Abstract:
Scuba tank compressed air can now power a dual piston compound motor driving dual water thrusters of a steady pulling underwater propulsion vehicle. Motor exhaust provides diver breathing air through a demand regulator. Motor efficiency allows continual, powerful diver thrust without curtailing normal tank dive time. Lightweight vehicle can be strapped to the scuba tank for “hands free” operation or “diver held” for driving through the water. Diver controls off/on/variable speed with a simple throttle control. Propeller or battery is not required.

Description:
BACKGROUND 
       [0001]    1. Field of Invention 
         [0002]    My invention applies to underwater propulsion vehicles used by scuba divers to propel them effortlessly through the water. My invention is powered by compressed air from the scuba tank/s. 
         [0003]    Within my invention, is a dual piston compound motor operating in a push/return manner supplying constant thrust (continual pulling force). The pistons are secured to dual water disks used to smoothly thrust the diver through the water without need for a propeller or a battery. 
         [0004]    The discharged air leaving the motor accumulates within a housing of my invention from which the diver breathes through a demand regulator. The device uses the energy stored within scuba tank compressed air so efficiently that dive times are not shortened by introduction of my propulsion vehicle! In other words, the diver is propelled with powerful thrust without restriction on normal “bottom time” or “down time”. 
         [0005]    A diver has options of securing my invention to their scuba tank for “hands free” operation or holding my invention in front of them to drive it though the water. 
         [0006]    2. Description of Prior Art 
       Battery Propulsion Vehicles 
       [0007]    The art of underwater diver propulsion vehicles can be divided into three fields of work. 
         [0008]    One field can be identified as “battery propulsion vehicles”. These inventions use electric motors connected to a propeller providing thrust. Batteries within a watertight housing supply stored electric energy required to operate the motor. 
         [0009]    Disadvantages of these battery propulsion vehicles include: 
         [0010]    A heavy weight of the batteries and the ferrous electric motor. These vehicles are heavy and cumbersome to carry and transport to and from the dive site, especially through airports, and within taxis. 
         [0011]    A large bulky housing is required to contain the batteries and to provide buoyancy offsetting the vehicle weight. This large vessel is difficult for the diver to manipulate, and practically precludes the opportunity of attachment to the scuba tank for hands free operation. 
         [0012]    Batteries are selected by the manufacturer of the battery propulsion vehicles to provide an amount of energy required (when charged) for about one scuba tank dive (around 45 minutes). After a dive, the diver has to return to the surface, and open the housing to install a second battery if a recharging system is unavailable on the dive boat. If the boat has a charging system, the diver must wait a long recharging time (one or two hours) before the battery is again ready. There would be significant advantages to having a smaller, lighter, diver propulsion vehicle which operated without use of electric batteries. 
       Air/Propeller Propulsion Vehicles 
       [0013]    A second art field of work can be identified as “air/propeller propulsion vehicles”. These vehicles attempted to make efficient use of the stored compressed air energy available in the scuba tank by operating an air motor connected to a propeller. 
         [0014]    The inventors of some of these vehicles had the diver breathe the rotary motor exhaust so that motor exhaust air was not wasted by dumping into the water. Some inventors collected the motor exhaust air in a propulsion vehicle housing from which the diver breathed. Other inventors collected the motor exhaust air in an inflatable air bag from which the diver breathed. One example of an air/propeller vehicle is described in U.S. Pat. No. 3,128,739 by Schultz, Apr. 14, 1964. Schultz used an air motor of “conventional design”. Unfortunately, a conventional design air motor cannot provide adequate propelling thrust at an air consumption rate less than a diver&#39;s breathing rate consumption for reasons to be soon explained. 
         [0015]    Other inventors used no exhaust air accumulator at all, and relied on the motor running only with each diver inhaling. 
         [0016]    Inventors attempted to have air motors consume less air (while operating at practical diver thrust) than a diver&#39;s breathing rate of air consumption. For with such a condition, no scuba tank air would be wasted when providing practical diver transport. If this condition was not met, and if the motor (while providing practical thrust) consumed more air than a diver&#39;s breathing rate, than the diver “bottom time” or “dive time” would be curtailed. 
         [0017]    The two design criteria for meeting the above condition of practically can be stated:
       1. Use an air motor which operates at incoming pressure as high as is practical. This practical limit should be about 200 psig represented normal thought of “empty scuba tank pressure”. If one incorporated an air motor to operate above 200 psig, the scuba tank would become “empty” sooner than desired and curtail dive or bottom time.   2. Use an air motor which exhausts at as low of a pressure as possible. This practical limit will be about 15 psig. With 15 psig motor exhaust pressure, the vehicle housing can nominally operate around 10 psig without restricting motor efficiency/exhaust into the housing. Equally important, the diver can breathe easily from the housing if it operates near 10 psig using a hookah type demand regulator.       
 
         [0020]    By meeting these design criteria [motor operating at “pressure in” of 200 psig, and exhausting at 15 psig], an air motor will use all the energy possible from a scuba tank throughout the entire dive time. Dive time is normally defined as the dive time where tank pressure varies from fill pressure (about 3,000 psig) to about 200 psig practical tank empty pressure. 
         [0021]    All these prior air/propeller propulsion vehicle inventions shared a common impracticality: The rotary air motors used were not efficient enough to provide adequate diver thrust and at the same time consume scuba tank air at a rate less than the diver breathing rate. Because of this shortcoming, all prior air/propeller propulsion vehicle inventions wasted significant scuba tank air while the motor was operating at a practical thrust. This wasted air (beyond the diver&#39;s breathing rate consumption) was exhausted into the water, and cut the dive time or down time to much less than what it would be without the vehicle. 
         [0022]    The reason why practical motor operating criteria presented above were not achieved with air motors used in prior inventions is that no commercial manufacturer of rotary air motors offers such an efficient air motor for sale! 
         [0023]    Rotary air motors available include vane air motors being the least efficient in that the incoming air is typically 100 psig and exhaust air is typically 40 psig. All the scuba tank compressed air energy between 200 psig and 100 psig and between 40 psig and 15 psig is lost/wasted/not available for diver propulsion. In addition, vane air motor design allows a significant amount of air to slip/bypass the vane at both rotor and housing seals. Such slip/bypass air contributes nothing to motor power and wastes scuba tank air. 
         [0024]    Wobble plate multi-piston rotary air motors are about the most efficient commercial air motor available in that incoming air can be 200 psig, but exhaust air is correspondingly about 70 psig. All the scuba tank compressed air energy between 70 psig and 15 psig is lost/wasted/not available for diver propulsion. 
         [0025]    A commercial product called the Hydrojet is disclosed in a brochure by Hyde Power Systems, Inc. of 9340 W. Putter Court, Crystal River, Fla. 32629 of January 1987. This vehicle is powered by a five cylinder wobble plate air motor. The Hydrojet brochure describes a 50% (from 40 min to 20 min) loss of dive time if the vehicle operates at full speed (practical diver thrust). 
         [0026]    There would be a major advantage in making a propulsion vehicle for scuba divers which used a air motor that provided both practical diver thrust and an air consumption less than the diver&#39;s breathing air consumption so dive time available from a scuba tank is not curtailed. 
       Single Water Disk Propulsion Vehicles 
       [0027]    A third art field of work can be identified as “single water disk propulsion vehicles”. These air powered propulsion vehicles do not use a propeller or rotary air motor to provide diver thrust. Instead, they use a single reciprocating water disk attached to a single piston motor for the thrust/power stroke. 
         [0028]    The water disk of these inventions has attached one or more flexible flaps and a series of corresponding openings/holes through the water disk. The flaps and openings/holes cooperate so the water disk experiences nearly zero water resistance on the return stroke and maximum water resistance on the power stroke. 
         [0029]    U.S. Pat. No. 3,411,474 by Curtis, Nov. 19, 1968 describes a single water disk propulsion vehicle using two pistons axially aligned. One piston [45] drives the water disk in the thrust direction and another opposite piston [46] drives the water disk in the return direction. Another U.S. Pat. No. 3,066,638 by Andresen, Dec. 4, 1962 describes a single water disk propulsion vehicle using a single piston. A compressed spring [44] returns the thruster/piston combination in preparation for another thrust stroke. Andresen describes the propulsion [column 3 line 65] as “pulsating”. 
         [0030]    All these inventions share a same operational deficiency. The propulsion vehicle moves forward with intermittent forward thrusts each followed by a time period of zero thrust (as the water disk returns). As a result the diver propulsion is jerky and un-constant. 
         [0031]    A second even more significant deficiency of all prior art single water disk propulsion vehicles is that the air piston motor is a single stage type. As such, if the motor operates at the desirable 200 psig pressure discussed above, the single piston must exhaust air at the undesirable pressure of about 80 psig. This 80 psig pressure exhaust is necessary as the single piston/single water disk must provide reasonably constant thrust throughout it&#39;s entire power stroke. The range of 200 psig to 80 psig is constant enough, but does not meet the motor practicality definition discussed above. 
         [0032]    If one were to attempt to design a single piston long enough (over a foot long) to operate at the desired practicality pressure range of 200 psig input and 15 psig exhaust the thrust would become an order of magnitude even more jerky and un-constant. In addition, the one foot long piston when connected to another one foot long water disk would make the propulsion vehicle impractically long. There would be a major advantage in making a water disk propulsion vehicle for scuba divers which was able to have the motor operate at a pressure range of 200 psig “input” and 15 psig “exhaust” without jerky/un-constant motion and without impractical length. 
       SUMMARY OF MY INVENTION 
     General 
       [0033]    My invention discloses an air powered underwater diver propulsion vehicle. Some of the objectives of my invention include: 
         [0034]    Using energy available from the compressed air within the scuba tank to power the vehicle dual compound piston motor. Batteries are not required. 
         [0035]    Connecting the dual piston compound motor to dual water disks providing diver propulsion. 
         [0036]    Using dual water disks instead of only one water disk to achieve smooth continual propelling thrust with improved efficiency. 
         [0037]    Using mechanical linkage between the two pistons. One piston and attached water disk is linked to be 180 degrees out of phase with the second piston and attached water disk. Unlike prior art single water disk propulsion vehicles, my invention provides continuous diver thrust and is not intermittent. Also conservation of air pressure is realized by returning the inactive piston/water disk by the driving piston/water disk. 
         [0038]    Operating the dual piston motor at incoming air pressure with the highest pressure possible from a scuba tank normally considered “empty” at dive&#39;s end, (considered to be 200 psig). 
         [0039]    Operating the dual piston motor exhaust air at low pressure of only 15 psig. With such a low exhausting pressure, the motor utilizes nearly all the pneumatic energy available within the 200 psig incoming air. This efficient energy utilization is accomplished by using a compound dual piston motor. A higher pressure and smaller diameter piston/cylinder (at stroke&#39;s end) exhausts into the lower pressure and larger diameter cylinder driving the larger piston through it&#39;s power stroke. This dual piston compound motor is more air efficient than any motor described by prior inventors in this art. 
         [0040]    The air exhausted from the dual piston compound motor is collected within the vehicle housing which acts as a reservoir. Generally the invention will not exhaust/waste air into the surrounding water. 
         [0041]    The diver is supplied with an ample supply of breathing air from the vehicle housing used in conjunction with a breathing demand regulator and hose. 
         [0042]    Including a pressure regulator that can either add air to the housing or bleed air out of the housing into the surrounding water. This pressure regulator will compensate for instances where the diver breathing air consumption rate does not closely match the motor air consumption rate. This regulator maintains housing pressure so breathing air is always available for the diver. This regulator also controls housing pressure so it never builds up enough to inhibit full power motor operation. 
         [0043]    Matching the vehicle housing volume to the vehicle weight providing a near neutral or a slight positive buoyancy. 
         [0044]    Including an on/off and thrust speed control throttle, so the diver may vary their speed from zero to maximum thrust at will. 
         [0045]    Making the vehicle light enough and small enough to be attachable to the scuba tank positioned on the diver&#39;s back, so the diver can propel “hands free”. 
         [0046]    Including another option of allowing the vehicle to be detached from the scuba tank and be driven through the water by the diver holding onto the vehicle with their hands. 
         [0047]    Other and further objects of my invention will be apparent from the following description when read in conjunction with the accompanying drawings. 
         [0048]    By way of example, my invention is illustrated herein by the accompanying drawings, wherein: 
     
    
     
       DRAWING FIGURES 
         [0049]      FIG. 1  is a perspective view of my invention shown attached to a scuba tank used by a diver. 
           [0050]      FIG. 2  is a perspective view of my invention positioned in front of a diver. 
           [0051]      FIG. 3 . shows a fragmentary sectional elevation view as suggested by lines  3 - 3  of  FIG. 2  showing the motor/water disk components at the beginning of the small piston power stroke. 
           [0052]      FIG. 4  is a pneumatic interconnection diagram of my invention 
           [0053]      FIG. 5  shows internal component details of the pressure regulator of my invention. 
           [0054]      FIG. 6  shows component details of the fill valve assembly used in my invention. 
           [0000]    
         
           
                 
               
                 
                 
               
             
                 
                     
                 
                 
                   Names and Numbers used in Drawing FIG.&#39;s and Specification 
                 
                 
                     
                 
               
               
                 
                     
                 
               
            
             
                 
                   20 
                   large cylinder 
                 
                 
                   21 
                   large piston 
                 
                 
                   22 
                   attachment strap 
                 
                 
                    23a 
                   thrust housing a 
                 
                 
                    23b 
                   thrust housing b 
                 
                 
                   24 
                   flapper 
                 
                 
                    24a 
                   flapper p 
                 
                 
                   25 
                   water disk 
                 
                 
                    25a 
                   water disk p 
                 
                 
                   26 
                   main housing 
                 
                 
                   27 
                   push rod 
                 
                 
                   28 
                   scuba tank 
                 
                 
                    30a 
                   slide block a 
                 
                 
                    30b 
                   slide block b 
                 
                 
                   31 
                   pressure regulator 
                 
                 
                   32 
                   fill valve 
                 
                 
                   33 
                   pilot fill valve 
                 
                 
                   34 
                   small cylinder 
                 
                 
                   35 
                   small piston 
                 
                 
                   36 
                   arm pivot 
                 
                 
                   37 
                   pilot dump valve 
                 
                 
                   38 
                   exhaust spring 
                 
                 
                   39 
                   water spring 
                 
                 
                   40 
                   fill spring 
                 
                 
                   41 
                   fill poppet 
                 
                 
                   42 
                   piston seal 
                 
                 
                   43 
                   housing port x 
                 
                 
                   44 
                   water port 
                 
                 
                   45 
                   piston 
                 
                 
                   46 
                   passageway b 
                 
                 
                   47 
                   inlet port w 
                 
                 
                   48 
                   regulator body 
                 
                 
                   49 
                   rotating arm 
                 
                 
                   50 
                   push rod p 
                 
                 
                   51 
                   dump poppet 
                 
                 
                   52 
                   cam pivot 
                 
                 
                   53 
                   valve lobe 
                 
                 
                   54 
                   poppet spring 
                 
                 
                   55 
                   Line port b 
                 
                 
                   56 
                   Fill poppet b 
                 
                 
                   57 
                   Mounting plate 
                 
                 
                   58 
                   poppet pin 
                 
                 
                   59 
                   fill pivot 
                 
                 
                   60 
                   pivot spring 
                 
                 
                   61 
                   travel groove 
                 
                 
                   62 
                   first stage regulator 
                 
                 
                   63 
                   demand regulator 
                 
                 
                   64 
                   check valve 
                 
                 
                   65 
                   tube a 
                 
                 
                   66 
                   tube b 
                 
                 
                   67 
                   mounting bracket 
                 
                 
                   68 
                   tube c 
                 
                 
                   69 
                   tube d 
                 
                 
                   70 
                   tube e 
                 
                 
                   71 
                   tube f 
                 
                 
                   72 
                   tube g 
                 
                 
                   73 
                   tube h 
                 
                 
                   74 
                   tube i 
                 
                 
                   75 
                   throttle connection 
                 
                 
                   76 
                   spool valve 
                 
                 
                   77 
                   exit port 
                 
                 
                   78 
                   high pressure hose 
                 
                 
                   79 
                   breathing hose 
                 
                 
                   80 
                   tube 
                 
                 
                   81 
                   throttle cam 
                 
                 
                   82 
                   pin 
                 
                 
                     
                 
               
            
           
         
       
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Pressure Regulator  31   
       [0055]    A pressure regulator  31  in general maintains vehicle main housing  26  (shown in  FIG. 4 ) pressure within design limits. 
         [0056]      FIG. 5  shows components of pressure regulator  31 . A tube  80  exits on the right side of a regulator body  48 . Tube  80  is in conveyance with diver surrounding water. A water port  44  through regulator body  48  conveys water to the right side of a piston  45 . The internal pressure of vehicle main housing  26  is conveyed though a passageway b  46  to the left side of piston  45 . 
         [0057]    A piston seal  42  exists between piston  45  and regulator body  48 . As shown, piston seal  42  is an o-ring type, but other moveable sealing components such as a diaphragm could be used. Piston seal  42  allows piston  45  to move to the left or right within a cavity in regulator body  48 , yet separates pressurized air from the left side of piston  45  from water pressure on the right side of piston  45 . 
         [0058]    A fill poppet  41  is positioned to the left of piston  45 . Fill poppet  41  can be made from an elastomer such as polyurethane so it&#39;s face facilitates a pressure seal with a bore face in regulator body  48 . Pressurized air conveyed from a first stage regulator  62  shown in  FIG. 4  enters an inlet port w  47 , and is prevented from flowing to the left side of piston  45  unless piston  45  moves far enough to the left to move/unseat fill poppet  41 . 
         [0059]    A dump poppet  51  is positioned to the right of piston  45 . Dump poppet  51  can also be made from polyurethane so it&#39;s face causes a pressure seal with another bore face in regulator body  48 . Main housing  26  air entering a housing port x  43  is prevented from flowing to the right side of piston  45  unless piston  45  moves far enough to the right to move/unseat dump poppet  51 . 
         [0060]    A fill spring  40  forces fill poppet  41  against regulator body  48  aiding sealing. An exhaust spring  38  forces dump poppet  51  against regulator body  48  aiding sealing. 
         [0061]    A third water spring  39  forces piston  45  to the left with enough force to overcome fill spring  40  force and unseat fill poppet  41  when main housing  26  internal pressure drops too low to supply diver breathing air supply. 
         [0062]    When fill poppet  41  unseats, high pressure air from inlet port w  47  flows into main housing  26  through passageway b  46  thereby increasing main housing  26  pressure enough to supply sufficient diver breathing air. 
         [0063]    As main housing  26  pressure increases, the pressure on the left side of piston  45  also increases until piston  45  moves far enough to the right to overcome water spring  39  force and allows fill poppet  41  to close off air flow to main housing  26 . 
         [0064]    Main housing  26  internal pressure is also conveyed through housing port x  43  to the right side of dump poppet  51 . Whenever dump poppet  51  unseats (moves to the right), main housing  26  air exhausts past dump poppet  51 , to the right side of piston  45 , through water port  44  and tube  80  out into the surrounding water. 
         [0065]    A stable pressure differential range exists between main housing  26  internal pressure and the water pressure. This designed differential range can be on the order of 3 to 10 psig. If this differential range begins to drop below about 3 psig, then piston  45  will be forced by water spring  39  to unseat fill poppet  41  and bleed air from inlet port w  47  into main housing  26  through passageway b  46  until main housing  26  pressure exceeds 3 psig. If this differential range attempts to exceeds about 10 psig, piston  45  will be forced by main housing  26  air pressure (sensed through passageway b  46 ) to unseat dump poppet  51  allowing main housing  26  internal pressure to bleed from housing port x  43  out water port  44  and tube  80  into the water until pressure in main housing  26  decreases below about 10 psig. 
         [0066]    As described, pressure regulator  31  senses both water pressure and main housing  26  internal pressure. If the differential between these two pressures is not within the designed range, then pressure regulator  31  either flows additional air into main housing  26  or exhausts air from main housing  26  into the surrounding water. Pressure regulator  31  insures the diver always has sufficient air for breathing purposes. 
       Basic Drive Components 
       [0067]      FIG. 3  shows major drive components of my invention shown just as a small piston  35  is beginning it&#39;s thrust stroke (to the right). My invention includes two drives. 
         [0068]    One drive includes a small cylinder  34 , small piston  35  connected by a push rod  27  to a water disk p  25   a . Attached to water disk p  25   a  is a flapper p  24   a . Flapper p  24   a  is constructed so as water disk p  25   a  moves in shown direction B, water within thrust housing a  23   a  is forced in direction B moving the diver in the opposite reaction direction A. 
         [0069]    The second drive includes a large cylinder  20 , a large piston  21  connected by a push rod p  50  to a water disk  25 . Attached to water disk  25  is a flapper  24 . Flapper  24  is also constructed so as water disk  25  moves in direction B, water within thrust housing b  23   b  is forced in direction B also moving the diver in the opposite direction A. 
         [0070]    When either flapper is moving in return direction A, water flows through both the flapper and it&#39;s perforated water disk with little resistance as the flaps fold open as shown with flapper  24 . The two drive systems operate out of phase with each other. As the first drive system moves in thrusting direction B, linkage comprised of a slide block b  30   b , a rotating arm  49 , an arm pivot  36  and a slide block a  30   a  moves the second drive system in direction A and visa versa. Slide block a  30   a  is slideably attached to rotating arm  49  and pivotally fixed to push rod p  50 . Similarly, slide block b  30   b  is slideably attached to rotating arm  49  and pivotally fixed to push rod  27 . Rotating arm  49  pivots freely about arm pivot  36 . 
         [0071]    When the first drive system moves in direction B, the linkage components return/move the second drive system in the opposite direction A and visa versa. As such, my invention provides continuous/smooth thrust as either one water disk or the other is always applying a forward thrust to the diver. 
         [0072]    Flappers can be made from many types of elastomer/rubber like materials such as polyurethane of approximate thickness 0.04 inch. This material and thickness lets the flappers act rigid and behave like a leak proof solid when the pistons are moving in the trust direction B. The water disk  25  with attached flapper  24  should make a slideable seal with the inside of thrust housing b  23   b  so water will not bypass water disk  25  during it&#39;s stroke in thrust direction B. This seal can be effected by having a close tolerance between water disk  25  and thrust housing b  23   b  in the order of a few thousands of an inch. Alternately, the seal can be completed with an o-ring or a rolling diaphragm not shown. 
         [0073]    Rotating arm  49  can be made from a round stainless steel shaft of diameter about 5/16 inch. Slide blocks  30   a  and  30   b  can be made from delrin plastic as delrin provides an excellent bearing with the stainless steel shaft. 
         [0074]    My invention as shown in  FIG. 2  may be guided through the water by the diver. Alternately, my invention may be attached to a scuba tank  28  with a simple mechanism such as an attachment strap  22  shown in  FIG. 1 . A supplier for attachment strap  22  with a suitable spring loaded detachable catch is model SC-B-8331442, manufactured by Nielsen Hardware Corp., 770 Wetherfield Ave., Hartford, Conn., 06101. 
         [0075]    Large cylinder  20 , small cylinder  34 , arm pivot  36 , and valves  32 ,  37 ,  33 , shown in  FIG. 4  can all be attached to a mounting bracket  67  using standard hardware. 
       Fill Valve  32   
       [0076]    A fill valve  32  shown in  FIGS. 4 and 6  and it&#39;s position relative to rotating arm  49  determines how much high pressure air from first stage regulator  62  is applied to small cylinder  34 . No high pressure air may be applied to small cylinder  34  (representing motor off state). High pressure air may be applied for only a short length of small piston  35  travel (on the order of one half inch)(representing motor speed “slow” condition). Or high pressure air may be applied for a relatively long length of small piston  35  travel (on the order of one inch)(representing motor speed “fast” condition). As will be shown, motor speed conditions can be varied by the diver at will from “off” to “slow” to “fast”. 
         [0077]    Fill valve  32  rotates about a fill pivot  59  by action of a throttle cam  81 . The limits of fill valve  32  rotation is constrained by a pin  82  within a travel groove  61 . 
         [0078]    High pressure air from first stage regulator  62  is conveyed to fill valve  32  via a line port b  55 . Exiting high pressure air from fill valve  32  leaves an exit port  77  and is ultimately conveyed to small cylinder  34 . When fill valve  32  is on, and motor control conditions allow, high pressure air from fill valve  32  will power the thrust stroke of small piston  35 . The longer fill valve  32  is on, the more pressurized air flows into small cylinder  34  and the higher power/speed the motor will have. 
         [0079]    Fill valve  32  can be a poppet type valve including a slideable fill poppet b  56  capable of providing a pressure seal within fill valve  32  so normally no pressurized air can flow from line port b  55  to exit port  77 . However, when a poppet pin  58  is pushed by rotating arm  49 , fill poppet b  56  also moves breaking the pressure seal and allows pressurized air to pass through fill valve  32 . A poppet spring  54  pushes on fill poppet b  56  facilitating a pressure face seal when fill valve  32  is off. 
         [0080]    A pivot spring  60  maintains fill valve  32  in a normally “off” condition. 
         [0081]    As throttle cam  81  rotates about a cam pivot  52 , a valve lobe  53  part of fill valve  32  rotates fill valve  32  further toward or away from rotating arm  49 . In  FIG. 6 , fill valve  32  is shown when poppet pin  58  does not touch rotating arm  49  (shown at it&#39;s extreme travel position). With fill valve  32  and throttle cam  81  at this position the motor is “off” (not running). 
         [0082]    As throttle cam  81  rotates to a position shown as  81   a , valve lobe  53  also rotates to a position shown as  53   a  and moves poppet pin  58  toward rotating arm  49 . This condition is a motor “on” state. 
         [0083]    The further throttle cam  81  is rotated, the faster and more powerful will run the motor. Throttle cam&#39;s  81  rotational position is controlled by the diver as simply as connecting a throttle connection  75  linkage rod from throttle cam  81  to some position on the propulsion vehicle where a diver can access/push/pull throttle connection  75  at will. Throttle cam  81  position shown as  81   a  results when diver moves throttle connection  75  to position  75   a.    
       Pneumatics/Valves 
       [0084]      FIG. 4  shows an embodiment of pneumatics, valves, and interconnections for my invention. Note a spool valve  76  is shown in it&#39;s spring return position (pilot off). Spool valve  76  can also shift to it&#39;s second position whenever pressurized air is applied via a tube e  70  to it&#39;s valve pilot. 
         [0085]    My invention shown is at state where small piston  35  is about to begin it&#39;s power/thrust stroke. 
         [0086]    High pressure air from first stage regulator  62  is conveyed via high a pressure hose  78  through main housing  26  and a tube h  73  to fill valve  32 . Fill valve  32  is on/open (because of poppet pin  58  contact with rotating arm  49  see also  FIG. 6 ). High pressure flows through fill valve  32 , through a tube d  69 , through spool valve  76 , through a tube a  65 , and into small cylinder  34 . Small piston  35  is forced forward by the high pressure air. Fill valve  32  remains “on” as small piston  35  advances a selected distance. Throughout this selected distance, fill valve  32  supplies pressurized air to small cylinder  34  until rotating arm  49  rotates far enough to lose contact with poppet pin  58  and shuts off fill valve  32 . As mentioned before, throttle connection  75  positions/controls when this fill valve  32  shut off condition occurs (i.e. how long fill valve  32  keeps supplying pressurized air to small cylinder  34 ). 
         [0087]    As small piston  35  thrusts forward, rotating arm  49  rotates and returns large piston  21 . Air contained within large cylinder  20  exhausts through a tube b  66 , and through spool valve  76  exhausting into main housing  26 . 
         [0088]    At the end of small piston  35  thrust stroke, rotating arm  49  moves to position shown as  49   a . At position  49   a , a pilot fill valve  33  is opened supplying pressurized air from small cylinder  34  through a tube c  68 , through a tube f  71 , through a check valve  64 , to the pilot of spool valve  76 . The pilot shifts spool valve  76 , conveying small cylinder  34  high pressure air through tube b  66  to large cylinder  20 . Large cylinder  20  pressurization (from small cylinder  34 ) forces large piston  21  forward on it&#39;s power/thrust stroke, and also returns small piston  35 . 
         [0089]    As large piston  21  travels forward, large cylinder  20  pressure decreases steadily and can become less than the minimum pressure required to shift spool valve  76  pilot. However, the one way check valve  64  maintains high pilot pressure until near the end of large piston  21  travel. At the end of large piston  21  travel, rotating arm  49  actuates a pilot dump valve  37 . Pilot dump valve  37  exhausts pilot air through a tube g  72 . When the pilot pressure of spool valve  76  is relieved by pilot dump valve  37 , spool valve  76  shifts back to it&#39;s spring return normalized position as shown in  FIG. 4 . After this happens, all controls are prepared for the next motor cycle as just described above. 
         [0090]    As the dual piston compound motor operates, exhausted air from large cylinder  20  collects in main housing  26  with each cycle of the motor. A scuba diver can breathe air from main housing  26  through a breathing hose  79  and a demand regulator  63 . If main housing  26  pressure ever falls below the design pressure limit (as discussed above 3-10 psig), pressure regulator  31  will supply air from high pressure hose  78  through a tube i  74 , through pressure regulator  31  and into main housing  26  until pressure exceeds the minimum design pressure limit (3 psig). 
         [0091]    First stage regulator  62  can be any one of many commercial diving regulators adjustable to the output pressure of 200 psig. One source of a suitable first stage regulator  62  is model Conshelf XII manufactured by US Divers Co., 3323 West Warner Ave., Santa Ana, Calif. 92702. 
         [0092]    Demand regulator  63  can be a commercial hookah low pressure type. One such manufacturer of both demand regulator  63  and breathing hose  79  is Sea Hornet, 1 Kenneth Road, Manly Vale, 2093 NSW Australia. This demand regulator  63  also includes an integral one way valve to keep water from ever going into main housing  26  if main housing  26  is left un-pressurized. The poppet valves  32 ,  33 ,  37  are typical valves used by those skilled in the art of pneumatics controls. The poppets of these valves can be made from polyurethane material to effect face pressure seals. 
         [0093]    A source for spool valve  76  can be model 1800 available from MAC Valves Inc., Wixom, Mich. 
         [0094]    Check valve  64  can be obtained from McMaster Carr, 6100 Fulton Industrial Blvd., Atlanta, Ga. 30336, part number 7768K11. 
         [0095]    Main housing  26  can be made from a layered composite material about ⅛ inch thick such as fiberglass and epoxy. A gasket seal (not shown) can be placed between a mounting plate  57  and a flange formed on the main housing  26  to effect a pressure seal. This pressure seal is necessary as main housing  26  pressure is designed to be about 3 to 10 psig above that of the surrounding water. 
         [0096]    Small cylinder  34  and small piston  35  will begin their thrust stroke at first stage regulator  62  pressure of 200 psig. At the end of the small piston  35  stroke, the small cylinder  34  pressure will be about 57 psig (depending on throttle cam  81  selected position of  FIG. 6 ). 
         [0097]    As discussed, at the end of small piston  35  stroke, pressurized air within small cylinder  34  will be conveyed to large cylinder  20 . Accordingly, large cylinder  20  pressure at the beginning of large piston  21  thrust stroke will also be about 57 psig and will decrease with large piston  21  stroke to about 15 psig (it&#39;s exhaust pressure). 
         [0098]    As designed, the dual piston compound motor meets the former criteria for an effective air motor which both supplies adequate diver propulsion and consumes less air than a diver normal breathing consumption! 
         [0099]    The embodiments and descriptions above have been by way of illustration, rather than limitation. The scope and content of my invention
       “Scuba tank air powered, steady pulling, diver propulsion device uses dual compound pistons attached to dual water thrusters at efficiency where breathing air is supplied to diver without curtailing normal dive time.”
 
being determined by the following claims: