JPH112551A - Piston reciprocating type flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress lowering of durability due to large ICSS caused by fluid pressure acting upon a selector valve of a flowmeter. SOLUTION: A selector valve 36 is rotatably provided in an under casing 41. It is so constituted that pressure of an inflow port 25 does not act upon the interior of a cylindrical part 36c of the selector valve 36. A coil spring 40 for pressing a body 36a of the selector valve 36 to a seal member 39 above is provided in a bottomed cylindrical part 38. Pressure of a fluid discharged from measuring chambers 23A-23D through a communicating hole 36e piercing the body 36a of the selector valve 36 is led into the bottomed cylindrical part 38. Since the upper end part, sliding against the seal member 39, of the cylindrical part 36c is formed in nearly annular shape, pressing force of the coil spring 40 and fluid pressure led into the bottomed cylindrical part 38 act uniformly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston reciprocating flow meter, and more particularly to a piston reciprocating flow meter configured to reciprocate a piston in accordance with a flow rate of a fluid to be measured and measure the flow rate.

[0002]

2. Description of the Related Art For example, a refueling device for refueling a fuel tank of an automobile with an oil liquid as a fuel is provided with a flow meter for measuring a refueling amount. In particular, when refueling an oil liquid such as gasoline, it is necessary to measure the refueling amount using a flow meter capable of accurately measuring a minute flow rate in order to maintain fairness of the transaction. As this type of flowmeter, there is a four-piston type flowmeter having two pairs of piston and cylinder mechanisms in which two pistons make a pair and reciprocate.

[0003] The features of this type of four-piston type flow meter are that not only can it measure a very small flow rate, it can be easily handled and adjusted, and it can be used to rapidly start and stop refueling by a refueling nozzle or pump. This is also a structure having a mechanically strong strength. Further, this flow meter has a wide range in which the flow rate can be measured, and can obtain linear instrumental characteristics even when the flow rate changes.

FIG. 6 is a cross-sectional view of a conventional piston reciprocating flow meter, FIG. 7 is a longitudinal cross-sectional view of a conventional piston reciprocating flow meter, and FIG. FIG. As shown in FIGS. 6 and 7, such a piston reciprocating flow meter has two pairs of cylinders 1A to 1A which are arranged to face each other on two axes orthogonal to each other.
D. Casing 2
A casing main body 4 having the cylinders 1A to 1D and having a communication chamber 3 in the center where the cylinders 1A to 1D communicate with each other; an upper lid 5 covering an upper opening and a lower opening communicating with the communication chamber 3 of the casing main body 4; Lid 6 and each cylinder 1A
And side lids 7A to 7D that cover the outer openings of the first to the first ID.

[0005] Each of the cylinders 1A to 1D has a piston 8A.
8D are slidably fitted. Of these four pistons 8A to 8D, a pair of pistons 8A and 8B, which are arranged on the same axis, are connected to a yoke 9A, and another pair of pistons is formed. 8C and the piston 8D are connected to the yoke 9B. The yokes 9A and 9B include a pair of arms 10 formed in a curved Y shape on the left and right, and a connecting portion 11 for connecting the pair of arms 10. Both ends of the pair of arms 10 are pistons 8A to 8A, respectively. Each of the pistons 8A to 8A is
Fixed to D.

Each of the pistons 8A to 8D includes a piston body 13, a seal member 14 and a retainer 15 arranged on the outer surface of the piston body 13, and a retainer 15 is provided.
Are integrated with the piston body 13 by bolts 12. The casing 2 is rotatably supported at two points via a bearing 17 provided on the upper lid 5 and a bearing 18 provided at a lower portion of the casing body 4 with a rotating shaft 16 having the communication chamber 3 extending in the vertical direction. . An eccentric cam 19 is attached to the rotating shaft 16 in the communication chamber 3. The outer periphery of the eccentric cam 19 is in contact with a cam roller 22 which is rotatably attached to a boss 20 projecting from the back surface of each of the pistons 8A to 8D using a bolt 21.

The yokes 9A and 9B extend corresponding to the upper and lower positions of the eccentric cam 19, and the central portion thereof is curved upward or downward to avoid interference with the eccentric cam 19. . The center of the pair of arms 10 of the yokes 9A and 9B is set to a minimum interval that allows the rotation shaft 16 to pass therethrough. On the other hand, a pair of arms 10
Are set wide so as to avoid interference with the cam roller 22.

Further, between each of the pistons 8A to 8D and the side wall 7 attached to the casing 2, there is provided a measuring chamber 23A to 2D.
Defined as 3D. The measuring chambers 23A and 23B
Flow paths 24A, 2 formed at the bottom in casing body 4
4B (in FIG. 7, the cylinders 1C and 1D sides are not visible so the flow paths 24C and 24C are omitted) and communicate with the inflow port 25 of the lower lid 6 attached to the lower surface of the casing body 4. Further, the measuring chambers 23A and 23B are communicated with the outlet 26 of the upper lid 5 through the flow path 30 around the lower bearing 18 and the communication chamber 3.

As shown in FIG. 8, the lower bearing 18 is provided in a bridge portion 4b crossing the virtual circular hole 4a, and the flow path 30 is formed in the bridge portion 4 of the virtual circular hole 4a.
It is formed by a semicircular arc-shaped hole 30a excluding b. On the other hand, a cup-shaped switching valve 27 is attached to the lower end of the rotating shaft 16 that extends through the lower wall of the casing main body 4 into the lower lid 6. On the bottom side of the switching valve 27, an annular spring receiver 28 which is prevented from rotating with respect to the switching valve 27 is arranged. The switching valve 2 is provided between the spring support 28 and the inner surface of the lower lid 6 via the spring support 28.
A coil spring 29 that presses the casing 7 to the casing body 4 is attached.

The switching valve 27 has a hollow portion 27a that selectively faces one of the flow paths 24A and 24B, so that when one of the measuring chambers 23B communicates with the inflow port 25, the other of the measuring chamber 23B is connected to the other. The chamber 23A acts so as to communicate with the outlet 26. In the piston reciprocating flow meter configured as described above, a liquid feeding means (not shown) such as a pump is connected to the inflow port 25. In addition, a liquid supply means (not shown) such as an oil supply nozzle (not shown) is connected to the outlet 26. Then, the fluid (oil liquid) sent from the liquid sending means enters the lower lid 6 from the inflow port 25 as shown by the solid line arrow in the state shown in FIG. Further, the fluid enters one measuring chamber 23B via the flow path 24B.

At this time, the other measuring chamber 23A is connected to the outlet 2
6 and a pair of pistons 8
A and 8B move integrally in the left direction in FIG. Then, the fluid in the measuring chamber 23A flows into the flow path 24 as indicated by the dotted arrow.
A, it is discharged to the outside from the outlet 27 through the cavity 27a of the switching valve 27, the flow path 30, and the communication chamber 3. This piston 8
The rotation shaft 16 is rotated 90 degrees via the eccentric cam 19 by the leftward movement of A and 8B. At the same time, rotating shaft 1
The switching valve 27 connected to 6 also rotates 90 degrees. Thereby, a pair of pistons 8C in the other cylinders 1C and 1D,
8D moves in one direction and the corresponding weighing chambers 23C, 23D
The fluid inside is sucked and discharged.

Further, when the rotating shaft 16 rotates 90 degrees,
The flow path 24A communicates with the inlet 25 and
B is communicated with the outlet 26. As a result, the pair of pistons 8A and 8B move rightward in FIG. Therefore, the fluid flows into one measuring chamber 23A and the fluid in the other measuring chamber 23B is discharged to the outside. Thus, 2
Since the strokes of the pistons 8A to 8D of the paired piston / cylinder mechanism are constant, the amount of fluid discharged per rotation of the rotating shaft 16 is constant. Therefore, the rotating shaft 1
By measuring the number of rotations of 6, the flow rate of the fluid to be measured in proportion to the number of rotations of the rotating shaft 16 can be obtained. still,
As a flow meter configured as described above,
There is one disclosed in Japanese Patent No. 7296.

[0013]

However, in the piston reciprocating flow meter constructed as described above, the inlet 2
The switching valve 27 that rotates at the center of the casing 5
, The sliding resistance of the switching valve 27 fluctuates due to the pressure difference between the inflow port 25 and the inside of the switching valve 27. Further, the switching valve 27 is such that the switching valve 27
6 is formed so as to communicate with a flow path 30 formed concentrically with the flow path 6 and any one of the flow paths 24A to 24D disposed outside the flow path 30 at intervals of 90 degrees.

Therefore, a uniform pressing force does not act on the sliding portion of the switching valve 27 due to the pressure difference between the central portion communicating with the flow channel 30 and the outer peripheral portion communicating with the flow channels 24A to 24D. Therefore, an unbalanced mechanical seal structure is provided between the switching valve 27 and the seal member 4c. for that reason,
Switching valve 27 that rotates while being pressed by seal member 4c
Does not act on a uniform pressing force, and the seal pressure differs between the rotation center portion of the switching valve 27 and the outside separated from the rotation shaft 16. Therefore, since the magnitude of the sliding resistance is different between the rotation center portion and the outside of the switching valve 27, the sliding resistance with the seal member 4c is not constant. As a result, the sliding portion of the switching valve 27 was liable to be unevenly worn.

Accordingly, an object of the present invention is to provide a piston reciprocating flow meter that solves the above problems.

[0016]

In order to solve the above problems, the present invention has the following features. According to the first aspect of the present invention, two pairs of piston-cylinder mechanisms are arranged in a casing so as to intersect with each other. A switching valve that is driven to rotate in the same direction by rotation of a rotating shaft connected with the piston, and connects one of the plurality of measuring chambers to the outlet, and communicates one of the other measuring chambers to the inlet. Wherein the switching valve is a piston reciprocating flow meter provided at the inflow port,
The switching valve is provided with a circular member extending coaxially with the rotation axis and having a circular outer peripheral surface, and the casing is rotatably guided in the casing to form a chamber isolated from the inflow port. A guide portion is provided, and a pressure introduction path is provided to make the pressure in the chamber equal to the pressure upstream of the switching valve.

Therefore, according to the first aspect of the present invention, the casing is provided with a guide portion for rotatably guiding the circular member to form a chamber separated from the inflow port, and the pressure in the chamber is upstream of the switching valve. Is provided, the pressure in the chamber formed in the circular member of the switching valve can be offset. Therefore, it is possible to reduce the variation of the sliding resistance at the seal portion where the switching valve slides, and to suppress uneven wear of the sliding portion.

According to a second aspect of the present invention, there is provided the piston reciprocating flow meter according to the first aspect, wherein the switching valve is provided so as to prevent leakage from between the switching valve and the casing. An urging member for urging the casing is provided in the room.

Therefore, according to the second aspect of the present invention, the biasing member for biasing the switching valve to the casing is provided in the room so as to prevent leakage from between the switching valve and the casing. The pressing force against the casing can be secured, and the sealing performance at the seal portion where the switching valve slides can be enhanced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a piston reciprocating flow meter according to the present invention. The main part of the piston reciprocating flow meter shown in FIG. 1 is the same as that of the conventional one described above, and the same parts are denoted by the same reference numerals and description thereof is omitted.

In this embodiment, a lower casing 41 formed in a tubular shape is attached to a lower portion of the casing body 4. A bearing 31 that supports an intermediate portion of the rotating shaft 16 is disposed in the communication chamber 3, and as shown in FIG. It is provided on an integrally formed angled bridge portion 33.

The rotating shaft 16 is arranged at the center of the circular hole 32, and an annular hole 34 around the circular hole 32 forms a flow path 35 connecting the communication chamber 3 and the inside of the cup of the lower lid 6. The operations of the pistons 8A to 8D, the yokes 9A and 9B, the rotary shaft 16, the eccentric cam 19, and the like in the present embodiment are the same as those in the above-described conventional case, and the description thereof will be omitted. Next, the main part of the present invention will be described.

As shown in FIGS. 3 and 4, a switching valve 36 is rotatably provided inside the under casing 41. The switching valve 36 has a main body 36a formed in an annular shape outside the flow paths 24A to 24D, and a semi-spherical shape protruding radially from the outer periphery of the main body 36a so as to pass through the same radial position as the flow paths 24A to 24D. The formed flow path forming part 3
6b, a cylindrical portion (circular member) 36c formed to have substantially the same diameter as the outer diameter of the main body 36a, and formed concentrically with the rotating shaft 16 and extending downward from the lower surface of the main body 36a;
a holding portion 36d formed on the inner wall of the main body 36a and holding the connecting member 37 connected to the lower end of the rotary shaft 16, and a communication hole (pressure introduction passage) penetrating the lower surface of the main body 36a and communicating the inside and the outside of the main body 36a. ) 36e.

At the center of the inlet 25 of the casing 2,
A bottomed cylindrical portion 38 formed in a cup shape is provided. The bottomed cylindrical portion 38 has a cylindrical guide portion 38 a formed concentrically with the rotating shaft 16. The cylindrical portion 3 of the switching valve 36 is provided at the upper opening of the guide portion 38a.
6c is rotatably fitted. That is, the guide portion 3
8a guides the cylindrical portion 36c rotatably and forms a chamber 38b isolated from the inflow port 25 therein.

Therefore, the pressure of the inflow port 25 does not act inside the cylindrical portion 36c of the switching valve 36. A coil spring 40 for pressing the main body 36a of the switching valve 36 against the upper seal member 39 is provided in the chamber 38b of the bottomed cylindrical portion 38. Further, inside the chamber 38b, a communication hole 36 penetrating the main body 36a of the switching valve 36 is provided.
The pressure of the fluid discharged from the measuring chambers 23A to 23D via e, that is, the pressure upstream of the switching valve 36 is introduced. For this reason, the inside of the chamber 38b formed inside the bottomed cylindrical portion 38 is maintained at the same pressure as the discharge pressure (pressure upstream of the switching valve 36) due to the operation of each of the pistons 8A to 8D.

Therefore, there is almost no difference between the discharge pressure supplied to the inside of the switching valve 36 and the internal pressure of the bottomed cylindrical portion 38 acting on the outside of the switching valve 36, and the switching valve slides on the seal member 39. The uneven wear due to the pressure difference of 36 is prevented.
Accordingly, the sliding portion of the switching valve 36 is evenly worn, so that the life of the switching valve 36 can be extended as compared with the conventional one. Further, since the upper end portion of the cylindrical portion 36c that slides on the seal member 39 is formed in a substantially annular shape, the pressing force of the coil spring 40 and the fluid pressure introduced into the bottomed cylindrical portion 38 are evenly distributed. It is configured to work. That is, the sliding portion between the switching valve 36 and the seal member 39 has a balanced mechanical seal structure.

As described above, since the switching valve 36 is sealed by the balanced mechanical seal structure, even when the switching valve 36 is driven to rotate by the flow rate measuring operation, the sliding portion with the sealing member 39 is hardly unevenly worn, and the switching valve is accordingly reduced. 36 has a longer life and improved durability. Further, since the pressure loss can be reduced by reducing the ratio of the switching valve 36 narrowing the flow path through which the fluid flows, the measurement accuracy can be further improved as compared with the conventional flow meter.

Each time the switching valve 36 rotates 90 degrees, the flow path forming part 36b is in a state of communicating with the flow paths 24A to 24D, and the fluid discharged from the measuring chambers 23A to 23D is transferred to the flow path forming part 36b. The fluid reaches the communication chamber 3 through the communication channels 24A to 24D, and is discharged from the outlet 26 thereafter. Therefore, the inflow pressure supplied to the inflow port 25 acts on the flow path forming portion 36b that protrudes in the radial direction from the main body 36a. However, the flow path forming portion 36b is provided with the switching valve 3
6, and the uneven wear is reduced as compared with the case where the inflow pressure acts on the whole.

Since the cylindrical portion 36c serves as a shaft when the switching valve 36 rotates, it is sufficient that at least the outer periphery is a circle. Therefore, since the shape of the inner peripheral side of the cylindrical portion 36c is the spring receiver of the coil spring 40, it can be a shape other than a circle (for example, a square or a hexagon). Further, it is also possible to form the cylindrical portion 36c in a cylindrical shape (solid shape) without providing a concave portion on the inner peripheral side of the cylindrical portion 36c.

Here, the action of the pressure in the driving state of this embodiment will be described. The pressure Pa of the fluid flowing from the inflow port 25 of the under casing 41 passes through the side of the switching valve 36 and presses the piston 8B of the measuring chamber 23B.
Thereby, the rotating shaft 16 rotates via the roller cam 22 and the eccentric cam 19. Then, the switching valve 36 also rotates integrally with the rotating shaft 16 and switches the flow paths 24A to 24D.

At the same time, the piston 8A discharges the fluid (oil liquid) in the measuring chamber 23A to the flow path 24A through the yoke 9B pressed by the piston 8B, and communicates through the flow path forming portion 36b of the switching valve 36. Discharge into chamber 3. At this time, the pressure of the fluid supplied to the communication chamber 3 becomes Pb. Then, the oil liquid is sent to the oil supply nozzle at the pressure Pb. Now, the force F1 applied to the seal member 39 when the communication hole 36e is not provided on the lower surface of the main body 36a of the switching valve 36 can be expressed by the following equation (1).

F1 = (Pa−Pb) · S (1) where S is an effective differential pressure area. On the other hand, in the case of the present embodiment in which the pressure Pb of the flow path 24A is introduced into the bottomed cylindrical portion 38 through the communication hole 36e, the force F2 applied to the seal member 39 is expressed by the following equation (2). Can be expressed as

F2 = (Pa−Pb) · S1 + (Pa−Pb) · S2 (2) S2 = S−S1 (3) where S1 is the pressure receiving area in the guide portion 38a, and S2 is the pressure of the switching valve 36. Pressure receiving area. In the equation (2), the switching valve 3
(Pa-Pb) · S2 acting on the whole 6 is an unbalanced mechanical seal, and (Pa-Pb) · S1 acting on the flow path forming portion 36b corresponds to a balanced mechanical seal. That is, the switching valve 36 of the flow meter of the present embodiment is a combination of an unbalanced mechanical seal and a balanced mechanical seal.

Here, the switching portion 36 is provided at the guide portion 38a.
Of the inflow side pressure Pa does not act on the pressure receiving area S1 in the guide portion 38a, and (Pa−Pb) · S1 = (Pb−Pb). )
S1 = 0. Therefore, the force F2 applied to the seal member 39 is F2 = (Pa−Pb) · S2, and the influence of the pressure Pa applied to the pressure receiving area S1 is reduced as compared with the conventional one, and the pressure loss is reduced to 以下 or less. Is done. Therefore, F1 <F2.

The mechanical loss when the switching valve 36 rotates is proportional to the friction coefficient μ · F. Therefore, a decrease in the load applied to the seal member 39 leads to an improvement in the measurement accuracy of the flow meter. Further, since (Pa−Pb) is the pressure loss itself of the flow meter, it becomes possible to further improve the durability of the flow meter itself. Next, a modified example of the present invention will be described.

As a first modification of the present invention, as shown by a dashed line in FIG. 1, one of the measuring chambers 23A to 23D is connected through a communication pipe (pressure introduction path) 42 provided outside the flow meter. The discharged fluid pressure may be introduced into the chamber 38b of the bottomed cylindrical portion 38. In this case, by providing a check valve in the middle of the communication pipe 42, the pressure in the chamber 38b can always be maintained at the discharge pressure, so that the side lids 7A to 7D or the flow path 2
The discharge pressure upstream of the switching valve 36 may be introduced into the chamber 38b from any of 4A to 24D.

Also in this case, the inside of the chamber 38b formed inside the bottomed cylindrical portion 38 is maintained at the same pressure as the discharge pressure, so that the discharge pressure supplied to the inside of the switching valve 36 and the switching valve 36
And there is almost no difference from the internal pressure of the bottomed cylindrical portion 38 acting on the outside. Therefore, uneven wear due to the pressure difference of the switching valve 36 sliding on the seal member 39 is prevented, and the switching valve 3
The sliding portion of No. 6 is evenly worn.

As a second modification, as shown by a broken line in FIG. 4, a communication passage 16a communicating with the inside of the switching valve 36 is provided at a lower end portion of the rotary shaft 16 inserted into the switching valve 36, and a holding portion is provided. A communication hole (pressure introduction path) 36f for communicating the communication path (pressure introduction path) 16a with the chamber 38b may be provided in 36d. Incidentally, the communication passage 16a has a first passage 16a ₁ that opens to the inside of the switching valve 36 extends in the radial direction of the rotary shaft 16, a first passage extending in the axial direction at the center of the rotary shaft 16 intersecting and a second passage 16a ₂ Metropolitan to.

In this case, the pressure inside the switching valve 36 (same as the pressure upstream of the switching valve 36) is introduced into the chamber 38b through the communication passage 16a and the communication hole 36f. for that reason,
The pressure in the chamber 38b is kept the same as the pressure inside the switching valve 36. Thereby, the same effect as when the communication hole 36e or the communication pipe 42 is provided can be obtained. FIG. 5 is a longitudinal sectional view for explaining a third modification of the present invention.

As shown in FIG. 5, a guide wall 43 extending in the horizontal direction is provided on the inner wall of the under casing 41. The partition 43 slides on the outer periphery of the cylindrical portion 36c of the switching valve 36 to rotatably guide the switching valve 36, and divides the inside of the under casing 41 into the upper chamber 41a.
And the lower chamber 41b. The inflow port 25 is provided on a side wall of the under casing 41 and communicates with the upper chamber 41a. Therefore, the lower chamber 41 b is connected to the inflow port 2 by the partition 43.
5 and isolated. The lower chamber 41b is provided with a coil spring 40 for pressing the main body 36a of the switching valve 36 against the upper sealing member 39.

Further, the measuring chamber 23A is connected to the lower chamber 41b through a communication hole 36e penetrating the main body 36a of the switching valve 36.
To 23D are introduced. For this reason, the inside of the lower chamber 41b is maintained at the same pressure as the discharge pressure by the operation of each of the pistons 8A to 8D. Therefore, there is almost no difference between the discharge pressure supplied into the switching valve 36 and the internal pressure of the bottomed cylindrical portion 38 acting on the outside of the switching valve 36, and the pressure of the switching valve 36 sliding on the seal member 39 is reduced. Uneven wear due to the difference is prevented. Therefore, the pressing force of the coil spring 40 can uniformly act on the seal member 39, and the sliding portion between the switching valve 36 and the seal member 39 can be moved by the pressure difference introduced into the lower chamber 41b.
The balance becomes a mechanical seal structure.

As described above, since the switching valve 36 is sealed by the balanced mechanical seal structure, even when the switching valve 36 is rotationally driven by the flow rate measuring operation, the sliding portion with the seal member 39 is hardly unevenly worn. Since the sliding parts are evenly worn, the life of the minute switching valve 36 is extended, and the durability is improved. In addition, in this modification 3, as shown by the dashed line in FIG. 41b. In this case, by providing a check valve in the middle of the communication pipe 42,
Since the pressure in the lower chamber 41b can always be maintained at the discharge pressure, the discharge pressure may be introduced into the lower chamber 41b from any of the side covers 7A to 7D or the flow paths 24A to 24D.

Also in this case, since the inside of the lower chamber 41b is maintained at the same pressure as the discharge pressure, the discharge pressure supplied to the inside of the switching valve 36 and the internal pressure of the lower chamber 41b acting outside the switching valve 36 are reduced. The difference between them almost disappears. Therefore, uneven wear due to the pressure difference of the switching valve 36 sliding on the seal member 39 is prevented. Thereby, the sliding portion of the switching valve 36 is evenly worn, so that the life can be extended as compared with the conventional one.

The rotary shaft 16 inserted in the switching valve 36
Communication passage 16a communicating with the lower end portion of the switching valve 36 inside the switching valve 36
And a communication hole 36f can be provided in the holding portion 36d. In this case, the pressure inside the switching valve 36 (same as the pressure upstream of the switching valve 36) is introduced into the lower chamber 41b through the communication passage 16a and the communication hole 36f. Therefore, the pressure in the lower chamber 41b is kept the same as the pressure inside the switching valve 36. Thereby, the same effect as when the communication hole 36e or the communication pipe 42 is provided can be obtained.

Although the above embodiment has been described as a flow meter used in a refueling device, the present invention can of course be applied to a flow meter installed so as to measure the flow rate at a location other than the refueling device. It is.

[0046]

As mentioned above, according to the first aspect of the present invention, the casing is provided with the guide portion for rotatably guiding the circular member to form a chamber separated from the inflow port, and the pressure in the chamber is switched. Since the pressure introduction path for matching the pressure upstream of the valve is provided, the pressure in the chamber formed by the circular member of the switching valve and the guide portion can be offset. Therefore, it is possible to reduce the variation of the sliding resistance at the seal portion where the switching valve slides, and to suppress uneven wear of the sliding portion. As a result, the sliding portion of the switching valve is evenly worn, so that the life can be extended as compared with the conventional one.

According to the second aspect of the present invention, since the urging member for urging the switching valve to the casing is provided in the room so as to prevent leakage from between the switching valve and the casing, the switching valve is provided in the casing. Force can be secured,
It is possible to enhance the sealing performance at the seal portion where the switching valve slides.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a piston reciprocating flow meter according to the present invention.

FIG. 2 is a view partially showing a semicircular flow path formed around a bearing of the flow meter shown in FIG. 1;

FIG. 3 is a transverse sectional view taken along the line III-III in FIG.

FIG. 4 is an enlarged longitudinal sectional view showing a main part of the present invention.

FIG. 5 is a longitudinal sectional view for explaining a third modification of the present invention.

FIG. 6 is a cross-sectional view of a conventional piston reciprocating flow meter.

FIG. 7 is a longitudinal sectional view of a conventional piston reciprocating flow meter.

FIG. 8 is a cross-sectional view partially showing the shape of a flow path around a bearing of a rotating shaft.

[Explanation of symbols]

 1A to 1D Cylinder 2 Casing 3 Communication chamber 4 Casing main body 5 Upper lid 6 Lower lid 7A to 7D Side lid 8A to 8D Piston 9A, 9B Yoke 10 Arm 13 Piston main body 16 Rotating shaft 19 Eccentric cam 22 Cam roller 23A to 23D Measuring chamber 24A to 24D flow path 25 inflow port 26 outflow port 30 flow path 36 switching valve 36a main body 36b flow path forming part 36c cylindrical part 36e communication hole 38 bottomed cylindrical part 38a guide part 41 under casing 42 communication pipe 43 partition wall

Claims (2)

[Claims] 1. A pair of piston-cylinder mechanisms are arranged in a casing so as to intersect with each other, and each of the pistons moves sequentially and a plurality of pistons are connected by a fluid to be measured flowing into a measuring chamber formed in the casing. A switching valve that is driven to rotate in the same direction by the rotation of the rotating shaft, connects one of the plurality of measuring chambers to the outlet, and connects one of the other measuring chambers to the inlet, The switching valve is a piston reciprocating flow meter provided at an inflow port, wherein the switching valve is provided with a circular member that extends coaxially with the rotation axis and has a circular outer peripheral surface, and the casing has the circle. A piston that rotatably guides a member to form a chamber separated from the inflow port; and a pressure introduction path that matches a pressure in the chamber with a pressure upstream of the switching valve. Reciprocating flow meter . 2. The piston reciprocating flow meter according to claim 1, wherein the biasing member biases the switching valve to the casing so as to prevent leakage from between the switching valve and the casing. Is provided in the chamber.