1、BS 8490:2007Guide to siphonic roof drainage systemsICS 91.060.20; 91.140.80NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARDPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the document was last issued. BSI 20
2、07ISBN 978 0 580 50206 4The following BSI references relate to the work on this standard:Committee reference B/505Draft for comment 06/30150944 DCPublication historyFirst published March 2007Amendments issued since publicationAmd. no. Date Text affectedBS 8490:2007 BSI 2007 iBS 8490:2007ContentsFore
3、word iiIntroduction 11 Scope 22 Normative references 23 Terms, definitions and symbols 24 General 65 Performance 76 Design parameters 77 Components of siphonic systems 108 Hydraulic design 109 Validation of designs 1710 Installation 1711 Testing and commissioning 1912 Maintenance, inspection and cle
4、aning 2013 Information to be provided 21AnnexesAnnex A (informative) Principles of operation of siphonic systems 23Annex B (normative) Testing of siphonic outlets 26Annex C (informative) Simplified checking procedure for siphonic systems 29Bibliography 31List of figuresFigure 1 Principal components
5、of siphonic roof drainage systems 3Summary of pagesThis document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 31 and a back cover.BS 8490:2007ii BSI 2007ForewordPublishing informationThis British Standard is published by BSI and came into effect on 30 March 2007. It was
6、 prepared by Technical Committee B/505, Waste water engineering. A list of organizations represented on this committee can be obtained on request to its secretary.Relationship with other publicationsThis British Standard should be read in conjunction with BS EN 12056-3.BS EN 12056-3 deals with the l
7、ayout and calculation of roof drainage. The provisions for non-siphonic systems are described in detail, but those for siphonic systems are limited to performance requirements. The standard applies to all materials used for roof drainage systems.This British Standard gives information facilitating t
8、he use of BS EN 12056-3 in the United Kingdom with regard to siphonic roof drainage systems; it does not alter any of the provisions of that standard. It is based upon work carried out under a separate study part-funded by the Department of Trade and Industry as part of its Partners in Innovation sc
9、heme 1.The study involved extensive consultation with manufacturers and installers of siphonic roof drainage systems used in the UK and also with specifiers.Use of this documentAs a guide, this British Standard takes the form of guidance and recommendations. It should not be quoted as if it were a s
10、pecification and particular care should be taken to ensure that claims of compliance are not misleading.This British Standard has been prepared to give information about the majority of installations of siphonic systems but it is impractical to cover every eventuality. In some particular cases, it m
11、ight not be possible to reflect all the provisions of this standard. In such cases it is advisable to discuss any departures with the client or the clients appropriately qualified representative.Any user claiming compliance with this British Standard is expected to be able to justify any course of a
12、ction that deviates from its recommendations.Presentational conventionsThe provisions in this standard are presented in roman (i.e. upright) type. Its recommendations are expressed in sentences in which the principal auxiliary verb is “should”.Commentary, explanation and general informative material
13、 is presented in italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer im
14、munity from legal obligations. BSI 2007 1BS 8490:2007IntroductionBS EN 12056-3:2000, 6.2 specifies the performance requirements for siphonic systems as follows:6.2.1 The system shall drain the runoff from the impermeable area served, calculated in accordance with clause 4, without taking gutter stor
15、age into consideration. It is recommended that the recurrence period method (see 4.2.1) should be used whenever possible.6.2.2 For flat roof drainage, the system shall conform to clause 5.4. For gutter drainage, the system shall conform to clauses 5.1 and 5.2.6.2.3 The siphonic effect shall commence
16、 quickly enough to prevent design water depths on the roof or in the gutter being exceeded.6.2.4 The flow capacity of individual outlets shall be balanced to ensure the entire system performs as specified.6.2.5 The siphonic system shall be designed to take into account any surcharging of the buried
17、drainage.6.2.6 Pipes and fittings shall withstand the maximum positive and negative pressures encountered under design conditions.6.2.7 The minimum velocity in the system at the design rainfall shall be chosen to prevent deposition in pipework and to ensure rapid commencement of the siphonic effect.
18、6.2.8 Outlets shall be fitted with strainers to exclude solid material and prevent blockages. The effect of a strainer on water levels in gutters or on flat roofs shall be taken into account.6.2.9 The minimum internal pipe diameter, di, shall be 32 mm.6.2.10 The design method shall be validated by p
19、hysical testing.6.2.11 The lowest design pressure shall be chosen to prevent possible cavitation damage and collapse of pipes.6.2.12 Reductions in diameter in the direction of flow are permitted in siphonic systems.6.2.13 The system shall be installed in accordance with the design assumptions. The e
20、ffect of any difference between the design and the system as installed shall be calculated and appropriate action taken.BS 8490:20072 BSI 20071 ScopeThis British Standard applies to roof drainage systems using circular-section pipes that operate under siphonic action. It does not apply to siphonic d
21、rainage systems using rectangular or trapezoidal section conduits for water conveyance.It gives information and provides guidance on design parameters, installation, verification and maintenance needs of siphonic roof drainage systems conforming to the performance requirements specified in BS EN 120
22、56-3:2003, 6.2. Guidance is also given on carrying out checks of designs, for the use of specifiers and regulatory authorities.Particular issues for site drainage systems that receive flows from siphonic roof drainage systems are also covered.2 Normative referencesThe following referenced documents
23、are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.BS EN 12056-3:2000, Gravity drainage systems inside buildings Part 3: Roof drainage,
24、layout and calculationBS EN 752, Drain and sewer systems outside buildings3 Terms, definitions and symbols3.1 Terms and definitionsFor the purposes of this British Standard, the terms and definitions given in BS EN 12056-3 and the following apply.NOTE The principal components of a siphonic roof drai
25、nage system are illustrated in Figure 1. BSI 2007 3BS 8490:20073.1.1 cavitationphenomenon involving the formation and subsequent sudden collapse of vapour cavities in a liquid, with the cavities forming when the local pressure within the flow reduces close to that of the vapour pressure of the liqui
26、d3.1.2 collector pipehorizontal pipe installed below a roof, gutter or floor that collects and conveys the flow from the tailpipes of roof outlets3.1.3 conventional roof drainage systemnon-siphonic system in which the pipework between roof level and ground level is designed to flow part full with in
27、ternal pressures at or above atmospheric pressure3.1.4 design flow rateflow rate in a siphonic roof drainage system or associated gutter, calculated using design rainfall data from BS EN 12056-3 plus a safety factor of not less than 10%3.1.5 downpipesection of vertical pipe in pipework connecting a
28、collector pipe to a siphon break or to the point of discharge from a siphonic system3.1.6 full-bore flowflow conditions under which the water (and any entrained air carried by the water) occupies the full cross-section of a pipe3.1.7 overflowdevice installed in a gutter or flat roof that discharges
29、the flow if the water level rises above a limiting level (e.g. due to exceptional rainfall or blockages at outlets)NOTE Possible devices include weirs, chutes, additional conventional outlets, or additional siphonic outlets.Figure 1 Principal components of siphonic roof drainage systemsKey1 Siphonic
30、 outlet2Tailpipe3 Collector pipe4Downpipe5 Siphon break12345BS 8490:20074 BSI 20073.1.8 primary systemfittings and pipework designed to drain a roof or gutter for rainfall conditions up to a selected frequency of occurrence3.1.9 rating curve of outletrelationship between the flow rate entering an ou
31、tlet and the water depth in a gutter or flat roof close to the outlet3.1.10 secondary systemfittings and pipework designed to drain a roof or gutter if rainfall conditions exceed the capacity of the primary system or if a failure of the primary system were to occur3.1.11 siphon breaktermination poin
32、t of a siphonic system at which the pressure is maintained equal to atmospheric pressure and which is designed to stop siphonic action downstream3.1.12 siphonic outletfitting at the entrance to a siphonic roof drainage system to permit rainwater to drain from a roof or gutter and designed to exclude
33、 air entering the pipework3.1.13 soffit of pipehighest part of the internal bore of a pipe3.1.14 tailpipesection of vertical and possibly horizontal pipework connecting a roof outlet to a horizontal collector pipe3.1.15 warning pipepipe that indicates whether the limiting water level in a gutter or
34、flat roof has been exceeded but does not itself provide a significant discharge capacity3.2 SymbolsFor the purposes of this British Standard, the following symbols apply.A effective roof area draining to outlet, in square metres (m2)diinternal diameter of pipe, in metres (m)g acceleration due to gra
35、vity, in metres per second per second (m/s2)NOTE The value of g is taken as 9.81 m/s2.HAoverall head of water available for functioning of siphonic system, in metres (m) HBvertical height between floor of test tank and bottom of downpipe, in metres (m)HDloss of water head between top of downpipe and
36、 point of discharge from system, in metres (m) hMminimum pressure head of water occurring in system (relative to atmospheric pressure), in metres (m)HOlocal atmospheric pressure measured above vacuum, expressed as equivalent head of water, in metres (m)HTtotal loss of water head in system between an
37、 outlet and point of discharge, in metres (m) BSI 2007 5BS 8490:2007HTFtotal frictional loss of water head in system between an outlet and point of discharge, in metres (m) HVvelocity head of flow, in metres (m)h static pressure head of water at point in flow (relative to local value of atmospheric
38、pressure), in metres (m) hivalue of h at point number i in system, in metres (m)hminminimum allowable value of h in system, in metres (m)hvpvapour pressure of water (expressed as equivalent head of water), in metres (m) iFfrictional head loss gradient in pipe, in metres loss of water head per metre
39、length of pipe (m/m)kPvalue of pipe roughness in ColebrookWhite equation, in millimetres (mm)LPlength of section of pipe in siphonic system, in metres (m)Qininitial flow rate of water entering collector pipe during priming of siphonic system, in litres per second (l/s)Qmaxmaximum flow rate of water
40、used in test of outlet, in litres per second (l/s)Qodesign flow rate of water to an outlet (equal to area drained multiplied by design rainfall intensity multiplied by factor of safety), in litres per second (l/s)QPflow rate of water in pipe, in litres per second (l/s)QTflow capacity of tailpipe whe
41、n acting siphonically and discharging to collector pipe at atmospheric pressure, in litres per second (l/s)r design rainfall intensity, in litres per second per square metre (l/s per m2)S plan area of water surface in tank for testing outlet, in square metres (m2)SFfactor of safety for design of sip
42、honic system and associated gutters, applied as multiplier to flow rates determined using design rainfall intensityTFtime to fill siphonic pipework, in seconds (s)u mean flow velocity, in metres per second (m/s)uivalue of u at point number i in system, in metres per second (m/s)uEmean flow velocity
43、at exit from downpipe assuming full-bore flow, in metres per second (m/s)VPtotal volume of collector pipe(s) and downpipe to the point of discharge from siphonic system, in litres (l)ZDheight of lip of siphonic outlet above top of downpipe, in metres (m)z elevation of point above datum, in metres (m
44、)h loss of energy head in pipe length, in metres (m) (water head)hFloss of energy head in pipe length due to wall friction, in metres (m) (water head)BS 8490:20076 BSI 20074GeneralNOTE Annex A describes how siphonic systems operate.4.1 To ensure efficient long-term working of a siphonic system, the
45、following points should be addressed. An effective periodic maintenance regime should be implemented to prevent accumulations of debris (e.g. leaves etc.) blocking rainwater outlets at roof or gutter level. Correctly dimensioned siphonic systems might have less reserve capacity than that of equivale
46、nt gravity systems and therefore adequate safety margins should be considered, i.e. design safety factors and/or suitable overflows should be included. If a siphonic system is subject to a change (during construction and/or throughout the life of the building), a hydraulic reassessment of the system
47、 should be carried out.4.2 When operating under full-bore flow, a siphonic roof drainage system creates a direct flow path between roof level and the site drainage system to which it discharges. Problems below ground can therefore cause flooding at roof level. For this reason, siphonic systems shoul
48、d be designed as an integral component of the building and the drainage infrastructure of the site. Designers of buildings should therefore ensure that appropriate information on requirements for satisfactory installation and operation of siphonic systems is exchanged with others responsible for the
49、 design of roofs, gutters, structures and site drainage systems (see also Clause 13). Specific examples include the following.hLlocalized loss of energy head at pipe fitting, in metres (m) (water head)holoss of energy head at siphonic outlet, in metres (m) (water head)h12loss of energy head between points 1 and 2, in metres (m) (water head)ymaxmaximum allowable increase in water depth in non-steady test of outlet relative to steady-state water depth at same rate of flow, in metres (m) z12vertical height of point 1 above point
