Abstract:
A modular radial compressor for compressing fluids includes a compression vessel having a collapsible vessel internal space having expanded and a compressed sizes, the compression vessel having an intake structure for passing fluid into the vessel internal space from a fluid source and an output structure for passing fluid out of the vessel internal space; a rotatable arm structure having an arms structure rotational axis and at least one radial arm protrusion positioned to periodically about one or multiple compression vessels and compress the vessel internal spaces; a rotational drive mechanism drivably connected to the rotatable arm structure for rotatably driving the arm structure and the arm protrusion about the arm structure rotational axis; and a compression vessel expansion mechanism for expanding the vessel internal space to its expanded size subsequent to each vessel internal space compression.

Description:
FILING HISTORY 
     This application is a continuation-in-part of application Ser. No. 11/284,335 filed on Nov. 21, 2005 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to the field of compression and storage of fluids and particularly to compression of gaseous matter. More specifically the present invention relates to an apparatus in the form of a modular radial compressor for compressing any gas or gaseous matter hereinafter referred to as a fluid, including at least one cylinder and piston assembly including a cylinder having a cylinder head and a tubular cylinder side wall and a piston structure slidably retained within the tubular cylinder side wall, the cylinder head having an intake port fitted with an intake valve for passing fluid into the cylinder from a fluid source and an output port fitted with an output valve for passing fluid out of the cylinder such as to a fluid reservoir, valve operating means, a rotatable arm structure in the form of an arm wheel having an arm structure axle and radial arm protrusions in the form of arms positioned to periodically abut and displace the piston structure inwardly toward the cylinder head, and rotational drive means drivably connected to the rotatable arm wheel for rotatably driving the arm wheel and the arms about the arm wheel rotational axis, and a piston structure return means for displacing the piston structure outwardly away from the cylinder head subsequent to each piston structure inward displacement. The compressor manufacturer decides the number of arms per arm wheel, and the number of cylinder and piston assemblies to be included is determined by the purchaser as a result of the compressor modularity. The valve operating means opens the output valve and an arm abuts and displaces the piston structure toward the cylinder head, driving fluid within the cylinder out of the cylinder through the output port, and then the valve operating means closes the output valve and opens the intake valve and the piston structure return means displaces the piston structure outwardly, away from the cylinder head and the intake port, thereby drawing fluid through the intake port into the cylinder from the fluid source, in a periodically repeating cycle. The cylinder and piston assembly and arm wheel preferably are both fastened to an apparatus framework to position them in operational relation with each other. The apparatus framework preferably includes an apparatus housing preferably having a polygonal or round shape and enclosing at least the arm wheel. The intake port optionally is covered by an air filter retained within an air filter housing. 
     Modularity is a key inventive feature of the present invention. Either one or several single cylinder and piston assemblies can be removably fastened to the framework, such as to the housing, with any suitable removable fastening means such as mounting bolts passing through the housing into or through the cylinder and piston assembly. Where mounting bolts are used, bolt holes are provided in the housing for passing the mounting bolts for each cylinder and piston assembly. These bolt holes preferably are pre-cut during housing manufacture, but alternatively may be cut any time thereafter. As a result, any desired number of cylinder and piston assemblies up to the maximum number the particular housing can accommodate can be mounted. Thus the number of cylinder and piston assemblies needed for a specific use or application can be selected and provided on an individual modular radial compressor of the present invention. 
     The number of arms provided on the arm structure determines the number of compression cycles the cylinder and piston assembly performs for each revolution of the arm structure, and is selected to meet the requirements of the given application. A flywheel preferably is provided adjacent the arm wheel and mounted to the arm wheel axle to provide smooth arm rotation. The piston structure preferably includes a piston connected to a piston rod. The rotational drive means preferably includes an electric drive motor connected to the arm structure with a belt and pulleys or other drive connection. Thus each modular radial compressor typically has one flywheel and one pulley, although additional ones may be added. Between the flywheel and the arm wheel, a clutch optionally connects the arms wheel to the pulley shaft after a few seconds, thereby avoiding the stress for the electric motor and avoid what is known as demand factor to the electric motor, in a 3-phase system. 
     The number of arms on the arm structure preferably can be altered such that the volume of fluid compressed per arm structure revolution can be altered to accommodate any of a wide variety of applications. Another variation of the present modular radial compressor includes a plurality of cylinder and piston assemblies positioned and secured to the apparatus framework to extend radially and equidistantly from the arm structure to be operated by the arms in sequence. Yet another variation of the compression apparatus includes multiple arm structure and cylinder units. The arm structures preferably are arm wheels mounted on a common arm structure axle and thus driven by a common motor drive means. 
     2. Description of the Prior Art 
     There have long been compressors for compressing gaseous matter for storage or immediate use. These prior compressors typically have included a cylinder and piston combination driven by a motor or engine. A problem with these prior compressors has been that they can produce only one compression per motor or engine revolution, limiting compression to a specific rate which may or may not be suited for a given application. If a larger compression rate is needed, a different and larger compressor must be located. 
     Stanziola, et al., U.S. Pat. No. 3,697,764, issued on Oct. 10, 1972, discloses a method and apparatus for generating electricity including a series of cylinder and piston assemblies arranged radially around and in operational relation with a cam wheel. A shortcoming of Stanziola, et al. is that there is no provision for altering the number of cylinder and piston assemblies positioned around the cam wheel to meet specific requirements. 
     Other references cited in the parent application are incorporated by reference into this section, including but not limited to Palmer, U.S. Pat. No. 1,904,799; Cornwell, U.S. Patent Publication Number 2004/0213679A1; Goettel U.S. Pat. No. 5,711,206; Hedstrom U.S. Pat. No. 895,755; Wang U.S. Patent Publication Number 2004/0141855 A1; Tyler U.S. Pat. No. 2,631,538; Lochmann, et al., U.S. Pat. No. 3,951,046; Roberts, U.S. Pat. No. 4,132,512; Pepperman, U.S. Pat. No. 5,720,596; and Kubeczka, U.S. Pat. No. 4,313,714. 
     It is thus an object of the present invention to provide a modular radial compressor which can compress a fluid at any of several different rates selectable for a given job or application, the apparatus including an arm structure or a multiple arms structure rotatably driven by drive means and at least one cylinder and piston assembly driven through compression cycles by contact with at least one arm protrusion on the rotating structure. 
     It is another object of the present invention to provide such a modular radial compressor for which a specific desired rate of fluid compression can be selected by: selecting the number of cylinder and piston assembly compressions per revolution of motor drive means by altering the number of arm protrusions on the rotating arm structure, or by selecting the number of cylinder and piston assemblies operated with each revolution of the motor drive means, or by selecting the number of arm structure and corresponding cylinder and piston assemblies, or by altering all three variables as needed. 
     It is yet another object of the present invention to provide such a modular radial compressor which is modular in that cylinder and piston assemblies are removable and re-attachable to the compressor housing so that a desired number of cylinder and piston assemblies can be selected and attached for each particular use or application, making the compressor highly versatile. 
     It is a further object of the present invention to provide such a modular radial compressor which is inexpensive to manufacture, in part because the compressor is made in only one standard size for all applications, and which also saves money because a single modular radial compressor can be purchased, rather than several compressors have different fixed numbers of cylinder and piston assemblies for different jobs. More than the standard number of cylinder and piston assemblies for a given compressor can be installed by enlarging the size of the compressor housing or adding other cylinder and piston assembly mounting means. 
     It is still another object of the present invention to provide such a modular radial compressor with which such selections can be made automatically by computer program operated electric switches. 
     It is finally an object of the present invention to provide such a modular radial compressor which is reliable, durable, operates on less electricity, and is economical to manufacture. 
     SUMMARY OF THE INVENTION 
     The present invention accomplishes the above-stated objectives, as well as others, as may be determined by a fair reading and interpretation of the entire specification. 
     A modular radial compressor is provided for compressing fluids, including a compression vessel having a collapsible vessel internal space having an expanded size and a compressed size, the compression vessel having intake structure for passing fluid into the vessel internal space from a fluid source and output structure for passing fluid out of the vessel internal space; a rotatable arm structure having an arm structure rotational axis and at least one radial arm protrusion positioned to periodically abut the compression vessel and compress the vessel internal space; a rotational drive mechanism drivably connected to the rotatable arm structure for rotatably driving the arm structure and the arm protrusion about the arm structure rotational axis; and a compression vessel expansion mechanism for expanding the vessel internal space to its expanded size subsequent to each compression of the vessel internal space; so that compression of the vessel internal space drives fluid within the vessel internal space out of the vessel through the output structure, and then the compression vessel return mechanism expands the vessel internal space, thereby drawing fluid through the intake structure into the vessel internal space from the fluid source, in a repeating cycle. 
     The compression vessel preferably includes a cylinder and piston assembly having a cylinder interior and the vessel internal space comprise the cylinder interior. 
     A modular radial compressor for compressing fluids is further provided, including at least one cylinder and piston assembly including a cylinder having a cylinder head and a tubular cylinder side wall and a piston structure slidably retained within the cylinder, the cylinder having an intake port fitted with an intake valve for passing fluid into the cylinder from a fluid source and an output port fitted with an output valve for passing fluid out of the cylinder; a valve operating mechanism in operational relation with the intake valve and the output valve; a rotatable arm structure having an arm structure rotational axis and at least one radial arm protrusion positioned to periodically abut and displace the piston structure inwardly toward the cylinder head; a rotational drive mechanism drivably connected to the rotatable arm structure for rotatably driving the arm structure and the arm protrusion about the arm structure rotational axis; and a piston structure return mechanism for displacing the piston structure outwardly and away from the cylinder head subsequent to each piston structure inward displacement; so that the valve operating mechanism opens the output valve and the arm protrusion abuts and displaces the piston structure toward the cylinder head, driving fluid within the cylinder out of the cylinder through the output port, and then the valve operating mechanism closes the output valve and opens the intake valve and the piston structure return mechanism displaces the piston structure outwardly, away from the cylinder head and the intake port, thereby drawing fluid through the intake port into the cylinder from the fluid source, in a repeating cycle, as in any conventional cylinder and piston operation. 
     The cylinder and piston assembly and the arm structure preferably are both fastened to an apparatus framework to position the cylinder and piston assembly and the arm structure in operational relation with each other. The apparatus framework preferably includes an apparatus housing. The intake port preferably is covered by an air filter structure. The at least one arm protrusion preferably is at least one arm and the arm structure preferably includes an arm wheel having an arm wheel circumferential surface to which the at least one arm is mounted. The modular radial compressor preferably additionally includes a flywheel mounted to rotate in unison with the arm structure to provide smooth arm structure rotation. 
     The piston structure preferably includes a piston connected to a piston rod extending out of the cylinder opposite the cylinder head having a piston rod abutment end. The piston preferably is fitted with at least one piston ring seated in a circumferential piston ring groove to slide sealingly along the cylinder side wall. The cylinder preferably includes a cup-shaped cylinder bottom wall opposite the cylinder head with a central piston rod passing port for funneling blow-by oil to the piston rod so that the piston rod is lubricated by the oil and carries oil out of the cylinder with each cylinder and piston assembly cycle. The piston rod preferably includes at least one oil receiving depression for receiving and retaining oil to carry oil out of the cylinder through the piston rod passing port. 
     The rotational drive mechanism preferably includes an electric drive motor connected to the arm structure with a drive connection. The drive connection preferably includes a drive belt engaging a motor pulley mounted on the motor drive shaft and an arm structure pulley mounted on an arm structure axle. 
     The piston structure return mechanism preferably includes a piston rod biasing spring mounted to be compressed between a framework. The piston rod biasing spring preferably is a coil spring encircling the piston rod and optionally having a progressively narrowing, conical configuration, or a cylindrical configuration. The piston structure return mechanism preferably includes a piston return lever pivotally mounted on a lever fulcrum pin secured to the apparatus framework, having a return lever first end engaging the piston structure and a return lever second end positioned for periodic displacement by the at least one arm protrusion, with a solenoid coil preferably encircling the piston rod. 
     The arm protrusions may be fixed arms but preferably are selectively movable out of rotational alignment with the piston structure so that a desired number of the arm protrusions can be selected to displace the piston structure for each arm structure rotation; so that the volume of fluid compressed per arm structure rotation can be altered to accommodate requirements of any of a wide variety of applications. The where each arm includes an expanded mounting end which fits engagingly into any of several arm channels each having an outwardly narrowing arm engaging channel outward channel opening and extending laterally across the width of and spaced periodically around the arm wheel circumferential surface; so that each arm is slidably retained within a corresponding the arm channel. The arm wheel circumferential surface preferably is sufficiently wide and the arm channels therefore sufficiently long that one the arm can be slid to a first channel end of the given the arm channel and thus to a first side of the arm wheel circumferential surface to align with and abut the piston structure during arm wheel rotation, and slid to a second channel end and thus to a second side of the arm wheel circumferential surface to be out of registration with the piston structure during arm wheel rotation; so that a selected number of the arms can be slid to the first channel end to register with the piston structure as needed for a given apparatus application. 
     The arms preferably are each moved to one of the first side of the arm wheel circumferential surface and the second side of the arm wheel circumferential surface by electro magnets mounted adjacent opposing faces of the arm wheel and adjacent to the arm wheel circumferential surface; so that activation of either the electro magnet pulls each immediately adjacent arm to the adjacent the side of the arm wheel circumferential surface, and the given the electro magnet can be activated as the arm wheel is rotated by the drive mechanism so that only selected arms are moved to a given side of the arm wheel circumferential surface to provide a desired number of arms in registration with the at least one cylinder and piston assembly associated with the arm wheel. 
     The modular radial compressor optionally includes several of the cylinder and piston assemblies positioned to extend radially and equidistantly from the arm structure, so that the at least one arm protrusion abuts and displaces each piston structure in sequence with each the arm structure rotation. 
     More than one modular radial compressor can be installed over the same axle as shown in  FIG. 10  and the clutch in each compressor will engage it to rotate with the axle or disengage it from the rotating axle as needed. The option of multiple modular radial compressors over the same axle is not conditioned upon the configurations of the individual modular radial compressors, and thus the modular radial compressors may have any desired numbers of arms or cylinders and still be installed over the same axle. The clutch of each compressor in the series individually engages or disengages the compressor from the common axle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various other objects, advantages, and features of the invention will become apparent to those skilled in the art from the following discussion taken in conjunction with the following drawings, in which: 
         FIG. 1  is a side view of the a preferred embodiment of the modular radial compressor with the housing broken away to reveal the arm wheel, arm structures, and a cross-sectional view of the cylinder and piston assembly. The housing perimeter wall is shown in edge view, extending into the page. Piston return means shown in this FIGURE include the return spring and return lever. 
         FIG. 2  is an end view of the modular radial compressor of  FIG. 1 . 
         FIG. 3  is a close-up cross-sectional side view of the cylinder and piston assembly of  FIG. 1 . A cylindrical piston rod biasing spring is shown next to the cylinder and piston assembly to illustrate this alternative spring shape. 
         FIG. 4  is an end view of the apparatus of  FIG. 1  but adding the preferred sliding arm structure feature and showing some of the arm structures slid to a first channel ends to register with the piston structure and other arm structures slid to second channel ends to be out of registration with the piston structure. Opposing electro-magnets for moving the arm structures to selected first or second channel ends are also shown. 
         FIG. 5  is a side view of the arm wheel having the arm channels of  FIG. 4 . 
         FIG. 6  is an end view of the modular radial compressor of  FIG. 5 . 
         FIG. 7  is a side view of the arm wheel of  FIG. 5  additionally showing the preferred spring-loaded retaining protrusions for retaining the arm structures at their selected first or second channel ends. 
         FIG. 8  is an end view of the arm wheel of  FIG. 7 , showing the preferred central position of the retaining protrusions in the arm channels. 
         FIG. 9  is a view as in  FIG. 1 , except that the modularity of the present invention is fully illustrated with the mounting of a second cylinder and piston assembly in a second mounting opening in the housing, thus exercising the option of providing two or more such assemblies on a given apparatus arm structure and cylinder unit. The housing can have a round, polygon or any other perimeter shape. 
         FIG. 9A  is a view as in  FIG. 9 , except that four rather than eight arm structures are provided. The locations and potential locations of eight cylinder and piston assemblies are labeled as CYLINDERS  1 - 8 . 
         FIG. 9B  is a broken away perspective view of a portion of the housing wall showing an exemplary bolt hole and piston shaft passing hole and mounting bolt for mounting one of the single cylinder and piston assemblies. 
         FIG. 10  is an end view of the apparatus of  FIG. 4 , showing an optional second arm structure and cylinder unit, to illustrate the option of providing two or more such units in an individual modular radial compressor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
     Reference is now made to the drawings, wherein like characteristics and features of the present invention shown in the various FIGURES are designated by the same reference numerals. 
     First Preferred Embodiment 
     Referring to  FIGS. 1-10 , a modular radial compressor  10  is disclosed including at least one cylinder and piston assembly  20  having a cylinder  22  having a cylinder head  24  and a tubular cylinder side wall  26  and a piston structure  40  slidably retained within the cylinder side wall  26 , the cylinder head  24  having an intake port  32  fitted with an intake valve  34  for passing fluid into the cylinder  22  from a fluid source FS and an output port  36  fitted with an output valve  38  for passing fluid out of the cylinder  22  such as to a fluid reservoir FR, valve operating means  50 , a rotatable arm structure  60  having an arm structure rotational axis A and at least one radial arm protrusion  62  positioned to periodically abut and displace the piston structure  40  inwardly toward the cylinder head  24  and rotational drive means  80  drivably connected to the rotatable arm structure  60  for rotatably driving the arm structure  60  and the arm protrusion  62  about the arm structure rotational axis A, and a piston structure return means  90  for displacing the piston structure  40  outwardly away from the cylinder head  24  subsequent to each piston structure  40  inward displacement. As a result, such that the valve operating means  50  opens the output valve  38  and the arm protrusion  62  abuts and displaces the piston structure  40  toward the cylinder head  24 , driving fluid within the cylinder  22  out of the cylinder  22  through the output port  36 , and then the valve operating means  50  closes the output valve  38  and opens the intake valve  34  and the piston structure return means  90  displaces the piston structure  40  outwardly, away from the cylinder head  24  and the intake port  32 , thereby drawing fluid through the intake port  32  into the cylinder  22  from the fluid source FS, in a periodically repeating cycle. Cylinder head  24  preferably is an integral part of the cylinder  22 , although it is contemplated that it be made removable for servicing. Cylinder side wall  26  preferably is surrounded by heat fins  26   a  to increase outer surface area and thus increase the dissipation of heat from compressing a fluid. The cylinder and piston assembly  20  and arm structure  60  preferably are both fastened to an apparatus framework  100  to position them in operational relation with each other. The framework  100  may include an assembly  20  mounting perimeter wall, as shown in the various FIGURES. The apparatus framework  100  preferably includes an apparatus housing  110  which is optionally round or polygonal in perimeter shape, as shown in the various FIGURES, and alternatively may have any other desired shape. The intake port  32  optionally is covered by an air filter  122  retained within an air filter housing  124 . 
     Modularity is a key inventive feature of the present invention. Either one or several single cylinder and piston assemblies  20  can be removably fastened to the framework, such as to the housing  110 , with any suitable removable fastening means such as mounting bolts  112  passing through the housing  110  into or through the cylinder and piston assembly  20 . Where mounting bolts  112  are used, bolt holes  114  are provided in the housing  110  for passing the mounting bolts  112  for each cylinder and piston assembly  20 . These bolt holes  114  preferably are pre-cut during housing  110  manufacture, but alternatively may be cut any time thereafter. A piston shaft passing hole  116  may also be needed to mount a cylinder and piston assembly, as well as a supporting framework inner brace  108  extending from the housing  110 . As a result, any desired number of cylinder and piston assemblies  20  up to the maximum number the particular housing  110  can accommodate can be mounted. Thus the number of cylinder and piston assemblies  20  needed for a specific use or application can be selected and provided on an individual modular radial compressor  10  of the present invention. The maximum efficiency is attained where eight cylinder and piston assemblies  20  are fastened to the housing  110 . 
     The number of arm protrusions  62  provided on the arm structure  60  determines the number of compression cycles the cylinder and piston assembly  20  performs for each revolution of the arm structure  60 , and is selected to meet the requirements of the given job or application. The arm structure  60  preferably includes an arm wheel  70  having an arm wheel circumferential surface  72  to which one or more arm protrusions  62  are mounted. The arm protrusions  62  preferably each include a radially extending arm mounted to the wheel circumferential surface  72 . A flywheel  130  preferably is provided beside the arm wheel  70  and mounted to the arm wheel axle  74  to provide smooth arm structure  60  rotation. 
     The piston structure  40  preferably includes a piston  42  connected to a piston rod  44  extending out of the cylinder  22  opposite the cylinder head  24  and having a piston rod abutment end  44   a  fitted with a piston rod abutment end spring-loaded ball bearing  48  to ride over arm protrusions  62  with minimal friction and absorb the impact of abutting arm protrusions  62 . The piston rod  44  preferably is fixedly secured to the piston  42  to remain substantially parallel to the cylinder side wall  26 . The piston  42  preferably is fitted with conventional piston rings  42   a  seated in circumferential piston ring grooves  42   b  to slide sealingly along the cylinder side wall  26 . The cylinder  22  preferably has a cylinder bottom wall  28  opposite the cylinder head  24  with a central piston rod passing port  18 . Oil O lubricates the cylinder side wall  26  and is retained by the cylinder bottom wall  28 , which preferably is cup-shaped to gather the oil O and funnel it toward the piston rod  44 . Oil O thus deposited on the piston rod  44  enters and is retained by a longitudinal series of oil gathering depressions  46  in the piston rod  44 , preferably in the form of a series of notches  46 , and thus is carried by the piston rod  44  out of the cylinder  22 . This mechanism removes blow-by oil O accumulated in the cylinder  22  and at the same time lubricates the piston rod  44  so that it moves through the port  18  in the cylinder bottom wall  28  with minimal friction. 
     The rotational drive means  80  preferably includes an electric drive motor  82  connected to the arm structure  60  with a drive connection. The drive connection extends between the drive motor  82  and the arm structure  60  and preferably takes the form of a drive belt  84  engaging a motor pulley  86  mounted on the motor drive shaft  82   a  and an arm structure pulley  88  mounted on an arm structure axle  74 . The arm structure axle  74  preferably is mounted in bearings retained in axle retaining members  102  and  104  which form part of the apparatus framework  100 . 
     The piston structure return means  90  preferably is a piston rod biasing spring  92  mounted to be compressed between a framework outer brace  106  and a framework inner brace  108  and engaged by a return spring pin (not shown) passing through the piston rod  44 . The piston rod biasing spring  92  preferably is a coil spring encircling the piston rod  44  and preferably has a progressively narrowing, conical configuration, or a cylindrical configuration. Alternatively or additionally the piston structure return means  90  is a piston return lever  94  rotatably mounted on a lever fulcrum pin  96  secured to the apparatus framework  100 . See  FIG. 1 . A return lever first end  94   a  engages the piston structure  40  such as the piston rod  44  and a return lever second end  94   b  is periodically displaced by the arm protrusion  62  or arm protrusions  62 . Another alternative or additional piston return means  90  is a piston return solenoid coil  98  fitted around the piston rod  44  wired to a power source through a switch. When activated, piston return solenoid coil  98  rapidly drives the piston rod  44  and piston  42  away from the cylinder head  24 . 
     The number of arm protrusions  62  on the arm structure  60  preferably can be altered such that the volume of fluid compressed per arm structure  60  revolution can be altered to accommodate any of a wide variety of applications. Where the arm protrusions  62  are arms  62 , each arm  62  preferably has an expanded arm mounting end  64  which fits engagingly into any of several arm channels  76  having outwardly narrowing arm engaging channel outward ends  78  and extending laterally across the width of and spaced periodically around the arm wheel circumferential surface  72  such that each arm  62  is slidably retained within a corresponding arm channel  76 . See  FIGS. 4-6 . The wheel circumferential surface  72  preferably is sufficiently wide and the arm channels  76  therefore sufficiently long that an arm  62  can be slid to a first channel end  76   a  of the given arm channel  76  and thus to a first side of the arm wheel circumferential surface  72  to align and register with and abut the piston structure  40 , and slid to a second channel end  76   b  and thus to a second side of the arm wheel circumferential surface  72  to be out of registration with the piston structure  40  during arm structure  60  rotation. The arms  62  are retained against sliding out of their respective channels  76  by a retaining clip  77  at the outward-most portion of each channel end  76   a  and  76   b . See  FIG. 5 . As a result, a selected number of arms  62  can be slid into position to register with the piston structure  40  as needed for each given apparatus  10  application. The modular radial compressor  10  can start with zero compression and gradually the arms  62  can be moved to the aligned position for compression and out of alignment again, if there is no demand for compressed gas such as air. This arm sliding can be done electrically, by any suitable electric mechanism, and operated remotely such as through a computer. 
     An outwardly biased spring-loaded retaining protrusion  66  is provided in the a recess in the middle of each arm channel end  76   a  and  76   b  to obstruct movement of and thus retain the arm  62  in the channel  76  at either the first or second channel end  76   a  or  76   b , respectively. See  FIGS. 7 and 8 . The retaining protrusions  66  are outwardly rounded, and when sufficient lateral force is applied to a given arm  62 , such as be an electro-magnet  140  described below, the retaining protrusion  66  is forced inwardly into its protrusion recess  66   a  by the arm  62  to become flush with the channel  76  bottom wall, permitting the arm  62  to move over the retaining protrusion  66  to the opposing channel end, and then the protrusion  66  is freed to spring outwardly to its initial retaining position. 
     The arms  62  preferably are moved to first or second arm wheel  70  sides by electro magnets  140  mounted to the apparatus framework  100  on opposing sides of the arm wheel  70  adjacent the arm wheel  70  circumferential perimeter. A small air gap is provided between the arms  62  and the electro magnets  140  so that arms  62  and electro magnets  140  never touch each other. Activation of either electro magnet  140  pulls each immediately adjacent arm  62  to the adjacent side of the arm wheel  70 . The given electro magnet  140  are activated for only a fraction of a second as the arm wheel  70  is rotated by the drive motor  82  so that only selected arms  62  are moved to a given side of the arm wheel  70  to provide a desired number of arms  62  in registration with the at least one cylinder and piston assembly  20  associated with the given arm wheel  70 . Electric power delivered through a manual switch or a computer programmed controller (not shown) activates one or the other electro magnet  140  as needed. Many other arm protrusion  62  moving mechanisms are contemplated, and the electro magnets are merely illustrative. 
     Another variation of the present modular radial compressor  10  includes a plurality of cylinder and piston assemblies  20  positioned and secured to the apparatus framework  100  to extend radially and equidistantly from the arm structure  60 . See  FIGS. 9 and 9A . The rotating arm protrusion  62  or arm protrusions  62  abut and displace each piston structure  40  in sequence with each arm structure  60  rotation. 
       FIG. 9  is a view as in  FIG. 1 , except that the modularity of the present invention is fully illustrated with the mounting of a second cylinder and piston assembly  20  in a second mounting opening in the housing  110 , thus exercising the option of providing two or more such assemblies  20  on a given modular radial compressor. The housing  110  can have a round, polygon or any other perimeter shape. As can be deduced from this FIGURE, if eight cylinder and piston assemblies  20  are included in this way, numerically matching the eight arm protrusions  62  on the arm wheel  74 , the modular radial compressor  10  can produce 64 compressions with each revolution of the wheel axle  74 . 
       FIG. 9A  is a view as in  FIG. 9 , except that four rather than eight arm structures  62  are provided. As noted in the Description of Drawings, the locations and potential locations of eight cylinder and piston assemblies  20  are labeled as CYLINDERS  1 - 8 . Since the present compressor  10  is modular, a cylinder and piston assembly  20  can be removed from the housing  110  so that only one assembly  20  remains, and one or more cylinder and piston assemblies  20  can be added to increase compressed fluid capacity by fastening them to the housing  110  at equal radial distances from the motor drive structure axle, as may be needed for particular uses. Where eight cylinder and piston assemblies  20  are attached to this four arm compressor, 32 compressions are produced with each revolution of the wheel axle  74 . Of course the same modularity is provided for the compressor  10  of  FIG. 9 , or for such compressors  10  have any other number of arm structures  62 . 
     Yet another variation of the compression apparatus  10  includes multiple arm structure and cylinder units  200 . The arm structures  60  preferably are arm wheels  70  mounted on a common axle and thus driven by a common rotation drive means  180  in the form of a motor. See  FIG. 10 . Individual clutch means  182  are provided for each arm structure  60  so that only a selected number of the arm structures  60  rotate with the drive means  180 . 
     As an alternative to the one or more cylinder and piston structure assemblies  20 , a bellows or other collapsible vessel (not shown) may be provided. 
     While the invention has been described, disclosed, illustrated and shown in various terms or certain embodiments or modifications which it has assumed in practice, the scope of the invention is not intended to be, nor should it be deemed to be, limited thereby and such other modifications or embodiments as may be suggested by the teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended.