Abstract:
A combination sealing and restraint system for an as-cast ductile iron fitting is shown for both sealing and preventing separation of an iron pipe fitting and a mating male pipe. A sealing gasket body is provided with a series of integrally formed gripping segments. The gripping segments have teeth on an inner surface which are initially angled away from an outer surface of a mating male pipe. The teeth are forced into engagement with the exterior surface of the mating male pipe as the pipe joint at the fitting is assembled. The teeth are oriented to allow movement of the male pipe in a first direction relative to an end opening of the fitting during assembly, but to resist movement in a opposite direction after the fitting joint has been assembled. The combination sealing and restraining system is installed in the annular groove of the as-cast iron fitting after the iron casting operation at the factory.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of Applicant&#39; s prior U.S. application, Ser. No. 11/149,988, filed Jun. 10, 2005, entitled “Self Restrained Fitting for PVC and Ductile Iron Pipe.” 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention: 
         [0003]    The present invention relates generally to the field of pipe connections such as those used in the municipal water and sewer pipeline industries. More particularly, this invention relates to a combination sealing and restraint system for use in “as-cast” ductile iron pipe fittings. 
         [0004]    2. Description of the Prior Art: 
         [0005]    Pipes are commonly used for the conveyance of fluids under pressure, as in city water lines. They may also be used as free-flowing conduits running partly full, as in drains and sewers. Pipes for conveying water in appreciable quantities have been made of steel, cast iron, concrete, vitrified clay, and most recently, plastic including the various polyolefins and PVC. 
         [0006]    In many applications where lengths of pipe are joined in telescoping relationship, the spigot end of one pipe is inserted into the socket end of the engaging pipe at a pipe joint or “coupling.” The socket end has an opening large enough to receive the spigot end of the mating pipe. A gasket is typically present within the socket end of the pipe which is intended to prevent leakage of fluid from the joint by forming a seal between the two pipe sections. Piping systems of the above type also typically include “fittings” as that term is defined in the industry. A fitting is a term which will be familiar to those in the relevant industries and includes a piece, often curved or at an angle, as a coupling, an elbow, a valve, a Tee, etc. used for connecting lengths of pipe or as an accessory to a pipe in a piping system for conveying fluids. Exemplary “as cast” ductile iron pipe fittings are shown, for example, in the Tyler/Union Utilities Mini-Catalogue, May 2001, on pages 2-3, as the “Mechanical Joint C153 Ductile Iron Compact Fittings.” These fittings are merely intended to be exemplary, as there are a number of other commercial sources for such pipe fittings. 
         [0007]    One important consideration in piping systems of the above type, whether in a straight run of pipe or at a fitting, is to provide adequate sealing at the pipe joints or couplings. In addition to the necessity of providing effective sealing, another important design requirement exists when it becomes necessary to join the pipe components in a restrained manner. This is usually desired in order to prevent the pipe components from separating due to thrust forces that often occur when the pipeline is subjected to internal or external pressures, changes in direction or elevation of the pipeline, and sometimes when earthquakes or tremors or other external factors come into play. 
         [0008]    A particularly preferred method of forming a sealed joint in straight runs of pipe is sometimes referred to as a “mechanical joint” or simply as an “MJ”. The bell end of an iron pipe section has a flanged portion cast on it. The spigot end of a second iron pipe is fitted with a slidable gland fitting and a gasket that is conically shaped such that one face of the gasket is diametrically larger than the second face of the gasket. The conically shaped gasket is positioned between the gland fitting and the spigot end of the pipe with the smaller, second face of the gasket being closer to the spigot end than the larger, first face of the gasket. The gland fitting has a plurality of apertures for receiving standard bolts. The joint is formed when the spigot is axially inserted into the bell, and the gland fitting and the flanged portion are bolted together, causing the lip of the gland fitting to compress the gasket thus sealing the two pipe pieces. 
         [0009]    While the “internal” gasket used in the traditional MJ design for ductile iron pipe served to seal the joint, the gasket did not feature a cooperating “restraint” feature in order to assure the greater integrity of the joint of pipe. Instead, it was necessary to utilize a cumbersome external mechanical restraint system made up of the flange, bolts, screws, etc., as discussed above. 
         [0010]    Also, when the pipe component being joined was a fitting rather than a straight run of pipe, there was less room available on the exterior of the fitting to accept the various parts (flanges, bolts, screws, etc.) that were necessary to make up the MJ type restraint. 
         [0011]    A need exists, accordingly, for a sealing and restraint system for ductile iron pipelines, and particularly for fittings, which offers complimentary sealing and self restraining features in an internal sealing/restraint system. 
         [0012]    A need also exists for such a system which is cost-effective, easy to manufacture and easy to use in the field and which is dependable in operation. 
         [0013]    A need also exists for such a system which effectively restrains ductile iron fittings against internal and external forces without the need for an external flange, bolts or associated restraining screw mechanisms. 
       SUMMARY OF THE INVENTION 
       [0014]    The present invention has as one object to provide a combination sealing and restraint system for insertion within an annular groove within a mouth region located adjacent an end opening of an as-cast ductile iron fitting capable of both sealing and restraining the ductile iron fitting to a mating male pipe having an interior surface and an exterior surface. 
         [0015]    The preferred combination sealing and restraint system includes an annular gasket body made of a resilient elastomeric material, the annular gasket body having an inner circumferential region and an outer circumferential region. When installed within the annular groove provided in the mouth region of the as-cast fitting, the outer circumferential region forms a seal with the fitting mouth region and the inner circumferential region forms a sealing surface for a mating male pipe section. A plurality of generally planar gripping segments extending perpendicularly outward from the annular gasket body at a predetermined spacing around the circumference of the annular gasket body. Each of the gripping segments has an inner planar surface and an outer planar surface separated by a thickness. The inner planar surface has at least one row of gripping teeth capable of engaging selected points on the exterior surface of the mating male pipe. 
         [0016]    In one form, the sealing and restraint system features an annular gasket body that, when viewed in cross section, includes a leading nose region and a radially inwardly slanting sealing surface which forms a lip seal for engaging the mating male pipe end during insertion. The lip seal surface is joined to a secondary sealing surface, the secondary sealing surface comprising a planar circumferential region which terminates in an inside corner of the gasket. The inside corner is connected to an outer arcuate region of the gasket by a gently sloping exterior gasket surface. The outer arcuate region of the gasket is connected to the nose region of the gasket by a another gently sloping external gasket surface. 
         [0017]    Preferably, the generally planar gripping segments are integrally formed into the leading nose region of the annular gasket body during manufacture of the gasket body. For example, the gasket body may be injection molded with the gripping segments being integrally formed into the gasket body during the injection molding operation. The gripping segments extend outwardly from the nose section of the gasket. The outer planar surface of the gripping segments is at least partly covered by the rubber of the nose region of the gasket. Preferably, the majority of the outer planar surface is covered with rubber. The amount of elastomer utilized and the durometer of the elastomer control the force of the gripping tooth engagement with the mating male pipe. In one preferred form of the invention, only a single row of gripping teeth are present on the inner planar surface of the gripping segments. Where two rows are present, one row has a greater relative height than the other row. 
         [0018]    A method is also provided for forming a pipe joint with the sealing and restraining system described above. To begin, a fluid piping system is provided which has one or more as-cast ductile iron pipe fitting, previously cast at a foundry, each having a mouth region adjacent an end opening thereof. The mouth region has an annular groove therein, and the end opening of the fitting is sized to receive a mating male pipe having an interior surface and an exterior surface. In a post-casting operation, the sealing and restraining system is installed within the annular groove provided in the end opening of the as-cast fitting. The plurality of integrally formed gripping segments extend outwardly from the annular gasket body at a predetermined spacing around the circumference of the annular gasket body. The spacing is sufficient to allow the gasket body to be flexed to thereby allow the sealing and restraint system to be installed in the pipe during a post-casting operation. A mating male pipe is installed within the end opening of the mouth region of the as-cast fitting by pushing the male pipe within the end opening, and the sealing and restraint system contacts the external surface of the mating male pipe in order to both seal and restrain the mating male pipe and form a secure joint. 
         [0019]    The mating male pipe may be made from a plastic material or from iron. In the case where the mating male pipe is formed of iron, the gripping segments are preferably formed of hardened steel which has been treated to at least about 370 Brinell hardness (BHN) so that the gripping teeth of the segments can penetrate the mating male iron pipe exterior surface or form a buttress on the pipe surface. 
         [0020]    Additional objects, features and advantages will be apparent in the written description which follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0021]      FIG. 1  is a perspective view, partly broken away, of an as-cast ductile iron pipe fitting showing the combination sealing and restraint system of the invention in place within a mouth region of the fitting. 
           [0022]      FIG. 2  is a partial sectional view of one end of the ductile iron pipe of  FIG. 1  showing the combination sealing and restraint system thereof in greater detail. 
           [0023]      FIG. 3A  is a partial, sectional view of one end of the pipe fitting of  FIG. 1 , illustrating the assembly of the male pipe end. 
           [0024]      FIG. 3B  is a sectional view of the combination sealing and gripping system of  FIG. 3A . 
           [0025]      FIG. 4  is a perspective view of the combination sealing and restraint system of the invention. 
           [0026]      FIG. 5  is a partial sectional view of a prior art MJ style restraint system. 
           [0027]      FIG. 6  is a side, partial sectional view which shows another form of the sealing and restraint system of the invention in which the rubber of the nose region of the gasket covers the outer planar surface of the gripping elements. 
           [0028]      FIG. 7  is an isolated, cross-sectional view of the sealing and restraint system used in  FIG. 6 . 
           [0029]      FIG. 8  is a view of a C-shaped gasket which houses a split gripping ring or a plurality of gripping segments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0030]    The present invention deals with piping systems of the type used in water, sewage and other municipal fluid conveyance systems. In the past, such pipelines were traditionally formed of a ferrous metal. By “ferrous metal” is meant iron and alloys of iron. For example, one type of ferrous metal which is commonly encountered in the water works industry is “ductile iron.” This particular type of metal is widely used because it offers a combination of a wide range of high strength, wear resistance, fatigue resistance, toughness and ductility in addition to the well-known advantages of cast iron-castability, machinability, damping properties and economy of production. It takes its name from the fact that it is “ductile” in nature, rather than being brittle, as was the case with earlier cast iron products and materials. Today, grades of ductile iron are available offering the option of choosing high ductility with grades guaranteeing more than 18% elongation, or high strength, with tensile strengths exceeding 120 ksi (825 MPa). Austempered ductile iron (ADI), offers even greater mechanical properties and wear resistance, providing tensile strengths exceeding 230 ksi (1600 Mpa). 
         [0031]    In forming a pipeline of ductile iron components, one end of each section is typically enlarged, forming a “bell” at one end sufficient to join the next adjacent pipe section by receiving in the belled end the unenlarged or “spigot” end of the next adjacent length of pipe within the bell end opening. The inside diameter of the bell is formed sufficiently large to receive the spigot of the next section of pipe with sufficient clearance to allow the application of an elastomeric gasket or other sealing device designed to prevent leakage at pipe joints when a plurality of pipe lengths are joined to form a pipeline. 
         [0032]    Straight runs of ductile iron pipe of the above type have, for many years, been joined by utilizing an elastomeric gasket which is compressed between the inside walls of the bell and the outside wall of a mating spigot end of the next pipe in a series of telescoped pipes. The gasket is typically retained within the groove provided in the bell end opening of the female pipe section. However, as discussed above, one problem which exists is finding a way to “restrain” the assembled pipe joints so that the joint will not be separated due to internal or external pressure, or due to environmental factors such as earth movement. 
         [0033]    As mentioned in the background discussion of the invention, the iron pipe industry has generally addressed the problem of providing a restrained pipe joint by utilizing an external sealing “gland” or flange, sometimes referred to as a “mechanical joint” or simply as an “MJ”. The MJ style restraint has worked satisfactorily in the past on straight runs of pipe. However, fittings typically do not present as large an exterior surface for receiving the various components needed to make up the MJ type restraint. Also, an internal combination sealing and restraint system would offer greater ease and speed of assembly in the field. Because the gripping components would be internal rather than external, there would be less opportunity for corrosion of the metallic components in use. 
         [0034]    Turning to  FIG. 5 , there is shown a typical mechanical joint of the prior art. The joint shown in  FIG. 5  is formed between a pipe bell end  11  of one ductile iron pipe and the plain spigot end  13  of a second ductile iron pipe. The second pipe  13  is inserted into the belled end  11  of the enclosing pipe. The inner surface of the pipe bell end  11  has a retainer groove  17  for retaining a gasket  15 . The belled pipe end  11  also has a flanged region  27  which includes a plurality of apertures  29 . A circumferential gland  31  is sized to be received about an outer surface of the mating male ductile iron pipe. The gland  33  has a forward lip portion  35  which contacts and compresses the body of the gasket  15  as the joint is assembled. The gland  31  also has a plurality of apertures  37  which are arranged to be aligned with the apertures in the flange collar region of the bell pipe end. Bolts  39  and nuts  41  are used to join the apertures of the bell pipe end and the gland as shown in  FIG. 5 . 
         [0035]    While the mechanical joint illustrated in  FIG. 5  has been utilized for a number of years in the industry, it is somewhat cumbersome and time consuming to assemble. Additionally, the external metallic components are subject to wear, damage and corrosion. As mentioned above, it may be too bulky for use on some fittings. The present invention, therefore, has particular application to as-cast “fittings” which are used to make up a joint between two plain end pipe sections. By “as-cast” is meant that no additional machining is involved to form the bell, as with traditional systems. As-cast fittings of the type under consideration are commercially available from a number of sources, for example, the Tyler Pipe/Utilities Division of Union Foundry Company located in Anniston, Ala., as previously mentioned in the Background discussion. 
         [0036]    While the invention will be primarily described with respect to ductile iron pipelines, it will be understood that the mating male pipe could also be formed of another material, such as a suitable plastic such as PVC or a suitable polyolefin such as polyethylene. Such “hybrid” systems are becoming increasingly common in use in the rehabilitation of existing ductile iron pipe lines. 
         [0037]      FIG. 1  illustrates an as-cast ductile iron elbow fitting which has installed therein the combination sealing and gripping restraint system of the invention. The as-cast fitting  39  illustrated in  FIG. 1  has opposing end openings  41 ,  43 . Each end opening has an adjacent mouth region ( 45  in  FIG. 1 ) and can be provided with a slight upset  47 . It is not necessary that the upset  47  be provided as an apertured flange, however. An annular groove  49  is provided within the mouth region  45  slightly spaced back from the end opening  41 . 
         [0038]    The combination sealing and restraint system of the invention includes an annular gasket body  51  ( FIG. 1 ) having an inner circumferential region  53  and outer circumferential region  55  (see  FIG. 4A ). The annular gasket body  51  is installed within the annular groove  49  provided in the mouth region  45  of the as-cast fitting so that the outer circumferential region  55  forms a seal with the fitting mouth region and the inner circumferential region  53  forms a sealing surface for a mating male pipe section. The lip region  54  of the inner circumferential region  53  forms a primary lip seal for engaging the mating male pipe end during insertion. 
         [0039]    One preferred form of the combination sealing and restraint system of the invention is shown in  FIGS. 1-4 . Turning to  FIG. 4 , the combination sealing and restraint system includes the previously described sealing gasket body, designated generally as  101 , together with an integral restraint system. The gasket portion of the device (indicated generally at  101  in  FIG. 3B ) includes a leading nose region  103  which is joined to a radially inwardly slanting sealing surface  105 . The inwardly slanting sealing surface  105  extends outwardly to form a lip seal region  107  for engaging the mating male pipe end during insertion. Whether the gasket body features a lip seal, as shown in  FIG. 3B , or more of a bulbous “compression seal region”, the sealing surface of the gasket body will generally extend further radially inward (toward the centerline of the pipe) than the gripping surfaces of the companion gripping segments ( 123  in  FIG. 4 ). 
         [0040]    The lip seal region  107  of the gasket body is joined to a secondary sealing surface  111 . The secondary sealing surface  111  comprises a generally planar circumferential region  113  which terminates in an inside corner  115  of the gasket. The inside corner  115  is connected to an outer arcuate region  117  of the gasket by a gently sloping exterior gasket surface  119 . The outer arcuate region  117  of the gasket is connected to the nose region  103  of the gasket by a downwardly sloping external gasket surface  121 . 
         [0041]    A plurality of integrally formed gripping segments  123  (see  FIG. 4 ) extend perpendicularly outward from the nose region  103  of the annular gasket body  101  at a predetermined spacing around the circumference of the annular gasket body  101 . By “extending perpendicular outward” is meant that the segments extend generally along a 180 degree axis from the inside corner  115  of the gasket body. In the example shown, there are ten evenly spaced gripping segments. The gripping segments are typically formed of a metal such as steel, although the segments might be formed of a hard plastic where the mating male pipe to be gripped is formed of, for example, PVC. The number of gripping segments will vary depending upon the diameter of the sealing and gripping assembly. For example, in the case where the annular gasket body  101  has a six-inch diameter, nine separate gripping segments  123  will typically extend outwardly around the circumference of the gasket body  101 . The gripping segments  123  are generally planar with a length, a width, an inner circumferential surface and an outer circumferential surface separated by a thickness. There exists a series of generally uniform gaps or spaces (generally shown at location  125  in  FIG. 4 ) between each adjacent gripping segment. The gaps  125  between the metallic gripping segments  123  provide some degree of flexibility for the assembly, thereby facilitating its installation within the mouth region  41  of the pipe fitting  39 . In some forms of the invention, the gaps  125  may be filled with rubber which is extruded as a part of the sealing gasket body, as well. 
         [0042]    The gripping segments are preferably integrally formed into the leading nose region of the annular gasket body during manufacture of the gasket body. For example, the gasket body may be injection molded with the gripping segments being integrally formed into the gasket body during the injection molding operation. In that event, a portion of the length of the gripping segments would be enclosed within or be embedded within the elastomeric body of the sealing gasket. Alternatively, it may be possible to glue or otherwise adhere the gripping segments to the elastomeric gasket body in some circumstances so that the segments are held in the position shown in  FIG. 4 . 
         [0043]    The inner planar surface of each gripping segment  123  has at least one row of teeth  127  capable of engaging selected points on the exterior surface of the mating male pipe. In the version of the device illustrated in  FIG. 4 , there are three rows of teeth  127  on the inner planar surface. As illustrated in  FIG. 3B , the teeth are formed on an acute angle “α” with respect to a horizontal axis (illustrated as  128  in  FIG. 1 ) of the mouth opening  45  once assembled within the as-cast fitting  39 . The shape and inclined angle of the teeth allow a mating male pipe end to be received within the end opening  41  of the fitting  39  and move in a direction from right to left as viewed in  FIG. 3A . However, the shape and inclined angle of the teeth  127  resist opposite relative movement of the mating male pipe  130  and thereby exert a restraining force on the mating male pipe  130  once the male pipe has be fully inserted into the fitting  39 . 
         [0044]      FIG. 2  provides an enlarged cross-sectional view of one end of the ductile iron pipe of  FIG. 1 , specifically showing the combination sealing and restraint system thereof in greater detail. The annular gasket body  101  of the sealing and restraint system is shown installed within the annular groove  49  provided in the mouth region of the as-cast fitting. The gripping segments  123  extend outwardly from the nose region  103  of the annular gasket body  101 . As mentioned, there is a slight space between each gripping segment, as shown at location  125  which is either open, or which is filled with rubber. 
         [0045]    As has been mentioned, the mating male pipe may be made from a plastic material, such as from PVC, or from iron. In the case where the mating male pipe is formed of iron, the gripping segments are preferably formed of hardened steel which has been treated to at least about 370 Brinell hardness (BHN) so that the gripping teeth of the segments can penetrate the mating male iron pipe exterior surface or form a buttress on the pipe surface. 
         [0046]      FIGS. 6 and 7  show another preferred form of the sealing and restraint system of the invention, designated generally as  129 . The sealing and restraint system  129  is generally similar to that which has been previously described with respect to FIGS.  1  and  2 - 4 . However, as best appreciated from the isolated view of  FIG. 7 , it will be seen that the gripping segments  131  now have at least a slight covering of rubber material on the outer planar surfaces  135  thereof. This is conveniently achieved as a part of the injection molding process of the elastomer portion  137 . By providing a rubber covering layer on the outer planar surface of the gripping segments, the force which the teeth ( 139 ,  141  in  FIG. 6 ) apply to the mating male pipe end can be more fully controlled. In other words, the amount of rubber present on the outer planar surfaces  135  and the durometer of the rubber will determine the amount of ultimate force which the combined sealing and restraint system applies to the mating male pipe. 
         [0047]    With reference to  FIG. 7 , a preferred form of the sealing and restraint system of the invention is shown in which a single row of gripping teeth  143 . Note that the teeth may be provided with a slight “hook” of backward angle “β” with respect to the central axis  145  of the female belled pipe end. In other words, the angle “β” is not perpendicular to the longitudinal axis  145 . Where the gripping elements are provided with, for example two rows of teeth, one row will typically be taller than the other row. 
         [0048]    While the elastomer body portion of the sealing and restraint system is shown in one form in  FIGS. 6 and 7 , it will be appreciated that it may take other forms, as well. For example, rather than a combined compression and lip seal design, as shown in  FIGS. 6 and 7 , the gasket body could be more of a traditional “C-shaped” gasket ( 147  in  FIG. 8 ) having a generally C-shaped cross section. 
         [0049]    Such C-shaped gasket designs are known and commercially available. See, for example, the Victaulic C-shaped Gasket For Water, Sewer and Drain Fittings, sold by Victaulic Corporation of Easton, Pa. In the case of the C-shaped gasket shown in  FIG. 8 , however, a plurality of gripping segments  149  are located on the underside of the gasket in a channel formed between the edges thereof. The segments  149  in  FIG. 8  have at least one row of gripping teeth  151  on the inner planar surfaces thereof. With the C-shaped gasket, hydrostatic pressure acts to assist in the ultimate sealing action, making the gasket pressure responsive. 
         [0050]    The operation of the sealing and restraint system of the invention will now be briefly described. The system will typically be utilized with a fluid piping system which includes one or more as-cast ductile iron pipe fittings. With reference to  FIG. 1 , the as-cast fitting  39  typically requires no modification from the item typically produced as-cast from the foundry. As mentioned earlier, it is not necessary for the upset  47  to be provided with apertures for receiving connecting bolts since the internal restraint system of the invention replaces the prior art external components. The combination sealing and restraint system is then typically installed within the internal groove  49  provided within the mouth region  45  of the fitting. The annular gasket body  101  is installed within the annular groove  49  so that the outer circumferential region forms a seal with the fitting mouth region and the inner circumferential region forms a sealing surface for a mating male pipe section. 
         [0051]    As has been mentioned, the combination sealing gasket and gripping mechanism is inserted within the pipe mouth opening in a post cast operation, thus requiring the body to remain flexible for ease of insertion. The spacing between each gripping segment may assist in maintaining the flexibility of the gasket body. Alternatively, the gaps or spacing between segments may be filled with rubber from the elastomer body of the gasket. If the gripping segments are viewed as forming an imaginary ring, the diameter of the imaginary ring will be slightly less than the outer diameter of the mating male pipe which is inserted within the female, belled pipe end to form a pipe connection. This means that the gasket body nose region, with its associated gripping segments must be expanded at least slightly to pass over the outer diameter of the mating male pipe end. The inner circumferential surface of the gripping segments, with the rows of gripping teeth  127  are capable of engaging selected points on the exterior surface of the mating male pipe. 
         [0052]    Once the sealing and restraint gasket is in place, the mating male pipe is installed within the end opening of the mouth region of the as-cast fitting by pushing the male pipe within the end opening. Upon insertion of the male pipe end, the sealing and restraint system contacts the external surface of the mating male pipe in order to both seal and restrain the mating male pipe and form a secure pipe joint. 
         [0053]    An invention has been provided with several advantages. The combination sealing and restraint system of the invention is capable of joining and sealing an as-cast ductile iron fitting to a mating male pipe section. The system of the invention is simple in design and economical to manufacture and does not require any drastic changes in existing ductile iron components. The present invention can be used to join ductile iron fittings to mating pipe sections without the need for external mechanical restrain components which complicate assembly and can be subject to corrosion or deterioration in use. By providing the individual gripping segments with a backing of elastomer from the sealing gasket body, the ultimate gripping force of the gripping teeth can be more effectively controlled. Changing the amount of rubber, or the durometer of the rubber, changes the amount of force applied to the external surface of the mating male pipe. 
         [0054]    While the invention has been shown in several of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.