JPH0311425Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a liquid injector that measures and injects a predetermined liquid into a predetermined location.

[Background technology]

Conventionally, syringes have been well known as devices for measuring and discharging liquid, but since the suction and discharge passages for the liquid are the same, some kind of valve is required to separate the suction and discharge passages. is necessary. In this case, if the valve is used completely separately from the syringe, the entire device will become larger, so a structure in which the valve is incorporated into the syringe is known.

FIG. 1 shows a schematic structure of a conventional liquid injector of this type. In the figure, a center hole 2 is provided in the axial center of a cylinder 1, and
An injection liquid suction passage 3 and an injection liquid discharge passage 4 communicating with the center hole 2 are provided opposite each other at 180 degrees. A piston 5 is housed in the center hole 2 of the cylinder 1 so as to be slidable in the axial direction and rotatable in the circumferential direction.
A notched groove 6 is provided that communicates the bottom side of the center hole 2 with either the injectate suction passage 3 or the injectate discharge passage 4. The length of this notch groove 6 is made longer than at least the axial stroke of the piston 5.

In such a configuration, in order to suck the injection liquid into the center hole 2 of the cylinder 1, the piston 5 is inserted to the bottom of the center hole 2 and the piston 5 is inverted 180 degrees from the illustrated state, In this state, the piston 5 is sequentially pulled up, and the injection liquid is supplied from the injection liquid suction passage 3. By performing this operation until the piston 5 is pulled up by a predetermined amount, a predetermined amount of injection liquid is sucked into the center hole 2.

Next, in order to discharge the injection liquid, the piston 5 is moved.
When rotated 180 degrees to the state shown in the figure, the suction passage 3 is closed by the circumferential surface of the piston 5 on which the notch groove 6 is not formed, while the discharge passage 4 is connected to the center hole 2 through the notch groove 6. communicated. When the piston 5 is pushed into the center hole 2 in this state, the injection liquid in the center hole 2 is sequentially discharged from the discharge passage 4, and when the stroke end is reached, a prescribed amount of injection liquid has been discharged.

However, in the conventional structure with such a configuration, the switching between the suction passage 3 and the discharge passage 4, that is, the valve switching operation, is a rotational movement, while the suction (filling) and discharge operation of the injection liquid is an axial movement. Since it is a reciprocating motion, it has the disadvantage that it is necessary to perform both rotational and reciprocating motion, making the motion complicated. In addition, the sealing structure between the piston 5 and the cylinder 1 must be adapted to both rotational and reciprocating motion, particularly rotational motion that is difficult to seal, resulting in a disadvantage that the structure is complex and difficult.

[Purpose of invention]

An object of the present invention is to provide a liquid injector that is easy to operate and has a simple seal structure.

[Structure of the idea]

In the present invention, the valve body is attached to a base member, the valve body and the piston are provided in an axially movable cylinder so that the valve body and the piston can be slid in the axial direction, and the outer periphery of the fitting surface of the valve body and the piston to the cylinder is fixed. An injection liquid suction passage having the same shape and allowing direct communication between the inside of the cylinder and the injection liquid supply source side through an opening formed in the valve body, and a valve between the inside of the cylinder and the injection liquid discharge side. An injectate discharge passage that allows direct communication through an opening formed in the body is provided, and further, communication between the injectate suction passage and the infusion discharge passage and the inside of the cylinder is blocked between the cylinder and the valve body. A valve mechanism is provided that changes the state as the cylinder slides in the axial direction with respect to the valve body, so that a predetermined amount of injected liquid can be sucked and discharged only by the axial movement of the cylinder and piston with respect to the valve body. In addition, because the outer circumferential shape of the cylinder fitting surface between the valve body and the piston is the same, movement of only the cylinder does not have any effect on the injected liquid interposed between the valve body and the piston. It is characterized by the following. In the present invention, the cylinder and piston only need to be moved in the axial direction with respect to the valve body, and rotational movement is not required, so that the movement is simple. In addition, since the movement is only in the axial direction, there is no need to provide a seal with a complicated structure in the direction of rotation, and a seal only in the axial direction is sufficient, making it possible to have a simple seal structure, thereby achieving the above purpose. It is something.

〔Example〕

Hereinafter, embodiments of the present invention will be described, and the reference numerals of the same or equivalent components in each embodiment will be the same and the explanation will be omitted or simplified.

A first embodiment is shown in FIGS. 2-4. In the overall structure diagrams in Figures 2 and 3,
A cylindrical valve body 12 is screwed and fixed to a base plate 11 that is a base member, and a cylindrical cylinder 13 is attached to the outer periphery of this valve body 12.
The center hole 14 of the holder is fitted to be slidable in the axial direction. A piston 15 is slidably fitted into the center hole 14 of the cylinder 13.
The outer circumferential shape of the fitting surface to the cylinder 13 of the valve body 12 is the same as the outer circumferential shape of the fitting surface to the cylinder 13 of the valve body 12. Therefore, the entire length and the inside of the center hole 14 having the same diameter are the same as the valve body 12. The piston 15 is designed to be able to slide in common.

Inside the valve body 12, there are four passages that do not intersect with each other internally, that is, they can communicate directly with an injection fluid supply source (not shown) through an opening 16A at one end, and the other end is connected to the cylinder. 1
3, an injection liquid suction passage 16 opened on the fitting surface with 3;
An injection liquid return passage 17, which is also connected directly to a return tank on the side of an injection liquid supply source (not shown) through an opening 17A at one end, and whose other end is open to the fitting surface with the cylinder 13; An injectable liquid discharge passage 18 that can communicate directly with the liquid discharge portion side through an opening 18A at one end and has the other end open to a fitting surface with the cylinder 13, and a fitting between the cylinder 13 and the valve body 12. An intra-cylinder communication passage 19 is provided, one end of which communicates with the center hole 14 located inward from the mating surface, and the other end of which is open to the mating surface of the cylinder 13. At this time, the openings to the fitting surfaces of the passages 16 to 19 are opened at different positions from each other so that they do not directly communicate with each other, and
A circumferential groove is formed on the circumferential surface of the valve body 12 in which each opening is formed. In addition, each passage 16
- 19, the inner peripheral surface of the cylinder 13 is provided with two upper and lower circumferential grooves 20 and 21 as connection switching grooves, and the upper circumferential groove 20 connects the discharge passage. 18 and the cylinder internal communication path 19 are communicated with each other or are blocked (see FIG. 4),
The lower circumferential groove 21 allows the suction passage 16 and the return passage 17 or the suction passage 16 and the in-cylinder communication passage 19 to communicate with each other or to be shut off. Here, a valve body 12 having respective passages 16 to 19 and upper and lower circumferential grooves 2 of a cylinder 13 are provided.
0 and 21 constitute a valve mechanism 22, which causes the cylinder 13 to move relative to the valve body 12 in the axial direction.
A center hole 1 located inward of the fitting surface between the suction passage 16 and the valve body 12 in the cylinder 13.
4, or the inside of the center hole 14 located inward from the fitting surface of the discharge passage 18 and the valve body 12 of the cylinder 13. .

A pair of guide shafts 23 are erected on the base plate 11 on both sides of the cylinder 13, and a support plate 24 is fixed between the upper ends of these guide shafts 23. A pair of air cylinders 25 are fixed to the lower surface of the support plate 24 on both sides of the guide shaft 23, and both ends of a connecting plate 28 are connected to the piston rods 26 of the air cylinders 25 via connecting shafts 27. Fixed, this connecting plate 2
8 is guided by the guide shaft 23 and fixed to the upper end of the cylinder 13 with a screw. Thereby, as the air cylinder 25 is driven, the cylinder 13 can slide up and down relative to the valve body 12 by an amount that allows the switching operation. Here, the air cylinder 25, the connecting shaft 27, and the connecting plate 28 constitute a valve switching drive mechanism 29 that drives the cylinder 13.

A ball screw shaft 31 is integrally fixed to the upper surface of the piston 15 via a rod 30, and the upper end of this screw shaft 31 extends through the support plate 24, and a ball screw shaft 31 extends through the support plate 24. The support plate 2 is
4 with a nut 33.
A bearing 35 with a collar 34 interposed between the outer periphery of the bush 32 and the upper surface of the support plate 24 is provided.
A timing pulley 36 is fixed to the outer periphery of the bearing 35. A ball screw nut 38 is fixed to the upper surface of this timing pulley 36 via a fixture 37.
8 is rotatably screwed onto the upper end of the ball screw shaft 31.

A stepping motor 39 is mounted on the support plate 24.
is attached to the timing pulley 41 fixed to the output shaft 40 of the motor 39 and the bush 3.
A timing belt 42 is wound between the timing pulley 36 supported by the motor 39 and the timing pulley 36 supported by the motor 39.
rotation is transmitted to the nut 38.

A pair of cover cylinders 43 and 44 are provided around the rod 30 fixed to the piston 15 and the screw shaft 31, and the cover cylinders 43 and 44 are nested in each other. The lower end of the large-diameter cylinder 44 is fixed to the piston 15 at its lower end. A rotation prevention plate 45 is fixed to the upper end of this lower cylinder 44, and U-shaped grooves 4 are formed at both ends of this rotation prevention plate 45.
6 is fitted to the pair of guide shafts 23, and the piston 15 and the ball screw shaft 31 are prevented from rotating by the action of the rotation prevention plate 45. Therefore, the piston 15 and the screw shaft 31, which are prevented from rotating by the rotation prevention plate 45, are rotated by the rotation of the motor 39.
It is designed to move up and down as the number 8 rotates. Here, the piston rod 15 is moved relative to the valve body 12 in the axial direction by means of consecutively numbered members from the rod 30 to the rotation prevention plate 45 to perform suction and discharge operations of the injected liquid. A drive mechanism 47 is configured,
The cylinder 1 is driven by the piston 15 that moves up and down within the cylinder 13 by driving the drive mechanism 47.
The injection liquid can be sucked into the cylinder 3 or discharged from the cylinder 13.

Next, the operation of this embodiment will be explained with reference to FIGS. 4A and 4B.

First, in order to draw the injection liquid into the center hole 14 of the cylinder 13, the pair of air cylinders 25 of the valve switching drive mechanism 29 are actuated, and the piston rod 2
6 and raise the cylinder 13 by a predetermined amount, as shown in FIG. The circumferential groove 21 is arranged to face the opening of the fitting surface between the injection liquid suction passage 16 and the cylinder internal communication passage 19. As a result, the discharge passage 18 is connected to the outer peripheral surface of the valve body 12 and the cylinder 13.
On the other hand, the suction passage 1
6 is the lower circumferential groove 21 and the cylinder internal communication passage 1
9 into a center hole 14 located inside the fitting surface of the cylinder 13 with the valve body 12.

In this state, injectate is supplied at low pressure to the suction passage 16 from an injectate supply source (not shown) by the action of a low-pressure pump or a pressurized tank, and the stepping motor 39 of the suction/discharge operation drive mechanism 47 is rotated at a predetermined speed. When the ball screw nut 38 is rotated several times, the ball screw nut 38 is rotated via the timing pulley 41 and the like, and as the ball screw shaft 31 rotates, the rotation of the ball screw shaft 31 is prevented by the action of the rotation prevention plate 45.
It is moved in the upward direction by a predetermined amount without rotating.
As a result, a predetermined amount of injection liquid is sucked into the center hole 14 of the cylinder 13. At this time, if the injection liquid is not very viscous and the distance from the supply source is short, pressurization is not necessarily required.

Next, in order to discharge the injection liquid sucked into the cylinder 13 to a predetermined discharge part, as shown in FIG. 4B, the air valve 2 of the valve drive mechanism 29 is activated.
5 in the opposite direction to the above, and move the piston rod 2.
6 is projected downward, and the cylinder 13 is lowered. As a result, the upper circumferential groove 20 is opposed to the opening of the fitting surface between the discharge passage 18 and the cylinder communication passage 19, allowing the passages 18 and 19 to communicate with each other, while the lower circumferential groove 21 is the suction passage. 16 and the return passage 17 to communicate with each other, and the injection liquid from the suction passage 16 is transferred to the return passage 1.
7 to return to the supply source side again. In this switching of the valve mechanism 22, since the outer peripheral shapes of the fitting surfaces of the valve body 12 and piston 15 to the cylinder 13 are the same, unless the relative axial position of the valve body 12 and piston 15 is changed, The injection liquid sucked into the cylinder 13 never leaks.

In this state, if the stepping motor 39 of the suction/discharge operation drive mechanism 47 is rotated a predetermined number of revolutions in the opposite direction to that described above, the piston 15 will be pushed down by a predetermined amount, and the center hole 14 of the cylinder 13 will be pushed down by a predetermined amount. The injection liquid sucked into the inside is discharged to a discharge portion (not shown) via the communication passage 19, the circumferential groove 20, and the discharge passage 18.

By repeating the above operations, the injection liquid can be measured in predetermined amounts and sequentially inhaled and expelled. On this occasion,
If it is desired to change the suction and discharge amounts, the number of rotations (total rotation angle) of the stepping motor 39 may be changed.

According to this embodiment as described above, there are the following effects.

That is, when injecting and discharging injected liquid, the valve body 12 is not operated, and only the cylinder 13 and piston 15 are operated, and the cylinder 13 and piston 15 are not rotated but reciprocated in the axial direction. Only. Therefore, cylinder 1
3 and the piston 15 are simplified, and the structure of the valve switching drive mechanism 29 and the suction/discharge operation drive mechanism 47 that operate each can be made simpler than when rotary motion is applied.

Furthermore, since the valve body 12, cylinder 13, and piston 15 do not rotate, each seal structure can be simplified and costs can be reduced. Furthermore, since the cylinder 13, valve body 12, and piston 15 do not rotate, each sliding part can be easily lubricated, and the valve mechanism 2
The driving force in step 2 may be small. In addition, since it does not rotate, each part can be connected simply with a retaining ring or screw without using a locking part such as a key, which simplifies the fixing structure.
The number of parts can also be reduced.

Furthermore, the injection liquid is measured by the space between the valve body 12 and the piston 15, and at this time, the valve body 12 does not move and only the piston 15 moves, so the injection liquid can be measured with high precision. be able to.

In addition, a cylinder 13 which is a measuring part for injection liquid,
Since the valve mechanism 22 is integrated,
Each of the passages 16 to 19 in the valve mechanism 22 can be shortened, and can be applied to high-viscosity injection liquids.

Furthermore, since the valve body 12 does not move, the connecting pipes and the like with the supply source side and the discharge part side of the injection liquid are not moved or bent, and durability can be improved.

In addition, suction, discharge, return passages, 16, 17, 1
8 are provided in the same member, that is, the valve body 12, so the entire circumference of the cylinder 13 can be easily placed in a cooler, heater, thermostat, etc., and can be used to cool or heat reactive injection liquids. Easily manage temperature. Furthermore, since the stepping motor 39 is used as the driving source for the suction/discharge operation drive mechanism 47, the capacity can be easily changed even during operation.

FIG. 5 shows a system diagram when the embodiment is actually used, and a pump 52 as an infusion solution supply source is connected to the infusion solution suction passage 16 of the embodiment through a pipe 51. The suction side of this pump 52 is inserted into a tank 53 containing an injection liquid. Further, the return passage 17 is connected to the tank 53 via a pipe 54 (in FIG. 5, the valve mechanism 2
2 is drawn using JIS symbols, the return passage 17 and piping 54 are not directly connected,
In the specific structure of the embodiment described above, one end of the pipe 54 is directly connected to the return passage 17 shown in FIG. 2. ), suction passage 1 when discharging injectate
The injection liquid from the 6 side is returned to the tank 53. Further, the discharge passage 18 is connected to the nozzle 5 as a discharge part via a piping 55 made of a flexible tube.
6 (the reason why it is not directly connected in FIG. 5 is the same as mentioned above), and the injected liquid in the cylinder 13 when discharging the injected liquid is transferred to the nozzle 56.
It is now possible to discharge from.

A dosing valve 5 is provided in the middle of the pipe 55.
7 is provided to prevent the injection liquid from dripping from the nozzle 56 when no discharge occurs. This dosing valve 57 includes a pair of first and second air cylinders 58, 59, and these air cylinders 58, 59.
The first and second valve bodies 6 press the piping 55 made of a flexible tube to shut off the flow of the injection liquid.
0,61, and the first valve body 60 has a spring 62
so that it is always closed.

Note that numerals 63, 64, and 65 are electromagnetic valves that control the supply of air to each air cylinder 25, 58, and 59, respectively.

In such a configuration, the operations of the cylinder 13 and the valve mechanism 22 are completely the same as in the previous embodiment, and will therefore be omitted, and only the operation of the dosing valve 57 will be described. When discharging the injection liquid, the first and second air cylinders 58 and 59 of the dosing valve 57 are both connected to the first and second valve bodies 6.
0 and 61 away from the piping 55, that is, in the direction of the arrow in the figure, in other words, the first air cylinder 58
The piston of the second air cylinder 59 is driven to the left in the figure against the spring 62, while the piston of the second air cylinder 59 is driven to the right in the figure, the pressure on the pipe 55 is released, and the injection liquid is discharged from the pipe 55. It can be done.

Next, when stopping the injection liquid discharge, the first,
The air supply to the second air cylinders 58, 59 is switched, and contrary to the above, the first and second valve bodies 60,
61 are both driven in the direction of crushing the pipe 55, thereby blocking the discharge of the injection liquid. Then, the air supply to only the lower second air cylinder 59 is switched again, and the air supply to the piping 55 by the second valve body 61 is switched again.
As the pressure is released and the pipe 55 expands due to its own elastic force, a negative pressure is generated on the nozzle 56 side, and the injection liquid stored between the second valve body 61 and the nozzle 56 flows into the second valve body 61. The liquid is slightly sucked toward the valve body 61, and dripping of the injection liquid from the nozzle 56 is prevented.

6 and 7 show a second embodiment of the present invention, in which the cylinder 13 and part of the valve body 12 are directly inserted into a container 70 containing an injectate. The overall structure of the device is simplified by eliminating the need for a pressurizing pump or the like. The valve body 12 in this embodiment is provided with only two passages, an injection liquid suction passage 16 and an injection liquid discharge passage 18. The suction passage 16 has one end communicated with the center hole 14 of the cylinder 13, and the other end opened to the fitting surface of the valve body 12, and this opening 16A is formed by the inner peripheral surface of the cylinder 13. When the cylinder 13 is moved upward by a predetermined amount from this closed state, it is removed from the lower end of the cylinder 13 and opened into the container 70. Further, the discharge passage 18 is similar to that of the first embodiment, but only one circumferential groove 20 is provided on the inner circumferential surface of the cylinder 13, and this circumferential groove 20 is located at the lowest point of the illustrated cylinder. In this position, its lower end faces the fitting surface opening of the discharge passage 18, and its upper end faces the valve body 1.
The center hole 1 extends beyond the top of the cylinder 13 and is located inward from the fitting surface of the cylinder 13.
4, and the discharge passage 18 is communicated with the inside of the cylinder 13.Furthermore, when the cylinder 13 is raised, the circumferential groove 20 is connected to the valve body 1.
2, the fitting opening of the discharge passage 18 is closed by the inner peripheral surface of the cylinder 13.

In such a configuration, the injection liquid is transferred to the cylinder 13.
To inhale into the air, raise the cylinder 13 by a predetermined amount from the state shown in the figure using the air cylinder 25.
Suction passage 16 that was blocked by cylinder 13
is exposed in the container 70 and is in a state where the injection liquid in the container 70 can be sucked, while the fitting surface opening of the discharge passage 18 is closed by the inner circumferential surface of the cylinder 13.
In this state, if the stepping motor 39 is driven to raise the piston 15, the injected liquid in the container 70 is suctioned into the cylinder 13 through the suction passage 16 due to the negative pressure caused by the rise of the piston 15. be done. At this time, since the suction passage 16 of this embodiment is formed to have a relatively large diameter, even if the injection liquid has a somewhat high viscosity, it can be sufficiently inhaled.

After suction is completed in this way, the air cylinder 25 is driven in the opposite direction to lower the cylinder 13 to the state shown in FIG.
9 and lower the piston 15, cylinder 1
The injection liquid in 3 is discharged to a predetermined discharge portion via the circumferential groove 20 and the discharge passage 18.

Thereafter, inhalation and exhalation will be repeated in the same manner.

According to this embodiment as described above, the same effects as those of the first embodiment can be achieved, and the additional effect can be added that the pressurizing pump etc. can be omitted and the apparatus can be made simpler than the first embodiment. .

A third embodiment of the present invention is shown in FIGS. 8 and 9, and this embodiment has a seal member 80 between the valve body 12 and the cylinder 15 of the first embodiment.
It is an intervening one. That is, the valve body 12
The upper outer periphery of the valve body 12 is machined to have a slightly smaller diameter, and a cylindrical seal member 80 made of fluororesin (trade name: Teflon) is press-fitted into the small diameter outer periphery of the valve body 12. A retainer plate 81 fixed to the end (upper end) with screws ensures that it does not come off. The sealing member 80 also includes passages 16 and 1 formed in the valve body 12, as shown in FIG.
A large number of communication holes 82, 83, 84, 85 are formed along the circumferential direction at positions facing the circumferential openings of the valve body 12 of 7, 18, and 19, respectively, and these communication holes 82 to 85 Each of the passages 16 to 19 can communicate with the circumferential groove 20 or 21 through the groove.

According to this embodiment, in addition to achieving the same effects as those of the first embodiment, the sealing member 80 can more completely seal the valve body 12 and the cylinder 13. At this time, communication between each of the passages 16 to 19 and the circumferential grooves 20 and 21 via the seal member 80 is achieved by providing a circumferential groove on the opening side of the circumferential surface of each passage 16 to 19, and on the side of the seal member 80. A large number of communication holes 82 to 85 having an opening area smaller than these circumferential grooves are provided in the passages 16 to 19, and since the side of each passage 16 to 19 is always on the high pressure side in either the suction or discharge state, the communication holes 82～
Due to the difference in pressure receiving area between 85 and the circumferential groove on the valve body 12 side, the seal member 8
A force that tends to spread from the inner circumferential side, which is the valve body 12 side, toward the outer circumferential side, that is, the cylinder 13 side always acts on the valve body 12, and this force makes the sealing more complete. In addition, the seal member 8
No. 0 has good lubricity because its plate material is a fluororesin.

In addition, in carrying out this embodiment, the seal member 8
0, one to several circumferential grooves may be formed between each communication hole 82 to 85 to make the seal more complete.

In addition, in carrying out the present invention, the present invention is not limited to the structure of each of the above-mentioned embodiments, and other structures may be used. For example, the drive source of the suction/discharge operation drive mechanism 47 is not limited to the stepping motor 39, but may be an air cylinder or It may be a combination of a rack and pinion, or it may have a structure in which the main part does not have any rotating parts. However, if the stepping motor 39 is used, it has the advantage that the capacity can be changed extremely easily during operation. Moreover, the center hole 14 of the cylinder 13,
Therefore, the outer circumferential shapes of the valve body 12 and the piston 15 are not limited to cylinders, but may be other shapes such as rectangular cylinders. In short, as long as the outer diameters of each part are the same,
There is no problem because leakage of the injected liquid in the suction state due to the sliding of the cylinder 13 does not occur. Furthermore, the rotation of the ball screw shaft 31 is not limited to the portion of the cover cylinder 44, and may be prevented from rotating at other portions, such as the inner diameter portion of the ball screw shaft 31 located within the cover 48.

[Effect of idea]

As mentioned above, according to the present invention, the operation is simple;
Moreover, it is possible to provide a liquid injector with a simple sealing structure.

[Brief explanation of drawings]

Figure 1 is a sectional view showing the main parts of a conventional liquid injector;
Fig. 2 is a longitudinal sectional view showing the first embodiment of the present invention, Fig. 3 is a partially cutaway front view, and Figs. 4A and B.
5 is a system diagram showing the actual application state of the first embodiment, FIG. 6 is a longitudinal sectional view showing the second embodiment of the present invention, and FIG. 7 is a front view thereof.
FIG. 8 is a sectional view of essential parts showing a third embodiment of the present invention, and FIG. 9 is a perspective view showing the shape of a sealing member used in the third embodiment. 11... Base plate, 12... Valve body, 13... Cylinder, 15... Piston, 16
... Infusate suction passage, 18... Infusate discharge passage,
20, 21... Full circumference groove, 22... Valve mechanism, 2
9... Valve switching drive mechanism, 47... Suction and discharge operation drive mechanism, 70... Container.

Claims (1)

[Scope of utility model registration request] a cylinder adapted to be axially movable; a valve body fitted within the cylinder for axial sliding relative to the cylinder and attached to a base member; The piston is positioned inwardly from the fitting surface of the cylinder with the valve body and the piston is able to be fitted with the piston, and the outer circumferential shape of the fitting surface is the same as the outer circumferential shape of the fitting surface of the valve body. an injectate suction passage that enables direct communication between the inside of the cylinder and the injectate supply source side through an opening formed in the valve body;
an injectate discharge passage that enables direct communication between the inside of the cylinder located inward of the fitting surface of the cylinder with the valve body and the injectate discharge section side through an opening formed in the valve body; and a valve body, the valve mechanism switches between communicating or blocking the injectate suction passage and the injectate discharge passage with the inside of the cylinder as the cylinder slides in the axial direction with respect to the valve body, and the valve body. a valve switching drive mechanism that slides a cylinder axially against the valve body to perform a switching operation of the valve mechanism; and a valve switching drive mechanism that slides a piston axially relative to the valve body to perform suction or discharge operation of the injected liquid. A liquid injector characterized by comprising a suction and discharge operation drive mechanism.