Patent Publication Number: US-6212748-B1

Title: Self-contained and self-propelled machine for heat fusing polyolefin pipes

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 08/934,305, SELF-CONTAINED AND SELF-PROPELLED MACHINE AND METHOD FOR HEAT FUSING POLYOLEFIN PIPES, filed Sep. 19, 1997 now U.S. Pat. No. 5,814,182. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to portable machines for fusing polyolefin pipe and more particularly concerns a self-contained and self-propelled machine and method for the end-to-end treatment of two axially aligned pipe ends for the purpose of heat fusing such pipes together. 
     The principle of heat fusion is to heat two surfaces to a designated temperature and then fuse them together by application of force. The pressure causes flow of the melted materials, which causes mixing and thus fusion. When the polyolefin pipe is heated, the molecular structure is transformed from a crystalline state into an amorphous condition. When fusion pressure is applied, the molecules from each pipe end mix. As the joint cools, the molecules return to their crystalline form, the original interfaces are gone, and the two pipes have become one homogeneous pipe. The joint area becomes stronger than the pipe itself in both tensile and pressure conditions. 
     The principle operations of this fusion process include clamping the pipe pieces axially to allow all subsequent operations to take place, facing the pipe ends to establish clean parallel mating surfaces perpendicular to the centerline of the pipes, aligning the pipe ends with each other to minimize mismatch or high-low of the pipe walls, heating at a first specified force in a melt pattern that penetrates into the pipe around both pipe ends, joining the melt patterns with a second specified force which must be constant around the interface area and holding the molten joint immobile with a third specified force until adequately cooled. 
     Presently known portable pipe fusion machines are typically four wheeled cart type machines such as described in U.S. Pat. No. 3,729,360; U.S. Pat. No. 4,352,708 and U.S. Pat. No. 5,013,376. While these machines perform quite well, they require a good deal of labor and additional expensive equipment such as cranes, forklifts, tractors, trucks and the like to load, unload and precisely position the machine on the pipeline. Many machines are damaged during the loading and unloading process. Furthermore, the operators experience stress and fatigue in maneuvering the machines over difficult terrain and conditions. 
     In addition to the mobility, maneuverability and stability problems of the overall machines, various known machine components also present additional problems. The hydraulic systems are complex and unwieldy and require expenditure of considerable time and labor in preparation for off-cart use. The hydraulics are limited in that they permit selection of only a few operating pressures. The facing operation is complicated because the facer is not easily maneuverable into and out of position between the pipes by one operator when working with the machine off-cart. The facer guide bearings, which are traditionally integral to the body, wear and eventually accuracy in axial registration of the fixed and moving pipes is diminished. This results in undesirable down time of the machine during repair and costly repair to the facer. The jaw assembly necessary to grip and move the pipes during the process requires the front of the cart to be at the free pipe end of the pipe line. The heater is awkward to store for transport and to support on site during periods of non-use. 
     It is, therefore, an object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which are fully self-contained. Another object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which requires no additional equipment to support operation of the machine. Still another object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which has transport tracks aligned for movement along an axis parallel to the axial pipe alignment within the machine jaws. It is also an object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which is fully self-propelled for forward or reverse movement, left or right movement and pivotal movement about its center. A further object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which is movable along the pipeline from a completed joint to the next joint location. Another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which has a tracked undercarriage to increase mobility, stability and maneuverability. Yet another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which is easily maneuverable over difficult terrain. It is also an object of this invention to provide a machine, and a method using the machine, for fusing polyolefin pipes which facilitates axial alignment of the machine with the pipeline. A further object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which has a low center of mass to increase stability. Another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which has a jaw assembly easily removed from the machine into remote or in-ditch positions. Yet another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which is computer controlled for operation in a variety of modes. Another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which is computerized to permit selection of a wide range of operating pressures. Still another object of this invention is to provide a machine, and a method using the machine, for fusing polyolefin pipes which having a facer with wear compensating guide bearings which are easily replaceable in the field. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a machine and method are provided for end-to-end welding of polyolefin pipes. The machine is self-propelled and self-contained to perform all steps necessary to the welding process without need for any other machines or equipment. A chassis is supported on a pair of independently rotatable parallel tracks so as to permit lineal motion of the chassis in forward or reverse direction, turning motion of the chassis in left or right directions and rotational motion of the chassis about its center. 
     A jaw assembly mounted on one side of the chassis has a pair of fixed jaws for gripping an end of an existing pipe line and a pair of sliding jaws for gripping an end of free section of pipe to be welded to the existing pipe line. The sliding jaws move in unison on a carriage mounted on parallel guide rods extending on diametrically opposite axes in a horizontal plane in relation to the longitudinal central axis of the pipe line. Preferably, the pipe line and guide rod axes are parallel to the longitudinal axes of the tracks. It is also preferred that the jaw assembly be mounted on a skid that can be secured to the chassis in either a fixed jaw or sliding jaw forward position and that the jaw clamps be reversible so that the operator can access the jaws without reaching over the jaw assembly or the machine regardless of the skid position. 
     The tracks and the carriage are driven by a power system mounted on the other side of the chassis. Preferably, the power system includes a diesel engine which drives an hydraulic quad pump and a generator. A 12 volt battery, an electrical control box including a microprocessor and supporting electronic devices and a diesel fuel tank are also part of the power system. The tracks are hydraulically driven by two of the quad pump sections and are manually controlled by the operator at a first control station at the rear of the power system. The first control station includes separate track control valves and an operator&#39;s instrument panel. 
     The hydraulic system reservoir is located between the power system and the jaw assembly system on the chassis. An operator pendant and a hydraulic valve system are mounted on the chassis at a second operator&#39;s station toward the rear of the jaw assembly side of the chassis. The valve system allows the operator to manually control the hydraulic operation of the motor of a facer which is used to trim the pipe ends to parallel alignment for junction. It is preferred that the facer and the pipe lifts be driven by the same pump section as serves one of the tracks. The pendant allows the operator to electronically control the hydraulic pressure of the sliding carriage, control the operations of the sliding jaws between “apart ” and “together” conditions and monitor the carriage pressure and the operation of a heater that is used to melt the pipe ends for fusion throughout the welding process. The pendant includes a microprocessor which preferably enables the operator to operate the machine in a normal mode in which the operator manually controls the facing, soaking and fusing processes or an automatic mode in which the fusing process is automatically controlled by the microprocessor. The pendant microprocessor also allows the operator to choose a data logging mode in which the carriage pressure, heater temperature and time data are recorded to provide a history for each joint made by the machine. 
     Pipe lifts are provided on the chassis forward and rearward of the jaw assembly to facilitate adjustment of the pipe position in the machine by use of the hydraulic system at the second operator&#39;s station. Preferably, the pendant microprocessor includes a calculation algorithm to enable the operator to easily determine the fusing pressure to be applied to the pipe ends being joined. Furthermore, the pendant microprocessor, in cooperation with a rotary encoder and various electrical and hydraulic components, enables the operator to select at least as many as six operating pressures to be applied to the jaw assembly carriage. 
     The facer is preferably mounted on the machine by use of a removable pivot pin on a facer linkage mounted on the power system side of the machine. The linkage facilitates manual transfer of the facer from a hold position in which the linkage is closed to a use position in which the linkage is open and facer guide brackets are seated on the carriage guide rods with the facer centered on the pipe line axis. The heater is stored in a bag mounted on a frame. The frame is adapted for insertion between the fixed jaws with brackets riding on spacers connecting the fixed jaws during machine transport and for free standing during the welding processes. Furthermore, the skid can be removed from the chassis and placed into the pipe ditch, if desired. The operator pendant, the facer and the heater may be extended away from the machine by umbilicals for use with the jaw assembly in in-ditch or remote operations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
     FIG. 1 is a perspective view of a preferred embodiment of the welding machine; 
     FIG. 2 is a side elevation view of the machine of FIG. 1; 
     FIG. 3 is a front elevation view of the machine of FIG. 1; 
     FIG. 4 is a top plan view of the machine of FIG. 1; 
     FIG. 5 is an assembly perspective view of the machine of FIG. 1; 
     FIG. 5A is a side elevational view of a preferred embodiment of the carriage of the machine of FIG. 1; 
     FIG. 6 is a perspective view of the undercarriage and tracks of the machine of FIG. 1; 
     FIG. 7 is a perspective assembly view of a preferred embodiment of the reservoir of the machine of FIG. 1; 
     FIG. 8 is a bottom perspective view illustrating a preferred embodiment of the chassis of the machine of FIG. 1; 
     FIG. 9 is a side perspective view of the chassis of FIG. 8; 
     FIG. 10 is a top perspective view of the chassis of FIG. 8; 
     FIG. 11 is a left side perspective view of a preferred embodiment of the power system of the machine of FIG. 1; 
     FIG. 12 is a right side perspective view of the power system of FIG. 11; 
     FIG. 13 is a rear perspective of the power system of FIG. 11; 
     FIG. 14 is a rear perspective of the power system of FIG. 11; 
     FIG. 15 is a perspective view of a preferred embodiment of the pivot mechanism of the machine of FIG. 1; 
     FIG. 16 is a front elevation illustrating the operation of the pivot mechanism of FIG. 15; 
     FIG. 17 is a front elevation illustrating the operation of the pivot mechanism of FIG. 15; 
     FIG. 18 front elevation illustrating the operation of the pivot mechanism of FIG. 15; 
     FIG. 18A is a perspective view of a preferred embodiment of the frame for supporting the heater of the machine of FIG. 1; 
     FIG. 19 is a schematic diagram illustrating a preferred embodiment of the hydraulic system of the machine of FIG. 1; 
     FIG. 20 is a schematic diagram illustrating the electrical system of the machine of FIG. 1; 
     FIG. 21 is a schematic diagram illustrating a preferred embodiment of the portion of the electrical system of the machine of FIG. 1; 
     FIG. 22 is a schematic diagram illustrating a preferred embodiment of the portion of the electrical system of the machine of FIG. 1; 
     FIG. 23 is a schematic diagram illustrating a preferred embodiment of the portion of the electrical system of the machine of FIG. 1; 
     FIG. 24 is a schematic diagram illustrating a preferred embodiment of the portion of the electrical system of the machine of FIG. 1; 
     FIG. 25 is a graphic representation of a typical display on the operator pendant of the machine of FIG. 1; 
     FIG. 26 is a flow diagram illustrating the enabling and accessing procedures for optional data logging and automatic modes of the machine of FIG. 1; 
     FIG. 27 is a graphic representation of a microprocessor calibration array for the machine of FIG. 1; 
     FIG. 28 is a flow diagram for the pressure calibration process for the machine of FIG. 1; 
     FIG. 29 is a flow diagram illustrating the automatic pressure control operation of the microprocessor of the machine of FIG. 1; 
     FIG. 30 is a graphic demonstration of a display screen shown on the operator pendant of the machine of FIG. 1 for diagnostic purposes; 
     FIG. 31 is a flow diagram illustrating the data logging process of the machine of FIG. 1; 
     FIG. 32 is a front end plot of a pressure profile during fusion generated in the data logging mode of the machine of FIG. 1; 
     FIG. 33 is a summary plot of a pressure profile during fusion generated in the data logging mode of the machine of FIG. 1; 
     FIG. 34 is a flow diagram illustrating of the report upload process of the machine in FIG. 1 in the data logging and automatic modes; 
     FIG. 35 is a flow diagram illustrating of the report download process of the machine in FIG. 1 in the data logging and automatic modes; 
     FIG. 36 is a top plan view of a modified portion of the machine frame for use with a preferred embodiment of the jaw assembly skid; 
     FIG. 37 is a side elevation view of the modified portion of the machine frame shown in FIG. 36; 
     FIG. 38 is a top plan view of a preferred embodiment of the jaw assembly skid; 
     FIG. 39 is a side elevation view of the skid of FIG. 38; 
     FIG. 40 is a rear elevation view of the skid of FIG. 38; and 
     FIG. 41 is a side elevation view illustrating first and second mounting positions of the skid of FIGS. 38,  39  and  40  on the modified frame of FIGS. 36 and  37 . 
    
    
     While the invention will be described in connection with a preferred embodiments and methods of operation, it will be understood that it is not intended to limit the invention to those embodiments or methods. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     GENERAL ARRANGEMENT 
     A preferred embodiment of a fully self-contained and self-propelled welding machine M for on-site alignment, facing, heating and fusion of the ends of two axially aligned polyolefin pipes is illustrated in FIGS. 1 through 5. The welding machine M consists essentially of a machine frame or chassis C mounted on a track drive T and carrying a power supply system P, a jaw assembly J, lift roller assemblies L and hydraulic and electric operating systems Y and E. 
     The power supply system P has an electrical generator and hydraulic pumps driven by a diesel engine to provide all power required for the transportation and operation of the machine M. The jaw assembly J has fixed and sliding pipe gripping jaws mounted on a skid which can be reversibly loaded on the machine M in forward or reverse alignment. The jaw assembly J aligns the connected and free sections of pipe to be joined and reciprocates the free section of pipe toward and away from the connected section of pipe or the welding process apparata that may be inserted between the pipes. The pipe lift roller assemblies L have V-seats at the front and rear of the chassis C which are hydraulically raised and lowered to maintain the connected and free sections of pipe at a desired level in relation to the machine M and the jaw assembly J. The hydraulic and electric operating systems Y and E consist of a total package of components and connections including microprocessors necessary to allow an operator to control the operation of the power supply system P and the jaw assembly J in the performance of their various functions. A facing assembly F is preferably pivotally mounted on the machine M for insertion of its hydraulically driven facer between the pipe ends to plane their surfaces into proper alignment for fusing to a good joint. A free standing heater H is connect able to the generator for power and is connect able to the electrical operator system E for control and is insertable between the pipe ends to be joined to heat them to a molten or fusible state. The operations of the facer and the heater H are controlled by the hydraulic and electric systems Y and E of the machine M. 
     TRACK DRIVE 
     The track drive T is illustrated in greater detail in FIG.  6  and includes left and right tracks  11  and  13  mounted on track frames  15  and  17  and driven by hydraulic wheel motors  19  and  21 . Preferably, the tracks  11  and  13  are made of rubber and travel on roller sprockets and the motors  19  and  21  include parking brakes and dynamic brakes. An adjustable track tension mechanism is also desirable. The HINOWA model PT15G track assembly with anti-cavitation valves, negative brakes and rubber tracks has been found to be quite suitable for the purpose. The track frames  15  and  17  are secured in parallel alignment by an undercarriage assembly  23 . Mounting brackets  25  and pads  27  are provided on the undercarriage assembly  23  for purposes hereinafter explained. 
     HYDRAULIC FLUID RESERVOIR 
     Looking at FIGS. 7 and 8, the hydraulic fluid reservoir  31  which serves the hydraulic system of the machine M includes a fluid retaining basin  33 . Pads  37  are provided on the lower portion of the basin  33  to rest on the undercarriage pads  27  to support the reservoir  31 . Hose connections  39  and a refill port  41  are provided in the reservoir  31 . A control manifold  43  and an hydraulic system electrical junction box  44  are mounted at the rear of the reservoir  31  above the reservoir drain plug  45 . 
     CHASSIS 
     Looking at FIGS. 8-10, the chassis C consists of a tubular frame essentially arranged in rectangular sections extending in the longitudinal direction of the machine M, the right hand rectangular section  47  generally supporting the power supply system P of the machine M, the middle rectangular section  49  generally supported by the hydraulic reservoir  31  and the left hand rectangular section  51  generally supporting the jaw assembly J of the machine M. As shown, the rear of the right hand rectangular section  47  of the chassis C is divided into forward and rear sections. The rear section includes the engine mounts  53 . Two pairs of oppositely directed latching members  55  and a pair of centrally located ears  57  with holes  59  are fixed to the left hand rectangular section  51  for purposes hereinafter explained. The pairs of latching members and ears  57  are transversely aligned in relation to the longitudinal or travel direction of the machine M. The chassis C also has a front bumper  61  along the front portion of its right hand rectangular section  47 . As seen in FIGS. 1-5 and  8 - 10 , the chassis C also supports an operator pendant  63  which is pivotally connected in a pendant bracket  65  for 180 degree rotation from the operable condition illustrated to a storage condition in which the pendant  63  is shielded and protected by the walls of the bracket  65 . The pendant  63  will generally be carried within the bracket  65  during transit of the machine M and is preferably maintained in the transit position by a gas spring which will allow the pendant  63  to rotate into the operating position shown. 
     PIPE LIFT ROLLER ASSEMBLIES 
     Continuing in FIGS. 1-5 and  8 - 10 , the pipe lift roller assemblies L, which facilitate manipulation of the pipe sections to be welded to a proper elevation in relation to the machine M and the jaw assembly J, have longitudinal members  67  which are pivotally mounted to the chassis C by hinge pins  69 . Vertical U-shaped plates  71  are welded to the free ends of the longitudinal members  67 . A pair of rollers  73 , preferably sections of pipe cut to a desired length and having nylon bearings  75  on their ends, are mounted in a V arrangement between ears  77  on each of the plates  71 . As can best be seen in FIG. 3, shafts  79  extending through the roller bearings  75  are connected at the bottom of each V by a pin  81  extending through apertures in flatted ends of the shafts  79 . The level of each of the V aligned rollers  73  of the pipe lifts L is independently changed by operation of an hydraulic cylinder  83  or  84  which is pivotally pinned between the plate  71  and the undercarriage mounting bracket  25 , as is best seen in FIGS. 2 and 8. An hydraulic pipe lift valve assembly  85  is mounted on the chassis C adjacent the operator pendant  63  for operator control of the cylinders  83  and  84 . 
     POWER SUPPLY SYSTEM 
     The power supply system P is illustrated in greater detail in FIGS. 11-14. A diesel engine  91  with an engine alternator  92  is served by a fuel tank  93  and battery  95  which also provides power to the control circuits of the electric operating system E. A radiator  97  and an air filter  99  are located behind the engine  91 . An hydraulic pump  101  is mounted rearwardly of the radiator  97  in alignment with the engine crank shaft on an engine mount bracket  103 . The hydraulic pump  101  shown is a quad pump having a manifold  105  connected between its third and fourth stages. Four hoses (not shown) extend from the reservoir connections  39  to the pump  101 . Left and right control valves  107  and  109  which operate the left and right tracks  11  and  13 , respectively, are mounted on the rearmost portion of the power supply system P on an operator&#39;s station  111  which includes the engine instrument panel (not shown). An exhaust pipe  113  extends from the engine  91  to a muffler  115 . A generator  117  is aligned on the engine crank shaft in front of the bell housing  119 . An electrical junction box  121  is mounted on the generator  117 . A vertical plate  123 , best seen in FIGS. 3-5, separates a main electrical control box  125  from the fuel tank  93 . The front portion of the power supply system P is covered by a front shroud or hood  127  and the rear portion of the power supply system P is covered by a rear shroud or hood  129 . 
     FACING ASSEMBLY 
     A pivot mechanism for the facing assembly F is mounted on the front shroud or hood  127 , as can best be seen in FIGS. 1-5,  11  and  12 . The pivot mechanism is shown in greater detail in FIG.  15 . The pivot mechanism consists of a horizontal section of U-shaped channel  131  fixed on its side to the front hood  127  and extending parallel to the longitudinal axis of the tracks  11  and  13  with the open side of the channel  131  facing toward the left side of the machine M. A cam follower  133  is slidably engaged for travel within the channel  131 . A pair of spaced apart vertical plates  135  and  137  are fixed to the front hood  127  with a rod  139  fixed therebetween and aligned in parallel relationship with the channel  131 . A sleeve  141  is mounted in sliding engagement on the rod  139 . A bracket  143  is fixed to the cam follower  33  and the sleeve  141  for forward and rearward motion parallel to the longitudinal axis of the machine M. The bracket  143  consists essentially of a pair of parallel plates  145  and  147  in a tilted T configuration with the base of the T mounted on the sleeve  141  and the lower end of the top of the T fixed to the cam follower  133 . A facer linkage is connected between the parallel plates  145  and  147 . A tubular member  149  of the linkage is pivotally mounted at one end at the bottom of the T by a pin (not shown) which extends through the plates  145  and  147  and a sleeve  151  which extends through the tubular member  149 . An H-bar  153  is pivotally connected to the other end of the tubular member  149  by another pin (not shown) which extends through one end of the H-bar  153  with the free end of the tubular member  149  between the H bar uprights. The cross member of the H-bar  153  is seated on the tubular member  149  when the linkage is in a closed condition. Thus, the tubular member  149  limits the downward motion of the H bar  153  in the linkage closed condition. Furthermore, the pin connecting the H bar  153  to the tubular member  149  is longer than the distance between the plates  145  and  147 , so that the pin can engage on the edge of the vertical portion of the T-shaped plates  145  and  147 . Thus, the downward motion of the tubular member  149  is limited by the engagement of the pin with the bracket  143  when the linkage is in the closed condition. Holes  157  are also provided in the free end of the H-bar  153  for insertion of a removable pin (not shown) to connect the facer to the linkage, as will hereinafter be explained. A pair of L-shaped detents  159  project upwardly from the bottom of the T on each of the plates  145  and  147 . A pin (not shown) that is inserted into the holes  157  through the H bar  153  to secure the facer to the linkage is longer than the distance between the detents  159  so that, when the facer is mounted on the linkage and the linkage is in its closed condition supporting the facer for transport, the detents  159  will engage with the pin (not shown) to prevent the linkage and the facer from rolling over should the machine M traverse a hill so steep as to urge the facer linkage. The free or upper end of the cross portion of the bracket  143  is provided with a bumper  161  on which the facer will be seated when the linkage is in the closed condition. This portion of the bracket  143  is also provided with a latch  163  made of sheet metal with nylon rollers  165  mounted on the upper portion of the latch  163  and aligned on an axis parallel to the longitudinal axis of the machine M for a purpose hereafter explained. The operation of the pivot mechanism of the facing assembly F can best be understood in reference to FIGS. 16,  17  and  18 . The facer  167  is seated in the pivot mechanism and its removable mounting pin (not shown) inserted through the H-bar  153  and its facer  167  at the first pivot point  169 . The linkage, shown in its closed condition in FIG. 16, has its middle pin (not shown) resting on the bracket plates  145  and  147 . The middle pin also provides a second pivot point  171 . The cross member of the H-bar  153  is seated on top of the tubular member  149 . The connection of the tubular member  149  to the bracket plates  145  and  147  provides the third pivot point  173  of the linkage. In the closed condition of the linkage shown in FIG. 16, the facer  167  is seated on the bumper  161  and is mounted for rotation about the first pivot point  169 . In this position, the rollers  65  of the latch  163  ride above a top rest button  175  provided on the facer  167  to prevent the facer from tipping in a clockwise direction. The facer  167  is provided with a first handle  177  which is positioned at approximately 3 o&#39;clock when looking at the facer  167  from the front. A second handle  179  is located between approximately 10 and 11 o&#39;clock on the facer  167 . The second handle  179  is pivotally connected to the facer  167  about a pin  181  and has a latching portion  183  at its free end which extends around and cooperates with a guide rod bracket  185  for reasons to be hereinafter explained. An identical guide rod bracket  187  is also provided on the facer  167  at a point diametrically opposite the first bracket  185 . As shown, the guide rod brackets  185  and  187  are substantially one-half octagons in cross section and are mounted by bolts (not shown) in conforming seats provided in the facer  167 . The first bracket  183  is aligned with its opening transverse to the facer diameter and on its clockwise side when viewing the facer  167  from the front of the machine M. The second bracket  187  has its opening aligned with the facer diameter with the opening away from the facer  167 . To use the facer  167 , it is necessary to transfer it to a position in which its center axis  189  is in alignment with the center axis  191  of the jaw assembly J of the machine M. Looking at FIGS. 16 and 17, the movement of the facer  167  from the linkage-closed position to an intermediate position is illustrated. As shown, the operator O grasps the first handle  177  of the facer  167  and pulls the facer  167  toward the operator O. Initially, the first pivot point  169  will be moved along an arcuate path to a point  193  during which motion the second pivot point  171  will have rotated from approximately a 9 o&#39;clock position to a 12 o&#39;clock position  195 . The downward motion of the facer  167  in moving to the intermediate position shown in FIG. 17 is limited by the engagement of the second guide rod bracket  187  on one of the guide rods  197  of the jaw assembly J. In this position, the first handle  177  of the facer  167  will have moved to approximately between 4 and 5 o&#39;clock and the upper handle  179  will have shifted to approximately 12 o&#39;clock. The operator O then releases the first handle  177  and grasps the second handle  179 , continuing to pull the facer  167  toward the operator O to continue the movement of the facer  167  into its use or linkage-opened position, as is shown in FIG.  18 . As this motion continues, the first pivot point  169  of the linkage moves arcuately from the intermediate point  193  on its path to the final point  199  on its path. During this motion, the second pivot point  171  of the linkage will move substantially horizontally from its intermediate position  195  to its final position  201 . During the motion of the linkage from the intermediate to the final position, the second guide rod bracket  187  on the facer  167  remains engaged with the J assembly guide rod  197  until the first bracket  185  on the facer  167  engages with a second guide rod  203  which is diametrically opposite and parallel to the first guide rod  197 . While the guide rod brackets  183  and  185  are semi-octagonal in configuration, they function as V-blocks with only two sides of each bracket  183  and  185  coming into contact with their respective guide rods  203  and  197 . The two surface seating of the diametrically opposed guide rod brackets  185  and  187  on the diametrically opposed guide rods  203  and  197 , respectively, biased by the torque of the facer  167  during the facing process, assures the accurate registration of the center axes  189  and  191  of the facer  167  and the jaw assembly J, respectively. Since the guide rod brackets  185  and  187  are replaceable, down time of the machine M resulting from misalignment of the axes  189  and  191  of the facer  167  and the jaw assembly J as a result of wear to the guide rod brackets  185  and  187  is minimized, replacement of each bracket  185  and  187  being possible without detachment of the facer  167  from the linkage. In the operating or linkage-open position, the latch  183  of the second handle  179  on the facer  167  engages with the guide rod  203  to lock the facer  167  in position with respect to the jaw assembly J. Preferably, the latch  183  is spring loaded to hold it in its closed position on the guide rod  203 . After use of the facer  167 , the operation of the linkage to return the facer  167  to its linkage-closed position is simply the reverse of the procedure hereinbefore described. Looking back to FIG. 16, a third handle  205  is located at approximately 8 to 9 o&#39;clock on the facer  167  to provide additional maneuverability for the operator O when the facer  167  is used independently of the linkage. All that is necessary to disconnect the facer  167  from the linkage for independent use or transport is to remove the pin at the first pivot point  169  between the H-bar  153  and the facer  167 . The operation of the facer  167  in facing the ends of the pipes is thoroughly explained in U.S. Pat. No. 3,729,360 and that disclosure is herein incorporated by reference. The McElroy Rotating Planar-Block facer with three cutter blades on a rotating block chain driven by a hydraulic motor is suitable for the purposes of this invention. 
     JAW ASSEMBLY 
     Looking again at FIGS. 2-5 and  16 - 18 , the configuration of the jaw assembly J can be understood. A basic explanation of the structure and operation of jaw assemblies for pipe welding machines is given in U.S. Pat. No. 3,729,360 entitled “Portable Thermoplastic Pipe Fusion Apparatus” and U.S. Pat. No. 4,352,708 entitled “Defined Force Fusion Machine for Jointing Plastic Pipe.” The present jaw assembly J includes a front moving jaw  207  and a rear moving jaw  209  moved in unison by a moving jaw carriage  210 , a front fixed jaw  211  and a rear fixed jaw  213 . All of the jaws  207 ,  209 ,  211  and  213  are substantially identical. A skid  215  has a vertical yoke plate  217  fixed to and extending upwardly from its front end. The front fixed jaw  211  is fixed to and extends upwardly from the rear end of the skid  215 . The guide rods  197  and  203  are fixed between the yoke plate  217  and the front fixed jaw  211 . The moving jaws  207  and  209  are connected to form a carriage  210  mounted for reciprocating motion on the guide rods  203  and  197 . As can best be seen in FIG. 4, the rear fixed jaw  213  is fixed to the front fixed jaw  211  by spacers  219  aligned with the guide rods  197  and  203  so as to be removable from the jaw assembly J if the assembly J is used separately of the machine M. Removal of the rear fixed jaw  213  results in an assembly J that is much lighter and easier to handle and also facilitates the use of the assembly J to fuse a section of pipe to a T junction which makes gripping the pipe between two jaws impossible. As can best be seen in FIGS. 3 and 5, the upper and lower portions of each of the jaws  207 ,  209 ,  211  and  213  are connected by a pivot pin  221  and on their opposite sides by eye bolts connected by pivot pins identical in diameter. Thus, the direction of opening of each of the jaws  207 ,  209 ,  211  and  213  can be reversed by pulling the pins  221  and inverting and repinning the upper portion of each of the jaws to the opposite side of its lower portion. In addition, the front end of the skid  215  includes a transverse member  223  engagable with the front or rear latching members  55  on the chassis C shown in FIG.  8 . Holes  225  are also provided through the sidewalls of the skid  215  for alignment with the holes  59  through the ears  57  on the chassis C. Thus, the skid  215  is readily reversible on the chassis C by removal of the locking pins (not shown) from the holes  59  and  225  in the ears  57  and the skid  215 , disengagement of the skid  215  from one pair of latching members  55 , 180 degree rotation of the skid  215 , re-engagement of the skid  215  with the opposite pair of latching members  55  and reinsertion of the locking pins (not shown) through the holes  59  and  225 . Thus, the skid  215  can be supported on the frame or chassis C with the first or moving jaws  207  and  209  forward of the second or fixed jaws  211  or  213  in a first mounting position and with the second or fixed jaws  213  and  211  forward of the first or moving jaws  209  and  207  in a second mounting position. Depending on the desired orientation of the skid  215  on the chassis C, the hinging of the upper portions of the jaws  207 ,  209 ,  211  and  213  can be selected by use of the jaw pins  225  to assure that the operator O can access the jaw assembly J without reaching over the machine M. The moving jaw carriage  210  is shown in greater detail in FIG.  5 A. The guide rod  203  is fixed at one end  216  to the vertical yoke plate  217  and at the other end  218  to the front fixed jaw  211 . Bearings  212  and  214  slide on the guide rod  203 . The bearings  212  and  214  are connected by a cylinder  222  and are sealed to the guide rod  203  to define an hydraulic chamber  224  around the guide rod  203  which is divided by a piston  226 . The hydraulic fluid source is connected to the chamber  224  on each side of the piston  226  by ports  228  and  230 . The other guide rod  197  supports an identical arrangement. The moving jaw carriage  210  is hydraulically reciprocated on the guide rods  197  and  203  by the hydraulic system Y in a manner hereinafter described. 
     TRAPEZOIDAL SKID JAW ASSEMBLY 
     A specially preferred embodiment of the reversible jaw assembly is illustrated in FIGS. 36-41. Looking first at FIGS. 36 and 37, to accommodate the preferred skid arrangement, the frame F of the machine M shown in FIGS. 8-10 is modified to include a base  701  with upwardly extending parallel sidewalls  703 . The parallel sidewalls  703  support spaced apart parallel rods  705  and  707  which are rigidly fixed to the sidewalls  703 . In addition, the sidewalls  703  have two pairs of apertures  709  and  711  which are oppositely aligned and symmetrically displaced between the rods  705  and  707 . As shown, the central portion of the base  701  has a large opening  713 , preferably substantially symmetrically located between the axes of the oppositely aligned apertures  709  and  711 . The base  701  is reinforced by end cross members  715  and  717  fixed to the base  701  and to the ends of the sidewalls  703 . A rod  719  L-shaped at one end to form a handle  721  is slidably insertable through either pair of aligned apertures  709  or  711 . Seats  723  are fixed to one of the sidewalls  703  proximate each aligned pair of apertures  709  and  711  so as to support the handle  721  of the rod  719  inserted through the adjacent pair of apertures  709  or  711 . 
     Turning to FIGS. 38-40, the preferred embodiment of the skid  731  includes a pair of parallel spaced apart angle irons having one wall  733  forming the base portion of the skid  731  and upright sidewalls  735 . The sidewalls are spaced apart by cross members  737  and  739  at a distance such that the sidewalls  735  may be snugly nestled between the sidewalls  703  on the machine frame F. As shown, one of the cross members  737  is provided with mounts  741  for connecting the jaw assembly hereinbefore described to the skid  731 . As can best be seen in FIG. 39, the sidewalls  735  of the angle iron are cut at an angle so as to take on a trapezoidal configuration with the lower parallel side of the trapezoid being along the base  733  of the angle irons. The length of the angle irons is such that, when the skid  731  is nestled on the base  701 , the center of the angled edges  743  and  745  will be substantially tangent to one pair of aligned apertures  709  or  711  while the other angled edge  745  or  743  will be substantially tangent to the more distant opposite rod  707  or  705  fixed to the frame base sidewalls  703 . 
     The reversibility of this preferred embodiment of the skid  731  is best seen in reference to FIG. 41 which illustrates the modified base  701  of the machine M and the skid  731  disposed for mounting in forward  751  and reverse  753  positions on the base  701  of the machine M. As shown, in the first or forward position  751 , one angular edge  743  of the skid  731  will be tangent to the forward aperture  709  when the other angular edge  745  of the skid  731  slides into tangential abutment against the rear fixed rod  707 . Conversely, in the second or rearward position  753 , the other angular edge  745  of the skid  731  will be tangent to the rearward aperture  711  when the one angular edge  743  of the skid  731  slides into tangential abutment against the forward fixed rod  705 . 
     Thus, in operation of the trapezoidal skid jaw assembly, assuming the skid  731  is mounted in the forward position on the machine M, the handle  721  on the rod  719  is rotated out of its seat  723  and withdrawn from the forward apertures  709  in the machine M. The skid  731  is then slid in a forward direction to clear the rod  707  at its rear. The skid  731  can then be removed and rotated 180 degrees and again nestled in position on the base  701 . The skid is then slid forward until the edges  745  come into tangential abutment with the forward rod  715  on the machine frame F. The rod  719  is then inserted through the rearward apertures  711  in the machine M. The edges  743  of the skid  731  should then be substantially tangent to the rod  719 . The handle  721  is then rotated into its seat  723  to lock the rod  719  in place. The pivot positions of the jaws of the jaw assembly are then reversed as hereinbefore described to complete the transition. 
     HEATER 
     The heater H is shown in FIGS. 20 and 21 in block and schematic form. Typical heaters suitable for the purposes of this invention are described in greater detail in U.S. Pat. No. 3,846,208 entitled “Combination Pipe Fusion Unit” and U.S. Pat. No. 4,227,067 entitled “Heater Adapter for Making Polyethylene Pipe Connections.” Looking at FIGS. 2 and 4, a frame  220  shown in FIG. 18A for supporting the heater bag (not shown) in which the heater H is stored is insertable in the space  227  between the front and rear fixed jaws  211  and  213  and is supported by the spacers  219  connecting the rear fixed jaw  213  to the front fixed jaw  211 . The frame  220  consists of a pair of horizontal bag supports  229  integrally extending across a pair of parallel U-shaped base members  234 . The parallel base members  234  and bag supports  229  are spaced apart by a pair of side plates  236 . A pair of legs  238  of elongated W shape are pivotally connected to the plates  236  so as to be expandable into a broader base area for increased stability of the frame  220  on the ground. A pair of inverted U-brackets  242  are fixed to the plates  236  for seating on the spacers  219 . The heater bag (not shown) has a collar into which the supports  229  are inserted as the bag is dropped into the frame  220  and the heater H rests on the top edge of the side plates  236 . 
     HYDRAULIC SYSTEM 
     Turning to FIG. 19, the hydraulic system Y of the machine M is illustrated. Four lines  231 ,  233 ,  235  and  237  connect the left track section  239 , the right track section  241 , the high volume low pressure carriage section  243  and the low volume high pressure carriage section  245  of the quad gear pump  101 , such as a CASAPPA PLP20, 8-03S1-LOC/OC/20.8-LOC/OC/20.4-LOC/BA/10.1-LOB/BA-S+VEP/FC38GR.1-1, to the reservoir  31 . The left track section  239  of the pump  101  is connected through a line  247  to the single spool monoblock valve with power beyond  107 , such as a WALVOIL SD5/1-P(KG3)/28L/AE valve, which is in turn connected across the left track hydraulic drive motor  19 . The right track section  241  of the pump  101  is connected by a line  251  to the single spool monoblock valve with no power beyond  109 , such as a WALVOIL SD5/1-P(KG3)/28L/AET valve, which is in turn connected across the right track hydraulic drive motor  21 . The valves  107  and  109  as well as the drive motors  19  and  21  are connected by return lines to the reservoir  31  to complete the continuous flow of hydraulic fluid when the left and right tracks  11  and  13  are being operated. The line  247  extending to the left track valve  107  is serially connected to the three spool monoblock valve  85 , such as a WALVOIL SD5/3-P(SV)/18L/416L/18L/AET valve, which is in turn connected across the pipe lift cylinders  83  and  84  at the front and rear of the chassis C and the facer motor  167 . The pipe lift valve  85  is also connected by a return line to the reservoir  31  so as to complete the path of hydraulic fluid flow when the left track  11  is not in use and the pipe lift cylinders  83  and  84  are being operated. The line  247  is also serially connected through the pipe lift valve  85  to a first quick disconnect  257 . A second quick disconnect  259  is connected by a return line to the reservoir  31 . The motor of the facer  167  is insertable between the quick disconnects  257  and  259  and hydraulic fluid will flow through the motor of the facer  167  to the return  31  to maintain continuous flow of the hydraulic system when the left track motor  19  and the pipe lifters  83  and  84  are not in use. The left and right track valves  107  and  109  permit the operator to choose forward or reverse rotation of the tracks  11  and  13 , respectively. Looking at FIGS. 1 and 19, the left spool  86  of the pipe lift valve  85  controls the operation of the front pipe lift cylinder  83 , the center spool  87  controls the operation of the facer  167  and the right spool  88  controls the operation of the rear pipe lift cylinder  84 . As long as the engine  91  is running, hydraulic flow is continuous from the reservoir  31  through the left track pump section  239 , the left track valve  107 , the pipe lift valves  86  and  88 , the facer valve  87  and back to the reservoir  31 , as well as through the right track pump section  241  through the right track valve  109  and back to the reservoir  31 . Pressure gauges  261  and  263  are connected in the left and right track pump section lines  247  and  251  for use in setting up the system for operation. The high volume low pressure carriage section  243  of the pump  101  is connected by a line  265  through a check valve  267  and another line  269  to the carriage control manifold  43 . The line  265  leading into the check valve  267  is also connected to an unloading valve  273 . The low volume high pressure carriage section  245  of the pump  101  is also connected to the unloading valve  273  and to the input line  269  by a line  275 . The unloading valve  273  is thence connected by an outlet line  277  to a filter unit  279  and thence by a line  281  back to the reservoir  31 . In the operation of this part of the system Y, if the carriage  210  of the moving jaws  207  and  209  is idle, the hydraulic system Y maintains a constant pressure on the carriage control manifold  43 . When the pump  101  comes up to pressure, the unloading valve  273  passes the high volume path oil back to the reservoir  31  through the filter  279 . The low volume section  245  of the pump then maintains the pressure on the manifold  43  and seats the check valve  267 . Looking at the carriage control manifold  43 , a high pressure relief valve  283  connects the input line  269  to the reservoir  31 . The input line  269  also extends through a pressure reducing valve  285 , such as a Sun PVDB-LAN, to a pressure transducer  287 , such as a SQD PTA6093. A servo valve  289 , such as a FEMA 85820 PPC valve, is responsive to a DC current derived from the pressure transducer  287  to meter the flow of oil back to the reservoir  31  and controls the pressure reducing valve  285  which controls the pressure applied to the carriage  210 . The manifold reduced pressure outlet line  286  is then connected to a directional control valve  293  with a return to the reservoir  31 . A directional control valve  293  is connected to quick disconnects  295  and  296 , to and from which the carriage cylinders  222  and  232  may be readily connected and disconnected by quick disconnect  297  for removal or reversal of the carriage jaw assembly J from or on the machine M. 
     ELECTRICAL SYSTEM 
     The electrical system E of the machine M is illustrated in block form in FIG.  20 . The generator  117  is connected by a cable  301  to the generator junction box  121 . From the junction box  121 , another cable  303  extends to one side of a connector  305 . The other side of the connector  305  is connected by a cable  307  to the heater H. The junction box  121  is also connected by another cable  309  through a connector  311  to the main electrical control box  125 . Three other connectors  313 ,  315  and  317  are also mounted on the control box  125 . One connector  313  connects a cable  319  which extends to the engine  91  and the engine instrument panel at the operator&#39;s station  111  for connection of a multitude of electrical components which will be denoted hereinafter in the electrical schematic diagrams of FIGS. 21-24 by the symbol a if they are on the engine  91  and by the symbol β if they are on the instrument panel at the operator&#39;s station  111 . The control box  125  is connected through the other two connectors  315  and  317  by cables  321  and  323 , respectively, to the hydraulics junction box  44 . The hydraulics junction box  44  is in turn connected by a cable  325  to the operator pendant  63 . As seen in FIGS. 1 and 20, externally, the operator pendant  63  has an emergency stop switch  327 , a key pad  329 , two toggle switches  331  and  333 , a rotary encoder  335  and an LCD display  337 . The operator pendant  63  is also adapted for connection by a cable  339  to an external peripheral device such as a printer (not shown). Internally, the operator pendant  63  houses a variety of electrical components which will be identified hereafter in the electrical schematic diagrams of FIGS. 21-24 by the symbol y. The hydraulic junction box  44  is also connected by four separate cables  341 ,  343 ,  345  and  347  to the carriage pressure control valve  289 , two carriage control valve solenoids  288  and  290  and the carriage pressure transducer  287 , respectively. The internal components of the control box  125  are identified hereafter in the electrical schematic diagrams of FIGS. 21-24 by the symbol Δ. 
     The controls for the engine  91  are illustrated in the electrical schematic diagram of FIG.  21 . The generator  117  is connected through a protection device such as a breaker  353  and a normally open contact  354  of a heater control relay  356  to the heater H and back to the generator  117 . The voltage across the generator  117  is indicated by a voltmeter  355 . The system battery  95  is preferably a 12 volt lead/acid battery. The starter motor  359  is connected across the battery  95  through another normally open starter solenoid relay contact  361 . The starter solenoid relay  357  is connected across the battery  95  through a four-way key switch  363  which has start, glow plug, off and run positions. The switch contacts  365 ,  367  and  369  illustrate which switch contacts close in the start, glow plug and run positions. When the key switch  363  is in the start position, the circuit to the starter solenoid relay coil  357  is closed and the contact  361  connecting the starter motor  359  closes. The glow plug timer  371  is also connected across the battery  95  by the key switch  363  in the start position. The glow plug  373  is connected across the battery  95  by the key switch  363  in the glow plug position and a glow lamp  375  indicates the status of the glow plug  373 . An hour meter  377  is connected across the battery  95  when the key switch  363  is closed in the start, run and glow plug positions. When the glow lamp  375  is out, the key switch  363  can be turned from the glow plug position to the start position. The start, run and glow plug positions of the key switch  363  also connect a control circuit relay coil  379 , a throttle relay coil  381 , an oil pressure switch  383  and a water temperature switch  385  across the battery  95 . The control circuit relay coil  379  is protected by a fuse  387 . The operation of the throttle relay coil  381  is controlled by a throttle speed switch  389 . The oil pressure switch  383  and water temperature switch  385  are each series connected with indicating lights  391  and  393 , respectively. The control circuit relay coil  379 , throttle relay coil  381 , oil pressure switch  383  and water temperature switch  385  are also connected across the battery  95  along with a voltage regulator  395  and alternator  397 . A charge indicator light  399  connected between the regulator  395  and the battery return line indicates when charging is taking place. The throttle speed switch  389  is open for low speed operation and closed for high speed operation. An input terminal of a microprocessor  401  in the main electrical control box  125  detects the position of the throttle speed switch  389 . A throttle speed solenoid  403  having pull in and holding currents is connected across the battery  95  by a contact  405  of the throttle relay coil  381 . A timer  407  connected across the battery  95  by a contact  409  of the fuel shut-off relay  467  applies an approximately 40 amp pull in current and then an approximately 0.8 amp holding current to a fuel shut off solenoid  411  connected across the timer  407 . A fuse  413  protects this circuit. Thus, the engine  91  can be shut off by operation of the key switch  363  to open the starter solenoid contact  409  or by the operation of the fuel shut off solenoid  411  resulting in cutting off the fuel supply to the engine  91 . The remainder of the control circuit is protected by a fuse  415  and a contact  417  of the control circuit relay coil  379  which are series connected to the positive terminal of the battery  95  as well as by the surge suppressor  416  and the reverse voltage protection diode  418 . 
     The hydraulic system controls are illustrated in FIG.  22 . The FEMA PPC servo valve  289  is connected across the battery  95  through a current control device  419  located in the main electrical control box  125 . The device  419  is also connected to the control box microprocessor  401  which provides a control voltage to the device  419  indicative of the pressure desired at the carriage  210 , as is hereinafter explained. The output of the carriage pressure transducer  287  is compared with the voltage desired to determine when the desired pressure is obtained. The voltage applied to the current control device  419  by the microprocessor  401  is selected by use of the encoder  335  in the operator pendant  63  as will hereinafter be explained. A +/−12 volt dc-dc converter  423  converts 12 volts to 24 volts to power the devices contained in the main electrical control box  125 . The converter  423  is connected to a plus 24 volt terminal and a ground terminal of the control box microprocessor  401  and also through an LED  425  which indicates when power to the control box microprocessor  401  is on. For reasons to be hereafter explained, the hydraulic control system Y may also include a linear transducer  427  connected across the battery  95  and mounted on the jaw assembly carriage  210  to measure the travel distance of the carriage  210  if the machine M is operated in an automatic mode. A digital converter  429  counts the transducer pulses to determine the relative position of the carriage  210  on its travel path and provides a signal to the control box microprocessor  401  usable to determine when to stop and start the carriage  210  and how far the carriage  210  is to move. A +/−15 volt dc/dc converter  431  is also connected across the battery  95  through a protective fuse  433 . The converter  431  powers a low pass filter  435  which provides a signal derived from the output of the carriage pressure transducer  287  which is connected across the battery  95  to a terminal of the control box microprocessor  401 . 
     Continuing on to FIG. 23, an audio alert device  437  mounted in the operator pendant  63  is connected between terminals in a microprocessor  440  in the operator pendant  63  and to the positive side of the battery  95 . One terminal of the microprocessor  440  is also connected to the battery return or ground. A 5 volt regulator  441  serving the back light of the LCD  337  in the operator pendant  63  is also connected across the battery  95 . An RTD module  445  is connected across the battery  95  and to several contacts in the control box microprocessor  401  and the operator pendant microprocessor  440 . The module  445  senses the temperature in the heater H and provides signals to the microprocessors  401  and  440  as is hereafter explained. The return line of the battery  95  is also connected to the rotary encoder  335  with the output terminal of the encoder  335  being connected to the operator pendant microprocessor  440 . The encoder  335  is connected to the integrated circuit decoder chip  447 . The decoder chip  447  has an output to a port of the operator pendant microprocessor  440 . It also has an output which extends through a flip-flop switch  449  to another port of the operator pendant microprocessor  440 . Finally, an output of the encoder  335  is connected with an output of the decoder chip  447  to another port of the operator pendant microprocessor  440 . The encoder  335  is toggled to select a desired carriage operating pressure at which the encoder  335  is to be set. 
     Looking now at FIG. 24, the control system E may also include a photo sensor  453  connected across the battery  95  to determine whether the heater H, the facer  167  or any other object has been inserted into the path of the carriage  210 . The photo sensor  453  provides a signal to the control box microprocessor  401  to indicate the presence of such an object. The heater control relay  356  is connected between a port of the control box microprocessor  401  and the positive side of the battery  95 . A pair of relay coils  455  and  457  are connected between the positive side of the battery  95  and a pair of ports at the control box microprocessor  401 . The contacts  459  and  461  connect carriage together and carriage apart solenoids  288  and  290 , respectively, across the battery  95 . The right toggle switch  331  on the operator pendant  63  is connected between the battery return line and two inputs to the operator pendant microprocessor  440 . When the toggle switch  331  is flipped to the “apart” position, the carriage apart relay coil  457  causes its contact  461  to close and the carriage  210  will move for its full travel distance or until the operator O moves the toggle switch  331  or the microprocessor  440  automatically stops movement of the carriage  210 . When the toggle switch  331  is in the “together” position, the carriage together coil  455  closes its contact  459  to cause the carriage  210  to move in a closing direction, again until either the operator O or the microprocessor  440  terminates motion. The left toggle switch  333  of the operator pendant  63  is also connected between the battery return line and inputs to the operator pendant microprocessor  440 . The left toggle switch  333  is the pressure select switch enabling the operator O to control the pressure applied to the carriage  210  at various stages of operation of the machine M. The signal at the ports of the operator pendant microprocessor  440  are delivered to the FEMA PPC valve  289  via the control box microprocessor  401 . Serial ports are also provided in the operator pendant microprocessor  440  for program downloading or report downloading via the cable  339  to the operator pendant  63 . Finally, the emergency stop switch  327  connects the engine kill relay coil  467  across the battery  95  and also connects ports on the operator pendant microprocessor  440  and the control box microprocessor  401 . The engine kill relay  467  is energized when the key switch  363  is on. 
     SOFTWARE 
     The control system of the machine M includes three computer units. All operation and user interface controls reside in the main or operator pendant microprocessor  440  which is preferably a Z-World BL 1600 with 512K battery-backed SRAM and 512K EPROM. The control box microprocessor  401 , preferably a Z-world PK2120 with 32K battery-backed SRAM and 32K EPROM, is physically connected to input and outputs of the machine M. It is responsible for reading inputs, including pressure transducer and digital inputs, and writing digital and analog pressure control valve outputs. The RTD module  445 , preferably a Dataforth SCM9B-1412, is responsible for acquiring heater temperature readings. These three computers  440 ,  401  and  445  are connected to a two-wire RS-485 communications network. The operator pendant microprocessor  440  sends commands in ASCII format and polls the control box microprocessor  401  and the RTD module  445  via a half-duplex protocol. 
     The software of the machine M permits selection of any of three operational modes for the machine M including a semi-automatic mode, an automatic mode and a data logging mode. Preferably, the latter modes are enabled only upon entry of an enabling password. Typically, the pipe welding process requires application of at least three different pressures to the pipe. The first is the facing pressure P1 which the carriage  210  must exert in holding the pipe ends against the facer  167  to trim the pipe ends to be welded. The second is the soak pressure P2 which the carriage  210  must exert in holding the faced pipe ends against the heater H to bring them to a molten condition. The third is the fuse pressure P3 that must be exerted by the carriage  210  in holding the molten pipe ends together during the fusion process. In some applications, it is also necessary to apply a unique heat pressure P4 greater than the soak pressure P2 which the carriage  210  will exert on the faced pipe ends at the initiation of the heat cycle and a cool pressure P5 less than the facing pressure P3 which the carriage  210  will exert on the faced pipes. 
     The control box microprocessor  401  and the operator pendant microprocessor  440  are operational whenever the key switch  363  is in the glow plug, start or run positions. In the semi-automatic mode, the LCD  337  displays the screen  501  shown in FIG. 25 on the operator pendant LCD  337 . The screen  501  includes a timer status  502 , a date  503 , real time in hours, minutes and seconds  504 , a pressure display definition prompt  505 , a pressure calculation prompt  506 , a direct pressure set prompt  507 , a programmed pressure selection indicator  508 , a label toggle switch  509 , a menu  510 , the desired temperature  511  of the heater H, a pressure adjustment knob or encoder dial lock indicator  512 , a real time carriage pressure monitor  513 , a carriage control direction indicator  514  and a heater temperature indicator  515 . The timer  502  allows the operator O to time all or a portion of the pipe fusing process and is reset by a single press of the “O” key on the keyboard  329 . The pressure display definition prompt  505  allows any of a number of pressures up to six to be displayed for selection. The pressure calculation prompt  506  permits calculation of the recommended fusion pressure, including drag pressure, and assignment of that pressure to any one of the six displayed pressure selection positions  508 . The direct pressure set prompt  507  allows the operator to enter or type in the desired pressure using the keypad  329 . The operator O can also change the carriage pressure by depressing the rotary encoder knob  335  to unlock the dial and then rotating the encoder dial. The pressure adjustment knob lock indicator  512  indicates by the symbol “X” that the pressure cannot be varied. The symbol “X” is removed when the rotary encoder pressure adjustment knob  335  is depressed. The pressure selector toggle switch  333  allows the operator to select among the preprogrammed pressures  508 . The real time carriage pressure readout  513  constantly advises the operator of the carriage pressure in real time. The desired heater temperature  511  allows the operator O to key in the desired operating temperature of the heater H and commands the operator pendant microprocessor  440  to set and maintain that temperature through the heater temperature control components. The heater temperature readout  515  allows the operator to observe the heater temperature in real time. The on screen pressure and temperature readouts  513  and  515  eliminate the need for conventional pressure and temperature gauges. The carriage direction indicator  514  enables the operator O to reverse the carriage control direction by use of two key strokes, the position of the arrow indicating the status of the carriage direction. The label toggle switch  509  provides visual indication as to the identity of the pressure selected. For example, P1 may be indicated as the “facing” pressure, P2 as the “soak” pressure and P3 as the “fuse” pressure. The menu  510  allows the operator O to access the other modes of operation of the machine M including the automatic mode and the data logging mode. 
     The flow diagram for enabling and accessing the optional data logging and automatic modes is shown in FIG.  26 . After the operator uses the menu  510  to “select-an-optional-mode”  516 , the system “compares the user password in EEPROM to the factory password in EEPROM”  517 . The system then inquires if this is the “valid password for this optional mode”  518 . If the answer to this inquiry is “YES”, the system “compares user confirmation number in EEPROM to factory confirmation number in EEPROM”  519 . If the answer to the inquiry  518  is “NO”, then the system “prompts the user for password”  525 . If the user types in a “valid password for this operational mode”  521 , then the system “saves user entered password in EEPROM”  522  and “compares user confirmation number in EEPROM to factory confirmation number in EEPROM”  519 . Otherwise, the system returns to “user selects an optional mode”  516 . After the system “compares user confirmation number in EEPROM to factory confirmation number in EEPROM”  519 , the system inquires if this is the “valid confirmation number for this optional mode”  523 . If the answer to this inquiry is “YES”, the system “proceeds to selected optional mode”  524 . If the answer to the inquiry  523  is “NO”, then the system “prompts the user for confirmation number  525 . If the user types in a “valid confirmation number for this operational mode”  526 , then the system “saves user entered confirmation number in EEPROM”  527  and “proceeds to optional mode”  524 . 
     Thus, the owner of a machine M can enable and disable the optional data logging and automatic modes by entering factory programmed passwords into the system. Each of these modes has its own unique password and no two machines or modes would have similar passwords. The passwords cannot be modified in the field as they are factory installed. The first time an optional data logging or automatic mode is selected from the main menu  510 , the machine owner will be prompted for a password and a confirmation number. If the correct password and confirmation number are entered, the optional mode will be enabled as explained above for subsequent use without any re-entry of the password. Once so enabled, the optional mode for which the password has been entered cannot be disabled by turning off the machine M. To disable an optional mode, the machine owner must enter the enabling password into the system. The same password is thus usable to enable and disable a machine M. 
     Each machine M has a unique pressure calibration table which is maintained in battery backed SRAM for instant access. The calibration table contains digital to analog converter DAC voltages required to produce desired pressure readings at the transducer  287 . When a certain pressure is required at the carriage  210 , the software looks up the corresponding DAC voltage and sends it to the pressure control valve  289 . The calibration table contains two subtables, one for DAC voltages used for stepping to a higher pressure than the current pressure level and one for stepping to a lower pressure than the current pressure level. Calibration is accomplished by writing a DAC voltage and waiting for a time interval to read the pressure transducer  287 . The voltage is then increased by a given increment and the process repeated until the maximum pressure or DAC voltage is obtained. During calibration, the software attempts to find the most ideal DAC voltages that produce the pressure readings closest to their targets. The pressure increments will be determined by the resolution of the digital to analog converter and the accuracy of the pressure transducer  287 . The DAC voltage increment is chosen to produce a sufficient pressure transducer resolution for the software to build the calibration table. Increments of 20 psi have been found to be suitable. The calibration subtables are represented by two arrays and the number of array elements is equal to the maximum system pressure transducer reading divided by the pressure increments. For example, if the maximum system pressure is 2,000 psi and the pressure increments are 20 psi, there will be 100 elements in each array. During calibration, the software reads the pressure transducer  287  to determine the array element at which the DAC value is to be saved. The index to the array element is determined by dividing the pressure transducer reading by the pressure increment. A typical array is illustrated in FIG.  27 . In the array illustrated and assuming 10 psi increments, at  500  millivolts a range of pressures from 103 to 108 psi resulted, giving a table index of 10, while at 564 millivolts a range of pressures from 142 to 145 psi was obtained, providing a table index of 14. The flow diagram for pressure calibration is provided in FIG.  28 . At “initialization”  531 , the DAC voltage equals zero volts. The system “writes the DAC voltage”  532  and “waits a given amount of time for hydraulic system to settle”  533 . The pressure transducer  287  is then “read”  534  and the system inquires as to whether “difference between target and previously saved pressure is greater than difference between target and currently read pressure”  535 . If the answer is “NO”, then the DAC voltage is “increased”  536 . If the answer to the inquiry is “YES”, then the DAC voltage is “saved and used for current pressure reading”  537  before proceeding to an “increase of the DAC voltage”  536 . After “increasing the DAC voltage”  536  the system inquires as to whether the “DAC voltage is at a maximum”  538 . If the response to this inquiry is “YES”, this is the “end of calibration”. If the answer to the inquiry is “NO”, then the system returns to the step of “writing the DAC voltage”  532 . 
     The operator pendant microprocessor  440  continuously monitors the pressure adjustment knob of the encoder  335 . If the operator O turns the pressure adjustment knob  335 , the software reads its position and computes an offset into the calibration table to locate a DAC voltage. This voltage is written to the pressure control valve  289  and the reading of the pressure transducer  287  is displayed giving real time pressure readings to the operator O at the pressure monitor position  513  on the display screen  501 . The pressure adjustment knob  335  allows the operator O to increase the pressure in small increments. However, the operator O may key in a desired pressure for large changes. The calibration table also permits an on demand pressure setting feature which allows the operator O to recall a stored pressure setting instantly. 
     During operation of a machine M from an hydraulic fluid temperature at a cold start condition through increased fluid temperatures due to system warm up or other factors, the preset hydraulic pressure may change. In order to maintain constant pressure on the carriage  210 , the operator pendant microprocessor  440  monitors the pressure transducer  287  and makes corrections at given intervals. The reading of the pressure transducer  287  is compared to the target setting and as the difference in pressure warrants a correction, the microprocessor  440  makes incremental corrections of sufficient magnitude to prevent large pressure fluctuations that would contribute to oscillation. This automatic pressure control operation of the microprocessor  440  is illustrated in the flow diagram of FIG.  29 . The pressure transducer  287  is “read”  541  and then inquiry is made as to whether the “pressure is equal to the target”  542 . If the answer to this inquiry is “YES”, the system proceeds directly to the “end of pressure correction”  543 . If the answer to this inquiry is “NO”, the system next inquires as to whether the “pressure is greater than the minimum system pressure”  544 . If the answer to this inquiry is “NO”, the system again proceeds to the “end of pressure correction”  543 . If the answer to this inquiry is “YES”, the system proceeds to inquire as to whether the “pressure difference is less than 160 psi”  545 . If the answer to this inquiry is “NO”, the system again proceeds to the “end of pressure correction”  543 . If the answer to this inquiry is “YES”, the system proceeds to inquire as to whether the “pressure is less than the target”  546 . If the answer to this inquiry is “NO”, the system proceeds to “decrease the pressure by small increment  547  and then proceeds to the “end of pressure correction”  543 . If the answer to this inquiry is “YES”, the system proceeds to “increase the pressure by small increment  548  and again proceeds to the “end of pressure correction”  543 . 
     Referring again to FIG. 25, the operator pendant microprocessor  440  allows the operator O to input six pressures either by dialing in the pressure using the pressure adjustment knob  335 , by entering the pressure directly by using the keypad  329  or by using the calculator  506  to compute a recommended pressure. Furthermore, the operator O may assign the six pressures for different functions by putting them in order at the programmed pressure selector display  508 , for example in the order necessary to face, heat, soak, fuse and cool in the welding process. To access the desired pressure, the operator O simply shifts the pressure or left toggle switch  333  upwards or downwards to go from one pressure setting to the next. Furthermore, the operator O can label each of these pressures by use of the toggle switch label display  509 . The reversal of the carriage directional control switch  331  by use of the two key press operation of the carriage direction indicator  514 , enables the operator O to use the operator pendant  63  on either side of the carriage without disorientation. 
     By entering the desired heater temperature at the desired heater temperature display  511  by use of the keypad  329 , the operator O allows the microprocessor  440  to set and maintain the correct heater temperature. The operator pendant microprocessor  440  monitors the heater temperature RTD  445  continuously and turns on the elements of the heater H when the temperature falls below the set point and turns off the elements when the temperature rises above the set point. 
     Preferably, the operator pendant key pad  329  is multi-functional in that all of the keys can be assigned for multiple functions under program control depending on the context of the operation. For example, while the numeric keys are used to enter numbers in most cases, they may also be used to access menu items when a menu is presented to the operator O. 
     The operator O may use the calculator  506  to determine the heat, soak, fuse and cool pressures to use in the system operation. The calculator will compute the pressure if the operator O inputs data with respect to pipe diameter and thickness, inter facial pressure and drag pressure. Use of the calculator of the microprocessor  440  for this purpose is more accurate than nomographic determination of these pressures. 
     Diagnostic information can be accessed at all times to monitor criteria indicative of the internal status of the control system. Thus, if the operator O suspects that a part of the machine control is not operating properly, the menu  510  will route access to the diagnostic information, a typical display of which is illustrated in FIG.  30 . The display screen  551  shown on the operator pendant LCD  337  indicates the date  552 , time  553  and machine number  554 . It also indicates the milivoltage  555  at the FEMA PTC valve  289 , the milivoltage  556  at the pressure transducer  287 , the temperature  557  of the heater H, the position in inches and direction of motion  558  of the carriage  210 , whether the heater H is on or off  560 , whether the engine  91  is in high speed mode which enables the heater H or in low speed mode which disables the heater H and, in the automatic mode of the machine M, whether the heater H is in or out of place  562  on the carriage  210 . The screen  551  also indicates whether there is communication  563  between the pendant microprocessor  440  and the control box microprocessor  401 , whether malfunctions  564  are in reception or in transmission whether the RTD  445  is converting temperature to a digital signal  565 , whether the control box microprocessor  401  is operational  566  and whether the emergency stop button  327  has been operated  567 . 
     In addition to the above described functions, the data logging mode allows the operator to record machine and employee information, record pipe material and size information, record interfacial pressures, drag pressure, and recommended fusion pressures, record heater temperature, log pressure profiles during fusion, view recorded data on screen after fusion, view pressure profiles on screen after fusion, print recorded data and pressure profiles to a printer and upload recorded data and pressure profiles to a personal computer for further analysis and archive. 
     The data logging mode begins logging data as soon as the operator O presses a designated log key. Although the operator pendant microprocessor  440  scans the pressure transducer  287  every 60 milliseconds, it only saves data changes instead of recording every data point read at  60 ms intervals. When the log key is pressed, the operator pendant microprocessor  440  saves the joint information including pipe size, employee number, joint and job numbers, etc. to report memory. It then saves the first data record and initializes the second data record. Each record is made up of two elements. The first element is the time stamp, preferably at 100 millisecond resolution, and the second element is the pressure reading in PSI. Every 100 milliseconds, the operator pendant microprocessor  440  updates the time stamp of the second data record and checks the pressure reading. If the current pressure reading is different than the pressure recorded in the second data record, then third and fourth data records are created to record the change in pressure. This process is repeated until the operator terminates the data logging, or the report memory is full or the maximum recording time of 65,500 milliseconds is exceeded. The flow diagram of FIG. 31 illustrates the data logging process. When the operator O presses the log key, the microprocessor  440  “assigns new report memory space”  571 . It then “copies the pipe and joint information to report memory”  572 . It then “sets up first and second data records”  573  beginning at a time stamp of zero milliseconds. It then inquires as to whether “100 milliseconds has passed”  574 . If the answer to this inquiry is “NO”, it continues to inquire as to whether “100 milliseconds has passed”  574 . If the answer to this inquiry is “YES” it “reads the pressure transducer”  575 . It then inquires as to whether the “pressure has changed since it was last saved”  576 . If the answer to this inquiry is “YES”, it “creates two new data records and saves new pressure reading”  577  and then “updates the time stamp for current data records”  578 . If the answer to the “pressure change since last saved” inquiry  576  is “NO”, it passes immediately to the “update time stamp for current data record”  578 . After each update  578 , it returns to the “100 milliseconds passed” inquiry  574  for repetition of the process. 
     
       
         
           
               
             
               
                   
               
               
                 Typically, the data logging mode printout 
               
               
                 shows the following information: 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                  1. Date and Time: 
               
               
                   
                  2. Joint Number: 
               
               
                   
                  3. Job Number: 
               
               
                   
                  4. Employee No.: 
               
               
                   
                  5. Machine ID: 
               
               
                   
                  6. Machine Model: 
               
               
                   
                  7. Piston Area: 
               
               
                   
                  8. Pipe Material: 
               
               
                   
                  9. Pipe Size: 
               
               
                   
                 Interfacial Pressures: 
               
               
                   
                 12. Heat: 
               
               
                   
                 13. Soak: 
               
               
                   
                 14. Fuse: 
               
               
                   
                 15. Cool: 
               
               
                   
                 Recommended Gauge Pressures: 
               
               
                   
                 18. Heat: 
               
               
                   
                 19. Soak: 
               
               
                   
                 20. Fuse: 
               
               
                   
                 21. Cool: 
               
               
                   
                 Recorded Data: 
               
               
                   
                 24. Drag Pressure: 
               
               
                   
                 25. DataLogger Probe: 
               
               
                   
                 26. External Probe: 
               
               
                   
                   
               
            
           
         
       
     
     Typically, the data logging mode report also includes two graphs of the pressure profile during fusion, illustrated in FIGS. 32 and 33. The front end plot of FIG. 32 expands the front end of the pressure profile to reveal the heat and soak profile in more detail than the summary plot of FIG.  33 . The summary plot shows the entire pressure profile from the time the operator O starts logging until the time the operator O stops logging data. Looking at the summary plot of FIG. 33, when the operator O presses the log key, the system reads the pressure P 0  at the time T 0  and proceeds with the flow chart process of FIG.  31 . The P 0 -T 0  reading provides an initial data point and every 100 milliseconds the system extends the line from the P 0 -T 0  data point until a pressure change is noted at data point P 0 -T 1 . The system then begins two new data records beginning at the data point P 1 -T 1  and executes another straight line plot until another pressure change occurs at a data point P 1 -T 2 . This process is continued throughout the operation of the system. 
     The automatic mode automates the fusion procedure and allows the operator O to record machine and employee information, record pipe material and size information, record recommended fusion parameters, record actual fusion parameters, view recorded data on screen after fusion, print recorded data to printer and upload recorded data to a personal computer for further analysis and archive. In the event operator intervention is required, the automatic mode prompts the operator O with an audible buzzer  437  and displays the appropriate message on the screen  337 . The automatic mode interacts with the operator O with step-by-step instructions, and performs automatic pipe fusion. The automatic mode begins by prompting the operator O to enter joint information and select a pipe and enter its size. It then prompts the operator O to prepare the pipe for fusion, which includes facing the pipe, cleaning the heater H and installing the heater H. After the pipe is prepared, the operator O presses a key to start the fusion process. The operator pendant microprocessor  440  starts the fusion process by closing the carriage  210  to bring the two pipe ends against the heater H. After the pipe ends contact the heater H, the microprocessor  440  begins to count down from the programmed heat time under heat pressure. At the end of the heat cycle, the microprocessor  440  drops carriage pressure to drag pressure and locks the carriage to enter the soak cycle. Near the end of the soak cycle count down, the microprocessor  440  sets a high carriage pressure with the carriage locked and prompts the operator O to standby to remove the heater H. At the end of the soak cycle, the carriage opens automatically for heater removal. The operator O must remove the heater H within a given amount of time. The carriage closes to bring the melted pipe ends together. Once the pipe ends make contact, the microprocessor  440  begins counting down for fuse cycle. Some jointing procedures call for a cool cycle with a lower interfacial pressure than the fuse cycle. At the end of the fusion, the operator O is given an opportunity to view the joint report on the screen, and print the joint report to an optional printer. After that, the operator O may choose to fuse another joint using the same parameters, or select another pipe material. 
     
       
         
           
               
             
               
                   
               
               
                 The automatic mode printout typically shows the following information: 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                  1. Date and Time: 
                   
                   
               
               
                   
                  2. Joint Status: 
               
               
                   
                  3. Machine ID: 
               
               
                   
                  4. Machine Model: 
               
               
                   
                  5. Employee No.: 
               
               
                   
                  6. Job Number: 
               
               
                   
                  7. Joint Number: 
               
               
                   
                  8. Pipe Material: 
               
               
                   
                  9. Pipe Size: 
               
               
                   
                   
                 Target 
                 Actual 
               
               
                   
                 12. Heater Temp.: 
               
               
                   
                 13. Heat Time: 
               
               
                   
                 14. Heat Pressure: 
               
               
                   
                 15. Soak Time: 
               
               
                   
                 16. Soak Pressure: 
               
               
                   
                 17. Open/Close: 
               
               
                   
                 18. Fuse time 
               
               
                   
                 19. Fuse Pressure: 
               
               
                   
                 20. Cool time: 
               
               
                   
                 21. Cool Pressure: 
               
               
                   
                 22. Drag Pressure: 
               
               
                   
                   
               
            
           
         
       
     
     The target column shows the time and fusion pressures recommended by the pipe manufacturer. The actual column shows the actual time and pressures used in the automatic fusion. 
     In the automatic mode, the pipe and fusion parameters are preprogrammed. In the field, the operator O selects from a list of preprogrammed pipe materials and pipe size, and the computer looks up the corresponding fusion parameters for the selected pipe. While the automatic mode comes with a factory installed list of parameters, the owner of the machine may replace the factory installed parameters by downloading custom parameters via a PC serial port. The parameter download protocol is similar to that for uploading reports to the PC as is hereinafter described in relation to both the data logging and automatic modes. However, instead of the PC requesting data from the operator pendant microprocessor  440 , the operator pendant microprocessor  440  requests data from the PC in the case of parameter downloading. 
     The data logging and automatic mode reports can be uploaded to an IBM PC compatible computer for further analysis and archive. A companion program that runs on the PC can transfer data stored in the battery-backed SRAM of the operator pendant microprocessor  440  to the PC hard drive. The optional RS-232 serial cable  339  connects the serial port of the PC to the serial printer port of the operator pendant microprocessor  440 . The data transfer is based on a polling protocol, in which the PC requests data from the operator pendant microprocessor  440 . The microprocessor  440  responds by sending the requested data blocks to the PC. To minimize data transmission error, the data blocks are marked with a data block prefix and a checksum suffix. If the PC received a data block with the incorrect prefix or checksum, the PC will resubmit the request for the same data block. 
     The report upload flow diagram is illustrated in FIG.  34 . The microprocessor  440  “listens for request”  581  from the PC. It then inquires as to whether the request made is a “valid header request”  582 . If the answer to this inquiry is “YES”, the microprocessor  440  then “sends the header block”  583  to the PC and “resumes listening for the request”  581 . If the answer to the “valid header request”  582  is “NO”, the microprocessor next inquires whether that is a “valid data block request”  584 . If the answer is “YES”, the microprocessor  440  “sends the requested data block”  585  to the PC and resumes “listening for requests”  581 . If the response to the inquiry is “NO”, the microprocessor  440  inquires as to whether an “end of request message”  586  has been received. If the response to this inquiry is “NO”, the system returns to “listen for request”  581 . If the answer to this inquiry is “YES”, the microprocessor  440  will “end data transfer”  587 . 
     The report download flow diagram is illustrated in FIG.  35 . In this process, the operator pendant microprocessor  440  will first “request a header”  591  from the PC. It then “listens for the response”  592 , and inquires as to whether the response is a “valid header block”  593 . If the answer to this inquiry is “NO”, the system returns to “request headers”  591 . If the answer to this inquiry is “YES”, the microprocessor  440  will “process header information”  594 . The microprocessor  440  will then inquire as to whether it is “finished reading all data blocks”  595  and if the answer to this inquiry is “YES”, it “sends an end of request message”  596  to the PC. If the answer to this inquiry is “NO”, the microprocessor  440  “requests the next data block”  597  and again “listens for response”  598 . The microprocessor  440  then inquires as to whether the information received from the PC is a “valid data block”  599 . If the answer to this inquiry is “NO”, the microprocessor  440  will “request the next data block”  600  and “return to listen for response”  598 . If the answer to this inquiry is “YES”, the microprocessor  440  “processes and saves the data”  601  and then returns to the “finish reading all data blocks” inquiry  595 . 
     OPERATIONAL 
     The machine M, already calibrated by the manufacturer, is transported to the pipeline site, preferably by a pickup truck or trailer. In the normal mode of operation, the switch  353  is set to the glow plug position  367  until the glow plug indicator light  375  goes off. The switch  363  is then turned to the start position  365  in which the engine  91  is started. The operator O selects low throttle speed by flipping the throttle speed switch  389  to the “open” condition. The hydraulic pump  101  operates immediately upon starting of the engine  91 . The operator O maneuvers the machine M from the transport vehicle by use of the left and right track control valves  107  and  109  at the operator&#39;s instrument panel  111 . Once the machine is in position, the facer  167 , which was transported resting on the guide rods  197  and  203 , is rotated on the linkage to the linkage closed position illustrated in FIG.  16 . The heater frame  220  along with the heater H and bag are removed from their transport position on the jaw spacers  219  and set in a convenient ground condition. The carriage skid  215  is aligned on the chassis C, if necessary, by removal of the pins through the skid ears  57 , disengagement of the skid  215  from the latches  55 , 180 degree rotation of the skid  215 , reengagement of the skid  215  with the opposite latches  55  and reinsertion of the pins in the skid ears  57 . If the skid  215  is rotated, the jaw pins are removed and the upper portions of the jaws  207 ,  209 ,  211  and  213  repinned for opposite hand rotation to that previously selected. Sizing rings are mounted on the inside surface of the jaws  207 ,  209 ,  211  and  213  to reduce the jaw opening to a diameter suitable for the size of the pipes to be joined. The operator O then uses the valves  86  and  88  of the pipe lift valve assembly  85  to position the roller assemblies L at an initially desired level. The operator O then further utilizes the track control valves  107  and  109  to finally position the machine M in longitudinal alignment with the axes of the pipes to be joined. The pipe lift control valves  86  and  88  are then further used if necessary to assist in manipulating the pipe to its desired level in the machine M. With the pipes extending at least one inch inwardly of the fixed  207  and  209  and moving  211  and  213  jaws, the jaws  207 ,  209 ,  211  and  213  are locked to secure the pipes in proper alignment. The throttle speed is then increased to high by closing the throttle speed switch  389 . In the high speed position, the circuit for the heater H is closed and the heater H begins to warm up. The operator O then selects the “facing”, “soaking” and “fusing” pressures. The “fusing” pressure can be determined by use of the calculation algorithm by entering appropriate pipe size, wall thickness and other manufacture information in response to prompts in the calculation loop of the system. When all necessary pressure, time and temperature selections have been made and the heater H reaches the desired fusion temperature as is indicated at the display position  515  on the operator pendant LCD as illustrated in FIG. 25, the operator O and the machine M are ready to perform the fusion operation. 
     With the moving jaws  211  and  213  spaced apart from the fixed jaws  207  and  209 , the operator rotates the facer  167  to the linkage fully opened position with the facer brackets  185  and  187  seated on the guide rods  203  and  197 . Facer operation is then initiated by use of the facer control valve  87 . This is usually done at maximum speed but the operator O may change the valve position if a lower speed is desired. The operator O then toggles the carriage control switch  331  to the “together” position, at facing pressure, to bring the pipes against the facer  167 . If the facer  167  is not turning freely to trim the pipe edges, the operator O may reduce the pressure applied by the carriage  210 . The operator O continues operation of the facer  167  to trim the pipe until the operator O is satisfied that the pipe ends have been sufficiently trimmed so as to lie in parallel planes. The operator O then moves the carriage switch  331  to its “stop” position and moves the facer valve  87  to its “stop” position to terminate the facing process. The carriage switch  331  is then moved to the “apart” position until the moving jaws  211  and  213  are sufficiently spaced apart from the fixed jaws  207  and  209  to remove the facer  167 . The operator O then switches the carriage switch  331  to the stop position and removes the facer  167  by rotating the facer  167  back to the linkage fully closed condition. The operator O then inspects the pipe to be assured that a clean and satisfactory surface has been put on the ends of the pipes. The operator O then moves the carriage switch  331  to the “together” position at the fusion pressure so as to abut the pipes and permit an alignment check to assure that there are no gaps between the pipes, that the pipes are not off axis and the pipes will not slip. If the operator O is not satisfied with the mating of the pipes, the facing process will be repeated until a satisfactory result is achieved. When the result is satisfactory, the operator O will place the carriage switch  331  in its “apart” position to space the pipes apart sufficiently for insertion of the heater H. The operator O will then place the carriage switch  331  in its “stop” position and will check the heater temperature reading  515  on the display of the operator pendant  63 . If the heater H is at the proper temperature, the operator O will move the carriage switch  331  to the “together” position to bring the pipe ends into contact with the heater H. The operator O will then select the “soak” pressure which may be typically, but not necessarily, selected as  30  psi or may be determined as the minimal force necessary to move the carriage  210  with a pipe connected in the moving jaws  211  and  213 . Thus, the “soak” pressure is the pressure at which the pipes will be maintained in contact with the heater H with minimal or zero force applied against the heater H. When the zero force condition is achieved, the operator O will change the position of the carriage switch  331  to “stop” in which both carriage solenoids  288  and  290  are deenergized and the carriage pistons are locked to maintain contact of the pipes with the heater H at substantially zero force. The operator O may then press the “0” key on the pendant  63  to initiate operation of the timer  502  so as to time the “soaking” of the pipe ends. The operator O will generally be guided by the elapsed time of the “soaking” process and also by observation of the bead formed on the perimeter of the pipes as the polyolefin melts. When the soaking process is completed to the satisfaction of the operator O, the operator selects the “fusion” pressure which is generally the highest pressure selected for operation of the carriage  210 . The operator O then moves the carriage switch  331  to its “apart” position to move the pipes away from the heater H. Operating the carriage  210  at the “fusion” pressure assures that the moving jaws  211  and  213  will be spaced apart as quickly as possible from the fixed jaws  207  and  209 . The operator O then removes the heater H as quickly as possible from its position between the pipes and moves the carriage switch  331  to its “together” position at the fusion pressure to bring the pipe ends together. The operator then restarts the timer  502  by using the “0” key on the pendant  63 . When the timer  502  indicates that the desired fusion time has elapsed, the operator O moves the carriage switch  331  to its “stop” position, the jaws  207 ,  209 ,  211  and  213  are opened to unclamp the pipe and the pipe lifts L are operated to lift the pipe out of the jaws  207 ,  209 ,  211  and  213 . With the pipe disengaged from the jaws  207 ,  209 ,  211  and  213 , the operator O then moves the carriage switch  331  to the “apart” position at any desired pressure and the fusion process is complete. 
     In the automatic mode, the machine M is operated identically as in the normal mode until the heater H has been inserted between the pipes. At this point, the operator O presses the key pad assigned to the “auto run” mode and the system will automatically select the soaking and fusing pressures and time for the pipe identified to the system. The fusion process is then fully automatic. In this mode, the carriage audio alert  437  will sound whenever the carriage  210  is moving. When the heater H is removed from between the pipes, the sensor  453  causes the carriage switch  331  to move to its “together” position and, if the heater H is not removed by the operator O in time to permit the pipes to come together, the cycle will be automatically aborted. Furthermore, the operator pendant microprocessor  440  continually monitors the pressure applied to the carriage  210  and the temperature of the heater H and if, at any time during the process, they are not within the limits required, the microprocessor  440  will automatically abort the cycle. This is true with respect to any condition that would cause an interruption in the proper execution of the cycle, including, for example, a loss of diesel fuel or a shifting or slippage of the pipes within the jaws. When the fusion cycle is complete, the operator O continues the process as in the normal mode of operation. 
     In the data logging mode, when the heater H has been inserted between the pipes, the operator O will press the keypad assigned to “start logging”. The system will then begin logging the carriage pressure, the heater temperature and the time as hereinbefore explained for the fusion process. When the fusion process is completed, the operator O will press the keypad assigned to “stop logging” to terminate use of the data logging mode. 
     Thus, it is apparent that there has been provided, in accordance with the invention, a machine and method that fully satisfies the objects, aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art and in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit of the appended claims.