The sewerage system is divided into two parts: internal and external. Internal system consists of outlets (from bathtubs, showers, sinks, toilets), a riser and outlet from the house. The external system consists of a pipeline and a storage tank or septic tank. The internal pipeline, in turn, can be divided into vertical (risers) and horizontal (branches).
Sewage pipes
The vertical part requires ventilation and protection from clogging. Horizontal sections They are called so conventionally, since in practice they are mounted at a certain angle relative to the horizontal surface.
The norm for the slope of sewer pipes is snip 2.0401-85. This document also defines the conditions for installing the system from the exit from the house to the first well, which must be located no less than 12 m apart.
Calculation of the slope of a sewer pipe: basic concepts
If the sewage system is gravity-flowing, then its efficiency in transporting wastewater due to the laws of gravity depends entirely on the angle of inclination. It is believed that wastewater should move through the pipeline at a speed of 0.7-1 m/s. Only in this case is the flow able to remove solid particles from the system. To maintain the flow rate, for each separate diameter you need to calculate the slope angle sewer pipe.
At first glance, it may seem that the angle should be measured in degrees. But in building codes and sewerage reference books, this parameter is defined as a decimal fraction. These figures reflect the ratio of the level reduction to the length of a certain pipeline section.
For example, on a section of pipeline 5 m long, one end is 30 cm lower than the other. In this case, the slope of the sewer pipe will be 0.30/5=0.06.
Formula - determining the maximum, minimum value
Formula for calculating the slope of a sewer pipe wherein:
- V speed of fluid flow (m/s);
- H pipeline filling;
- d pipe diameter;
- K is the calculated slope coefficient.
To determine the coefficient (slope), you can substitute V = 0.7-1, d - the value of the diameter of a specific section of the pipeline, H = 0.6xd (according to building codes and regulations). It turns out that for a pipeline with a diameter of 100 mm per meter a slope of 2 cm is required, with a diameter of 50 mm - 3 cm per meter.
From the formula it is clear that the flow rate of wastewater directly depends on the angle of inclination (coefficient). For optimal speed, a minimum sewer pipe slope of 0.02 and a maximum of 0.03 is required. If the tilt is less than 0.02, large particles will settle and form a blockage.
If the roll is too great, the speed will increase, which will also lead to the formation of precipitation, since the water will flow away too quickly, not having time to take away heavy waste particles with it. Increasing the flow rate can also lead to failure of siphons and constipation.
Necessary standards in the apartment
When installing a sewer system, there is no need to use a formula for calculations. There is a table that defines the slopes for all outlets from plumbing fixtures.
| Optimal slope of sewer pipes in an apartment | |||
| Device | Drain diameter (mm) | Distance to siphon (cm) | Incline |
| Bath | 40 | 100-130 | 0.033 |
| Shower | 40 | 150-170 | 0,029 |
| Toilet | 100 | No more than 600 | 0,05 |
| Sink | 40 | Up to 80 | 0,08 |
| Bidet | 30-40 | 70-100 | 0,05 |
| Washing | 30-40 | 130-150 | 0,02 |
| Combined drain for bath, sink and shower |
50 | 170-230 | 0,029 |
| Riser | 100 | ||
| Branch from the riser | 65-754 | ||
Each section of the sewerage system in the apartment must have a siphon at the end in the form of a device or a bend so that unpleasant odors do not enter the premises. To determine the required values, the principle of the golden mean is important - 1.5-2.5 cm per meter. This is quite enough for an apartment or country house. The use of formulas is necessary when constructing large facilities with a maximum volume of wastewater.
In addition, the formula is difficult to use for domestic sewerage, since there is no constant flow. Here it is better to pay attention to another indicator - the ability to self-clean (remove solid particles).
Since domestic wastewater contains waste of different weights, the determining factor for heavy components is the flow speed, for floating ones - the filling of the diameter of the system. When determining the correct slope, it should be taken into account that it will be different in each individual area.
Slope of the external and internal parts of the system
In private country house It is necessary to arrange not only internal, but also external sewerage. In addition, outlets are needed for water that is formed as a result of melting snow and precipitation in the form of rain. Storm drainage can be installed together with the main system or separately.
The slope of the internal sewer pipe is strikingly different from the same indicator outdoor system. Pipe products are required for storm drainage large diameter(from 100 mm) and gratings, since various contaminants of plant origin will certainly get into this system. Sewer slope for storm water should also be greater - 0.05-0.07, but no more than 0.15.
External waste from the house is usually directed to a central sewer or septic tank and is laid underground. The diameter of this pipeline is most often 100-150 mm. Minimum slope- 0.02. Based on this, you should dig a trench. If at earthworks If there are any inaccuracies, the situation can be corrected using a sand cushion.
Any sewerage system must provide unimpeded flow for drains and guarantee high level self-cleaning. You should definitely take into account that the standards and textbooks indicate average indicators, so common sense and practicality will never hurt.
Discharge of sewage into the city sewer system or into an autonomous septic tank is carried out through pipes by gravity. Therefore, it is important to maintain a slope of sewer pipes of 1 meter in accordance with the requirements of SNiP. The normal operation of the drainage system is influenced by a number of factors, from diameter and material to location: internal wiring or external.
General information
The main task when arranging sewer system consists in configuring the pipeline in such a way that wastewater, including liquid and solid fractions, passes without being delayed or creating blockages and traffic jams. It is necessary to observe the inclination of the pipes through which, under the influence of gravity, wastewater will immediately flow into the collector and further to treatment plants.
Requirements for the organization of internal and external sewerage, required slopes and other parameters are strictly specified in SNiP SNiP 2.04.01-85 “BUILDING STANDARDS AND RULES FOR INTERNAL WATER PIPING AND SEWERAGE OF BUILDINGS” and SNiP 2.04.03-85 “SEWERAGE. EXTERNAL NETWORKS AND STRUCTURES".
Behind established standards It is not a strict calculation that matters, but the result of tests and observations. The nature of the wastewater and its consistency is not constant, but the sewage system must work without failures. It is necessary to exclude or minimize the sedimentation of solid inclusions and sludge on the walls of the channel, to ensure that the sewer system operates silently, preventing reverse flow and ingress unpleasant odors back to the room.
It has been established that at a speed of movement of wastewater of 0.7 m/s, water flows evenly and solid inclusions more easily follow the flow of liquid, without staying in one place. This is provided that the diameter is selected so that with a normal number of drains for a given connection, they are filled by approximately 50-60%, but not less than a third.
The basic formula, obtained empirically based on observations, is:
where V is the flow rate of the wastewater, H is the height of the level of the wastewater in the pipe, d is the diameter of the pipe, K is the slope coefficient, the value of which is a reference value established depending on the material of the pipes.
K = 0.5 for plastic and glass.
K = 0.6 for other materials (steel, cast iron, asbestos cement).
The coefficient depends on the roughness of the inner surface and the resistance created by the fluid flow.
If the slope is too great, the water will drain quickly and solids will settle on the surface of the pipe, creating a blockage. With a large slope, the flow of water will be turbulent with turbulent noise and increased air vacuum in the upper part of the pipe, which will lead to breakage of shut-off valves, breakdown of siphons, or, at a minimum, retraction of the water seal and the flow of gases from the sewer into the room. A build-up will form on turns.
If the slope is too shallow or absent, then heavy fractions will have time to settle on the surface and ultimately cause a blockage. Since water cannot quickly travel the entire route to the discharge point, there will be an overflow when the next portion arrives.
There are two conditions for pipes to ensure normal functioning of the sewer system:
- The diameter is selected based on the average volume of waste.
- The slope is determined to ensure an optimal flow speed of 0.7 m/s.
Permissible deviations are different for external and internal networks, since the priorities are different. In the first case, to put it simply, the sewage system should not be heard, and without the appearance of unpleasant odors. For external installations, the priority is uninterrupted operation, which does not require constant monitoring and cleaning.
Slope depending on diameter
The speed of the flow of waste and the fullness of the pipe are important so that they flow freely into the collector or septic tank. However, both of these points depend on the size of the pipe itself and the volume of waste, and the diameter is selected based on the average daily volume of waste and filling the pipes by 50-60%, but not less than a third at a speed of 0.7 m/s.
Any calculations come down to choosing one of the standard sizes: 50, 80, 100, 150, 200 mm. In practice, all that remains is to clarify the slope for each standard size and the limits of permissible error.
The slope is defined in SNiP as a fractional coefficient. The value is determined by the ratio of the length to the required distance between the top and bottom points at the edges. The coefficient is numerically equal to the difference in height between the edges of a one-meter long pipe, expressed in meters.
To get the slope of a sewer pipe of the same diameter on a flat area, you need to multiply the length by the slope coefficient. If the result is multiplied by an additional 100, you get the value in centimeters.
Why is the angle of inclination different for different diameters? To comply with the requirement for the flow rate of wastewater.
A pipe with a diameter of 50 mm has much less volume, if only the fullness is taken into account, but the contact of water with the surface increases, compared to 150 and 200 mm. A pipe with a smaller cross-section is placed at a large angle so that water flows down it at the required speed and takes solid inclusions with it.
However, this only applies general requirements to the formation of internal and external sewerage and slope on flat, extended areas in the absence of direct connection to siphons, outlet pipes, etc. There are a number of rules used for fittings and connection points.
Internal
Pipe slope:
- D 40 mm – 0.035;
- D 50 mm – 0.03;
- D 80 mm – 0.2;
- D 100 mm – 0.015.
In internal sewerage pipes with a diameter of 40, 50, 80 mm are used, and a diameter of 100 mm is used for common area at the connection point where the lines meet.
Adapters from one diameter to another are mounted so as to make straight line along the very bottom, creating a continuous channel for drainage. The slopes on different sides of the adapter are set according to their coefficient value.
The required slope is formed by the fasteners on which the pipe rests, or by the inclination of the groove or box in which the sewer will be sewn up.
An area of up to 1.5 meters from the sink drain or connection household appliances can be laid in any way while maintaining the required slope from the drain to the sewer pipe.
The turn to the sewer pipe line must be formed by an elbow or tee with a slope of 67 degrees. The slope of the elbow or the top of the knee is oriented along the route towards the riser.
The connection to the riser must be formed by a cross or tee with a branch inclination of 67 (87) degrees. It is advisable to replace rectangular tees, which can still be found in apartment buildings when replacing internal sewerage.
Slope diagram of tees and sewer turns Outdoor
Pipe slope:
- D 100 mm – 0.012;
- D 150 mm – 0.01;
- D 200 mm – 0.07.
The external sewer line from the house to the discharge point must be in the same plane and with the same slope along its entire length. Combining several pipe diameters or having transitions in the slope of the line is not allowed. If for some reason it is necessary to deviate from this rule, then a manhole is formed at the junction of various sections.
To form the required angle of descent, it is advisable to dig the trench itself taking into account the increase in depth. Be sure to select soil 20-25 cm deeper than the sewerage system requires to form a sand cushion. After this, part of the sand is poured in, and supports are formed under each separate element. Next, the rest of the sand is poured with compaction.
How to set the pipe angle
The easiest way– using a bubble level with additional risks. If the flask with a bubble has three lines on each side, then this level is just right. Each line corresponds to a slope of 1 cm per meter.
The tool is fixed on top of the pipe, and then, using pads, the slope is set so that the bubble touches the desired mark.
Second way- This is a measurement of the distance from the horizontal plane of the ends of the site. The ratio of the length of the pipe and the lifting height of the upper side corresponds to the required slope coefficient.
Third way This is the leveling of two marks along the edges of the route. A thread or twine is stretched between them, which is used to guide when drawing up the pipeline.
Most visual way - use laser level And laser level to construct the required plane. This will especially help when laying pipes in a groove and lining them in walls using a box.
What is a properly selected slope sewer pipelines for a private home? This is primarily 50% freshness in the bathroom. And secondly, there is a lot of free time that would have to be spent on cleaning pipes. Indeed, if the slope of the sewer pipes is insufficient, solid particles gradually accumulate in them due to friction forces, which will ultimately lead to blockage.
In case it's too large slope the likelihood of leaks will increase, and the noise level will also rise. In addition, separation of the liquid into fractions is inevitable. In other words, particulate matter will settle at the bottom of pipes, since their speed is significantly less than the speed of water.
Recommended pipe slope values can be found in SNiPs 2.04.03-85 (SP 32.13330.2012). "Sewerage, external networks and structures" and 2.04.01-85* (SP 30.13330.2012) "Internal water supply and sewerage of buildings." Since they contain information about maximum and minimum pipe slopes for external and internal sewerage. But if the goal is to lay a sewer system in a private house to a septic tank or cesspool, then the latest regulatory document will be sufficient.
Slope of external sewer pipes
The values for the minimum slope of pipes for external sewerage can be found in paragraph 5.5. SP 32.13330.2012. So, according to it, the minimum slopes of pipelines and channels for the following pipe diameters must be taken:
- 150 mm- from 0.007 to 0.008 (7-8 mm per 1 m);
- 200 mm- from 0.005 to 0.007 (5-7 mm per 1 m).
In general, for gravity flow systems this parameter depends on the speed of wastewater movement and does not depend on the total volume of liquid.
As for the maximum slope of pipelines, it is 0.15, provided that the pipe is longer than 1.5 meters.
Slope of internal sewerage pipes
The smallest slope for internal pipelines is determined in the following paragraphs of SP 30.13330.2012. Thus, clause 8.3.2 states that in non-pressure sewer networks, where the liquid must move by gravity, the slope must be at least 1/D (D - outside diameter pipes in millimeters). Also in this regulatory document there is clause 8.6.6, which limits the minimum slope of overhead pipelines to 0.005.
The maximum value of the pipeline slope here is limited to 0.15 (15 cm per 1 meter). But experts still recommend laying sewer pipes with a slope of 0.04-0.07 or 4-7 cm per 1 meter.
Next I would like to present two tables in which you can find not only the minimum and maximum slope values for the internal water supply, but also its optimal values when connecting to various sanitary fixtures.
Table 1. Limit values for the slope of sewer pipes depending on their diameter.
Table 2. Optimal pipe slope for plumbing fixtures.
Example
Calculation of the slope of sewer pipes
All of the above was the definition optimal slope sewer pipes without calculation (well, or almost without calculation). But this parameter can also be determined using a special calculation, depending on the speed of fluid movement, the diameter of the pipes and the level of filling of the pipelines. True, it's very long and tedious process, which is usually resorted to in the case large systems sewerage (industrial facilities, central sewerage for multi-storey buildings, etc.). Those interested can use the formula presented in paragraph 8.3.2. SP 30.13330.2012 or the Callbrook-White formula.
At the design stage, and then during installation, it is necessary to strictly observe the angle of inclination of the sewer pipes. And it doesn’t matter whether it’s an internal sewer or a pipe, the pipeline must have a slope.
This is due to the fact that the sewer system in most cases is gravity-fed, that is, wastewater is delivered to the treatment plant under the influence of gravity. Even a slight deviation from the standards will lead to the malfunction of the entire system.
What is the pipe angle
Pipe angle - change work surface relative to the horizon. In standard measuring systems, it is customary to measure angles in degrees, while the slope of pipelines is measured in centimeters per 1 meter.
How to calculate slope
There are two methods for calculating the angle of inclination of sewer pipes: calculated and non-calculated.
The calculation method is used for sewerage with constant wastewater pressure and, in turn, has two methods:
- calculation in accordance with the speed of movement of wastewater through the pipeline to the standard coefficient;
- Callbrook-White formula.
Pipe diameter
When laying internal sewerage, the correctly selected pipe diameter plays an important role. When choosing, you should be guided by the following parameters:
- The cross-section of the pipe must coincide with the pipe drain hole plumbing fixture;
- the permeability of the pipe depends on the diameter, that is, for a pipe with a diameter of 200 mm, the useful volume is 2 times greater than for a pipe with a cross-section of 110 mm;
- When draining water, the pipes should not be completely filled.
Slope angle according to SNiP
This method is suitable for large sewer networks. For small systems, the recommended values from SNiP are used. In this reference book you can find out the minimum and maximum values of the sewer slope angle.
Minimum slope
When installing an external sewer system, it is necessary to adhere to the minimum value - 0.015 m per 1 linear meter.
On a note!
When the minimum angle is reduced, solid and heavy particles will remain inside the pipeline and interfere with the passage of liquid (they will create a blockage).
The internal sewerage pipeline is made following the same parameters. As an exception, it is allowed to reduce these values in areas of less than 1 meter. In such areas, you can make a slope of 0.01 m. However, the risk of blockage increases significantly.
Maximum angle
The maximum permissible slope depends on the speed of passage of the wastewater. The flow velocity in should not be more than 1.5 m ⁄ s.
As the speed increases, solid particles will settle on the surface of the pipes, since their speed is less than the speed of the liquid. Therefore, the maximum slope angle should not exceed the recommended values by more than 3%.
Slope of the internal sewerage pipeline
To install the system inside the house, use a pipe with a diameter of 50 to 110 mm. The slope angle is taken from the reference book and is the same for home, country or production systems. To avoid complex calculations, you can use the table of inclination angles.
When calculating this data, all necessary parameters were taken into account:
- internal section;
- flow speed;
- fluid viscosity;
- smoothness of the walls.
Slope for sewer pipelines of different diameters
In conclusion, it’s worth adding a few tips:
- Lay the pipeline taking into account natural shrinkage. Over time, the pipe may bend or sag, which means it will need adjustment, and this requires space.
- Connect the pipes at an angle of at least 120 degrees. If such an angle cannot be set, install additional inspection hatches.
- When connecting, ensure that the pipeline is sealed.
- Try to avoid unnecessary joints and turns. Remember - than simpler system, the less likely it is to break.
When designing a sewer system, try to route the pipeline along shortest path. Don’t be afraid to seek advice; with the help of specialists you will get reliable, high-quality and efficient system sewerage.
Video: How to lay a sewer pipe, slopes and bends, do-it-yourself sewerage