Patent Publication Number: US-11376579-B2

Title: Pipette device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 371 application of the international PCT application serial no. PCT/JP2016/077716, filed on Sep. 20, 2016. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     TECHNICAL FIELD 
     The present invention relates to a pipette device that can suck and hold a liquid and can discharge the liquid in response to motion of a piston portion. 
     BACKGROUND ART 
     As such a pipette device, a micropipette device that includes removing means for removing and discarding a pipette tip disposed at a tip of the pipette device after use is disclosed in Japanese Patent No. 4989133 which belongs to the present applicant. In addition, a micropipette device is disclosed in Japanese Patent No. 5657861. The micropipette device is a pipette device including a knurled rotating ring that is fitted into a shaft portion common to a rotary digital meter and is for setting and regulating a suction collection amount of a liquid to be collected. A notch of the knurled rotating ring is lightly engaged with at least one protruding inner corner portion of a window edge portion of a pipette housing, and functions, with the protruding inner corner portion, as a mild stopper that can be released by finger movement instead of being naturally released. 
     As described above, the present applicant manufactures a pipette device having various functions. The pipette device is used in order to suck and collect various liquid chemical substances in the fields of medicine and science. Therefore, the pipette device corrodes in some cases depending on a liquid chemical to be used. 
     That is, as will be described later, the pipette device sucks a liquid into a pipette tip which is removably disposed at a tip thereof in response to movement of a piston portion. A packing portion that has an annular shape, that is, a ring shape and has a hole-shaped annular inner portion in a middle part thereof is disposed on a piston cylinder portion of the piston portion. A liquid is sucked by the piston portion sliding in the annular inner portion of the packing portion. As described above, the liquid is acidic or alkaline, and has a possibility of corroding a metal part. Since the piston portion is disposed such that watertightness is maintained by the packing portion, a possibility that the acidic or alkaline air easily enters a case portion in which the piston rod portion is disposed is relatively low. Therefore, air containing components of a chemical to be used is blocked by the piston portion and the packing portion, and thus a possibility that the air infiltrates into a case thereof is low in a short period of time. 
     However, probability that the air contains components of a sucked chemical solution, and the components corrode a metal part of the pipette device is high. Thus, there is a possibility that the air enters the case portion from a gap between the packing portion and the piston portion in long-term use. 
     Although the parts disposed in the case are relatively unlikely to corrode since the parts are mainly manufactured of a synthetic resin and stainless steel, the corrosion of the stainless steel progresses under certain conditions in some cases. In a stage when corrosion is found in particular under long-term use, the pipette device loses a function thereof in some cases. 
     When the prior art is examined to solve such a problem, no invention focusing on the problem is found. For example, using stainless steel as a material in order to resist corrosion is proposed in Japanese Patent No. 5511375. As described above, the proposal with respect to corrosion is changing the material to a material that is unlikely to corrode. However, as described above, all main metal parts are made of stainless steel in the pipette device sold by the present applicant. Therefore, a rise in manufacturing costs cannot be prevented by using a material that can resist corrosion or further carrying out surface treatment such as plating on the metal parts. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent No. 4989133 
     Patent Literature 2: Japanese Patent No. 5657861 
     Patent Literature 3: Japanese Unexamined Patent Application Publication No. 2009-013704 
     SUMMARY 
     Technical Problem 
     The present invention is devised in view of this point, and an object thereof is to provide a pipette device that prevents the corrosion of main metal parts without causing a significant rise in costs. 
     Solutions to Problem 
     According to a first aspect, in order to solve the problem as a result of thorough research and development, there is provided a pipette device including a piston portion that is movable in order to suck a liquid and an air hole for discharging an air generated from the liquid sucked by the piston portion to an outside. The air is discharged from the air hole in response to movement of the piston portion. 
     According to a second aspect, there is provided a pipette device including a pressing portion that is disposed on a rear end portion for a user to press, a piston rod portion that is connected to the pressing portion, a piston portion that is connected to the piston rod portion and is movable in order to suck a liquid, and a case portion in which the piston rod portion is disposed and which has an air hole for discharging an air generated from the liquid sucked by the piston portion to an outside. The air is discharged from the air hole of the case portion in response to movement of the piston portion. 
     According to a third aspect, there is provided a pipette device including a pressing portion that is disposed on a rear end portion for a user to press, a piston rod portion that is connected to the pressing portion, a piston portion that is connected to the piston rod portion and is movable in order to suck a liquid, and a piston accommodating portion in which the piston portion is movably disposed and which has an air hole for discharging an air generated from the liquid sucked by the piston portion to an outside. The air is discharged from the air hole of the piston accommodating portion in response to movement of the piston portion. 
     According to a fourth aspect, the pipette device of the second aspect further includes: a piston accommodating portion for movably disposing the piston portion. The piston accommodating portion has: a piston accommodating upper portion configuring the piston accommodating portion, a piston accommodating lower portion configuring the piston accommodating portion, and a packing portion that has an annular shape between the piston accommodating upper portion and the piston accommodating lower portion and has an annular inner portion. The piston portion is disposed to be slidable in the annular inner portion of the packing portion that has the annular shape. 
     According to a fifth aspect, in the pipette device of the third aspect, the piston accommodating portion has: a piston accommodating upper portion, a piston accommodating lower portion, and a packing portion that has an annular shape between the piston accommodating upper portion and the piston accommodating lower portion. The piston portion is disposed to be slidable in an annular inner portion of the packing portion. The air hole is disposed in the piston accommodating upper portion. 
     According to a sixth aspect, the pipette device of the third aspect to the fifth aspect further includes: a pipette tip holding portion that is disposed in a front end portion direction of the piston accommodating portion and removably holds a pipette tip. 
     According to a seventh aspect, the pipette device of the second aspect to the sixth aspect further includes: an elastic portion that biases the piston rod portion in a rear end portion direction. 
     Effect of the Invention 
     Since air having components of a chemical can be discharged from the air hole to the outside as the present invention is configured and acts as described above, the pipette device that prevents the corrosion of the main metal parts without causing a significant rise in costs can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a pipette device. 
         FIG. 2  is a longitudinal sectional view of the pipette device. 
         FIG. 3  is a longitudinal section enlarged view of a case portion of the pipette device. 
         FIG. 4 a    is a view illustrating a state where a second knob portion is disposed on a lower side of a second window portion,  FIG. 4 b    is a view illustrating a state where the second knob portion is disposed in a middle of the second window portion, and  FIG. 4 c    is a view illustrating a state where the second knob portion is disposed on an upper side of the second window portion. 
         FIG. 5  is a longitudinal section enlarged view of the case portion of the pipette device. 
         FIG. 6  is a longitudinal section enlarged view of a piston accommodating portion of the pipette device. 
         FIG. 7  is a longitudinal sectional view of a knob portion disposed to the right in the pipette device. 
         FIG. 8  is a longitudinal sectional view of the knob portion disposed to the left in the pipette device. 
         FIG. 9  is a perspective view of a pipette device of another embodiment. 
         FIG. 10  is a longitudinal sectional view of the pipette device of another embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A pipette device  10  of the embodiment will be described. The pipette device  10  of a first embodiment has a pressing portion  20  that is disposed on a rear end portion for a user to press, a piston rod portion  30  connected to the pressing portion  20 , a case portion  40  for the user to grab, a piston portion  50  that is connected to the piston rod portion  30  and is movable in order to suck a liquid, a piston accommodating portion  70  that accommodates the piston portion  50 . The case portion  40  has an air hole  49  for discharging air X generated from the liquid sucked by the piston portion  50  to the outside (refer to  FIGS. 1 and 2 ). 
     That is, the pipette device  10  is a device in which the air hole  49  is provided in the case portion  40  for a user to grab in order to discharge the air X, which is sucked by the piston portion  50  and is generated from a liquid chemical, to the outside. Therefore, the piston portion  50  is movable in a front end portion direction F and a rear end portion direction R of the pipette device  10 . In response to motion of the piston portion moving, the air X in the pipette device  10  can be discharged to the outside from the air hole  49 , or fresh air can be introduced from the air hole  49 . Consequently, corrosion can be prevented without making a metal part in the pipette device  10  of a material which is highly resistant to corrosion or performing surface treatment such as plating. 
     Each configuration of the pipette device  10  will be described. The pipette device  10  has the pressing portion  20 , the piston rod portion  30  connected to the pressing portion  20 , the case portion  40  that accommodates a part of the piston rod portion  30  and has the air hole  49  allowing outside air to pass therethrough, the piston portion  50 , a packing portion  60 , and the piston accommodating portion  70 . In addition, a pipette tip  80  is removably disposed. A center of each of the pressing portion  20 , the piston rod portion  30 , the case portion  40 , the packing portion  60 , the piston accommodating portion  70 , and the piston portion  50  is disposed on the same line. 
     The pressing portion  20  is literally for a user to perform an operation of pressing in order to discharge a liquid as will be described later. The pressing portion  20  has a long shaft portion  21 , a disk-shaped knob portion  22  in a rear end direction R, and an uneven portion  23  having a recessed portion and a projecting portion that are disposed on an edge of the knob portion  22 . As will be described later, the uneven portion  23  is provided as a slip stopper when a user rotates the shaft portion  21  about an axis. In addition, the pressing portion has a long hollow tubular portion  26 , and the long shaft portion  21  is disposed inside the tubular portion  26 . The shaft portion  21  is fixed such that the rotation of the shaft portion about the axis synchronizes with the rotation of the tubular portion  26  although not illustrated. When the shaft portion  21  rotates one time about the axis, also the tubular portion  26  rotates one time about the shaft portion  21 . 
     The tubular portion  26  rotates about the axis as described above. Since a female thread portion  41   a  is formed inside a first case portion  41  of the case portion  40 , which is to be described later, and also a male thread portion  26   a  is formed in the tubular portion  26 , the female thread portion and the male thread portion are screwed with each other in the tubular portion  26 . That is, the male thread portion  26   a  is screwed with the female thread portion  41   a . Therefore, when the shaft portion  21  rotates about the axis, also the tubular portion  26  rotates, and the shaft portion  21  relatively moves with respect to the tubular portion  26  in the front end portion direction F. When the shaft portion  21  rotates reversely, the shaft portion  21  relatively moves with respect to the tubular portion  26  in the rear end portion direction R. Accordingly, as will be described later, the piston portion  50  is moved forward in the front end portion direction F or is moved backward in the rear end portion direction R by the piston rod portion  30  connected to the shaft portion  21 , and thus the piston portion can adjust an increase or decrease in the amount of a liquid to be sucked. This will be further described later. 
     The piston rod portion  30  is disposed inside the case portion  40 . In addition, the piston rod portion  30  has a piston shaft portion  31  and a thick shaft upper end portion  32 . The thick shaft upper end portion  32  has a thick shaft portion  32   a  and an upper end portion  32   b . In addition, the piston shaft portion  31  literally has a long rod shape, and is disposed such that one end of the piston shaft portion  31  is covered by the thick shaft portion  32   a  which is thicker than the piston shaft portion  31 . That is, the thick shaft portion  32   a  has a hollow tubular shape, and the piston shaft portion  31  is disposed and fixed therein. In addition, the dish-shaped upper end portion  32   b  is fixed to an end portion of the thick shaft portion  32   a.  The other end of the piston shaft portion  31  in the front end portion direction F is connected to the piston portion  50  to be described later (refer to  FIG. 3 ). 
     An elastic portion  33  biases the piston rod portion  30  in a direction of the pressing portion  20 , that is, the rear end portion direction R. In the elastic portion  33 , a first spring portion  33   a,  a first washer portion  33   c,  a second washer portion  33   d,  and a second spring portion  33   b  are disposed in this order from the rear end portion direction R to an end portion direction F. The piston shaft portion  31  is inserted in all of the first spring portion, the first washer portion, the second washer portion, and the second spring portion. The piston shaft portion  31  is disposed to penetrate through a center of each of the first spring portion  33   a,  the first washer portion  33   c,  the second washer portion  33   d,  and the second spring portion  33   b . Therefore, in this case, it is preferable that the first spring portion  33   a  and the second spring portion  33   b  be coil springs. In addition, it is preferable that the first washer portion  33   c  and a second washer portion  33  each have a disk shape (refer to  FIG. 3 ). 
     The first spring portion  33   a  has one end that is in contact with the thick shaft upper end portion  32  of the piston rod portion  30 , and the other end portion that is in contact with the first washer portion  33   c.  In addition, the first washer portion  33   c  and the second washer portion  33   d  are disposed to be in contact with each other (refer to  FIG. 3 ). 
     In addition, the second spring portion  33   b  has one end that is in contact with the second washer portion  33   d,  and the other end that is in contact with a recessed portion  47  of a second case portion  46  to be described later. A center hole portion  33   cc , which is a circular hole, is disposed in the center of the first washer portion  33   c,  and the center hole portion  33   cc  has a diameter that allows the thick shaft portion  32   a  to pass therethrough. A second center hole portion  33   dd , which is a circular hole, is disposed in the center of second washer portion  33   d,  and the second center hole portion  33   dd  has a diameter that is smaller than the center hole portion  33   cc  so as not to allow the thick shaft portion  32   a  to pass therethrough. Therefore, the diameter of the center hole portion  33   cc , a diameter of the pressing portion  20 , and the diameter of the second center hole portion  33   dd  are set in diameter decreasing order. As described above, the piston shaft portion  31  of the piston rod portion  30  penetrates through all of the first spring portion, the first washer portion, the second washer portion, and the second spring portion. In addition, the second spring portion  33   b  has a spring constant higher than the first spring portion  33   a.    
     In addition, as described above, the piston shaft portion  31  is disposed to be inserted in all, that is, the first spring portion  33   a,  the first washer portion  33   c,  the second washer portion  33   d,  and the second spring portion  33   b.  Consequently, the piston rod portion  30  is biased in the rear end portion direction R by the first spring portion  33   a,  the first washer portion  33   c,  the second washer portion  33   d,  and the second spring portion  33   b,  and this serves as resistance when pressing the pressing portion  20  in the front end portion direction F. For this reason, also the piston portion  50  to be described later is biased in the rear end portion direction R. 
     As described above, the case portion  40  has the first case portion  41  and the second case portion  46 . The first case portion  41  has a hollow tubular inside, and an external shape thereof is almost a wedge shape allowing a user to grab. Therefore, the case portion  40  has a shape that allows the user to easily grasp. 
     In addition, the first case portion  41  has a window portion  42  and a second window portion  44 . A graduation portion  43  is disposed inside the window portion  42 . The graduation portion  43  displays a three-digit number, and displays a movement amount of the tubular portion  26 . The graduation portion  43  is configured of a transparent resin and has a hollow tubular shape. Inside the graduation portion, three stages of numbers are displayed. A lower stage  43   a  displays the tens&#39; place, an interruption  43   b  displays the hundreds&#39; place, and an upper stage  43   c  displays the thousands&#39; place. One graduation of the lower stage  43   a  indicates  10 , and a graduation indicating  50  is marked with one rotation. When the lower stage  43   a  rotates by ten graduations, a middle stage  43   b  rotates by one graduation. When the middle stage  43   b  rotates one time, the upper stage  43   c  rotates by one graduation. While graduations are marked from 0 to 9 in the upper stage  43   c,  the upper stage  43   c  is allowed to rotate up until a graduation of 6. This will be described later. 
     A second knob portion  27  fixed to the tubular portion  26  is disposed on the second window portion  44 . A user can increase or decrease the movement amount of the tubular portion  26  by rotating the second knob portion  27  about an axis through the second window portion  44  as in the case of rotating a knob portion  23 . By the second knob portion  27  disposed on the tubular portion  26  coming into contact with a second window upper end portion  44   a  of the second window portion  44 , the movement of the tubular portion  26  is limited, and the second knob portion  27  is set not to rotate any further. Therefore, as described above, the movement amount of the tubular portion  26  is limited such that  6  is the maximum of the tens&#39; place (refer to  FIGS. 4 a , 4 b , and 4 c   ). Therefore, the movement of the pressing portion  20  which is fixed thereto is limited, and thereby the movement of the piston rod portion  30  connected to the pressing portion and the movement of the piston portion  50  are also limited. 
     A step portion  45   b  is provided on an inner side of the other end portion  45   a  of the first case portion  41 , which has a hollow tubular shape, and is disposed to be engaged with the first washer portion  33   c  in a case of being connected to the second case portion  46  via a connecting portion  100 . Therefore, an outer diameter of the first washer portion  33   c  is almost the same dimension as an inner diameter of the step portion  45   b  such that the first washer portion can be disposed in the inner diameter (refer to  FIG. 5 ). 
     The second case portion  46  has a hollow tubular shape, and the piston rod portion  30  is disposed to be movable in the front end portion direction F or the rear end portion direction R in a tube hole  46   a  that is disposed in a center of the tubular shape. In addition, the other end of the second spring portion  33   b  is disposed in the recessed portion  47  as described above. 
     In addition, although the air hole  49  can be included in any one of or both of the first case portion  41  and the second case portion  46 , the air hole is provided in the other end portion  45   a  of the first case portion  41  in the embodiment. The air hole functions as a discharge outlet through which the air X containing a chemical solution is discharged or an introduction inlet through which fresh air is introduced. 
     The piston accommodating portion  70  functions as a so-called piston cylinder, and has a piston accommodating upper portion  71  and a piston accommodating lower portion  72 , both of which have bottomed tubular shapes. Since the piston accommodating upper portion and the piston accommodating lower portion respectively have a female thread portion  71   b  and a male thread portion  72   b  in opening portions  71   a  and  72   a,  the piston accommodating upper portion and the piston accommodating lower portion are screwed with and fixed to each other. That is, the male thread portion  72   b  is screwed with the female thread portion  71   b  (refer to  FIG. 6 ). 
     In addition, the packing portion  60  is disposed between the piston accommodating upper portion  71  and the piston accommodating lower portion  72 , and is fixed such that the packing portion  60  is sandwiched between the piston accommodating upper portion  71  and the piston accommodating lower portion  72 . The packing portion  60  has an annular shape, and has a hole-shaped annular inner portion  61 . The piston portion  50  is disposed to be slidable in the annular inner portion  61 . It is preferable to make the packing portion  60  of rubber or a synthetic resin which has flexibility. In addition, the packing portion  60  is configured to secure watertightness between the piston portion  50  and the packing portion such that the air X containing components of a sucked liquid is unlikely to infiltrate into the case portion  40 . For this reason, for example, the infiltration of the air X can be further blocked by applying grease to the piston portion  50  and the annular inner portion  61  of the packing portion  60 . In a case of long-term use, the invention is not limited thereto as described above. 
     The piston accommodating portion  70  has a hollow tubular pipette tip holding portion  71   c  which is long in the front end portion direction F, and the pipette tip  80  can be connected to the pipette tip holding portion  71   c.  The pipette tip holding portion  71   c  has a tapered shape that is gradually narrowed toward a tip portion direction F in plan view, and a filter  73  is fitted into a tip portion  76 . In addition, the pipette tip holding portion has a slip stopper  74  made of rubber on an outer periphery of the tip portion  76 , and the slip stopper makes connection to the pipette tip  80  reliable. 
     The pipette tip  80  has a shape in which a tip portion  81  is thin and pointed, and is configured to easily suck a small amount of a liquid. In addition, the pipette tip has a tapered shape that gradually becomes thicker toward the rear end direction R when seen from the side, and has a hollow tubular shape. A rear end portion  82  is open, and the slip stopper  74  disposed on the outer periphery of the tip portion  76  of the pipette tip holding portion  71   c  is fitted to the rear end portion as described above. It is preferable to make the pipette tip  80  removable and of a transparent synthetic resin, and accordingly, the pipette tip can be replaced for each chemical solution to be used (refer to  FIG. 6 ). 
     The pipette device  10  having such a configuration can adjust an amount of a liquid to be sucked. Herein, in a case where the knob portion  22  of the pressing portion  20  is positioned on the rightmost side in the drawings, that is, in the rear end portion direction R, a position of the piston portion  50  from a bottom portion  75  of the piston accommodating portion  70  is set as an original position t (refer to  FIG. 7 ). 
     When a user presses the pressing portion  20  in this state, the piston portion  50  approaches the bottom portion  75  of the piston accommodating portion  70 . This position is referred to as a first approach position t 1  (refer to  FIG. 2 ). The movement amount of the piston portion  50  in the piston accommodating portion  70 , which is from the original position t (refer to  FIG. 7 ) to the first approach position t 1 , is the amount of a liquid to be sucked. Herein, although the first approach position t 1  does not change except for a case to be described later even in a case where an amount to be sucked is adjusted, the original position t of the piston portion  50  from the bottom portion  75  of the piston accommodating portion  70  in a case of a state where the pressing portion  20  is not pressed changes to approach the bottom portion  75 . At the original position t which corresponds to a case where the pressing portion  20  is positioned to the farthest extent in the rear end portion direction R, a value of the graduation portion  43  is 6,000 (refer to  FIGS. 2 and 4   c ). The graduation portion indicates 6,000 microliters at the maximum. It is preferable that a range of use in the embodiment be a range of 1,000 to 5,000 microliters. In addition, although it is preferable that the value of the graduation portion  43  be a capacity in a range of 0.2 to 2 microliters, a range of 1 to 10 microliters, a range of 2 to 20 microliters, a range of 10 to 100 microliters, a range of 20 to 200 microliters, a range of 200 to 1,000 microliters, or a range of 2,000 to 10,000 microliters, it is evident that the value is not limited to the capacities, depending on market requirements and a type of a chemical solution to be used. 
     As described above, when the knob portion  23  or the second knob portion  27  rotates, the tubular portion  26  rotates. Since the female thread portion  41   a  is formed inside the first case portion  41  of the case portion  40  to be described later and the male thread portion  26   a  is formed also in the tubular portion  26 , the tubular portion  26  is screwed with the case portion. When the shaft portion  21  is rotated about the axis, also the tubular portion  26  rotates, and the tubular portion  26  moves in the tip portion direction F of the shaft portion  21  with respect to the shaft portion  21 . Accordingly, by moving the thick shaft upper end portion  32  of the piston rod portion  30  in the tip portion direction F, the piston portion  50  is also pressed and moves in the tip portion direction F. At this time, a graduation gradually decreases from 6,000 to 0. 
     At this time, since the second spring portion  33   b  has a spring constant higher than the first spring portion  33   a  as described above, the first spring portion  33   a  is gradually compressed first. Simultaneously, the piston portion  50  also moves to approach the bottom portion  75  of the piston accommodating portion  70 . 
     When the knob portion  23  or the second knob portion  27  rotates, the first spring portion  33   a  is gradually compressed. When the piston portion moves to approach the bottom portion  75  of the piston accommodating portion  70 , the thick shaft portion  32   a  passes through the center hole portion  33   cc  of the first washer portion  33   c  and comes into contact with the second washer portion  33   d  while the thick shaft upper end portion  32  compresses the first spring portion  33   a.  This position is a point where a graduation is “0”, and is a position where an adjusted position ts of the piston portion  50  (refer to  FIG. 8 ) becomes the same position as the first approach position t 1  (refer to  FIG. 1 ). 
     To describe in further detail, a suction amount is defined by the compression of the extended first spring portion  33   a.  Therefore, a position where the first spring portion  33   a  is compressed at the maximum, that is, a position where the thick shaft portion  32   a  passes through the center hole portion  33   cc  of the first washer portion  33   c  and comes into contact with the second washer portion  33   d  is a position to become the adjusted position ts of the piston portion  50 . Also the adjusted position ts of the piston portion  50  is the same position as the first approach position t 1  where the piston portion approaches the bottom portion  75  of the piston accommodating portion  70 . Therefore, when the graduation becomes 0, the adjusted position ts separated away from the bottom portion  75  of the piston accommodating portion  70  in a state where the pressing portion  20  is not pressed becomes the point where the graduation is “0” (refer to  FIGS. 4 a    and  8 ), and the adjusted position ts of the piston portion  50  becomes the same position as the first approach position t 1  as described above. Thus, an amount of a liquid that can be sucked by the pipette device  10  becomes 0 since the first spring portion  33   a  cannot be compressed any further. 
     In addition, when the knob portion  23  or the second knob portion  27  rotates reversely, the piston portion  50  moves in the rear end portion direction R. Accordingly, the position of the piston portion  50  changes to a position separated away from the bottom portion  75  of the piston accommodating portion  70 . 
     Therefore, when the piston portion  50  is at a position where a distance from the bottom portion  75  of the piston accommodating portion  70  is short, this position is the position of the piston portion  50  in a case of a state where the pressing portion  20  is not pressed. Thus, the movement amount of the piston portion  50  from the piston portion  50  in a case of a state where the pressing portion  20  is pressed to a position to the bottom portion  75  of the piston accommodating portion  70 , that is, to the first approach position t 1  becomes an amount of a liquid to be sucked by the pipette device  10 . Consequently, when a distance between the piston portion  50  and the bottom portion  75  of the piston accommodating portion  70  is short, an amount to be sucked is small. When a distance between the piston portion  50  and the bottom portion  75  of the piston accommodating portion  70  is long, an amount to be sucked is large. The movement amount is made clear by the lower stage  43   a,  the middle stage  43   b,  and the upper stage  43   c  which are included in the graduation portion  43  displaying a three-digit number. The piston portion  50  can be disposed at any position between the original position t and the adjusted position ts, and this range can be freely adjusted. In addition, an accurate suction amount can be measured by the graduation portion  43 . 
     In a case of performing work of the pipette device  10  sucking a liquid, a user presses the pressing portion  20 , and then the piston portion  50  is moved from a position to the bottom portion  75  of the piston accommodating portion  70 , that is, any original position t to the first approach position t 1  after adjusting a suction amount as described above. After then, the user takes the hand off the pressing portion  20 , and a liquid chemical is sucked as the pressing portion  20  is restored in the rear end portion direction R by the elastic portion  33 . The piston portion  50 , the packing portion  60 , the piston accommodating portion  70 , the pipette tip holding portion  71   c,  and the pipette tip  80  are made of a synthetic resin, and thus there is no possibility of corrosion thereof in a case where this acidic or alkaline liquid is sucked. However, since the pressing portion  20  or the piston rod portion  30  is configured of stainless steel, there is a possibility of corrosion under certain conditions. While watertightness between the piston portion  50  and the packing portion  60  is maintained in a short period of time, the air X having a possibility of corrosion gradually leaks from a gap between the piston portion  50  and the packing portion  60  in long-term use, and infiltrates into the piston accommodating upper portion  71  of the piston accommodating portion  70  or the case portion  40  in some cases. 
     Thus, by discharging the infiltrated acidic or alkaline air X from the air hole  49 , corrosion of the piston accommodating upper portion or the case portion can be prevented. This can be performed by the following operation. That is, when a user presses the pressing portion  20  of the pipette device  10 , the piston portion  50  moves toward the bottom portion  75  of the piston accommodating portion  70  through the piston rod portion  30  (refer to  FIG. 2 ), and moves to the first approach position t 1  where the piston portion approaches the bottom portion  75  as described above. In this state, a liquid (not illustrated) infiltrates into a pipette tip  80 , and the user takes the hand off the pressing portion  20 . Accordingly, the elastic portion  33  returns the pressing portion  20  in the rear end portion direction R. Consequently, when the piston portion  50  moves in a direction of separating away from the bottom portion  75  of the piston accommodating portion  70 , that is, the rear end portion direction R, the liquid is simultaneously sucked from the pipette tip  80  (refer to  FIG. 7 ). When the user presses the pressing portion  20  of the pipette device  10  again, the piston portion  50  moves toward the bottom portion  75  of the piston accommodating portion  70  through the piston rod portion  30 , and the piston portion  50  is disposed at the first approach position t 1  where the piston portion approaches the bottom portion  75 . Thus, the sucked liquid can be discharged. The sucked liquid cannot be completely discharged in some cases depending on the viscosity of the liquid. At this time, the user further presses the pressing portion  20  of the pipette device  10 . Accordingly, the second washer portion  33   d  is further pressed from the position where the first spring portion  33   a  is compressed at the maximum, that is, the position where the thick shaft portion  32   a  passes through the center hole portion  33   cc  of the first washer portion  33   c  and comes into contact with the second washer portion  33   d.  Accordingly, the second spring portion  33   b  having a spring constant higher than the first spring portion  33   a  is further compressed, and the piston portion  50  comes into contact with the bottom portion  75  of the piston accommodating portion  70 . Accordingly, the sucked liquid can be completely discharged from the piston accommodating portion  70  (not illustrated), and the pipette device  10  can suck and discharge an accurate amount of the liquid. 
     However, in some cases, the air X containing components of the liquid enters the case portion  40  via the piston accommodating upper portion  71  of the piston accommodating portion  70  from between the piston portion  50  and the packing portion  60  in long-term use. Accordingly, metal parts disposed in the piston accommodating portion  70  and the case portion  40  have a possibility of corrosion. 
     In order to prevent the corrosion, the case portion  40  has the air hole  49 . That is, as the piston portion  50  moves from the first approach position t 1  in the rear end portion direction R, the air X staying in a case  40  is discharged from the air hole  49  (refer to  FIG. 7 ). 
     As the piston portion  50  is again pressed in the tip portion direction F after then, this time, external air is newly introduced into the case portion  40  or the piston accommodating portion  70  from the air hole  49  (refer to  FIG. 2 ). The air X is discharged from the air hole  49 , or fresh air is introduced in response to motion of the piston portion  50  moving in the front end portion direction F and the rear end portion direction R as described above. Therefore, although the piston rod portion  30  disposed inside the piston accommodating portion  70  and the case portion  40 , the long shaft portion  21  of the pressing portion  20 , and the first spring portion  33   a,  the second washer portion  33   d,  and the second spring portion  33   b  of the elastic portion  33  can be configured of a metal, a possibility that the metal parts are exposed to the acidic or alkaline air X generated from the sucked liquid for a long period of time is low. Although the air X is discharged from the air hole  49  in response to motion of the piston portion  50  moving in the front end portion direction F and the rear end portion direction R, the air X is not necessarily prevented from flowing out from the air hole  49  even in a case where the piston portion  50  is stopped. 
     In addition, such operation is repeated each time the piston portion  50  moves. Therefore, the corrosion of the metal parts can be prevented in normal use of the pipette device  10 . Since corrosion can be prevented by newly providing the air hole  49  as described above, making a change in a material of a metal part or performing surface treatment such as plating is not necessary, and thus corrosion can be prevented without incurring additional costs. 
     In another embodiment, it is preferable to dispose a second air hole  49   a  in the piston accommodating upper portion  71  of the piston accommodating portion  70  in another pipette device  10 A (refer to  FIGS. 9 and 10 ). Specifically, since the air X containing components of a liquid enters the piston accommodating upper portion  71  from between the piston portion  50  and the packing portion  60 , the corrosion of metal parts disposed in the piston accommodating portion  70  and the case portion  40  can be prevented by providing the second air hole  49   a  in the piston accommodating upper portion  71 . A method of discharging the air X, in this case, is the same as described above. Therefore, although the air X is discharged from the air hole  49   a  in response to motion of the piston portion  50  moving in the front end portion direction F and the rear end portion direction R, the air X is not necessarily prevented from flowing out from the air hole  49   a  even in a case where the piston portion  50  is stopped. 
     It is preferable to provide the air hole closer in the rear end portion direction R than the piston accommodating upper portion  71  of the piston accommodating portion  70  is. Another pipette device  10 A has the same configurations as the pipette device  10  of the first embodiment except for the position of the air hole  49   a.  It is preferable to dispose the air hole to be positioned closer in the rear end portion direction R than the position of the packing portion  60  is. In such a manner, it is also possible to additionally dispose the second air hole  49   a  while disposing the air hole  49 . Therefore, a plurality of air holes  49  and a plurality of second air holes  49   a  can also be disposed although not illustrated. In addition, the plurality of air hole  49  or the plurality of second air hole  49   a  can also be disposed.