bcd02_groundworks 29/1/10 10:50 Page 3
Protecting Drains
eter Jennings, Technical
P
Director ACO Building
Drainage, discusses the
options available for
protecting drains from flooding
and backflow
Flooding is rapidly becoming a major issue
challenging planners, national and local
government, builders and architects.
The incidence of homes and public buildings Backflow valves are designed to be installed
being damaged by flood waters has risen in-line with standard 110 mm and 160 mm
dramatically in the UK in recent years, with the diameter pipes, and typically comprise a simple to
record breaking levels of rainfall and tragic fit sealed unit within which are two backflow flaps
flooding in Cumbria during November this year set at 90° across the diameter of the pipe.
being just the latest in a long sequence of Under normal circumstances, the flaps are
disasters that have spread from Cornwall through simply opened by the force of waste water. types of device are explained in fig. 1, with units
the Midlands, to the North West and Scotland. When backflow occurs the reversed direction of being positioned in-line with horizontal drainage
The Environment Agency estimates that over flow forces the primary flap shut against a pipe runs or contained within a gully or other
two and a half million homes in England and watertight seal, with the secondary flap acting as a waste fitting. The valves can be passive, in that
Wales alone are at risk from flooding, highlighting failsafe, in case the first flap fails to seal correctly they operate under the pressure of water, or active,
the danger from rivers, sea, surface waters, due to the presence of dirt or debris. where they are powered by an external actuator.
sewers, and ground waters. To this list should be Different variations of this basic design are Valves are further distinguished in that they are
added the problems that can be caused by available for both grey and black water. automatic (passive or active) and capable of
incorrectly designed or installed storm and Additionally, versions can be supplied with sealed manual locking, or a combination of both.
household drains and sewer systems, from access chambers and manually operated shut-off Note, however, that Building Regulation
collapsed drains and restrictions in drainage valves, to allow for maintenance or sealing during Part H states a preference for a double valve
channels caused by, for example, a build up of prolonged periods of disuse. Similar versions can system, which effectively makes
debris or grease. be fitted into solid floors, with options for 50 mm types 0, 1 and 4 redundant.
The Pitt Report, published in 2008, made a shower or basin waste connections, or can be Selection of the correct backflow valve will
total of 92 recommendations to prevent or reduce supplied with motorised backflow valves that can depend principally on the effluent in the drain:
the risks from flooding. Included among these be remotely operated. The latter are generally black water, containing urine or faeces,
recommendations was the need for an overhaul of suitable for commercial or public buildings where requires the use of a Type 3 valve, whereas grey
Building Regulations for homes built or drainage systems have deep invert pipework in water can be drained via any of the other valve
refurbished in flood-prone areas, with particular access chambers; motors are rated to IP67, types. Beyond the valve assembly itself it may also
emphasis on the use of appropriate construction with remote control boxes having audible alarms, be necessary to consider the additional diagnostic
materials and techniques, together with the diagnostic features and standard 500 mA and remote control features of active electronic
adoption of efficient methods of drainage. outputs for connection directly to building devices, or the availability of optional chambers to
Preventing rare catastrophes such as the recent management systems. house each backflow valve below finished floor
large scale inundation in Cumbria requires huge In terms of where backflow valves can be fitted level or in external chambers.
investment in major flood defence projects and it is worth noting that the latest Building Ultimately, although the latest backflow valves
may, in practice, never be fully achievable in the Regulations Part H allows anti-flood valves to be need to be used as part of an integrated flood
face of such extreme weather events. used in basements where flooding risk is low, protection system to be truly effective, they
Most flooding, however, is far less severe, and in low lying sites (but not basements) in nevertheless offer an extremely efficient and
although just as distressing to those affected, higher risk areas. Where it is perceived that there competitively priced method of dealing with the
and tends to occur because storm drains or is a high risk of basement flooding, for example, problems of flooding and backflow through drains
sewers have become blocked, damaged or simply where there is no fall to the mains sewer, then a and sewers in many residential, public and
overwhelmed, resulting in flood water being wastewater lifting station should be installed. commercial buildings.
unable to escape and backing up through house Backflow valves should also meet the
drains into basements and cellars. requirements of BS EN 13564. The acceptable Fig. 1:
There are various solutions available to protect
Water contents: Grey Water Black Water
buildings from this type of event, of which
Valve actuation Passive Active
anti-flood or backflow valves offer in most
applications the best combination of value,
Valve configuartion: 1 x auto 1 x auto plus 2 x auto plus 1 x auto plus
features and reliability.
emergency emergency seperate
combined combined emergency
Position Type
In-line Type 0
UIcheck
In-line Type 1
UIcheck
In-line Type 2
UIcheck
In-line Type 3
UIcheck
Gully Type 4
UIcheck
Gully Type 5
UIcheck
3
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14