Patent Publication Number: US-6702556-B2

Title: Multi-cylinder compression pump

Description:
TECHNICAL FIELD 
     The present invention relates to an improved pump for compression of gases, such as air, comprising a first, stationary cylinder, wherein a piston is arranged for movement in the longitudinal direction of said cylinder so as to divide the latter into a first chamber located ahead of the piston, and a second chamber located behind the piston, a piston rod securely joining said piston to a second movable cylinder arranged externally of the first cylinder so as to ensure co-ordination of the movements of said piston and said second cylinder. The open end of said second cylinder is sealed against the external face of the first cylinder and the open end of the first cylinder is sealed against the internal wall of the second cylinder, whereby a third chamber is formed between the seals. 
     TECHNICAL BACKGROUND 
     Pumps of the above kind are known from SE 463 732 and could be regarded as a two-step pump because the compression of air takes place in two steps, viz. both when the cylinders pushed together and when the are pulled apart. Owing to this double compression feature, this type of pump is quite superior to the conventional bicycle pump when it comes to producing comparatively high pressures by means of comparatively moderate forces. However, when sufficiently high pressures are required, for example in the magnitude of 200 bars, pumps of the kind defined above are not satisfactory either. Pressures of this magnitude are required for instance for high-pressure cartridges for air guns. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a pump of the kind defined in the introduction, which offers an improved degree of compression by means of substantially unchanged forces. 
     The compression of air thus is effected in three steps. The first step takes place, when the air in the fourth chamber is forced into the second and third chambers. Since the goods in the first cylinder occupies some of the space between the second and third chambers, the total cross-sectional area of these chambers is inferior to the cross-sectional area of the fourth chamber, and consequently compression of the air takes place. 
     The second step is effected when the air is forced from the second and third chambers into the first chamber. The latter chamber has a considerable smaller cross-sectional area than the first-mentioned ones, since it is limited by the first, smallest cylinder. Consequently, the Air is Compressed Further in this Step. 
     The third step takes places exactly like in the above two-step pump, when the air in the second chamber is forced out through the outlet formed in the first end of the first cylinder. 
     The through-passage valve in the second cylinder inlet could be made adjustable to allow adjustment of the flow through the inlet. By throttling the inflow, the pumping movements consume less power because less air is introduced into the pump and consequently less compression work is done. If said through-passage valve is throttled, a predetermined negative pressure is created in the fourth chamber when the pumping house is extended in the course of the upwardly directed pumping movement. 
     Obviously, other gases than air could be compressed by means of the pump in accordance with the invention. 
     In accordance with a preferred embodiment a third cylinder, which is fixedly interconnected with the first cylinder surrounds the second cylinder. This third cylinder has sealing contact with the end wall of the second cylinder, whereby a fifth chamber is formed between said end wall and one end of the third cylinder. This fifth chamber communicates with said third chamber via a first through-passage valve and with the environment via a second through-passage valve. 
     In this case, when the second cylinder and the piston rod are moved away from the first cylinder, the pump is arranged to draw air past said second through-passage valve into the fifth chamber and in doing so close said first through-passage valve, and to force air from the fifth chamber past said first through-passage valve into the third chamber, and in doing so close said second through-passage valve. 
     In accordance with this embodiment, a three-step pump with double compression in the first step is provided. As described above, air passing from the fourth chamber to the second and third chambers is compressed, as is also air passing from the fifth chamber to said second and third chambers. 
     Since the two compression operations take place simultaneously, a considerable improvement of the total compression is achieved. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described in more detail in the following with reference to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: 
     FIG. 1 is a cross-sectional view of a pump in accordance with one embodiment of the present invention in a first, nearly completely pushed together (contracted) position. 
     FIG. 2 shows the pump of FIG. 1 in a second, nearly completely pulled apart (expanded) position. 
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
     The pump illustrated in FIGS. 1-2 comprises a pump housing  2  consisting of a first, stationary cylinder  3  and a second, movable cylinder  4  surrounding the first cylinder and arranged to move to and from in the lengthwise direction of the first cylinder. The lower end  4   a  of the movable cylinder  4  is formed with an annular end wall  5  in tightly sealed contact with the external face of the first cylinder  3 . At the upper end  4   b  of the second cylinder  4  an operating handle  6  is provided, making it more convenient for the user to effect pumping movements of the cylinders  3 ,  4  relative to one another. 
     The stationary cylinder  3  houses a piston  8  dividing the cylinder  3  into a first lower chamber  10  located ahead of the piston and a second upper chamber  11  located behind the piston. The chambers  10  and  11  communicate via a through-passage channel  12  formed in the piston  8  and formed with a through-passage valve  13 , such as an O-ring allowing air passage only from the upper chamber  11  to the lower one  10 . 
     The lower chamber  10  debouches into an outlet channel  40  in which a valve means  41  is mounted. 
     The piston  8  is fixedly secured to a piston rod  15 , which in turn is fixedly secured to a cylinder-end closing wall  16  at the upper end  4   b  of the second cylinder  4 , ensuring coordinated the movements of the cylinder  4  and of the piston  8  relative to the cylinder  3 . The piston rod  15  extends through a recess  17  formed in an end wall  18  arranged at the upper end  3   b  of the first cylinder  3 . 
     The end wall  18  is in tightly sealed contact with the internal face of the second cylinder  4  and thus it forms a partition wall  18 , dividing the cylinder into a third chamber  20  located below the partition wall and a fourth chamber  21  located above the partition wall. The chambers  20 ,  21  communicate via a through-passage channel  22  formed in the partition wall  18 , in which channel a through-passage valve  23  is located, such as an O-ring allowing air passage only from the upper chamber  21  to the lower one  20 . 
     In addition, the third chamber  20  communicates with the second chamber  11  via one or several apertures  25  formed in the casing wall of the first cylinder  3 . These apertures  25  ensure that an equal pressure P is maintained in the second and third chambers at all times. 
     At the upper end  4   b  of the second cylinder  4  an inlet channel  26  is formed, wherein a through-passage valve  27 , such as a ball valve, is provided, allowing passage of air into the upper chamber  21  of the cylinder  4 . The valve  27  is provided with a means  28  for regulating the flow through the inlet channel. 
     The inlet channel  26  could be a bore extending through the cylinder-end closing wall  16 , and a setscrew could be provided in the bore to allow regulation of the flow. 
     In accordance with the preferred embodiment shown in the drawing figures, a third cylinder  30 , which is fixedly secured to the first cylinder, surrounds the second cylinder. 
     Another annular end wall  31  is arranged at the lower end  4   a  of the second cylinder  4  so as to project radially outwards from the cylinder wall. The end wall  31  is in tightly sealed contact with the internal face of the third cylinder  30 , whereby a fifth chamber  32  is formed intermediate the end wall  31  and a cylinder-end closing wall  33  at the lower end  30   a  of the cylinder  30 . A second inlet channel  34  is formed in the end wall  31 , said channel being provided with an inlet valve  35  allowing passage of air only into chamber  32 . Chamber  32  further communicates with the lower chamber  20  of the second cylinder  4  via a through-passage channel  37  formed in the end wall  5 , said channel housing a through-passage valve  38 , such as an O-ring allowing passage of air only from the fifth chamber  32  to the third chamber  20 . 
     In the shown example, all three cylinders  3 ,  4 ,  30  are arranged in concentric relationship, nesting one in the other. Preferably, they have a circular cross-sectional area but other cross-sectional shapes such as hexagonal or square are not inconceivable. The cylinders  3 ,  4 ,  30  could be made e.g. from stainless steel or some other similar material. 
     The end walls  5 ,  18 ,  31  could be made from e.g. some plastics material and could be attached to the respective cylinder by means of a threaded joint or by gluing or the like. The end walls  5  and  31  could also be formed from one single annular element, should such a configuration be preferred. 
     The function of the pump will be described in the following. 
     When the pump housing  2  is pulled apart, the second cylinder  4 , the piston rod  15  and the piston  8  are moved in the direction indicated by A away from the first and third cylinders  3 ,  30  (see FIG.  1 ). Because of this movement the distance between the end wall  5  and the cylinder-end closing wall  16  of the cylinder  4  increases, and consequently the volume of the fourth chamber  21  increases. Air is therefore drawn from the surroundings into the inlet  26  in the cylinder-end closing wall  16 , past, the through-passage valve  27 , and fills the chamber  21 . Simultaneously, through-passage valve  23  closes, thus preventing air from passing upwards from the third chamber  20  to the fourth one  21 . 
     In a corresponding manner, the distance between end wall  31  and the cylinder-end closing wall  33  of the third cylinder  30  increases, whereby the volume of the fifth chamber  32  increases. Surrounding air thus is drawn through the channel  34  formed in the end wall  31 , past the valve  35 , and fills chamber  32 . At the same time, the through-passage valve  37  closes, preventing air from passing downwards from the third chamber  20  to the fifth chamber  32 . 
     The movement also reduces the distance between the end walls  5  and  18  as well as between the end wall  18  and the piston  8 , thus reducing the volumes of the third and the second chambers  20  and  11 , respectively. At the same time, the volume of the first chamber  10  increases. The air in the second and third chambers  11  and  20  that communicate via apertures  25 , cannot, as indicated above, pass the valves  23  and  37  and is instead forced to pass through channel  12 , past valve  13  and downwards into the first, expanding chamber  10 . 
     It is worth noting that the first chamber  10  has a cross-sectional area smaller than the sum of the cross-sectional areas of the second and third chambers  11 ,  20 . As the air from the second and third chambers is being forced downwards into the first chamber, it is therefore compressed at the same time. 
     When the pump housing is pushed together, the second cylinder  4 , the piston rod  15  and the piston  8  are moved in direction B towards the first and third cylinders  3 ,  30  (see FIG.  2 ). This movement reduces the distance between the cylinder-end closing wall  16  and the end wall  18 , whereby the volume of the fourth chamber  21  is diminished. The valve  27  in the inlet  26  prevents air from leaving the chamber  21  via the inlet, and instead the air is forced through the channel  22 , past the valve  23  down into chamber  20 . It is worth noting that the fourth chamber  21  has a cross-sectional area superior to the total cross-sectional areas of the second and third chambers  11 ,  20 , because the first cylinder  3 , forming a partition wall between the chambers  11  and  20 , occupies part of the cross-sectional area. The air is therefore compressed upon its passage from the fourth chamber  21 , the volume of which diminishes upon this movement, to the second and third chambers  11 ,  20 , the volumes of which, although increasing as a result of this movement, do not increase at the same pace. 
     In a corresponding manner, the distance between the end wall  31  and the cylinder-end closing wall  33  is reduced, the volume of the fifth chamber  32  thereby diminishing. The valve  35  in the inlet  34  prevents air from leaving the chamber  32  via the inlet  34  and instead the air is forced upwards through the channel  37  formed in the end wall  5 , past the valve  38 , and enters chamber  20 . It is worth noting that the fifth chamber  32  has a cross-sectional area superior to the sum of the cross-sectional areas of the second and third chambers  11 ,  20 , since the third cylinder  30  is larger than the second cylinder  4 . Thus, the air that is forced from the fifth chamber  32  to the-second and third chambers  11 ,  20  is compressed. 
     The movement also causes the piston  8  to move further downwards inside the first cylinder  3 , whereby the volume of the first chamber  10  is reduced, and the air contained therein is subjected to a pressure increase until the valve  41  is opened, letting the air leave through the outlet  40 . 
     It should be understood that the present invention is not limited to the embodiments described above but that on the contrary, it encompasses all varieties that are within the scope of protection of the appended claims.