface  30  also provides for a base surface upon which the gasket  26  can rest in its unloaded state. More specifically, with the housing  12  disposed with its central axis A-A in a vertical orientation, the gasket  26  rests upon the second gasket bearing surface  30  in the absence of a sprinkler  200  to load the gasket. In cross-section, the first gasket bearing surface  28  preferably includes a skewed portion  28   a  that is skewed with respect to the central axis A-A and a curved or radiused transition or portion  28   b  formed between the skewed portion  28   a  and the internal wall  32 . Accordingly, in the cross-sectional elevation views of the gasket chamber shown in  FIG. 3 , the gasket chamber  24  is preferably non-polygonal. In a preferred embodiment, the skewed portion  28   a,  defines an included angle α with a line perpendicular to the central axis A-A to deform and bear against the gasket  26  in a preferred manner as described herein. In a preferred embodiment, the included angle α measures twenty deggrees (20°) or more and is more preferably 30° or more but can define alternate angles provided that the gasket is deformed and acted upon in a manner as described herein. The internal wall  32  preferably extends parallel to the central axis A-A to define a preferably constant width of the chamber  24 . More preferably, where the internal wall  32  is circumscribed about the central axis A-A, the internal wall defines a preferably constant diameter annular sidewall of the gasket chamber  24 . 
     The first gasket bearing surface  28  is spaced from the second gasket bearing surface  30  to define the height or depth of the gasket chamber  24 . With the first gasket bearing surface  28  having a skewed portion  28   a,  the height of the gasket chamber  24  varies in the radial outward direction from the central axis A-A. At its maximum height, the gasket chamber  24  defines a preferred wall height-to-gasket height or thickness ratio that ranges from 1.2:1 to 1.25:1. For example, for a preferred gasket  26  having a thickness or height  26   h  ranging from 0.225-0.275 inch, the gasket chamber  24  defines a preferred maximum height of 0.275 inch at the internal wall  32 . Accordingly, a preferred gasket height  26   h  in an unloaded state has a maximum height range that is equal to or less than the maximum height of the chamber  24 . A preferred radiused portion  28   b  of the first bearing surface  28  defines a tangent perpendicular to the central axis A-A to define the maximum axial distance or height HMax from the second gasket bearing surface  30  and more preferably measures of 0.275 inches. 
     With the gasket chamber  24  being centered about the central passageway  18 , each of the first and second gasket bearing surfaces  28 ,  30  define a central opening  34 ,  36  sized to maintain the gasket  26  within the chamber  24  and permit a flow through the housing  12  to maintain the discharge characteristics of the sprinkler  200  in a loaded state of the gasket. Each of the central openings  34 ,  36  respectively defined by the first and second gasket bearing surfaces  28 ,  30  is smaller than the outer diameter DiaG 1  of the gasket  26  disposed in the chamber  24 . The central openings  34 ,  36  of the first and second gasket bearing surfaces  28 ,  30  are axially spaced apart and aligned to define the minimum axial distance therebetween and the minimum height of the gasket chamber  24  and is preferably equivalent to the height or thickness of the gasket  26  disposed therein. With the preferred gasket  26  having a central hole  26   o  and more preferably a circular central hole  26   o  having an inner diameter DiaG 2 , the central opening  34  defined by the first gasket bearing surface  28  has a preferred diameter Dia 1  that is preferably greater than the inner diameter DiaG 2  of the gasket  26 . The second bearing gasket surface  30  defines a central opening  36  having a preferred diameter Dia 2  that is also preferably greater than the inner diameter DiaG 2  of the gasket  26  and more preferably also greater than the inner diameter Dial of the central opening of the first gasket bearing surface  28 . The central opening  36  of the second gasket bearing surface  30  is the opening through which a sprinkler  200  engaged with the internal threads can extend to load the gasket  26 . Accordingly, the preferred diameter Dia 2  of the central opening  36  can be, at a minimum, equivalent to the nominal internal diameter ID of the internal thread  22  for receipt of the sprinkler  200 . 
     Referring to  FIG. 2B , the sprinkler  200  loads the gasket  26  and forms a fluid tight seal upon being fully received by or engaged with the internal threads  22  of the receptacle  20 . The formed seal is preferably a fluid tight seal sufficient to withstand a maximum pressure of  2300  psi delivered to the inlet  14   a  of the assembly. More particularly for the threaded engagement between the adapter  10  and the sprinkler  200 , the engagement in combination with the gasket  26  defines a preferred burst pressure ranging between 1000 psi-2300 psi. As shown in  FIG. 2B , the axially loaded gasket  26  bears against the skewed portion  28   a  of the first bearing surface  28 . The gasket  26  deforms and fills the expansion portion  24   b  of the gasket chamber  24 . Because of the preferred configuration of the expansion portion  24   b,  any deformation in the gasket  26  remains out of the fluid flow path of the adapter. More preferably, the central hole or opening  26   o  of the gasket  26  maintains its geometry or area constant from the loaded state to the loaded state without inward distortion under loading so as not to reduce the flow characteristics of the assembly. Thus, where the central opening of the gasket  26  is circular, the inner diameter DiaG 2  of the gasket  26  remains constant from the unloaded state to the loaded state. Thus, despite the loading on the gasket  26 , the assembled adapter  10  and sprinkler  200  maintains the rated flow characteristics of the sprinkler  200  as rated by the nominal K-factor of the sprinkler. 
     In one preferred embodiment, the housing  12  and gasket chamber  24  are sized for housing an annular circular gasket  26  having an outer diameter of DiaG 1  of 0.875 in. and an inner diameter DiaG 2  0.635 in. with a gasket height of 0.225 in. with a gasket height  26   h  preferably ranging from 0.225-0.275 inch. The gasket  26  preferably includes a chamfer  26   ch  along the upper and lower outer edges of each of the gasket  26  preferably specified as 0.02 in.×45°. The internal wall  32  of the chamber  24  defines a preferred internal diameter of 0.9 inches. The central openings  34 ,  36  of the first and second gasket bearing surfaces  28 ,  30  define respective diameters Dia 1 , Dia 2  preferably range between 0.63 in. to 0.85 in and are preferably about 0.65 inch. More preferably, the central opening  36  of the second gasket bearing surface  30  is greater than the central opening  34  of the first gasket bearing surface  28 . 
     The maximum height Hmax of the gasket chamber  24  is preferably 0.275 inches and the minimum height Hmin of the gasket chamber is 0.225. The minimum height Hmin of the chamber  24  is preferably defined by the axial distance between the central openings  34 ,  36  of the first and second gasket bearing surfaces  28 ,  30 . A preferred gasket  26  for use in the assembly has a preferred Durometer hardness ranging from 70 to 100 and more preferably ranges from 75-95 being more preferably one of 86 or 91 and is even more preferably 80. The gasket  26  is preferably made from a polyurethane material such as, for example, P5065A88 Low Temperature Polyurethane . 
     Referring again to  FIG. 3 , the inlet  14   a  of the internal passageway  18  is spaced from the gasket chamber  24  and centered along the central axis A-A. The inlet  14   a  has an inlet opening and an inlet floor  15  having a central opening  15   a.  The central opening  15   a  of the inlet floor defines an area perpendicular to the central axis A-A. The central opening  15   a  of the floor is smaller than the inlet opening such that the fluid passageway  18  decreases in the direction form the inlet to the gasket chamber  24 . Shown in  FIGS. 4C and 4D  are alternate embodiments of the adapter  10   c,    10   d,  in which the central opening  15   a  is sized and formed in any manner to reduce the passageway  18  from the inlet  14   a  to the gasket chamber  24 . Moreover, the axial distance between the inlet floor opening  15   a  and the gasket chamber  24  can be varied to facilitate the connection to the fluid supply piping  300  and provide the desired fluid flow. 
     Referring again to  FIG. 1 , the adapter  10  and its housing  12  are preferably formed by the assembly of two components or members  12   a,    12   b.  The first member  12   a  includes the first gasket bearing surface  28  and the second member  12   b  includes the second gasket bearing surface  30 . The second member  12   b  is coupled to the first member  12   a  such that the first and second gasket bearing surfaces  28 ,  30  are axially spaced apart to form the gasket chamber  24  previously described. As shown, the first and second members  12   a,    12   b  are preferably threaded together. In a preferred embodiment, one end of the first member  12   a  defines the first end  14  of the adapter  10  and includes the inlet  14   a.  At the opposite or second end portion of the first member  12   a  is a narrowed or stepped portion  40  having an external thread  42 . The second member  12   b  includes a bore  44  for receiving the narrowed portion  40  of the first member  12   a  with the bore  44  including an internal thread  46  for engagement with the external thread  42  of the first member  12   a.  In a preferred embodiment, each of the external thread  42  of the first member  12   a  and the internal thread  46  of the bore  44  of the second member are Unified Screw Threads of UN thread form such as, for example, 1¼-16 UN-28 Thread. In one preferred aspect of the loaded state of the assembly  10  and gasket  26 , the gasket bearing surfaces  28  and internal geometry of the chamber  24  define reaction forces directed axially along the threaded engagement between the external and internal threads  42 ,  46 . The internal bore  44  of the second member is preferably coaxially aligned with the receptacle  20  such that the second gasket bearing surface  30  is between the bore  44  and the receptacle  20 . 
     In another preferred aspect, the first and second members  12   a,    12   b  additionally or alternatively include a snap-fit engagement. Referring to  FIG. 3 , the narrowed portion  40  of the first member  12   a  includes a projection  48  and the internal bore  44  includes a groove  50  for receipt of the projection  48 . More preferably, an annular barb or projection  48  is formed distally of the external thread  42  and an internal annular groove  48  is formed at the bottom of the bore  44  distal of the second internal thread  46 . The projection  48  can be continuous about the narrowed portion  40  or alternatively defined by two or more spaced apart barbs. The projection  48  and the groove  50  form a preferred snap fit for coupling and/or securing the first and second members  12   a,    12   b  to one another. Accordingly, in one preferred aspect, the external and internal threads  42 ,  46  have thread lengths preferably ranging from 0.625-0.75 inch to locate the projection  48  and groove  50  for their snap-fit engagement. The groove and projection can be alternatively arranged where, for example, the projection includes an external groove and the internal bore includes an internal projection to form a snap fit. 
     In the preferred embodiment shown in  FIGS. 2A and 2B , the first member  12   a  provides a body and the second member  12   b  provides a cap threaded about the body  12   a . Each of the body  12   a  and the cap  12   b  have a first end portion and a second end portion with a through hole or passageway extending from the first end portion to the second end portion along respective central axes of the body  12   a  and cap  12   b.  Accordingly, each of the body  12   a  and cap  12   b  has an external surface and an internal surface. Preferably each component  12   a,    12   b  is a monolithic plastic from the external surface to the internal surface without the need for any internal support or structure of a dissimilar material such as metal. Upon coupling the first end portion of the cap  12   b  to the second end portion of the body  12   a,  the respective central axes and passageways are coaxially aligned with one another to define the central passageway  18  of the adapter  10 . 
     Referring again to  FIG. 3 , the first end portion of the body  12   a  includes a countersunk bore formed about the internal passageway of the body  12   a  to define the inlet  14   a  previously described. The countersunk bore has an axial depth to the floor  15  to define preferred a ratio to the total axial length of the internal passageway of the body  12   a  being about 0.4:1. The second end portion of the body  12   a  includes the narrowed portion  40  having the external thread  42 . The axial length of the external thread  42  defines a preferred ratio of the total axial length of the body  12   a  to the axial length of the external thread being about 2.4:1. Within the narrowed portion  40  at the second end portion of the body  12   a,  a countersunk bore is formed about the central opening  34  to define the gasket bearing surfaces  28  of the gasket chamber  24  including the internal wall  32 . The bottom of the countersunk bore forms the preferred angled and radiused surfaces  28   a,    28   b  of the first gasket bearing surface  28  about the central opening  34  previously described. 
     The cap  12   b  includes the enlarged bore  44  with the internal thread  46  for engaging the externally threaded narrowed portion of the body  12   a  and/or locating surfaces relative to one another. The bore  44  of the cap  12   b  includes a bottom surface to define the preferably planar second gasket bearing surface  30  and central opening  36  previously described. The bottom of the countersunk bore of the body  12   a  is opposed and spaced relative to the bottom of the bore  44  of the cap  12   b  to define the gasket chamber  24  upon the cap  12   b  engagement with the body  12   a.  For the cap  12   b,  the bottom surface of the bore  44  separates the through hole or internal passageway of the cap  12   b  into two portions. The first portion of the internal passageway of the cap  12   b  defines a first axial length and the second portion defines a second axial length of the internal passageway with a preferred ratio of first axial length to second axial length being about 2:1. The preferred cap  12   b  provides for the self-supporting structure in the adapter engagement with the sprinkler  200 . With reference to  FIGS. 2A and 2B , the second end portion of the cap  12   b  defines an external diameter or width DW and the receptacle  20  formed therein defines a maximum internal diameter ID at the second end portion of the cap  12   b.  A preferred ratio of the external diameter DW-to-maximum internal diameter ID of the second portion of the cap is about 1.7:1 and more preferably 1.67:1. 
     The preferred embodiments of the sprinkler adapter provide preferred methods of coupling a fire protection sprinkler to a fluid supply pipe and more preferably a plastic fluid supply pipe. One preferred method includes coupling a preferred embodiment of a plastic adapter  10  to the fluid supply pipe, placing a sprinkler  200  into contact with a first surface of an annular gasket housed in an initially unloaded state within an internal gasket chamber  24  of the plastic adapter  10 . The preferred gasket  26  has a central opening or through hole defining an internal diameter or area centered about the central axis of the adapter. The preferred method includes threading the sprinkler  200  within the adapter  10  to place the gasket  26  in a loaded state with a second surface of the gasket  26  against a bearing surface  28  of the gasket chamber to form a fluid tight seal with the internal diameter, central opening or area of the annular gasket being the substantially the same in the loaded state as in the unloaded state centered about the central axis. 
     Another preferred method couples a metal sprinkler to a firefighting fluid supply pipe and includes obtaining a preferred embodiment of a sprinkler adapter, for example, as any adapter previously described and providing the adapter for connection to the fluid supply pipe. The fluid supply pipe is preferably plastic. Obtaining the preferred sprinkler includes any one or more of acquiring, purchasing, or manufacturing and providing includes transferring, selling, or otherwise supplying. 
     While the present invention has been disclosed with reference to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof.