Abstract:
A combination pump and trap is disclosed which includes a snap-over mechanism useful for small floats with little buoyancy. The snap-over mechanism has a geometry in which the distance between the float or compression arm pivot point and the pivot for the portion of the spring connected to a first arm or toggle link is greater than the distance from the float or compression arm pivot point and the pivot for the portion of the spring connected to the float or compression arm. This geometry allows the magnification of buoyancy by the main arm which is transmitted to the first toggle link to be large and the magnification of buoyancy by the first toggle link which is transmitted to the change-over valve to be large. A trap which is connected to the float arm is also used, which allows a liquid seal to be maintained at the liquid discharge port. A double seal valve with a mechanism for allowing rapid opening of the valve upon movement of the float is also disclosed, as is a externally-cleanable working fluid feed valve.

Description:
This application is a division of U.S. patent application Ser. No. 08/529,966 filed Sep. 19, 1995, now U.S. Pat. No. 5,655,888. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pump and trap for feeding a liquid such as water, fuel, etc. The pump and trap of the present invention is suitable particularly for use in collecting a condensate generated in a steam piping system and feeding this condensate to a boiler or a waste heat recovery system. 
     2. Description of the Related Art 
     Condensate generated in a steam piping system in most cases still has a considerable quantity of heat. It therefore has been a widespread practice to provide a condensate recovery system, including a pump for recovering the condensate and feeding it into a boiler or a waste heat recovery system for the purpose of effective utilization of waste heat from the condensate, thus making effective use of this energy. 
     The pump used in prior art condensate recovery system collects the condensate in a vessel, and then introduces a high-pressure working fluid—such as steam—into the vessel by operating a change-over valve. The pressure of the high-pressure working fluid discharges the condensate from the inside of the vessel. To insure high-efficiency operation of the pump, it is necessary to collect as much condensate as possible within the vessel and to properly switch the change-over valve. 
     The pump of the prior art, therefore, generally adopts a snap mechanism, provided with a coil spring. in order to insure reliable switching of the change-over valve. A pump which is equipped with a built-in snap mechanism provided with a coil spring is disclosed in U.S. Pat. No. 5,141,405, to Francart. 
     FIG. 13 is a front view of a snap mechanism used in the prior art pump described in the Francart patent. In the pump disclosed in the Francart patent, the snap mechanism  100  comprises a main arm  101 , a first arm  102 , and a coil compression spring  103 . The main arm  101  is pivotally supported, by a first shaft  106 , on a supporting member or frame  105 . On the forward end of the main arm  101  is connected a float  108 , through a screw member  104  which is fastened to the float  108 . 
     The first arm  102  is connected at one end to the supporting member  105  by the first shaft  106 , and therefore to the main arm  101 , and at the other end to one end of the coil spring  103  by a third shaft  110 , through a spring bracket member  116 . The other end of the coil spring  103  is connected to the main arm  101  by a second shaft  112  through a spring bracket member  115 . A valve spindle operating rod  111  is connected by a shaft  107  to the center part of the first arm  102 . The valve spindle (not shown) and the snapping mechanism  100  are linked to the change-over valve through the valve spindle operating rod  111 . 
     In the prior art pump, accumulation of condensate in the vessel (not shown) causes the float  108  to rise. As the float  108  rises, the spring bracket member  115  side of the coil spring  103  moves upward, thus compressing the coil spring  103 . With further rise of the float  108 , the coil spring  103  is in line with the first arm  102 . The float  108  rises further until an angle between the coil spring  103  and the first arm  102  exceeds 180 degrees. As a result, the coil spring  103  suddenly recovers from compression, and the connecting section (the third shaft  110 ) between the coil spring  103  and the first arm  102  snaps downward. This movement results in downward movement of the valve spindle operating rod  111  connected to the first arm to thereby suddenly switch the change-over valve (not shown). 
     The prior art pump has a problem—notwithstanding its simple design and its ability to relatively efficiently pump liquid—that a great deal of buoyancy, or a large float, is needed to obtain a large force for proper switching of the change-over valve. This is because, in a triangle formed by the first shaft  106 , the second shaft  112 , and the third shaft  110 , the distance between the first shaft  106  and the second shaft  112  is longer than that between the first shaft  106  and the third shaft  110 . The distance between the first shaft  106  and the second shaft  112  is long, and accordingly the magnification of buoyancy produced by the main arm  101  and transmitted to the first arm  102  is small. Furthermore, since the distance between the first shaft  106  and the third shaft  110  is short, the magnification of buoyancy by the first arm  102  which is transmitted to the valve spindle operating rod  111  is also small. 
     SUMMARY OF THE INVENTION 
     In the view of the above-described disadvantages inherent to the prior art apparatus, it is an object of the present invention to provide a pump which is capable of actuating the change-over valve with a large force, even with a float with little buoyancy, while still performing reliably. 
     The present invention features a pump in which a float, a change-over valve, and a snap mechanism are built in a vessel having a working fluid inlet port, a working fluid discharge port, a liquid inlet port, and a liquid discharge port. The snap mechanism includes a first shaft pivotally supported within the vessel, a main arm rotating around the first shaft, a first toggle link rotating around the first shaft, a second shaft pivotally supported functionally on the main arm at a point spaced a small distance from the first shaft and parallel with the first shaft, a third shaft pivotally supported functionally to the first toggle link at a point spaced a large distance from the first shaft and parallel with the first shaft, and a second toggle link mounted between the second shaft and the third shaft and pivotable at both mounting positions. A connecting mechanism functionally connects the float to the main arm at a point spaced from the first shaft, and another connecting mechanism functionally connects the change-over valve to the first toggle link. A compressible-expandable mechanism, which compresses to keep the first toggle link at rest until the second shaft is aligned with the first shaft and the third shaft, extends when the second shaft has gone beyond the position of alignment with the first shaft and the third shaft, thus snapping to move the first toggle link. 
     In the pump of the present invention, accumulation of condensate in the vessel causes the float to rise to rotate the main arm around the first shaft, and the second shaft moves between the first shaft and the third shaft until aligning with the first shaft and the third shaft, thus compressing to deform the compressible-expandable mechanism. As the float goes further upward, the second shaft exceeds the position of alignment with the first shaft and the third shaft and the compressible-expandable mechanism suddenly extends to recover from deformation, thus snapping to move the third shaft. As a result, the change-over valve is suddenly switched, allowing liquid accumulated within the vessel to be pumped. 
     In the snap mechanism used in the pump of the present invention, the distance between the first shaft and the third shaft is longer than that between the first shaft and the second shaft. In a triangle formed by the first shaft, the second shaft and the third shaft, the distance between the first shaft and the second shaft is short while the distance between the first shaft and third shaft is long; the magnification of buoyancy by the main arm which is transmitted to the first toggle link is therefore large and the magnification of buoyancy by the first toggle link which is transmitted to the change-over valve is also large. Consequently, the change-over valve can operate properly with great force even when little buoyancy, i.e., a small float, is used. 
     The present invention also includes a valve at the liquid discharge port which acts as a trap for the vessel. The valve is connected to the float mechanism, so that the valve opens when the float rises in response to accumulation of liquid in the vessel. The valve ensures that a liquid seal is maintained at the liquid discharge port. The valve includes a double seal, to equalize fluid pressure on the valve and therefore make actuation of the valve easier. A mechanism for coupling the valve to the float is provided, as well as a mechanism for adjusting the double seal on the valve to ensure a good seal at both valve seats. The valve preferably moves downward to unseat, to thereby allow less space to be used in the interior of the vessel by the valve. 
     The above and other subjects, features and advantages of the present invention will become more clear from the following description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a first embodiment of a pump according to the present invention; 
     FIG. 2 is an enlarged cross-sectional view of a snap mechanism section of FIG. 1; 
     FIG. 3 is an enlarged cross-sectional view of a float arm section with the float in a raised position; 
     FIG. 4 is a cross-sectional view taken along line A—A of FIG. 2; 
     FIG. 5 is a cross-sectional view of a second embodiment according to the present invention; 
     FIG. 6 is a cross-sectional view of a third embodiment according to the present invention; 
     FIG. 7 is a cross-sectional view of a fourth embodiment according to the present invention; 
     FIG. 8 is a cross-sectional view of another snap mechanism section according to the present invention; 
     FIG. 9 is a cross-sectional view taken along line B—B of FIG. 8; 
     FIG. 10 is a cross-sectional view of another snap mechanism section according to the present invention; 
     FIG. 11 is an exploded perspective view of a main arm and a connecting member in FIG. 10; 
     FIG. 12 is a cross-sectional view of another snap mechanism according to the present invention; and 
     FIG. 13 is a cross-sectional view of a snap mechanism section in a prior art pump; 
     FIGS. 14A-14C show a cross-sectional side view and end views of the lower valve head of the present invention; 
     FIG. 15 shows a cross-sectional side view of the connecting tube of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a cross-sectional view of a first embodiment of the combination pump and trap of the present invention. FIG. 2 is an enlarged sectional view of the snap mechanism of FIG.  1 . FIG. 3 is an enlarged sectional view of the snap mechanism with the float of FIG. 1 in a raised position. FIG. 4 is a sectional view taken along line A—A of FIG.  2 . In FIG. 1, the pump  1  of the embodiment of FIG. 1 includes a float  3 , a change-over valve  4 , a snap mechanism  5 , and a valve  6 , all of which are disposed within a vessel  2 . 
     In the vessel  2  a body section  7  and a cover section  8  are connected by screws (not shown), and a liquid holding space  10  is formed inside. In the embodiment of FIG. 1, the body section  7  of the vessel  2  has no components mounted thereon; distinctive components of the embodiment are mounted on the cover section  8  of the vessel  2 . The cover section  8  is provided with four openings: a working fluid inlet port  11 , a working fluid outlet port  13 , a liquid inlet port  16 , and a liquid discharge port  17 . 
     Inside the working fluid inlet port  11 , a working fluid feed valve  20  is mounted, and inside of the working fluid outlet port  13 , a working fluid exhaust valve  21  is mounted. The working fluid feed valve  20  is composed of a valve case  22 , a valve head  23 , and a valve lifting rod  24 . The valve case  22  has a through hole provided in an axial direction; the upper end of the through hole functions as a valve seat  25 . In the intermediate part of the valve case  22  four openings  26 , connecting the through hole with the liquid holding space  10 , are provided. The valve head  23  is of a semi-spherical or spherical form and is integrally installed at the tip of the valve lifting rod  24 . 
     The working fluid feed valve  20  is particularly adapted to easy cleaning without disassembly of the vessel  2 . A sealing cap C is removably mounted, preferably by screw threads, on cover section  8  above valve head  23 , thereby allowing access to the working fluid feed valve  20  interior. A screen S may surround the valve head  23  to trap particles to prevent the particles from clogging the working fluid feed valve  20 . The valve head  23  and valve lifting rod  24 , integrally formed together, can be removed as a unit through the hole through cover section  8  into which the sealing cap is mounted. This ability is in part due to the absence of a fixed connection between valve lifting rod  24  and connecting plate  27 . This lack of a fixed connection also allows the working fluid feed valve  20  to be manufactured without the need for tight tolerancing between the valve lifting rod  24  and the valve spindle operating rod  28 . The valve case  22  can thereafter be removed from the cover section  8  through the same hole. Accordingly, each of the elements of working fluid feed valve  20  may be removed and cleaned externally of the vessel  2 , without the need to separate cover section  8  and body section  7 . 
     In the pump  1  of the present invention, the tip of the valve case  22  of the working fluid feed valve  20  is screwed into the working fluid inlet port  11 . The valve head  23  is located on the working fluid inlet port  11  side, and the valve lifting rod  24  is inserted through the through hole in the valve case  22  to the vessel  2  side into contact with a connecting plate  27 . The connecting plate  27  is connected to valve spindle operating rod  28 . The valve spindle operating rod  28  is connected to the snap mechanism  5 . 
     The working fluid exhaust valve  21  is composed of a valve case  29 , a valve head  30 , and a valve lifting rod  31 . The valve case  29  has a through hole in an axial direction, in which a valve seat  32  is provided. The valve head  30  secured on the tip of the valve lifting rod  31  comes from below into contact with the valve seat  32 , thus opening and closing the valve. The valve spindle operating rod  28  and the valve lifting rod  31  are connected by a pin  33 . The change-over valve  4  includes the working fluid feed valve  20  and the working fluid exhaust valve  21 ; when the working fluid feed valve  20  is opened, the working fluid valve  21  is closed, and when the working fluid feed valve  20  is closed, the working fluid exhaust valve  21  is opened. Any pressurized fluid may be used as the working fluid to power pump  1 . 
     The liquid inlet port  16  is located nearly at the center of the cover section  8  and the liquid discharge port  17  is in a position corresponding to the lower part of the vessel  2 . The float  3  is supported by a bracket  36  through a float arm  34  and a shaft  35 . The snap mechanism  5  is supported on a bracket  38  through a first shaft  37 . The bracket  36  and the bracket  38  are connected by screws (not shown), and are integrally attached to the cover section  8  of the vessel  2 . The float arm  34  is produced from a plate bent into a U shape, so that two parallel plates will face each other as shown in FIG.  4 . The float  3  is connected to the bent section of the float arm  34 ; to the other end of the float arm  34  is connected a shaft  40 . 
     The bracket  36  as viewed from above is composed of two L-shaped plates as shown in FIG. 4, with shafts  41  and  42  and the aforementioned shaft  35  connected across the plates. The shaft  35  also serves as a pivot; the float  3  moves up and down around the shaft  35 . The shafts  41  and  42  also serve as upper and lower limit stops, respectively, for the float  3 . On the side, the bracket  38  consists of two L-shaped plates, across which the shaft  43  and the first shaft  37  are mounted for connecting these two plates. The shaft  43  also functions as a stopper for a first arm  52 , described below. 
     The snap mechanism  5  includes a main arm  51 , a first arm  52 , a coil compression spring  54 , a spring bracket member  55 , and a spring bracket member  56 . The main arm  51  consists of two plates parallel with each other as shown in FIG.  4 . On the left-hand end (in FIG. 1) of the two plates a slot  57  is provided. The main arm  51  is pivotally supported by the first shaft  37  at the angled section of main arm  51 , thereby forming a first pivot connection. In the slot  57  of the main arm  51  is fitted the shaft  40  of the float arm  34 . Because of this connection, the main arm  51  follows up and down motions of the float  3 , rocking up and down on the first shaft  37 . 
     The left end (in FIG. 1) of the main arm  51  swings downward as the float  3  rises. On an opposite end of main arm  51  is mounted a second shaft  58  parallel with the first shaft  37 . The spring bracket member  55  is pivotally supported by the second shaft  58 , thereby forming a second pivot connection. The first arm  52  is pivotally supported on the first shaft  37 . The first arm  52  consists of two parallel plates facing each other as shown in FIG. 4, each of which is of an inverted L shape. The lower end of the first arm  52  has mounted on it the third shaft  59 , parallel with the first and second shafts  37  and  58 , and the spring bracket member  56  is pivotally supported on the third shaft  59 , thereby forming a third pivot connection. Between the spring bracket members  55  and  56  is mounted the coil compression spring  54 . The distance between the first shaft  37  and the third shaft  59  is longer than the distance between the first shaft  37  and the second shaft  58 . On the upper end of the first arm  52  a shaft  60  is mounted, to which the lower end of the valve spindle operating rod  28  is connected. The main arm  51  has a window  81 , which is open so as not to interfere with the operation of the shaft  60 . 
     On the liquid holding space  10  side of the liquid discharge port  17  is provided a valve  6  which is a double valve. The valve  6  is composed of upper and lower valve cases  61  and  62 , upper and lower valve heads  63  and  64 , and a drain valve shaft  71 . The upper valve case  61  and the lower valve case  62  are fastened together by screws or bolts (not shown) the upper valve case  61  is secured to the cover section  8  by screws or bolts (not shown). In the upper valve case  61  is formed an upper valve seat  66 , while in the lower valve case  62  is formed a lower valve seat  67 . The valve seats  66 ,  67  are in direct communication with the liquid holding space  10  such that liquid from the liquid holding space  10  flows out the fluid discharge port directly from the liquid holding space  10  directly through the openings surrounded by valve seats  66 ,  67 . The upper valve head  63  is connected by screw threads to a link  65 , which link  65  is locked from rotating by a nut  68 . On the lower shaft portion of the upper valve head  63  the lower valve head  64  is threadedly connected. A connecting tube  69  is provided between the upper valve head  63  and the lower valve head  64  to space the upper valve head  63  and the lower valve head  64  from one another at a specific distance, to thereby ensure accurate seating of both valve heads  63 ,  64  on the corresponding valve seats  66 ,  67  without the need for close tolerancing of the valve heads  63 ,  64 . 
     As shown in FIGS. 14A-C and  15 , the connecting tube  69  has an outer circumferential lower end  69   a  formed with a narrowed cone shape defined by an angle θ 1 . This lower end  69   a  mates with a recess  64   a  in the upper end of the lower valve head  64 , which recess  64   a  is formed as a conical hole defined by an angle θ 2 . As the lower valve head  64  is threaded onto the lower shaft portion of the upper valve head  63 , the conical surface of the recess  64   a  in the lower valve head  64  is forced against the lower end  69   a  of the connecting tube  69  so as to deform the lower end  69   a  inwardly. This arrangement between the connecting tube  69  and lower valve head  64  creates a seal between the members, thereby preventing leakage through the valve  6 . 
     The upper end of the link  65  is pivotally connected to the drain valve shaft  71 , and furthermore the upper end of the drain valve shaft  71  is pivotally connected by a shaft  72  to the float arm  34 . The shaft  72  is located slightly oblique and downward of the shaft  35  when the float  3  is in the lowermost position as shown in FIG. 2, and is almost immediately below the shaft  35  when the float  3  comes to the topmost position as shown in FIG.  3 . The upper and lower valve heads  63  and  64  move downwards with the rise of the float  3 , communicating the liquid holding space  10  with the liquid discharge port  17 , and move upwards with downward movement of the float  3 , thus closing the liquid discharge port  17 . 
     Next, operation of the present embodiment of the pump  1  will be explained according to a series of operational procedures in which steam is used as a working fluid. First, the external piping of the pump  1  is connected, on the working fluid inlet port  11  side, to high-pressure steam source, and, on the working fluid discharge port  13  side, to the steam circulation piping. The liquid inlet port  16  is connected to a load, such as a steam-using apparatus, via a check valve (not shown) which opens towards the liquid holding space  10 . The liquid discharge port  17  is connected to equipment to which liquid is pumped—such as a boiler—via a check valve (not shown) which opens away from the liquid holding space  10 . 
     When no condensate is present in the liquid holding space  10  of the combination pump and trap of the present invention, the float  3  is in the bottom position as shown in FIG.  1 . At this time, the working fluid feed valve  20  in the change-over valve  4  is closed, while the exhaust valve is open. The valve  6  is in a closed position, thereby preventing liquid from exiting through liquid discharge port  17 . When condensate is produced in the load, such as a steam-using apparatus, the condensate flows down through the liquid inlet port  16  to the pump  1 , accumulating in the liquid holding space  10 . 
     As the float  3  rises with the accumulation of the condensate in the liquid holding space  10 , the float arm  34  rotates clockwise on the center of the shaft  35 , the shaft  72  connected to the drain valve shaft  71  moves downwards, and the upper and lower valve heads  63  and  64  move downwards, through movement of the drain valve shaft  71  and the link  65 , thus opening the valve  6 . This allows communication between the liquid holding space  10  and the liquid discharge port  17 . The float  3  position and buoyancy is selected so that the valve  6  does not open until the liquid level in the liquid holding space  10  is above the level of the upper valve head  63 , thereby ensuring a liquid seal at valve  6 . Furthermore, the configuration of the float arm  34  and the drain valve shaft  71  are such that the initial rise of float  3  will cause rapid opening of the valve  6 , and, vice versa, the valve  6  will rapid close only as the float approaches its bottommost position. 
     On the snap mechanism  5 , the main arm  51  rotates counterclockwise on the center of the first shaft  37  through interlock with the downward movement of the shaft  40 , driven by rotation of the float arm  34 , and the second shaft  58  moves to the right to align with the first shaft  37  and the third shaft  59 , compressing the coil spring  54 . Then, with further rise of the float  3 , the second shaft  58  moves to the right past the position of alignment with the first shaft  37  and the third shaft  59 , the coil spring  54  extends suddenly to recover from a compressed state, thus allowing the clockwise rotation of the first arm  52  around shaft  37  to snap the third shaft  59  to the left. As a result, valve spindle operating rod  28  connected to the shaft  60  of the first arm  52  moves upwards, to thereby open the working fluid feed valve  20  and to close the working fluid exhaust valve  21 . 
     With the opening of the working fluid inlet port  11 , high-pressure steam is led into the vessel  2 . Vessel pressure increases on the condensate in the liquid holding space  10 , thereby forcing the condensate, with steam pressure, out the liquid discharge port  17  to an exterior boiler or waste heat recovery system via a check valve (not shown). 
     With discharge of the condensate, the water level in the condensate holding space  10  goes down, to lower the float  3 . The float arm  34  rotates in the counterclockwise direction on the center of the shaft  35 , thereby moving upwards the shaft  72  which is connected to the drain valve shaft  71 . Upward movement of drain valve shaft  71  moves the upper and lower valve heads  63  and  64  upwards via the link  65 , thus closing the valve  6 . In the process of operation of the valve  6  from the full-open position to the full-close position, the shaft  72  moves from a position nearly directly below the shaft  35  as shown in FIG. 3 to a position obliquely a little below the shaft  35  as shown in FIG. 2, and therefore the more the valve  6  approaches the full-close position, the more it displaces towards closing the valve. In other words, when the float  3  goes downwards from the level shown in FIG. 2, the valve  6  is held close to the full-open position during the initial period of downward movement, thus allowing quick discharge of the condensate. 
     On the snap mechanism  5  side, the main arm  51  rotates clockwise on the first shaft  37 , in interlock with the upward movement of the shaft  40 , driven by the rotation of the float arm  34 . The second shaft  58  moves to the left into alignment with the first shaft  37  and the third shaft  59 , compressing the coil spring  54 . With further downward movement of the float  3 , the second shaft  58  moves to the left past the position of alignment with the first shaft  37  and the third shaft  59 , and then the coil spring  54  suddenly extends to recover from compression, driving the first arm  52  to turn in the counterclockwise direction to snap the valve spindle operating rod  28 , connected to the shaft  60  of the first arm  52 , downwards. Thus the working fluid feed valve  20  is closed, while the working fluid exhaust valve  21  is opened. 
     In the above-described embodiment, the coil spring  54  is disposed between the second shaft  58  on the main arm  51  and the third shaft  59  on the first arm  52 . Next, a configuration in which the coil spring  54  is disposed between the first shaft  37  on the main arm  51  and the second shaft  58  on the main arm  51 , which is apart from the first shaft  37 , will be explained with reference to FIG.  5 . In the embodiment to be described below, members operating similarly to those explained in the above-described embodiment are designated by similar numerals in order to prevent redundancy. FIG. 5 is a sectional view of another embodiment of the pump of the present invention. 
     The snap mechanism  5  includes the main arm  51 , the first arm  52 , a second arm  73 , the coil compression spring  54 , the spring bracket member  55 , and the spring bracket member  56 . The main arm  51  is composed of two parallel plates, each of which is L-shaped when viewed from the front. The angled section of the main arm  51  is pivotally supported by the first shaft  37 . On the lower end of the main arm  51 , the second shaft  58  is mounted, parallel with the first shaft  37 . The second shaft  58  is movable only in the direction of the first shaft  37  along a long hole or slot  74  formed in the main arm  51 . The coil compression spring  54  is mounted between the spring bracket member  55 , supported on the first shaft  37 , and the spring bracket member  56 , supported on the second shaft  58 . 
     The first arm  52  is pivotally supported on the first shaft  37  at the angled section of first arm  52 . On the lower end of the first arm  52  the third shaft  59  mounted in parallel with the first and second shafts  37  and  58 . Between the third shaft  59  and the second shaft  58  the second arm  73  is mounted. The second arm  73  is composed of two parallel plates which are rotatable on the second and third shafts  58  and  59 . The distance between the first shaft  37  and the third shaft  59  longer than the distance between the first shaft  37  and the second shaft  58 . 
     In the present invention, it should be noted that the second shaft  58 , operating with rotation of the main arm  51 , is aligned with the first shaft  37  and the third shaft  59  while moving towards the first shaft  37  along the long hole  74 , to thereby compress the coil spring  54 . The coil spring  54 , therefore, is axially compressed to deform in the direction of the first shaft, only in the direction of extension and contraction. The coil spring  54  does not curve, and constantly maintains a straight-line state to thereby prevent damage of the coil spring as a result of bending of the coil spring  54 . 
     Next, an explanation will be given by referring to FIG. 6 of a coil spring  54  disposed between the third shaft  59  on the first arm  52  and a fourth shaft  75  on the first arm  52 , apart from the third shaft  59 . FIG. 6 is a sectional view of another embodiment of the pump of the present invention. 
     The snap mechanism  5  includes the main arm  51 , the first arm  52 , the second arm  73 , the coil compression spring  54 , the spring bracket member  55 , and the spring bracket member  56 . The angled section of the main arm  51  is pivotally supported by the shaft  37 . At the lower end of the main arm  51  is installed the second shaft  58  parallel with the first shaft  37 . 
     The first arm  52  is pivotally supported to the first shaft  37  at the angled section of the first arm  52 . At the intermediate part of the first arm  52  is installed the third shaft  59  parallel with the first and second shafts  37  and  58 . At the lower end of the first arm  52  is installed the fourth shaft  75  parallel with the first, second and to third shafts  37 ,  58  and  59 . The third shaft  59  is movable only in the direction of the fourth shaft  75  along the long hole  76  formed in the first arm  52 . Between the third shaft  59  and the second shaft  58 , the second arm  73  is pivotally installed. Between the spring bracket member  55  supported on the fourth shaft  75  and the spring bracket member  56  supported on the third shaft  59  is mounted the coil compression spring  54 . The distance between the first shaft  37  and the third shaft  59  is longer than that between the first shaft  37  and the second shaft  58 . 
     In the present embodiment, it should be noted that the third shaft  59  moves in the direction of the fourth shaft  75  along the long hole  76  to deform by compression the coil spring  54  when the second shaft  58 , operating in interlock with the rotation of the main arm  51 , comes in line with the first shaft  37  and the third shaft  59 . The coil spring  54 , therefore, is deformed only in the direction of the fourth shaft  75 , that is, in the direction of extension and contraction similar to the embodiment shown in FIG.  5 . This movement ensures that the coil spring  54  is not subject to damage or breakage as the result of bending. 
     Next, a embodiment with the coil spring  54  disposed between the third shaft  59 , functionally connected on the first arm  52  by a crank arm  77 , and a fourth shaft  75  on the first arm  52 , apart from the third shaft  59 , will be explained by referring to FIG.  7 . FIG. 7 is a sectional view of a further pump of the present invention. 
     The snap mechanism  5  is composed of the main arm  51 , the first arm  52 , the second arm  73 , the crank arm  77 , the coil compression spring  54 , the spring bracket member  55  and the spring bracket member  56 . The angled section of the main arm  51  is pivotally supported by the first shaft  37 . On the lower end of the main arm  51  is installed the second shaft  58  parallel with the first shaft  37 . The upper end of the second arm  73  is pivotally supported on the second shaft  58 . The third shaft  59  is installed on the lower end of the second arm  73 , which third shaft  59  is parallel with the first and second shafts  37  and  58 . 
     The first arm  52  is pivotally supported on the first shaft  37  at the angled section of the first arm  52 . On the lower end of the first arm  52  the fourth shaft  75  is installed parallel with the first second and third shafts  37 ,  58  and  59 . The coil compression spring  54  is mounted between the spring bracket member  55 , pivotally supported on the fourth shaft  75 , and the spring bracket member  56 , pivotally supported on the third shaft  59 . On the portion projecting to the right from the intermediate section of the first arm  52 , a fifth shaft  78  parallel with the first through to fourth shafts  37 ,  53 ,  59  and  75  is installed. Between the fifth shaft  78  and the third shaft  59  is mounted the crank arm  77 . The crank arm  77  consists of two parallel plates facing each other, and are rotatable at the points where the third and fifth shafts  59  and  78  are connected. The distance between the first shaft  37  and the third shaft  59  is longer than that between the first shaft  37  and the second shaft  58 . 
     In the present embodiment, it should be noted that the third shaft  59  moves in the direction of the fourth shaft  75  while rotating about the fifth shaft  78 . When the second shaft  58  comes in line with the first shaft  37  and the third shaft  59 , by rotation of the main arm  51 , the coil spring  54  is compressed. The coil spring  54 , supported by the crank arm  77  when snapping over, is not subject to lateral bending or vibration and accordingly is prevented from being damaged. 
     In the above-described embodiment, the float  3  is connected to the main arm  51  through the float arm  34 . Next, a construction in which the float  3  is directly connected to the main arm  51  will be explained by referring to FIGS. 8 and 9. FIG. 8 is a sectional view of another snap mechanism section to be employed in the present embodiment, and FIG. 9 is a sectional view taken along line B—B. 
     In the snap mechanism  5  of FIG. 8 the main arm  51  is supported on the bracket  38  through the first shaft  37 . The bracket  38  is integrally mounted on the vessel. The bracket  38  consists of two L-shaped plates as shown in FIG. 9 when viewed from above, the two plates being connected by the shaft  43  and the first shaft  37 . The shaft  43  serves also as a stopper for the first arm  52 . 
     The snap mechanism  5  is composed of the main arm  51 , the first arm  52 , the coil compression spring  54 , the spring bracket member  55 , and the spring bracket member  56 . The main arm  51  is formed by bending a plate into a U shape as shown in FIG. 9, that is, into two parallel plates facing each other. In the bent portion of the main arm  51  the float  3  is fastened by a bolt  82 . The float  3  rocks up and down on the center of the first shaft  37 . 
     The right end (in FIG. 8) of the main arm  51  swings down to the right; on the right end is installed the second shaft  58  which is parallel with the first shaft  37 . The spring bracket member  55  is pivotally supported on the second shaft  58 . Also, the first arm  52  is pivotally supported on the first shaft  37  at the angled section of the first arm  52 . The first arm  52  consists of two parallel plates as shown in FIG. 9, each of which is of an inverted L shape. On the lower end of the first arm  52  is installed the third shaft  59  which is parallel with the first and second shafts  37  and  58 , and the spring bracket member  56  is pivotally supported on the third shaft  59 . Between the spring bracket members  55  and  56  is mounted the coil compression spring  54 . Furthermore, on the upper medium part of the first arm  52  is installed the shaft  60 , to which the lower end of the valve spindle operating rod  28  is connected. 
     The operation of the snap mechanism  5  of the present embodiment differs from the above-described embodiment only in the direction of rotation of the main arm  51  and the first arm  52  which are operated by the upward and downward movement of the float  3 , and therefore a detailed operation procedure will not be described. 
     In the embodiment shown in FIGS. 8 and 9, the float  3  is fastened by a bolt  82  to the main arm  51 . Next, a way in which the float  3  and the main arm  51  are loosely connected will be explained with reference to FIGS. 10 and 11. FIG. 10 is a sectional view of another snap mechanism section to be adopted in the pump according to the present invention; FIG. 11 is an exploded perspective view of a member connected to the main arm of FIG.  10 . 
     The snap mechanism  5  includes the main arm  51 , the first arm  52 , the coil compression spring  54 , the spring bracket member  55 , and the spring bracket member  56 . The main arm  51  is composed of two parallel plates facing each other. On the left end (in FIG. 10) of the two plates in installed a shaft  83 , to which a connecting member  84 , fixedly attached to the float  3  by welding, is pivotally installed. The connecting member  84  is a round rod having at the forward end a rectangular projection  85  formed by cutting off both sides of the rod end. The projection  85  is inserted and pivotally connected by the shaft  83  between the two plates of the main arm  51 . The forward end face  86  of the shoulder of the connecting member  84  contacts the upper and lower faces  87  and  88  on the mating end side of the main arm  51 , serving as a stopper to prevent further rotation over a specific position. Thus, the float  3  rocks up and down on the center of the shaft  83  which is supported by the main arm  51 , according to a change in the liquid level in the vessel. The main arm  51  also rocks up and down on the center of the first shaft  37  with the up-and-down motion of the float  3  after the float  3  has moved a specific amount so that the forward end face  86  of the shoulder section of the connecting member  84  contacts the upper face  87  or the lower face  88  of the main arm  51 . 
     In the embodiment described above, after movement by a specific amount of the float  3  so that the face  86  contacts one of the faces  87 ,  88 , the main arm  51  rotates upon further rise or fall of the float  3 . Therefore, the change-over valve can be operated in the two specific upper and lower positions without extending the connecting section between the main arm  51  and the float  3 . 
     Another construction in which the float  3  and the main arm  51  are loosely connected will be explained with reference to FIG.  12 . FIG. 12 is a sectional view of another snap mechanism section to be adopted in the pump according to the present invention. 
     The main arm  51  includes two parallel plates facing each other inserted at the left end part (in FIG. 12) in a short pipe  88  securely attached to the float  3  by welding. The main arm  51  and the short pipe  88  are pivotally connected by a shaft  87 , and accordingly the float  3  rocks up and down on the center of the shaft  87 , supported on the main arm  51 , according to a change in the liquid level in the vessel. The main arm  51  rocks up and down on the center of the first shaft  37  after the float  3  has moved a specific amount until the forward end of the short pipe  88  contacts the main arm  51 . 
     The embodiments of FIGS. 10-12 are advantageous in that they allow a greater range of movement for the float  3  within the vessel, thereby allowing more complete filling, and more complete draining, of the vessel than a similarly constructed apparatus with a float rigidly affixed to the float arm. This is because the arrangements of the embodiments of FIGS. 10-12 include an additional range of motion of the float  3  corresponding to the pivot angle of the float  3  about the pin  83  or  87 , in addition to the range of motion of the float arm  51  about its own pivot  37 . This additional pivot angle would be included at both the upper and lower ends of the range of motion of the float arm  51 . 
     It should also be noticed in the present embodiment that, similarly to the embodiment shown in FIGS. 10 and 11, the change-over valve can be operated in the two specific upper and lower positions without extending the connection section between the main arm  51  and the float  3 . 
     It is to be understood that the above-described embodiments represent preferred constructions of the present invention. Other constructions are possible without falling outside of the scope of the present invention, which is defined according to the claims set forth below.