JP3321743B2 - Throttle mechanism of orifice flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a throttle mechanism of an orifice flow meter used in various plants such as petrochemical and chemical industries, and more particularly to an improvement of a throttle mechanism using a concentric orifice.

[0002]

2. Description of the Related Art An orifice flow meter of this type used for measuring the flow rate of various fluids such as liquid, gas, and vapor flowing in a steady flow in a pipeline is provided with two differential pressures generated by a throttle mechanism using an orifice. Is introduced to a differential pressure gauge by using a pressure guiding tube, and is converted into an electric signal by the differential pressure gauge, and a flow rate is calculated from the signal. That is, if a throttle mechanism that reduces the cross-sectional area of the pipeline is installed in the middle of the pipeline, a pressure difference occurs before and after the throttle mechanism when the fluid flows therethrough. Since there is a certain relation between the pressure difference and the flow rate, the flow rate of the fluid flowing in the pipeline can be obtained by measuring the pressure difference.

In measuring the flow rate, the pressure difference generated in the throttle mechanism is converted into a flow rate using an experimental coefficient called an outflow coefficient. When this is represented by an equation, W = CK ・ ΔP ^1/2 (1) Where: W is the flow rate, C is the outflow coefficient, K is a constant (including tube diameter, fluid density, etc.), and ΔP is the differential pressure.
This outflow coefficient C is a recognized coefficient determined and determined worldwide. Therefore, changing the shape of the pressure outlet determined by the standard means that the outflow coefficient C cannot be used.

There are various types of throttle mechanisms, such as concentric orifices, nozzles, venturi tubes, missing orifices, and eccentric orifices. The most common one uses a concentric orifice. In addition, there are three types of throttle mechanisms, DD taps, flange taps, and corner taps, depending on the position where the pressure outlet is formed.

FIG. 15 shows a throttle mechanism using a concentric orifice. In FIG. 15, the upper part from the center line of the pipe is DD / 2.
The drawing shows a tap drawing mechanism, and the lower side shows a flange tap drawing mechanism. 1, 2 are primary (upstream) and secondary (downstream) main pipes, 3 is a primary pressure outlet, 4 is a secondary pressure outlet, 5 is an orifice plate, and 6 is a main pipe. Orifices concentric with 1 and 2, 7 are flanges of main pipes 1 and 2, 8 is a pressure guiding pipe, D is the inner diameter of main pipes 1 and 2, d is the hole diameter of orifice 6, and δ is the pressure outlets 3 and 4. The hole diameter.

According to JIS, in the case of a DD tap and a flange tap, the inner diameter D (mm) of the main pipes 1 and 2 is
50 ≦ D ≦ 760, the aperture diameter d (mm) of the aperture is d ≧ 1
2.5, the aperture diameter ratio β (= d / D) is 0.2 ≦ β ≦
0.75 respectively. The hole diameter δ of each of the pressure outlets 3 and 4 is specified to be 0.08 D or less, but is preferably 12.5 mm or less. Accordingly, when the inner diameter D of the main pipes 1 and 2 is 50 mm, the hole diameter δ of the pressure outlets 3 and 4 becomes 3.8 mm or less, and when D exceeds 150 mm, it becomes 12.5 mm. The pressure outlets 3 and 4 are ＢB, which is often used for the pressure guiding tube 8.
The area ratio is about 1:17 even when compared to the inner diameter of the pipe of 16.1 mm, which indicates that only the pressure outlets 3 and 4 are very narrow. For this reason, a problem that is said to occur most frequently when using an orifice type flow meter is clogging in the pressure guiding portion. The clogging is caused by oil, iron rust, and the like, and solving the problem of the clogging is a major problem when using an orifice flow meter.

ASME (American Society of Mechanic)
al Engierring) specifies the hole diameter δ of the pressure outlets 3 and 4.
Is larger than the hole diameter according to the JIS standard, and is set to 6.35 mm in the above-described drawing mechanism. However, even so, the area ratio is 1: 6.4 compared to the inner diameter of the 1 / 2B pipe described above, which is not enough to eliminate the tendency to cause clogging.

[0008]

As described above, the conventional orifice flowmeter has a disadvantage that the pressure guiding portion is liable to be clogged because the hole diameter of the pressure outlet is small. Therefore, regular maintenance work is needed to remove this. In this case, if the hole diameter of the pressure guiding portion is increased, the occurrence of clogging can be reduced. However, in this case, the value of the outflow coefficient C changes, and the flow rate cannot be measured.

Therefore, the present inventors have manufactured a throttle mechanism conforming to the standard according to JIS and a throttle mechanism in which the hole diameter of the pressure outlet is enlarged. The effect of the size was examined. As a result, the hole diameter D of the main pipe, the hole diameter δ of the pressure outlet,
And the aperture diameter ratio β is within a certain range,
The error between the two is within 0.3%, and the flow rate can be calculated using the outflow coefficient C even if the hole diameter δ is larger than the standard,
It was confirmed that there was no practical problem.

Therefore, the present invention has been made based on the above-mentioned conventional problems and experimental results. It is an object of the present invention to determine a hole diameter of a main pipe, a hole diameter of a pressure outlet, and a restriction diameter ratio. By setting the pressure within the specified range, even if the hole diameter of the pressure outlet is larger than the hole diameter specified in JIS, the flow rate can be calculated using the outflow coefficient, so that the occurrence of clogging is reduced. To provide a throttle mechanism for an orifice flow meter.

[0011]

In order to achieve the above object, the present invention uses a concentric orifice to provide a pressure outlet on the primary side upstream from the orifice at a distance equal to the inner diameter of the main pipe. In the throttle mechanism of the orifice flow meter, the pressure outlet of the orifice is provided downstream of the orifice at a distance of の of the inner diameter of the main pipe, the throttle diameter ratio is set to 0.
2 to 0.6, and the inner diameter of the main pipe is 50 mm to 760 mm
And the hole diameter of the pressure outlet is 13 mm to 28 mm. Further, the present invention provides an orifice flow meter using concentric orifices, in which a primary side pressure outlet and a secondary side pressure outlet are respectively provided on flanges provided on the upstream and downstream main pipes and joined to each other. Wherein the diameter ratio of the throttle is 0.2 to 0.6, the inner diameter of the main pipe is 50 mm to 760 mm, and the hole diameter of the pressure outlet is 13 mm to 28 mm.

The hole diameter δ of the pressure outlet is JIS Z876.
According to the definition of “Flow measurement method by throttle mechanism” in 2,
0.8 for flange type and DD / 2 tap
D or 12.5 mm or less. On the other hand, in the present invention, the hole diameter δ of the pressure outlet is 13 mm.
Because it is 28 mm, clogging is small. The reason for setting the inner diameter D of the main pipe to 50 mm to 760 mm is to consider the use within the range specified in the drawing mechanism according to JIS Z8762. Hole diameter δ of pressure outlet is 13mm
When the throttle diameter ratio β is in the range of 0.2 to 0.6 and the flow rate is obtained by using the outflow coefficient C, the error can be reduced to 0.3% or less in terms of flow rate. The nominal accuracy of the aperture mechanism according to JIS Z8762 is 0.6
%, Even if the standard is deviated within the above range of 0.3%, the maximum is about 0.9%, and there is no practical problem. When the hole diameter δ is 13 mm or less, JIS
This is unfavorable because the value falls within the range defined by Z8762, and the effect of reducing clogging cannot be obtained. It is not preferable that the thickness be 28 mm or more, because a measurement error increases. In other words, when the hole diameter δ is increased, the influence of the fluid flowing through the orifice is increased, and the downstream pressure is increased. Therefore, the differential pressure value becomes small, and the flow rate is measured at a small value. On the other hand, if β = 0.6 or more, the downstream pressure is undesirably high. The reason why the lower limit of the aperture diameter ratio β is set to 0.2 is to make it equal to the lower limit specified by JIS.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an embodiment in which a throttle mechanism of an orifice flowmeter according to the present invention is applied to a throttle mechanism of a flange tap. The same components as those described in the section of the related art are denoted by the same reference numerals, and description thereof will be omitted. In the present embodiment, pressure outlets 11 and 12 each having a hole diameter δ1 and δ2 of 13 mm are respectively provided in flanges 7 and 7 of main pipes 1 and 2, and these pressure outlets 11 and 12 are connected by a pressure guiding tube 8. They are connected to a high pressure side and a low pressure side of a differential pressure gauge (not shown), respectively. Other configurations are exactly the same as those of the conventional flange tap throttle mechanism.

In the throttle mechanism having such a structure, the hole diameters δ1 and δ2 of the pressure outlets 11 and 12 are determined according to JIS.
The maximum hole diameter δ (1
2.5 mm), it is possible to reduce the occurrence of clogging in the pressure outlets 11 and 12 as compared with the conventional throttle mechanism. For example, if D is increased from 6 mm to 13 mm, the area ratio is increased by about 4.7 times, and the clogging is harder. The inner diameter D of the main pipes 1 and 2 is 50 mm to 760 mm, and the pressure outlet 1 is
When the hole diameters δ1 and δ2 of the holes 1 and 12 are in the range of 13 mm to 28 mm and the throttle diameter ratio β is in the range of 0.2 to 0.6, the flow rate is calculated by the above equation (1) in comparison with the throttle mechanism defined by JIS. The error can be suppressed within 0.3%. This error is in a sufficiently allowable range. That is, JIS Z
According to 8762, the nominal accuracy of the aperture mechanism is within 0.6%. Therefore, even if the standard is deviated within the above range, the error is only about 0.9% at the maximum, and there is no practical problem.

The inner diameter D of the main pipes 1 and 2 is set to 50 mm to 760.
The reason for setting mm is to match the range of the inner diameter D specified in JIS. The reason that the value of β is specified to be 0.2 or more is to make it equal to the lower limit (0.2 ≦ β) specified by JIS. The reason for setting β to 0.6 or less is that if β is set to a value larger than this, the differential pressures at the standard pressure outlets 3 and 4 and the pressure outlets 11 and 12 with the increased hole diameters δ1 and δ2 are considered.
This is because the difference between the differential pressures in is not constant, and the measurement error increases. Set the hole diameters δ1 and δ2 of the pressure outlets 11 and 12 to 1
The reason for setting it to 3 mm or more is that if it is 13 mm or less,
This is because the lower limit value d ≧ 12.5 according to the definition of S is included, and there is no difference in the effect of preventing clogging. However, 28
If it is not less than mm, the fluid that has passed through the orifice will enter the pressure outlets 11 and 12 in large amounts, and the influence of the fluid will increase, which is not preferable.

[0016]

FIG. 2 shows that the pressure outlets 3, 4 have a standard hole diameter δ.
FIG. 9 is a cross-sectional view showing an experimental device manufactured for examining what kind of change appears in a flow measurement value in the case of enlarged hole diameters Δ1 and Δ2. In this experimental apparatus, two pairs of large and small pressure outlets 3, 4 and 11, 12 are provided on the flanges 8, 8 of the main pipes 1, 2, respectively. In the figure, the inner diameter D of the main pipes 1 and 2 is 50 mm, and the diameter ratio β of the throttle is 0.6. A pair of pressure outlets 3 and 4 provided on the upper side of the flange 7 indicate a standard pressure outlet having a hole diameter δ of 6 mm, and are connected to a differential pressure gauge A (not shown) via a pressure guiding tube 8. I have. On the other hand, a pair of pressure outlets 11 and 12 provided below the flange 7 are provided with an enlarged hole diameter δ according to the present invention.
1, .delta.2 and is connected to the differential pressure gauge B by another pressure guiding tube 8. In the experiment, the inner diameter D of the main pipe
Is 50 mm, the aperture diameter ratio β is 0.2, 0.4, 0.6,
0.7, hole diameters δ1, δ2 are 13mm, 22mm and 2
An 8 mm device was manufactured, and an experiment was performed using water having a pressure of ² to 4 kgf / cm ² as a fluid for each device. The measurement results are shown in FIGS.

FIGS. 3 to 6 show a standard hole diameter of δ of 6 mm,
FIG. 6 is a diagram showing the relationship between differential pressure and time when δ1 and δ2 are enlarged hole diameters of 13 mm. 3 is β = 0.2, FIG. 4 is β = 0.4, FIG. 5 is β = 0.6, and FIG. 6 is β = 0.7.
Is the case. As is clear from these figures, the hole diameter δ
Is the differential pressure at the standard pressure outlets 3, 4 of 6 mm,
Pressure outlets 11 with hole diameters δ1, δ2 expanded to 13mm,
The difference between the differential pressures at 12 is substantially constant. δ is 6mm
Is less than 0.3% in terms of flow rate under the condition of β = 0.2 to 0.6 under the condition of β = 0.2 to 0.6. When β is 0.7 or more, the standard pressure outlets 3 and 4 having a hole diameter δ of 6 mm
And the pressure difference between the pressure outlets 11 and 12 in which the hole diameters δ1 and δ2 are increased to 13 mm are not constant, and the measurement error increases. Therefore, practically 0.2 ≦ β ≦
Preferably, it is 0.6. The reason why β is set to 0.2 or more is to make the same as the lower limit (0.2 ≦ β) specified by JIS as described above.

FIGS. 7 to 10 show the relationship between the differential pressure and time when the standard hole diameter is 6 mm and the enlarged hole diameters δ 1 and δ 2 are 22 mm. 7 is β = 0.2, FIG. 8 is β = 0.4, FIG. 9 is β = 0.6, and FIG.
= 0.7. As is apparent from these figures, the difference between the differential pressure at the standard pressure outlets 3 and 4 having the hole diameter δ of 6 mm and the differential pressure at the pressure outlets 11 and 12 having the hole diameters δ 1 and δ 2 expanded to 22 mm. Is the above 13mm
As in the case of, the difference from the measured value is β =
Under the conditions of 0.2 to 0.6, it was 0.3% or less in terms of flow rate.

FIGS. 11 to 14 are diagrams showing the relationship between the differential pressure and time when the standard hole diameter δ is 6 mm and the enlarged hole diameters δ 1 and δ 2 are 28 mm. 11 is β = 0.2, FIG. 12 is β = 0.4, FIG. 13 is β = 0.6, FIG.
Is the case of β = 0.7. As is apparent from these figures, the difference between the differential pressure at the standard pressure outlets 3 and 4 having the hole diameter δ of 6 mm and the differential pressure at the pressure outlets 11 and 12 having the hole diameters δ 1 and δ 2 expanded to 28 mm. Is the above 13m
As in the case of m and 22 mm, it was substantially constant, and the difference from the measured value was 0.3% or less in terms of flow rate under the condition of β = 0.2 to 0.6.

The tendency of the above experimental results is that the hole diameter δ
Increasing 1, δ2 tends to decrease the pressure. It was also found that the smaller β was, the smaller the tendency was. The hole diameters δ1 and δ2 of the pressure outlets 11 and 12 are JIS
The reason why the measured value is smaller when the hole diameter is larger than the hole diameter δ specified in the above is considered as follows. When the fluid passes through the orifice 6, a contraction occurs downstream of the orifice 6 and the pressure decreases. The pressure is restored by returning the contracted flow to the original flow (partly lost as a pressure loss). Therefore, a pressure distribution exists downstream of the orifice 6. Since the differential force outlets 11 and 12 are in the pressure distribution, the pressure transmitted to the differential pressure gauge B is expected to be the average value of the pressure distribution in the hole. When the hole diameters δ1 and δ2 are large, the average pressure value in the hole portion on the downstream side of the orifice 6 becomes high due to the pressure distribution. On the other hand, the pressure on the upstream side is considered to be stable, and is substantially constant near the pressure outlet 11,
The average value does not change depending on the size of the hole. As a result, the differential pressure value transmitted to the differential pressure gauge becomes smaller. Therefore, the flow rate is measured to be small apparently. Also, as the aperture diameter ratio β decreases, the effect is reduced
Since the distance until the contraction returns is extended to a position far from the orifice 6 and the pressure distribution near the downstream pressure outlet 12 is gentle, it is considered that the average value does not change much depending on the size of the hole.

In the above-described embodiments and examples, an example in which the present invention is applied to a throttle mechanism of a flange tap has been described. β is 0.2 ~
0.6, hole diameters δ1, δ2 of 13 mm to 28 mm, and inner diameter D of the main pipe of 50 mm to 760 mm, it was confirmed that exactly the same results were obtained. However, the corner tap cannot be applied because the structure is completely different from the flange tap and the DD / 2 tap. The reason is that, in the case of the corner tap, since the pressure outlet is provided in contact with the orifice, the fluid that collides with the orifice easily flows into the pressure outlet, and the pressure is easily affected. This is because only a small hole of about .03D can be used.

[0022]

As described above, the restricting mechanism of the orifice flow meter according to the present invention comprises a flange tap and a D.D.
In the 1/2 tap throttle mechanism, the hole diameter of the pressure outlet is set to J
Since the hole diameter is larger than the hole diameter specified in the throttle mechanism of ISZ8762, the occurrence of clogging at the pressure outlet is small,
Stable flow measurement over a long period of time,
The complexity of maintenance work can be reduced. Further, the inner diameter D of the main pipe is 50 mm to 760 mm, the reduction diameter ratio β is 0.2 to 0.6, and the hole diameter δ of the pressure outlet is 13 mm to 28.
mm, an error in flow rate conversion due to the enlargement of the pressure outlet can be suppressed to 0.3% or less. This is because the nominal accuracy of the aperture mechanism according to JIS Z8762 is within 0.6%, and even if the standard deviates within the above-mentioned range of 0.3%, the maximum is about 0.9%. no problem.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a throttle mechanism of an orifice flow meter according to the present invention.

FIG. 2 is a cross-sectional view of an experimental device manufactured for examining a change in a flow measurement value when a pressure outlet has a standard hole diameter and an enlarged hole diameter.

FIG. 3 shows a standard hole diameter where β is 0.2 and δ is 6 mm;
6 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 13 mm.

FIG. 4 shows a standard hole diameter where β is 0.4 and δ is 6 mm;
6 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 13 mm.

FIG. 5 shows a standard hole diameter where β is 0.6 and δ is 6 mm;
6 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 13 mm.

FIG. 6 shows a standard hole diameter where β is 0.7 and δ is 6 mm;
6 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 13 mm.

FIG. 7 shows a standard hole diameter where β is 0.2 and δ is 6 mm;
1 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 22 mm.

FIG. 8 shows a standard hole diameter where β is 0.4 and δ is 6 mm, and δ is 6 mm.
1 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 22 mm.

FIG. 9 shows a standard hole diameter where β is 0.6 and δ is 6 mm;
1 is a table showing the relationship between differential pressure and time when 1, δ2 is an enlarged hole diameter of 22 mm.

FIG. 10 shows a standard hole diameter where β is 0.7 and δ is 6 mm,
9 is a table showing the relationship between differential pressure and time when δ1 and δ2 are enlarged hole diameters of 22 mm.

FIG. 11 shows a standard hole diameter where β is 0.2 and δ is 6 mm,
6 is a table showing the relationship between differential pressure and time when δ1 and δ2 are enlarged hole diameters of 28 mm.

FIG. 12 shows a standard hole diameter where β is 0.4 and δ is 6 mm,
6 is a table showing the relationship between differential pressure and time when δ1 and δ2 are enlarged hole diameters of 28 mm.

FIG. 13 shows a standard hole diameter where β is 0.6 and δ is 6 mm,
6 is a table showing the relationship between differential pressure and time when δ1 and δ2 are enlarged hole diameters of 28 mm.

FIG. 14 shows a standard hole diameter where β is 0.7 and δ is 6 mm,
6 is a table showing the relationship between differential pressure and time when δ1 and δ2 are enlarged hole diameters of 28 mm.

FIG. 15 shows a DD / 2 using a conventional concentric orifice.
It is a figure showing a drawing mechanism of a tap and a flange tap.

[Explanation of symbols]

1, 2, main pipe, 3, 4 pressure outlet, 5 orifice plate, 6 concentric orifice, 7 flange, 8 pressure guide tube, 11, 12 pressure outlet.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-37342 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (2)

(57) [Claims] A concentric orifice is used to provide a pressure outlet on the primary side upstream from the orifice at a distance equal to the inner diameter of the main pipe, and a pressure outlet on the secondary side downstream from the orifice to the inner diameter of the main pipe. In the throttle mechanism of the orifice flow meter provided at a distance of 1/2 of the diameter of the throttle, the throttle diameter ratio is set to 0.1.
2 to 0.6, and the inner diameter of the main pipe is 50 mm to 760 mm
Wherein the diameter of the hole of the pressure outlet is 13 mm to 28 mm. 2. An orifice flow meter using concentric orifices and provided with a primary pressure outlet and a secondary pressure outlet on flanges provided on the upstream and downstream main pipes and joined to each other, respectively. In the throttle mechanism, the throttle diameter ratio is set to 0.2 to 0.6, and the inner diameter of the main pipe is set to 50 mm to 7 mm.
60 mm, and the hole diameter of the pressure outlet is 13 mm to 28 mm
A throttle mechanism for an orifice flow meter.