In simple terms, the aperture of a camera is a device through which light enters the camera's matrix. The diaphragm consists of the so-called "petals", the number of which can vary from three to twenty pieces. Depending on the intensity of illumination, the petals reduce or increase the diameter of the light-transmitting hole. The principle of their action is similar to the pupil: in dim light it expands, in bright light it narrows.
To better understand the principles of calculating the characteristics of a lens (including the aperture value), it is necessary to know what the focal length of a lens is.
Lens focal length
Focal length- this is the distance between the camera matrix and the main optical plane of the lens, subject to its focusing to infinity. This indicator determines the viewing angle achieved by a particular lens. The longer the focal length, the smaller the viewing angle. The specifications usually indicate the minimum and maximum focal length that the lens provides. It is customary to measure it in millimeters.
The ratio of the focal length to the aperture size is called the f-number. That is what determines the aperture value. The smaller this indicator, the larger the hole, and the more light penetrates the camera matrix. It is worth considering that the aperture value is often indicated as a denominator of a fraction, without specifying the focal length.
Possible values of f-numbers are described by a special aperture scale, which is a sequence of numbers:
1 - 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 and so on.
The essence of the scale is that narrowing the aperture of the lens by half leads to a decrease in the amount of light entering the matrix by four times. A similar effect has a double increase in focal length. The aperture scale is often applied to the lens barrel for the convenience of the photographer.
Lenses with the smallest f-numbers (f/1.2 - f/1.8) transmit the maximum amount of light. Such lenses are called fast lenses.
Lens aperture
Aperture- this is the degree of attenuation of the light flux by the camera lens, or, in other words, the ability of the lens to transmit the real brightness of the object. The larger the aperture, the better the pictures taken in poor lighting conditions without using a tripod and flash are obtained. In addition, fast lenses allow you to take pictures with the shortest possible shutter speeds.
The aperture value is determined by the value of the maximum open aperture. Together with the focal length, it is usually indicated on the rim of the lens. So, for example, the inscription 7-21 / 2.0-2.8 means that with a focal length of 7 millimeters, the aperture ratio is 2.0. Accordingly, with a focal length of 21 millimeters - 2.8.
When choosing a lens, it should be borne in mind that the maximum open aperture is used very rarely. At the same time, the price of fast lenses is significantly higher. For most buyers, there is no point in overpaying for an indicator of 1: 1.2; it is quite enough to buy a more budget option with an aperture ratio of 1: 1.8.
Relative hole
The reciprocal of the f-number is called relative bore. The relative aperture value determines how many times the focal length of the lens exceeds the diameter of its aperture. On the lens barrel, this indicator usually looks like a 1: 2 fraction. Such figures mean that the hole diameter is half the focal length.
In different sources, the concepts of the value of aperture ratio, the size of the relative aperture and the diaphragm itself are often described in a scientific, incomprehensible language. In order not to make a mistake when choosing a camera and not get confused in the characteristics of the lens, it is worth remembering the dependencies that exist between them.
So, luminosity is a constant property of optics that cannot be changed or adjusted. It should be remembered that aperture has nothing to do with the current aperture value. As mentioned above, its value is equal to the value of the aperture in the maximum open position.
The relative aperture, unlike aperture, is a variable value. You can adjust it with the aperture.
The most fully studied constriction devices, which are recommended for widespread use by Technical Committee 30 (TC 30) of the International Organization for Standardization (ISO), are the so-called normal diaphragm and normal nozzle [?]. Based on periodically issued ISO recommendations, almost all industrialized countries have developed standards or regulations for the use of these restrictive devices.
In our country, similar norms on the methodology and formulas for calculating standard narrowing devices, the basic requirements for flow meters, the methodology for their verification, as well as the methodology for determining the error in measuring flow, are established by Rules 28-64 of the State Committee for Standards, Measures and Measuring Instruments under the Council of Ministers of the USSR. The rules apply to flow measurements of single-phase liquids and gases, as well as superheated vapors using standard restrictors installed inside a pipeline with a diameter of at least 50 mm, provided that the flow is steady, Reynolds numbers exceed certain values and the pressure ratio before and after the restrictor does not reach a critical value.
Normal or standard diaphragm and nozzle are not chosen and recommended for use by chance. Their discharge coefficients in a wide range of Reynolds numbers almost do not change. An appreciable change occurs only at comparatively small Re. Therefore, for small R, standard diaphragms and nozzles are not used.
The standard diaphragm is a constriction device made in the form of a flat disk with a concentric hole for the fluid to flow out. A schematic representation of the diaphragm is shown in Fig. 3.
Above the axis, the measurement of the differential pressure through the annular chambers is shown, below the axis - through the individual holes. The following designations are adopted in the figure: D 20 - the inner diameter of the pipeline in front of the narrowing device at a temperature of 20 ° C; d 20 - the inner diameter of the diaphragm at the same temperature.
Rice. 3
The thickness of the disc should be in the range from 0.005D to 0.05D, where D is the diameter of the pipeline. If the disc thickness is more than 0.02D, then the hole on the exit side must have a conical bore with an angle ranging from 45 to 60° (previously from 30 to 45°). Thus, the thickness of the cylindrical hole of the diaphragm should be in the range from 0.005D to 0.02D. The entrance angle of the cylindrical hole should be strictly equal to 90 °, and the entrance edge itself should be sharp, without any burrs and notches. The degree of roughness k of the inlet end of the diaphragm is allowed by the Rules up to 0.005D, but it is stipulated that the wave (characterizing non-flatness) must exceed the height k by at least 200 times.
Rules 28-64 provide for only the angular method of taking pressures. In this case, two of its varieties are possible - point and chamber. In the first case, the selection is carried out by separate drillings, in the second, through the annular chambers, which are connected to the internal space of the pipeline using annular slots located directly at the diaphragm planes, or a group of holes evenly distributed around the circumference.
It is the latter method adopted in GOST 14321–73. Chamber diaphragms for R y up to 100 kgf / cm 2 (10 Pa). Annular chambers contribute to the selection of the average pressure in this section [?]. therefore, they are particularly useful when there is no certainty about the proper axial symmetry of the velocity profile, i.e. when there is insufficient length of straight pipe sections before and after the orifice.
Chamber diaphragms according to GOST 14321–73 are manufactured only with pipe diameters D no more than 400–500 mm. With large diameters, chamber pressure sampling is performed using two outer tubes of small (10–12 mm) diameter, bent into a ring around the main pipeline and connected to the space before and after the diaphragm using several (4–8) evenly spaced radial tubes.
The weak point of the diaphragm is the inlet edge, which becomes blunted under the action of the current flow, which leads to a gradual increase in its flow coefficient and the appearance of a negative sign error. In this regard, it is necessary to periodically monitor the condition of the diaphragm by removing it and inspecting it. To do this, it is necessary to turn off the section of the pipeline on which the diaphragm is installed. If an uninterrupted supply of the measured medium is required, then the diaphragm must be installed on a bypass line, equipped with locking devices to enable it to be turned off. The length of this line should be such that there are straight sections of sufficient length before and after the diaphragm. This greatly complicates the installation. In addition, the extraction process itself is laborious and is accompanied by damage to gaskets, and sometimes flanged pipes.
In this regard, in American practice, special devices have been widely used that allow you to remove diaphragms for revision and replacement without turning off the pipeline [?]. for this purpose, the disc diaphragm is placed in a special chamber, equipped with two flanges for installation in the pipeline. The chamber has two cavities separated by a locking element: in the lower one there is a diaphragm, the upper one acts as a gateway.
Diaphragms with one pair of differential pressure take-offs must be equipped with shut-off valves and nipples, as well as welded impulse pipes for connections 1-4; leveling condensation vessels according to GOST 14318-73 for connections 5-9; for connections 10-13 - impulse tubes and equalizing vessels in accordance with GOST 14319-73 or impulse tubes and separation vessels in accordance with GOST 14320-73. Diaphragms with several pairs of extractions are supplied with leveling condensate vessels, version 5 according to GOST 14319-73 without impulse tubes. The number of pairs of vessels must correspond to the number of differential pressure gauges supplied with the diaphragm. The designation of the chamber diaphragm indicates the conditional pressure, the conditional passage of the pipeline, the design of the seats, the material of the chamber and disk bodies, the connection number with impulse tubes or vessels and GOST.
Standard nozzles. Nozzles are especially convenient when measuring the flow of gases and superheated steam, as well as when measuring the flow of high pressure steam in pipelines with a diameter of D200mm. Compared to diaphragms, they are less sensitive to corrosion, contamination and provide somewhat greater measurement accuracy.
The standard Venturi nozzle consists of a shaped inlet, a cylindrical middle section and an outlet cone. The pressure loss in the Venturi nozzle increases with increasing cosine angle and decreasing cosine length. The Venturi nozzle is used where pressure loss is critical.
With the general well-being of our lives, we suffer from fires. No insurance will help compensate for the damage caused by fire, because the moral damage caused to the sufferer is not commensurate. Therefore, when constructing residential complexes and administrative buildings, the state, represented by a construction company, tries to protect itself from accidental fire by possible means.
For this purpose, fire hydrants are installed in places determined by the regulations - shut-off valves complete with a connecting head and a fire hose with a manual barrel.
When bringing the fire hydrant into working condition, a diaphragm is installed at the outlet of the valve (brass or stainless steel washer, 3 mm thick, with a hole in the middle). The diaphragm of the fire hydrant is used to reduce excess pressure in fire-fighting water supply systems.
Fire hydrant diaphragm diameter
According to the standards, the nominal passage of fire hydrants installed in buildings and structures is 50 and 70 mm, so the standard outer diameter of the diaphragm is 50 and 65 mm, respectively.
Fire hydrant diaphragm installation
To be able to connect fire equipment, connecting heads made of aluminum are used together. Saving time in the event of a fire is a must, which is why the heads are designed that way: quick-closing, easy to handle and reliable. To work with pressure equipment, depending on the outlet of the shut-off valve, there are two types of heads: coupling and pin.
Coupling heads connect the shut-off valve to the pressure fire hose. Their name matches the species. They are cylindrical with internal threads. The diaphragm is placed inside the head. The head is screwed onto the valve from above and holds the diaphragm in a perpendicular position.
The pin head performs the same functions, but has a different device. It is also cylindrical in shape, but its thread is not inside, but outside. In this case, the diaphragm is placed inside the head and fixed with a retaining ring. Then the pin head is screwed into the valve.
The principle of operation of the fire hydrant diaphragm
Any building of various heights involves the installation of many fire hydrants, each of which can be equipped with more than one pressure hose. The whole system should work stably and debugged. That is, when extinguishing several fires in a building at the same time, water should be distributed evenly depending on the height.
The water pressure in the fire water supply on each floor should be approximately the same and comparable. A stable pressure of water should make it possible to extinguish fires both on the ground floor and on the floors above.
It is for this purpose that the diaphragms of fire hydrants are used. The installed diaphragm, limiting the uncontrolled volume of water exit from the water supply system, prevents pressure drop in the system and reduces excess pressure. On all floors of the building, the water pressure at the fire hydrants is regulated by diaphragms. The water supply will work everywhere, which will eliminate all sources of ignition.
Fire hydrant diaphragm inner diameter
The installation of diaphragms is regulated by regulatory documentation. According to the set of rules, the required number of fire hydrants is installed in the building. The available table documented the water consumption. From these calculations and data, it is allowed to install diaphragms on 3-4 floors of a building with the same hole diameter.
The water pressure rate at the valve in the building is calculated in accordance with the area of \u200b\u200bthe room, as well as the length, width and height to the farthest point of overlap. In industrial buildings - up to 50 meters. Based on these calculations, the inner diameter of the diaphragm, that is, the size of the hole, is calculated.
For this, the old certified nomogram of 1985 is used.
To determine the desired diameter:
On the left vertical axis on the nomogram, we mark the excess pressure in meters, put a point;
On the right vertical axis, set the value of the water pressure that is required, measured in horsepower, put a point;
Connecting these two extreme points with a line, at the intersection of the middle line we find the desired value;
The middle scale is digitized on both sides, on the left side the values for the fire hydrant valve DN50 are indicated;
If the diaphragm is for the DN70 valve, we take the value on the right side of the central axis;
The desired value is obtained in millimeters, with an error of 0.5 millimeters.
Advantages of fire hydrant diaphragm
The advantage of the diaphragm is the versatility of its purpose, it is a fairly simple way to adjust the pressure in the internal fire water supply.
Disadvantages of fire hydrant diaphragm
The required dimensions of the inner diameter of the diaphragm are calculated rather inaccurately, with a large error.
The diaphragm for fire hydrants is a washer with a certain internal diameter, which is installed at the outlet of the fire hydrant valve. The purpose of the diaphragm is to limit the pressure between the fire hydrant itself and the connection head.
The fire hydrant diaphragm (stainless steel) Du-50 and Du-65 is a washer with a certain inner diameter, which is installed at the outlet of the fire hydrant valve.
We make any inner size of the diaphragm according to the customer's request: 12, 15, 20 mm, etc.
There are a number of requirements for internal fire water pipelines that they must comply with. If the fire hydrant has a head of more than 40 m between the faucet itself and the connection head, it is necessary to provide for the installation of such an element as the fire hydrant diaphragm. This is necessary in order to ensure the safety of working with a fire hose.
So what is a fire hydrant diaphragm?
The diaphragm is a washer made of stainless steel 3 mm thick, with a certain inner and outer diameter. The diaphragm is installed at the outlet of the fire hydrant directly between the faucet and the connecting head. The diaphragm is used to reduce excess pressure in fire water supply systems. By installing diaphragms to reduce excess pressure, the water pressure at fire hydrants on all floors of the building is regulated. Thus, in the event of a fire, with the simultaneous opening of fire hydrants on different floors, the water pressure will be the same everywhere.
Pumps K 20/18a create a pressure in networks that exceeds the maximum allowable
45 m p.6.7 for 5 m, pumps K 45/30 - for 20 m.
To reduce the hydrostatic pressure at fire hydrants on floors 1–7, we plan to install diaphragms.
Fire hydrants on the 1st floor are located at a height of 2.35 m from the ground, and each higher one is 2.8 m higher than the lower one. The values of the excess hydrostatic head for fire hydrants are equal to the difference between the excess pressure in the network and the geometric height of the faucets. The aperture diameter of the diaphragms is determined by the nomogram, hell. 5 . Diaphragms are installed between connecting heads and fire hydrants.
The calculation results are shown in Table 9.
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Table 9 Calculation of Diameters of Diaphragm Holes |
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Floor number |
The value of the excess pressure at the PC and connections, Nsr, m |
Diaphragm hole diameter, mm |
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Household drinking water supply |
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5 - 2,35 = 2,65 | ||||||||
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Hoz-fire-fighting plumbing |
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hot plumbing |
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To reduce the excess hydrostatic head in the hot water supply network at the water taps on floors 1–7, in accordance with the recommendations of clause 10.9, we provide for the installation of pressure regulators KFRD-10-2.0 on the connections to the apartments. The pressure after the regulator is 0.05 MPa (5 m).
5. Calculation and design of sewerage
When designing the internal sewerage of buildings, they are guided by the requirements. In a residential building, we design a domestic sewerage system for draining wastewater from sinks, washbasins, bathtubs, toilet bowls installed in kitchens and bathrooms. The diameters of the outlet pipes from sanitary appliances are assigned not less than those given in Appendix 2. We lay pipes with a slope of 0.03 with a nominal diameter
50 mm and 0.02 at 100 mm. We assign the diameter of the riser not less than the largest diameter of the outlet pipes attached to it and check for the passage of the calculated flow rate p.18.5.
The maximum second flow rate of wastewater q s , l/s, is determined in accordance with paragraph 3.5 by the formulas
a) with a total maximum second water flow in a building or structure q tot 8 l / s
b) at qtot 8 l/s
, l/s.
the value 
- the flow rate of wastewater from a sanitary appliance, l / s, is taken in accordance with Appendix 2. The device with the highest water discharge is taken as the calculated one.
The outlet diameter in accordance with clause 17.29 is assigned not less than the largest diameter of the risers attached to it.
For the designed residential building, we provide for the installation of an internal sewer network (drain pipes and risers), as well as sections laid in the basement, and outlets from low-pressure polyethylene pipes HDPE according to GOST 22689.2-89 with a diameter of 50 mm and 110 mm for outlet pipes, 110 mm for risers.
The calculation of sewer pipelines should be carried out in accordance with clause 18.2, assigning the fluid velocity V, m / s, and filling H / d in such a way that the condition is met
,
taking K = 0.5 - for plastic pipelines.
In this case, the velocity of the liquid must be at least 0.7 m/s, and the filling of pipelines must be at least 0.3.
We check the assigned pipe diameters for the passage of estimated costs by hydraulic calculation.
Total maximum flow per second q tot = 4.05 l/s* (Table 1), i.e. less
8 l/s. Therefore, the estimated wastewater consumption is determined by the formula
, l/s.
