Design of sewage systems

A sewage system is one of the most important engineering systems of a building. It shall be calculated at the stage of engineering of the whole object. All sanitary-engineering systems shall be engineered according to the current building rules, namely the building norm 60.13330.2012 “Internal water supply and sewage systems of buildings”.

The sewage system is divided into the following types depending on their functions:

• Sanitary sewer systems – wastes disposal from toilet bowls, sinks, showers, etc;
• Industrial sewage systems – wastes disposal from production processes;
• Combined sewage systems – wastes disposal of both types (for the premises where these systems may be used separately);
• Internal downpipes – disposal of rain waters from the roof.

What are precise calculations necessary for? Any sanitary or industrial waste waters contain lots of hazardous microorganisms, bacteria and viruses. Mistakes in an engineered project which are followed by the mounting mistakes result in forming stagnate zones and pipe-lines clogging. Such a sewage system may result in spreading unpleasant odors along the building, forming leaks and breaking joints of the pipe-lines.

The sewage systems engineering stage requires calculations of both dismantling and repairing processes as well as cleaning the clogged areas. Clogs or obstructions are cleaned by means of cleanout pipes and inspection fittings which are installed on the pipe-lines. Their amount and installation spots are regulated in the correspondent documents. Inspection fittings and cleanout pipes are necessary for installation on the waste water leaders – at the building output, on the highest floor and in the buildings whose height is more than 5 floors each 3 floors. Installation of the mentioned fittings is also obligatory at the beginning of horizontal areas and on the curves of pipe-lines.

Sewage system consumptions, diameters of water risers and main pipes as well as slopes of the installed pipes – all these parameters shall be calculated. Materials of the pipe-lines shall also be considered. Polymer pipes made from polyvinylchloride or polypropylene homopolymer butylene are mostly used in the modern construction. They are durable, corrosion resistant, lightweight and easy for assembly and transportation. Polymer materials do not corrode when in contacted with water, that’s why pipe-lines made of polymer are less corrosive. The disadvantage of such systems is that a polyvinylchloride sewage system may flow waste waters with the maximum temperature +60°C. Some manufacturers of polypropylene pipes extend this rate up to +95°C. Cast iron pipes are also durable. They are also corrosion resistant and may be used on industrial objects and in the premises with high fire precautions required. Unlike cast iron pipes which were used in the past the modern make the assembly period shorter. However, a proper installation requires the use of fittings which are sometimes more expensive than the cast iron pipes. The weight of cast iron pipes is more than that of polymer pipes.

Depending on the functions sewage systems are divided into forced and flow-free systems. The type and material of pipe-lines is chosen at the stage of engineering according to the object type, customer’s needs and calculations.

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