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[0001] This invention relates to a liquid pump used in the field where a small amount of liquid feed is required, for example feed of a sample to a tip of liquid chromatography or a chemical reaction microsystem (a micro total analysis system) and feed of a reagent to a 96-well plate
[0002] For a small amount of liquid feed, a manually-operated micropipette has been used for a long time. Automation of the operation of a micropipette has been achieved by using an automatic dispenser. A micro-dispenser has been used for the dispensing operation to a 96-well plate which stores many samples, and successive liquid feed in the micro-dispenser has been conducted by a cylinder-type liquid pump. In addition, some liquid pumps which have been widely used for liquid chromatography make use of a reciprocating motion of a plunger or a cylinder.
[0003] The foregoing widely used liquid pumps require a mechanical driving means using a motor and a cam. Furthermore, precise machining of the plunger for securing airtightness, selection of members which stand against frictional heat generated between the plunger and the tubular wall housing the plunger, desigining of valves suitable for continuous liquid feed, and collecting liquid for prevention of pulsating flow are also required.
[0004] Therefore, another liquid pump having bellows as a driving means instead of having the conventional mechanical driving means including the motor and the cam has been developed. This liquid pump is driven by a motion of the bellows caused by thermal expansion/contraction of liquid retained in the bellows. In particular, as shown in
[0005] Moreover, there has been another liquid pump of this type that is driven by elastic membranes functioning as valves without using the reciprocating motion of the plunger and the cylinder. As shown in
[0006] In addition, another proposed liquid pump of this type is a diaphram pump driven by static electricity. This pump supplies liquid by transforming a diaphram thereof. In particular, the liquid pump, as shown in
[0007] However, there has been a problem that the above-described conventional liquid pumps having the mechanical driving means for reciprocating motion of the plunger in the cylinder that they are expensive because the mechanical driving means requires precise machining.
[0008] There has been a further problem with these liquid pumps that the mechanical driving means and the cylinder generate unwanted noise. The noise generated by these liquid pumps when being installed in a medical device could be physiological burdens to patients and hindrances to medical practice. A liquid pump that does not generate such unwanted noise is desired not only in the medical field, but also in the acoustic field where extra attention not to cause unwanted noise is strongly demanded.
[0009] Additionally, there has been a problem with the above-described conventional liquid pump having the bellows as a driving means that a coefficient of thermal expansion of the liquid retained in the bellows is so small, and a large amount of liquid is required to obtain sufficient driving force; thereby a size of the liquid pump necessarily becomes big.
[0010] Furthermore, there has been a problem with the above-described conventional liquid pump having the elastic membranes functioning as valves, in which three or more of the elastic membranes placed in succession supply liquid, has complicated mechanism, and it is inferior in durability because the membranes are liable to deteriorate.
[0011] Finally, there has been a problem with any of the above-described conventional liquid pumps that they have difficulty in performing a microvolume flow by the microliter or the nanoliter because of generation of heat in the mechanical driving means and/or generation of pulsating flow.
[0012] Hence, an object of the present invention is to solve the above-mentioned conventional problems and to provide a liquid pump having a very simple and downsized structure with the smaller number of necessary components which provides superior cost performance and operates without generating unwanted noise. Another object of the present invention is not only to control the liquid flow but also to facilitate the feed of extremely small amount of liquid by the microliter or even by the nanoliter.
[0013] A liquid pump according to the present invention has a pressure vessel with end-openings for hermetically holding liquid therein. The liquid flows from one of the end-openings to the other end-opening by utilizing a difference in a coefficient of thermal expansion of the pressure vessel and the liquid caused by heating or cooling the pressure vessel and the liquid together.
[0014] The liquid pump may further comprise a heating-cooling bath for receiving the pressure vessel, and the pressure vessel may have sufficient heat conductibility, so that pressure vessel and the liquid hermetically held in the vessel may be heated or cooled together by placing the pressure vessel in the heating-cooling bath.
[0015] The pressure vessel may generate heat by voltage, so that the heating may be conducted by applying voltage to the pressure vessel.
[0016] Furthermore, the pressure vessel may be a tube having an inner diameter of about 0.5 mm or less and a length of about 10 m or more.
[0017] Additionally, the heating-cooling bath may be either an air bath or a liquid bath.
[0018] In the drawings:
[0019]
[0020]
[0021]
[0022]
[0023]
[0024]
[0025]
[0026]
[0027] A liquid pump of the present invention, as shown in
[0028] In particular, when the pressure vessel
[0029] To keep the liquid hermetically held in the pressure vessel
[0030] The pressure vessel
[0031] The pressure vessel
[0032] When the pressure vessel
[0033] The liquid may be alcohols, such as methanol and ethylene glycol, ethers, such as diethyl ether and isopropyl ether, ketones, such as acetone, and ethyl methyl ketone, paraffins, such as normal hexane and isohexane, naphthenes, such as cyclohexane, aromatics, such as benzene, toluene and xylene, and water, but not limited to them. The coefficient of thermal expansion of the liquid depends on a combination with the pressure vessel
[0034] The heating-cooling bath
[0035] In an example of the liquid pump according to the present invention, a pressure indicator
[0036] In another example of the liquid pump according to the present invention, liquid chromatography was carried out as shown in
[0037] In a further example according to the present invention, liquid chromatography was carried out as shown in
[0038] As a result, in both cases of
[0039] The liquid pump according to the present invention, composed as described above, has a very simple and downsized structure with the smaller number of necessary components and provides superior cost performance.
[0040] The liquid pump according to the present invention can easily control flow of the liquid therein by heating or cooling the pressured vessel thereof.
[0041] Furthermore, the liquid pump according to the present invention is operated by only heating or cooling the pressure vessel thereof so that it does not generate unwanted noise.
[0042] Additionally, the liquid pump according to the present invention has an extremely small inner diameter of the flow channel within the pressure vessel so that an extremely small amount of the liquid can be supplied by the microliter, or even by the nanoliter.