Water distribution system
The distribution of service and drinking water mostly takes place in a permanently installed water distribution system . This includes facilities for storage, pressure increase, distribution, quantity measurement and withdrawal. It may be necessary to take measures to treat the water before it is fed into the water distribution system. A distribution system must be designed in such a way that the required quantity is available in the required quality and with the correct pressure .
The comprehensive supply of clean drinking water was systematically organized from the second half of the 19th century onwards with water towers and pipes connected to them, with which sufficient amounts of water and the required pressure could be provided.
Regional differences
In Germany, the requirements for the distribution system for the distribution of drinking water are specified in the worksheets of DVGW e. V. established. In general, the municipal drinking water requirement is calculated taking into account the fire extinguishing event, since the public drinking water network usually also serves as the central fire water supply for cities or municipalities. According to Section 17 (2) of the Drinking Water Ordinance , the pipes for drinking water and rainwater must be permanently marked in different colors in Germany . Rainwater harvesting systems must not be connected directly to the house installation.
Elements of water distribution
storage
To store water in distribution systems, various forms of water storage can be used, which can differ from one another in terms of their location in the network and their design.
Pumping stations and pressure boosting systems
Pumping stations are used for pumping water. These can either convey directly into the network or into containers, on the other hand serve to increase pressure. As pumps usually come centrifugal pumps used. Piston pumps are to be regarded as historical. Centrifugal pumps can be operated at a constant speed or at a variable speed. Larger pumping stations usually have several pumps that can be arranged in two forms:
- pumps connected in parallel increase the delivery rate,
- Pumps connected in series increase the pressure and thus the delivery head.
The following methods are used to control the pumps:
- Two-point control according to the water level in an elevated tank,
- Controls taking into account the pressure in the supply network (on / off of pumps, change of speed).
To avoid pressure shocks in the pipe network are either surge tank (closed tank in which pressure surges are buffered by a volume of air) or suitable approach strategies speed-controlled pumps required. If the supply pressure of the network is not sufficient on site , the pressure required to supply all floors can be generated on and in the buildings by means of appropriate pressure boosting systems (DEA).
Penstocks
Line materials
Cast iron , steel and various plastics such as polyethylene , mostly PEHD, high-density polyethylene or polyvinyl chloride are used as pipe materials in drinking water . Lead pipes have not been used since 1973 because of their toxic effects and have been almost completely removed from the nets. In a few cases, house connection lines are still available as lead lines, but these had to be replaced by 2013 in order to comply with the limit value for lead according to the Drinking Water Ordinance , which came into force on December 1, 2013 . Asbestos-cement pipes are removed again under strict conditions, since there is a high risk of lung cancer from asbestos fibers that are absorbed through breathing. According to WHO studies, there is generally no health risk from asbestos fibers in drinking water, since asbestos fibers only pose a health risk if they are absorbed via the respiratory tract. The absorption of asbestos fibers from drinking water via the air requires very high asbestos concentrations in the water, which according to studies by the DVGW are unlikely, at least in German drinking water.
Supply pressure
For drinking water in the communal area, the pressure in the center of gravity of a pressure zone should be 6 bar . At the same time, there should be a minimum pressure of 1 bar at the most unfavorably located extraction point in the distribution network. As a rule, the highest static pressure is 8 bar and the highest system pressure 10 bar, the difference of 2 bar serves as protection against pressure surges. For buildings, depending on the number of floors, certain minimum pressures are prescribed at the point of transfer to the consumer. These requirements are different for new and existing networks. Usually the pressure should be 2 bar (ground floor) + 0.5 bar per upper floor. House pressure boosting systems may therefore have to be provided for higher buildings. Distribution systems without direct consumers can also be operated with pressure values above 10 bar, but the pressure should be reduced accordingly when the water is handed over to the customer.
Flow rate
The flow rate should be chosen so that, on the one hand, the pressure losses remain low (low speed) and, on the other hand, the dwell time does not become too long (recontamination, increase in temperature, impaired taste). The DVGW regulations specify the guideline value for an average hourly flow rate of greater than or equal to 0.005 m / s (432 m / d).
Pipeline construction
The pipes can be connected to pipelines either with welds or with fittings . Open trenches ( trenches ), tunnels or underground pipe jacking by pressing or flushing into the ground can be used for laying. Pipelines laid underground must be properly bedded in sand to avoid damage.
Gravity channels
Water can also be transported in canals with a clear water level ( gravity pipeline ). If necessary, are aqueducts required. Large water transport lines using gravity channels are, however, supplemented by culverts , i.e. pressurized pipelines for crossing valleys.
Fittings and water measuring devices
In the course of the pipeline network are slide , swing check valves , non-return valve , pressure limiter , venting equipment hydrants , withdrawals valves , pressure gauges and household connections with water House lead and water meters as necessary required.
Network forms
There are two basic types of networks: branching networks and meshed networks.
Branch networks are distribution networks that have a tree-like structure. This type of network has the advantage of clear flow conditions and less construction costs than meshed networks. The disadvantage lies in the high susceptibility of the system to failure, since all downstream power supply units can no longer be supplied in the event of an interruption in operation. Long-distance networks and local network parts in peripheral areas are often designed as branching networks. Further examples are the cold water distribution systems in house installations.
Meshed networks consist of individual strands linked together. The high security of supply in the event of malfunctions and peak loads such as the extraction of extinguishing water is advantageous. The disadvantages of this type of network are, in contrast to branching networks, the higher construction costs and less clear flow conditions. This type of network is used for most local networks. Ring line networks are a special form; In these, an attempt is made to establish a clear flow direction in the ring lines encompassing the distribution network. For this purpose, for example, transport lines encompassing a local area or, less often, installations such as non-return valves are used.
literature
- DVGW e. V .: Water transport and distribution . Oldenbourg Industrieverlag, Munich 1999, ISBN 3-486-26219-X .
- DVGW e. V .: Technical rules worksheet W 400-1, Technical rules for water distribution systems (TRWV) Part 1: Planning . DVGW German Association of the Gas and Water Industry e. V., Bonn 2013, ISSN 0176-3504 .
- DVGW e. V .: Technical information note W 401, decision aids for the rehabilitation of water pipe networks . DVGW German Association of the Gas and Water Industry e. V., Bonn 1997, ISSN 0176-3490 .
- Johann Mutschmann, Fritz Stimmelmayr: Pocket book of water supply . 13th edition. Vieweg, Braunschweig / Wiesbaden 2002, ISBN 3-528-22554-8 .
Individual evidence
- ↑ Archive link ( Memento from August 19, 2014 in the Internet Archive ) Wasserinformation Nr. 40 9/93 Investigation of asbestos fibers in drinking water. P. 5.