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:Slovak term: [[Slovenský termín]]
# Back water valve, sometimes referred to as a reflux valve or surcharge protection device, is a device used in drainage systems which only permits the drain to flow in one direction. It has a check valve arrangement which closes against any reverse flow. (American Society of Sanitary Engineering 2007).
# A device for preventing sewage or drainage water from flowing back into a building in the event of flooding or sewer blockage (WHO 2006).

==Explanation==
A back water valve, sometimes referred to as a reflux valve, surcharge protection device or
a blackflow prevention device, is designed to prevent any reverse flows of sewage, usually
from a public sewer network operator’s asset into a private property. The reverse flow of
sewage can be caused by a number of factors including; sewage backpressure due to
blockages, or from storm water overloading, or from a sewer system which is undersized.

The highest risk is usually at the lowest elevation in a sewer network. Properties at the foot
of hills are more vulnerable than those at the top.

In high risk or flood prone areas, plumbing codes may make the installation of a back water
valve a mandatory requirement (World Plumbing Council Working Group 2008).

==Example==
A back water valve or surcharge protection device is usually installed at the property
boundary. It may be required at the property owner’s expense, or installed by the public
sewer network operator. The valve is required when a property is connected to a sewer
which is receiving discharges from connections at a higher elevation. The lower property is
at a higher risk of flooding if the sewer system fails. (Standards Australia/Standards New
Zealand 2003).
A back water valve is also required where a sewer system is designed to drain storm water,
or where illegal storm water connections have been made to sewer. This sewer is then at
risk of overloading at times of storm activity. The lower property is again at a higher risk of
flooding (World Plumbing Council Working Group 2008).

==References==
* American Society of Sanitary Engineering (2007) Plumbing Dictionary. Sixth Edition
* Standards Australia/Standards New Zealand (2003) Plumbing and drainage. Part 0:
* Glossary of terms. AS/NZS 3500.0:2003
* WHO (2006) [http://www.who.int/water_sanitation_health/publications/plumbinghealthasp/en/ Health aspects of plumbing]

==Links==
* [http://apps.who.int/thelexicon/ WHO — The Health and Environment Lexicon]

[[Category:EN]]

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Back water valve - História úprav

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