Methods for measuring water flow. Methods for measuring water flow in pressure and free-flow flows Devices that determine water flow

3.1 Instruments and equipment.

To measure flow, in practice, a hydrometric turntable GR-21M is used; the number of the turntable is indicated on the blade propeller. Blade propellers are No. 1 main - with a diameter of 12 cm and a geometric pitch of 20 cm, No. 2 - non-component, with a diameter of 12 cm, a geometric pitch of 50 cm. It is imperative to indicate what the spinner is lowered into the water on (rod, cable). Main parts of turntables:

1) The bladed propeller or rotor is brought into a rotating state as a result of the force action of the oncoming flow.

2)The axis on which the bladed propeller or murmur rotates. The axis serves to strengthen the blade propeller; it can be movable and connected directly to the blade propeller.

3) Turntable body. It serves as a basis for strengthening and placing individual parts turntables, for strengthening the turntable on a rod or cable. The appropriate body shape is streamlined, creating the least resistance to flow.

4) Counting and contact mechanism. It is used to count the revolutions of the blade propellers.

5) Tail or rudder. Tail or rudder, serves to position the turntable in the flow in the direction of the flow, which is especially important when working with a cable.

Fig.2. Fig.3.

Floats are also used to measure water flow. Hydrometric floats are considered the most inaccurate way to measure water flow. For our river, surface floats were used, which were made in the form of circles, sawed off from a dry log with a diameter of 5-15 cm and a thickness of 2-3 cm. No more than 4 pieces.

3.2. Methods for measuring water flow.

Water flow is the volume of water passing through a given cross section river flow in 1 s. For large watercourses - rivers, canals, spillways hydraulic structures and so on. – water consumption is expressed in cubic meters per second. The water flow of small watercourses - springs, streams, wells, as well as laboratory flumes is expressed in liters per second.

There are the following methods for calculating water consumption; they can be divided into two main groups:

1. Direct flow measurement.

2. Indirect flow measurement.

The direct measurement of flow rate includes the so-called volumetric method, which is based on measuring flow rate using measuring vessels placed under a stream of water. The filling time of the measuring vessel is also measured. Consumption is determined by dividing the volume of water in the vessel by the duration of filling.

Indirect measurement of water flow can be performed various methods, common feature which is that they measure not the water flow itself, but individual elements flow, and the flow rate is obtained by calculation. These methods include:

A). Determination of flow using measuring devices: hydrometric flumes, weirs.

b). A mixing method that has several varieties (thermal, electrical and colorimetric).

V). Determination of flow rate from measured flow velocities and cross-sectional area of ​​the flow is called the “velocity-area” method. We used this method in practice. The cross-sectional area of ​​the flow is determined from the results of depth measurements, and the velocity at individual points of the live cross-section.

3.3. Measuring the flow rate of the hydrometric vertical.

Determination of water flow rates using hydrometric meters is carried out using the “velocity-area” method. To ensure sufficient accuracy in measuring flows, it is necessary that a smoothly changing movement of water be observed in the selected area; the flow of water both in the main channel and on the floodplain must have a general direction across the entire width of the river. The flow speed during low water should be at least 0.15-0.25 m/sec, so that it can be changed with a turntable. It is advisable that during periods of high water and floods, speeds do not exceed 3.0-4.0 m/sec. In winter, the river section should be covered with a continuous ice cover. There should be no areas with standing water or reverse currents on the site. When choosing a site for temporary work, it is enough to take into account the convenience of the location in this period of the year.

A hydrometric cross-section across a river at which water flows are measured. The position of the hydrometric alignment is fixed on the plane with strong pillars - benchmarks.

The hydrometric alignment is divided perpendicularly general direction rivers, focusing on the direction of the banks, since for correct definition flow, it is necessary that the cross section of the river along the target line be located normal to the average direction of the flow. As a rule, one gauging station is installed at the measurement site, coinciding with the station of the water gauging station or located close to it. However, in some cases it is necessary to have two, and sometimes three, alignments. This is due to the fact that in different periods of the year the conditions for water flow can change significantly.

Determination of the direction of the hydrological section using a turntable that measures the direction of the flow.

Work to determine the alignment direction is carried out in the following sequence:

1) depth measurements are taken at a pre-selected and fixed site, after which, in accordance with the width of the river and the outlines of the site profile, high-speed vertical lines are assigned in an amount of no more than 10-12;

2) on all speed verticals, current velocities and directions are measured at one point at a depth of 0.6 h from the surface; the resulting velocity value on the vertical is taken as average speed on the vertical.

3) water consumption is calculated (we multiply the speed of the river by the water cross-sectional area)* see KG-3 Water consumption for the turntable GMCM-1

When measuring water flow rates with turntables, three methods are used - detailed, composite and abbreviated, which differ in the degree of detail of velocity measurements in the live section.

Before measuring water flows, it is necessary to check the serviceability of the hydrometric instrument, as well as the condition of all equipment at the hydrometric station. When measuring water flow, the following steps are performed: following works:

1) description of the state of the river, weather, aquatic vegetation, state of the river bed, timber rafting indicating the type of rafting, wind strength and direction, waves, water turbidity, presence of ice phenomena.

2) observation of the water level.

3) depth measurements at the hydraulic station.

4)measurement of flow velocities on turntables.

When measuring speeds along each vertical, the following work is performed:

1) The weather and river conditions are different.

2) The water level is determined (in case of significant changes) based on observations at the water gauging station for the beginning and end of work on the turntables.

3) Vertical depth is measured; In winter, the thickness of snow, ice, submerged ice and slush is additionally measured.

4) The working depth on the vertical is calculated and the depths are calculated, the turntable is immersed in the speed measurement points.

5) Current velocities are measured at individual points.

To measure water consumption with a GR21-M turntable, you need to lower it to 0.6 depths in the central measuring vertical and count the number of calls. The first 2-3 signals are skipped without recording. This is necessary so that the bladed propeller acquires a rotation speed corresponding to the speed of water flow. Next, the stopwatch starts and after ≈ 100 seconds. Calls are counted (one call – 20 turns). The number of calls is multiplied by 20 and this result is divided by the number of seconds, we get the number of revolutions per second:

Using the calibration table we determine the speed:

V= 0.0408+0.3233*(0.2405) 2 = 0.1185 m/s

Q= 0.1185*2.2775= 0.27 m 3 /s

3.4 Measuring water flow using surface floats.

In addition to the hydrometric turntable, current speed can be determined using hydrometric floats. The method is based on recording the speed of a floating body-float. When determining speed with floats, it is assumed that the flow speed is equal to the speed of the float. To measure the water flow with surface floats above and below the hydrometric alignment, two additional alignments are set up at equal distances so that the duration of the floats' travel between the upper and lower alignments is at least 20 seconds. At current speeds of more than 2 m.s., the duration of the floats may be shorter, but not less than 10 seconds. The distance between the upper and lower sashes should be measured with greater accuracy - twice with a steel tape. In windy weather the use of surface floats is limited. When measuring velocities with floats, the result obtained in each case is the highest current speed along the float's trajectory; that speed is taken as the local speed at the point of intersection of the target line and the float's trajectory. Thin cords are pulled along the broken sections under water. One of the team members with a stopwatch stands at the top target, and the other two team members stand at the bottom and below. The student launches the float slightly higher than the upper target, throwing it onto the river core from the bank. At the moment the float passes through the upper gate, he starts the stopwatch and monitors the float. At the moment the float passes through the hydraulic gate, the observer monitors whether the float is on the river stem. At the moment the float passes the lower gate, the observer makes a signal (voice) and the student starts the stopwatch. From all the floats launched on the switch, three floats are selected, showing the shortest duration of travel between the flaps. The extreme value of the stroke duration of these three floats should not differ from each other by no more than 10%. The calculation of the flow rate measured by surface floats is given only based on the highest flow velocity according to the formula.

In river hydrometry, the most common method for measuring water flow is speed method-square". It lies in defining water cross-sectional area by measuring depths along the hydraulic channel and measuring with a hydrometric measuring instrument at individual points of the water section flow speed.

When measuring water flow you must:

1) record the work environment;

2) monitor the water level;

3) measure depths at the hydrometric site;

4) measure the speed of water flow at individual points of the live section on high-speed verticals.

All records of observation data and measurements of water flow are made with a simple black pencil in the “Book for recording water flow measurements” KG-ZM *.

Before starting work, it is necessary to check the serviceability of the hydrometric turntable and its accessories, the stopwatch, as well as the presence and serviceability of life-saving equipment to ensure the safety of work, the condition of all equipment of the hydrometric station (Appendix 1). To prevent accidents, students are required to study and strictly follow the safety instructions (Appendix 2).

To measure water flow, a section of the river is selected that meets, if possible, the following requirements:

1) the banks are smooth (not winding), parallel;

2) the channel is level, stable and not overgrown with vegetation;

4) absence of dead space (part of the water section where there is no flow).

For educational practice in the selected section of the river there must be depths of more than 1 m so that patterns of changes in flow speeds can be identified.

In the selected area, a hydrometric gauge (hydraulic gauge) is marked, at which water flow is measured. On small rivers, the waterworks are laid out by eye perpendicular to the direction of the river flow and secured on both banks with signs - stakes. A sign on one of the banks is taken to be constant start from which distances are measured before each measuring (speed) vertical. A cable (cord) marked every 1 m is stretched in the hydraulic channel. If measurements are made from a boat, a riding cable is stretched parallel to the marking cable (under it), which serves to move the boat along the channel and position it vertically.

Observations and measurements are carried out in the following order.

1. Information about the work environment (state of the river, weather, instruments and equipment) is recorded in the “Work Environment” section of the expense book. All phenomena that may affect the direction and magnitude of the flow velocity or affect the accuracy of determining water flow are noted. For example, the width of the mowed strip of the hydraulic drain is indicated and the condition it is in is noted: “cleanly mowed”, “at the bottom there are remains of aquatic vegetation ... cm high.” In addition, the degree of overgrowth of aquatic vegetation in the river bed below the hydraulic station is indicated (near the banks, completely, sparsely, densely). Shoals, spits, midstreams, structures (dams, cofferdams, dams, bridges) are noted: it is necessary to indicate at what distance from the hydraulic station they are located.

2. Observations of the water level are carried out at the main hydrological station before and after depth measurements, as well as before and after

measuring current velocities. Recording of observation data on the height of the water level during measurements and flow measurements is carried out in the corresponding tables of the flow book.

3. Depth measurements at the hydraulic gauge are made to calculate the water cross-sectional area, as described in the section “Surveying and processing of measurement results.” Depths are measured once before measuring current velocities and are recorded in. consumption book in the “Measurements” section (in column 11). In the first and last lines, corresponding to the first: and last measuring verticals at the water's edge, c. column 0 is written “Ur.l.b.” or “Lv. p.b." (edge ​​of the left or right bank), and in column I - depth at the edge. With steep banks, this depth may not be zero. Columns 3 and 4 are filled in only in cases where the depth is measured in an unstable channel twice: forward and backward.

4. Measurements of current velocities on verticals are usually carried out with one hydrometric turntable, sequentially moved to different points of the vertical.

Number high-speed verticals, at which current velocities are measured, with a river width of up to 50 m it is taken equal to five. When choosing locations for high-speed verticals, you should strive to ensure that they are as evenly distributed as possible across the width of the river and at the same time fall at the sharp turning points of the bottom and at the deepest point of the target. The extreme high-speed verticals should be as close to the shore as possible (as far as current speed and depth allow).

The number of points at which the flow velocity on the vertical is measured is set depending on the working depth of the high-speed vertical (Table 4).

Working depth The speed vertical, as well as on the measuring verticals, calculates the vertical distance from the bottom to the surface of the water. At a constant water level, the difference in vertical depths according to the sounding and at the time of measuring the speed in a stable channel should not exceed 2-3 cm at depths up to 1 m, 5 cm at depths from 1 to 3 m. If the difference is greater, the measurement should be repeat.

Table 4

Dependence of the number and location of vertical current velocity measurements on the working depth

Flow measurements using surface floats have a significantly lower accuracy than measurements using turntables, so surface floats are used in reconnaissance surveys of rivers when turntables fail. During intense ice drift, when measurements with turntables become impossible, individual ice floes can serve as floats.

Rice. 31.

AB - launch point; I- basis; 2 - upper; 3 - main;

4 - lower section of the river

Float measurements are carried out in calm conditions or a slight wind of 2-3 m/s. To measure velocities with surface floats in a section of the river that meets the requirements for hydrometric gauges, a highway is laid along the bank parallel to the main direction of the flow and a basis is selected on it - I(Fig. 31). Three alignments are broken perpendicular to it: the upper one - 2, the main one - 3 (middle) and bottom - 4. The distance between the alignments is such that the duration of the floats between them is at least 20 s. Main site 3 breaks approximately in the middle of the base.

If a bridge is used to simplify and speed up hydrometric work, then the main alignment is combined with the bridge alignment.

The position of the base and alignments on the ground is fixed with pegs and milestones. At the sites, cables marked at 1 m intervals can be stretched over the water. At all points along the water's edge, stakes are driven in; their distance to the base is measured with a measuring tape. To launch the floats, the launch gate AB is additionally broken 5-10 m above the top target.

Depth measurements are taken and the open section area along the main section is determined. Measurements are taken under each mark of the marked cable, starting from the “permanent beginning” (cutting stake). The measurement results are entered into a table. In the absence of a marked cable in the alignment, the distance from the measuring vertical to the shore is determined by the notch method, i.e. by measuring the horizontal angle between the base and the line of sight (see Fig. 15). The location of the measurement point on the target is controlled by milestones placed on the shore.

Measuring water flow velocities with floats is carried out in the following order. At the launch site, 15-25 floats are thrown into the water in succession, distributed approximately evenly across the width of the river. When a float passes through the gates, observers give signals with a go-ahead signal or voice. At these moments, the place of passage (distance from the shore) of the float in each alignment is recorded using the notch method or by an observer on the bridge using marking cables. At the same time, a stopwatch measures the time it takes the float to travel from the top to the bottom.

Rice. 32.

The results of measuring the speed of the floats are recorded in a table. Moreover, records of floats washed ashore are excluded. In Fig. Figure 32 shows the distribution of float travel times across the river width. On the graph, the distances from the permanent beginning to the place where the floats pass the middle alignment are plotted along the horizontal axis, and along vertical axis- duration of travel of the floats between the upper and lower sections. Using the plotted points, an averaged diagram of the distribution of the duration of the float's stroke across the width of the river is drawn. Velocity verticals are drawn at equal distances and at inflection points in the diagram. At least 5-6 high-speed verticals are assigned, which are combined with measuring verticals for ease of processing. For each speed vertical, the surface velocity of the current is calculated by dividing the distance between the upper and lower gates by the duration of the float stroke, taken from the diagram. The results of measuring water flow rates by floats are recorded in a table.

By multiplying the area of ​​the compartments between high-speed verticals by half the sum of the surface velocities on them, partial fictitious water flow rates are obtained. Their sum, taking into account the marginal coefficients, gives the total fictitious water consumption (2f:

where vi, v„ are surface velocities on high-speed verticals; coi, ..., co„ - areas of living sections between high-speed verticals; To- coefficient for the edge section equal to 0.7.

The actual flow rate is calculated using the formula:

Where TO- transition coefficient, from fictitious flow to real.

The value of the transition coefficient A^i can be found in tables or determined using formula 5.6, if Q- flow rate determined simultaneously by measurements with a turntable and floats. You can also define TO according to the formula:

Where WITH- Chezy coefficient, which is recommended to be calculated using the formula N.N. Pavlovsky:

where at R 1m And at R> 1 m; P- coefficient

roughness, determined from tables in hydraulic reference books.

If it is impossible to launch floats across the entire width of the river, for example on fast-flowing rivers where the floats are carried towards the middle of the flow, water flow is determined by the highest surface velocity. In this case, 5-10 floats are launched onto the core part of the flow. Of all the launched floats, three with the longest stroke duration are selected, differing from each other in time by no more than 10%; with a larger deviation in the stroke duration, another 5-6 floats are launched.

If the highest surface velocity is measured using floats, it is used to calculate water flow

where K max is the average speed of the three fastest floats; coefficient TO

Where AND- average flow depth; g - acceleration free fall; co is the water cross-sectional area.

Measuring water flow with deep floats is used to measure relatively low flow velocities (up to 0.15-0.20 m/s), when spinner measurements are unreliable and to determine the boundaries of dead space. Current speeds are measured from a boat equipped with

secured by three rigidly fastened parallel slats at a distance of 1 m from each other. Using a pole at a distance of 0.5 m from the slats (upper) located closer to the bow of the boat, a deep float is launched. A stopwatch is used to determine the time it takes the float to travel the distance from the upper to the lower target. At each point the float is launched at least three times. The speed at a point is calculated by dividing the length of the basis - the distance between the sash slats - by average duration float stroke. The average value is taken into account. Water flow is calculated analytically in the same way as water flow measured with a pinwheel.

Businesses and residential buildings consume a large number of water. These digital indicators become not only evidence of a specific value indicating consumption.

In addition, they help determine the diameter of the pipe assortment. Many people believe that calculating water flow based on pipe diameter and pressure is impossible, since these concepts are completely unrelated.

But practice has shown that this is not so. The throughput capabilities of the water supply network depend on many indicators, and the first in this list will be the diameter of the pipe assortment and the pressure in the main.

Perform calculation bandwidth pipes, depending on their diameter, are recommended at the design stage of pipeline construction. The data obtained determines key parameters not only domestic, but also industrial highways. All this will be discussed further.

Calculate the pipe capacity using an online calculator

ATTENTION! To calculate correctly, you need to note that 1 kgf/cm2 = 1 atmosphere; 10 meters of water column = 1 kgf/cm2 = 1 atm; 5 meters of water column = 0.5 kgf/cm2 and = 0.5 atm, etc. Fractional numbers entered into the online calculator through a dot (For example: 3.5 and not 3.5)

Enter parameters for calculation:

What factors influence the permeability of liquid through a pipeline?

The criteria that influence the described indicator make up a large list. Here are some of them.

1. The inner diameter that the pipeline has.
2. The speed of flow, which depends on the pressure in the line.
3. Material taken for the production of pipe assortment.

Determination of water flow at the outlet of the main is carried out by the diameter of the pipe, because this characteristic, together with others, affects the throughput of the system. Also, when calculating the amount of liquid consumed, one cannot discount the wall thickness, which is determined based on the expected internal pressure.

One could even argue that the definition of “pipe geometry” is not affected by the length of the network alone. And the cross section, pressure and other factors play a very important role.

In addition, some system parameters have an indirect rather than a direct effect on the flow rate. This includes the viscosity and temperature of the pumped medium.

To summarize, we can say that determining the throughput allows you to accurately determine optimal type material for the construction of the system and make a choice of technology used for its assembly. Otherwise, the network will not function efficiently and will require frequent emergency repairs.

Calculation of water consumption by diameter round pipe, depends on it size. Consequently, over a larger cross section, a significant amount of liquid will move within a certain period of time. But when performing calculations and taking into account the diameter, one cannot discount the pressure.

If we consider this calculation for specific example, it turns out that less liquid will pass through a meter-long pipe product through a 1 cm hole over a certain time period than through a pipeline reaching a height of a couple of tens of meters. This is natural, because the most high level water consumption on the site will reach its highest levels when maximum pressure in the network and at the highest values ​​of its volume.

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Section calculations according to SNIP 2.04.01-85

First of all, it is necessary to understand that calculating the diameter of a culvert is a complex engineering process. This will require special knowledge. But when carrying out the domestic construction of a culvert, hydraulic calculations of the cross-section are often carried out independently.

This type The design calculation of the flow velocity for a culvert can be carried out in two ways. The first is tabular data. But, turning to the tables, you need to know not only the exact number of taps, but also containers for collecting water (baths, sinks) and other things.

Only if you have this information about the culvert system, you can use the tables provided by SNIP 2.04.01-85. They are used to determine the volume of water based on the girth of the pipe. Here is one such table:

External volume of pipe assortment (mm)

Approximate quantity of water, which is obtained in liters per minute

Approximate amount of water, calculated in m3 per hour

If you focus on SNIP standards, you can see the following in them - the daily volume of water consumed by one person does not exceed 60 liters. This is provided that the house is not equipped with running water, and in a situation with comfortable housing, this volume increases to 200 liters.

Clearly, this volume data showing consumption is interesting as information, but the pipeline specialist will need to determine completely different data - this is the volume (in mm) and internal pressure in the highway. This cannot always be found in the table. And formulas help you find out this information more accurately.

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It is already clear that the cross-sectional dimensions of the system affect the hydraulic calculation of consumption. For home calculations, a water flow formula is used, which helps to obtain the result given the pressure and diameter of the pipe product. Here is the formula:

Formula for calculation based on pressure and pipe diameter: q = π×d²/4 ×V

In the formula: q shows the water consumption. It is calculated in liters. d is the size of the pipe section, it is shown in centimeters. And V in the formula is a designation for the speed of movement of the flow, it is shown in meters per second.

If the water supply network is powered by water tower, without the additional influence of the injection pump, then the flow speed is approximately 0.7 - 1.9 m/s. If any pumping device is connected, then the passport for it contains information about the coefficient of pressure created and the speed of movement of the water flow.

This formula not the only one. There are many more. They can be easily found on the Internet.

In addition to the presented formula, it should be noted that the functionality of the system is greatly influenced by internal walls pipe products. For example, plastic products differ smooth surface than their steel counterparts.

For these reasons, the resistance coefficient of plastic is significantly lower. Plus, these materials are not affected by corrosive formations, which also has a positive effect on the throughput of the water supply network.

Determination of head loss

The calculation of water passage is made not only by the diameter of the pipe, it is calculated by pressure drop. Losses can be calculated using special formulas. Which formulas to use, everyone will decide for themselves. To calculate the required values, you can use various options. The only one universal solution this question does not exist.

But first of all, it is necessary to remember that the internal lumen of the passage of plastic and metal-plastic construction will not change after twenty years of service. And the internal lumen of the passage metal structure will become less over time.

And this will entail the loss of some parameters. Accordingly, the speed of water in the pipe in such structures is different, because in some situations the diameter of the new and old network will be noticeably different. The resistance value in the line will also differ.

Also before calculating required parameters passage of liquid, you need to take into account that the loss of water supply flow rate is associated with the number of turns, fittings, volume transitions, and the presence shut-off valves and friction force. Moreover, all this when calculating the flow rate should be carried out after careful preparation and measurements.

Calculation of water consumption simple methods not easy to carry out. But, if you have the slightest difficulty, you can always turn to specialists for help or use online calculator. Then you can count on the fact that the installed water supply or heating network will work with maximum efficiency.

Video - how to calculate water consumption

Our company measures water flow, both pressure and non-pressure flows. Depending on the measurement method, appropriate equipment is used.

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The pressure flow is limited on all sides by the walls of the conduit, which is why the pressure at any point differs significantly from atmospheric pressure. A free-flow flow, in turn, has a free surface under the influence of atmospheric pressure.

Methods for measuring pressure flows

Water flow in pressure flows directly depends on the speed of the flowing liquid and the flow area. In this case, the cross-sectional area is limited by the walls of the water conduit and is therefore always known. To determine the flow rate, you need to multiply the cross-sectional area by the flow velocity.

Tachometer method. It is used by mechanical flow meters and is based on determining the rotation speed of a moving element under the influence of liquid flowing in a conduit.

Variable pressure differential method. Regardless of the measuring instrument, this method is based on the dependence of the pressure drop, which is formed using a primary converter, on the liquid flow rate.

Ultrasonic time-pulse method. It is based on measuring the speed of passage of an ultrasonic signal between two sensors installed on a water pipeline, alternately working as an emitter and a receiver.

Magnetic induction method. It is based on determining the magnitude of the electromotive force that occurs in a stream of water when it flows through a magnetic field artificially created by electromagnets.

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Methods for measuring free-flow flows

Currently, the two most widely used methods for measuring free-flow flows are acoustic and two-channel Doppler.

Acoustic method. It is based on the acoustic determination of the liquid level, the indicators of which are recalculated using calibration tables using the “level-flow” function.

Two-channel Doppler method. It is based on the simultaneous measurement of not only the flow speed, but also its level. In this case, the Doppler method is used only to determine the flow velocity.