Calculation of the sewage system for a private house is an important preliminary stage of the installation of a sewage pipe, which is necessary in order to avoid such problems as frequent pipe clogging, unpleasant odors and flooding of residential premises in the future.
Sewerage system design
At this stage, the following manipulations are performed:
- On the diagram of the built house, the location of plumbing and household appliances - washbasins, bathtubs, washing machines and dishwashers is noted.
- All drainage points in the graphic image are connected by pipe lines indicating their real length and internal diameter.
- The layout of the site plan the location of the external sewer network. At the same time, yard communications for draining drains flowing into the collector or septic tank must go to their final point at the smallest distance, without sharp and sharp turns.
- According to the requirements of SNiP 2.07.01-89, the laid sewage system must be located horizontally (in the light) not less than 1.5 m from the domestic water supply, underground gas pipe; 0.5 m from communication lines and power cables.
In the absence of a city sewage disposal network near the house, the end point of the yard communications is a septic tank (sedimentary and filtration well) - it is located on the outskirts of the site, near the entrance gate or road. At the same time, the distance from it to the nearest building should be at least 5 m.
Pipe selection
During the laying of the sewerage of a private house, circular water flows with an internal diameter of 40 to 110 mm from polyvinyl chloride wastewater resistant to the aggressive environment are used. Since various plumbing and household appliances are characterized by an unequal volume of drains, varying in consistency and composition, pipes with the following internal diameters are used:
- washbasins, kitchen sinks - 40-50 mm;
- bathtubs, shower trays - 50 mm;
- washing and dishwashers - 50 mm;
- urinals, bidet - 50 mm;
- toilet bowls - 110 mm.
If a private residential building has 2 or more floors, the upper bathrooms are connected to the lower sewers using vertically arranged communications - risers - with an inner diameter of 110 mm.
For the yard drainage network, a special bright orange flow is used, with a nominal passage of 110 or 160 mm.
Optimum pipe slope
This characteristic is important in simple non-pressure sewers, as it affects the speed of runoff and the performance of the system. Usually it is expressed in centimeters per meter of water flow or in% (the difference in height of the ends of the meter communication of 1 cm means that its slope is 1%).
The slope of the pipes depends on their diameter and on average for the following sizes is:
- 50 mm - 3 cm / 1 m (3%);
- 110 mm - 2 cm / 1 m (2%);
- 160 mm - 0.8 cm / 1m (0.8%).
With a small slope, the flow will be slow and the pipe will quickly become silted with heavy particles settling at its bottom. Too large a slope of communications also negatively affects their normal functioning - discharge of a significant amount of effluents will lead to their delamination and adhesion of a heavy fraction along the contour of the inner walls of the water flow.
A negative bias is strictly unacceptable, in which the water flow is directed not towards the main flow, but in the opposite direction.
Calculation of the volume of a septic tank
The required capacity of a simple stand-alone 2-chamber wastewater collector is calculated as follows:
Vseptic tank= 0.2 × KZh × 3 × 1.2, where:
- Vseptic - the volume of a septic tank, l;
- KZ - the number of residents in the house, people;
- 0.2 - average daily water consumption per 1 person (200 l or 0.2 m3);
- 3 - coefficient determining that the septic tank should accommodate a three-day sewage drain from all residents;
- 1,2 - correction factor used to increase the septic tank capacity by 20%, which is occupied by solid sediment falling to the bottom.
Calculation example:
For a family of three people, the volume of a septic tank is V septic = 0.2 × 3 × 3 × 1.2 = 2.16 cbm
It is unacceptable to use a simple, cesspool with unclad bricks for draining domestic wastewater. Sewage falling into it, being absorbed into the vertical earthen stratum, will intensively pollute the soil and groundwater. It is most beneficial and convenient to use such a reinforced concrete structure as a well ring with a diameter of 1 -1.5 m for arranging septic tank chambers.
Storm sewer design
In addition to the wastewater coming from the building, it is necessary to remove precipitation from the site. For these purposes, a special storm sewer (stormwater) is used, consisting of open gutters (ground gutters) that divert a large amount of water into the central special city collector, a separate home well, and an open gutter located near a pond.
It is strictly forbidden to dump such effluents into a household septic tank - in the case of frequent and intense rainfall, it will quickly fill up and become clogged with sand and soil contained in the water.
Calculation of storm sewage, necessary for the proper design of a sewage system, is carried out according to the following formula:
Vstorm drains= Fr. ×S× φ, where:
- V effluent - the amount of storm water that must be diverted using the sewer;
- Fr. - the intensity of precipitation falling in the region (l / s);
- S - area from which storm water will be collected for discharge into the sewer, ha;
- φ is the coefficient of water absorption of the material from which runoff will be produced.
Based on the calculations, a drainage open tray with a certain flow area is selected.
Calculation Example:
It is necessary to calculate the volume of storm water and select the optimal cross-sectional view of the drainage trays for a fully concrete section (φ of concrete = 0.85) located in the Moscow Region (Osr. = 80l / s) with an area of 500 m2 (0.05 ha) with a house having a roof (φ = 1) with an area of 60 m2 (0.006 ha).
V drainage runoff = (Rev. × S × φ) of the section + (Rev. × S × φ) of the roof. = (80 × 0.05 × 0.85) + (80 × 0.006 × 1) = 3.88 L / s.
Based on this amount of precipitation, a sewage storm chute is selected, which is able to pass through a volume of water 20-25% higher than the result when heavy rains occur.
Water throughput of various land gutters.
| Type of a drainage tray | Cross section, mm | Water throughput with a slope of 5 mm / 1m (0.5%), l / sec. |
| Plastic | 140 | 5,1 |
| Concrete | 136 | 5,2 |
| Polymer concrete | 92 | 5,0 |
| Polymer sand | 102 | 5,7 |
Using the above table, it can be said that storm sewage from plastic trays with a passage section of 140 mm and a water throughput of 5.1 l / s will be most effective.
You can perform the design and calculate the values of the main indicators for the sewerage of a private house yourself, following the recommendations and rules described above. If you need a more accurate hydraulic calculation of these communications, you should contact a highly specialized design organization.
