du calculation for house connection

8/7/2019 DU Calculation for House Connection

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APPLICATION

CRITERIA1.00

Hunter Underground Systems

1.01 Advantages of PVCu drainpipe1.02 Pipe Dimensions1.03 Recommended minimum gradients

for Foul DrainsChoice of gradientsHydraulic performanceFlow rate graphs

Pipe sizingSurface water drains

1.04 Graph for converting discharge units toflow rates (L/ S)

1.05 Design InformationGeneral LayoutAlternative pipe depth arrangementsAccess to DrainsAccess FittingsVentilationInspection Chambers, Access

and Manhole sizingMinimum dimensions for Rodding Eyes,Access Fittings, Inspection Chambersand Manholes

1.06 Rodding point system



N OM IN AL DIAM ETER M IN M AX WALL THICKN ESS M IN W EIGHT KG/ M (M EAN )

110mm (4in) 110.0mm 110.3mm 3.2 1.65

160mm (6in) 160.0mm 160.4mm 4.0 3.24

200mm (8in) 200.0mm 200.5mm 4.9 4.96

250mm (10in) 250.0mm 250.5mm 6.2 7.02

315mm (12in) 315.0mm 315.6mm 7.7 11.10

PEAK FLO W ( LITRES/ SEC) PIPE SIZE (mm) M IN IM UM GRADIEN T

<1 75++ 1:40

100 1:40

>1 75++ 1:80

100 1:80

150 1:150+

1.02 PIPE DIMENSIONS

1.03 RECOMMENDED MINIMUM GRADIENTS FOR FOUL DRAINS

1 .0 1 ADVAN TAGES OF HUN TER UNPLASTICISED POLYVIN YL CHLORIDE (PVCU) DRAINPIPE

• Strong, lightweight material with a high resistance to aggressive soil and chemicals found in domestic sewage.

• The ring seal push fit joints are easily and instantly jointed, making the system ready for testing even in bad weather.

• Joints capable of absorbing significant vibration and ground movement without joint failure.

• Flexible joints ensure that they remain watertight under working conditions to prevent pollution of the surrounding ground.

• Designed so that nothing in the pipes, joints or fittings projects into the pipeline to cause an obstruction.

• The smooth bore prevents particles clinging to the internal surface, reducing the accumulation of solids within the drain.

• The smooth bore aids higher velocity, which permits shallower falls and therefore less excavation.

• The infrequent joints and smooth internal bore result in lower turbulence and increased hydraulic performance thusconsiderably reducing the possibilities of a blockage.

Identification pointers

Colour: bronze/ golden brown

Lengths: 3m and 6m plain or single socketed ends.

British Standards: Hunter Plastics Ltd pipes and fittings are produced in accordance with BS EN 1401-1: 1998 whilst allancillary fittings and pipes are manufactured in accordance with BS 4660: 2000.

Design of Drainag e or Sew erage Systems

The designer of any drainage or sewerage system should make themselves fully conversant with the following, ApprovedDocument H of the Building Regulations (England & Wales). Technical Standards Part M of the Building Standards (Scotland)Regulations. Technical Booklet N of the Building N of the Building Regulations (Northern Ireland). BS EN 752: 1998 the BritishStandard for Drains and Sewers outside Buildings. Sewers for Adoption by the Water Services Association/ W Rc. StandardSpecification for Water and Sewerage Schemes, (Scotland) (Northern Ireland).

Pipe Sizing and Gradients

The table below lists the minimum pipe sizes and gradients to prevent sedimentation build up and blockages in foul drains.However, where the length of the drain or sewer that serves a small number of properties is very long the steeper gradient couldbe considered. Also, where the ground is expected to settle steeper gradients should be used to compensate for the eventualsettlement. Conversely flatter gradients can be achieved when the standard of design and pipe installation is high.

Notes: Minimum of 1 WC. + Minimum of 5 WCs. ++ No WCs.

The above table sets out the minimum gradients for foul drains as recommended in approved Document H1 of the BuildingRegulations 2002 and BS EN 752-4: 1998.

*

*



1.0 3 CON TIN UED - CHO ICE OF GRADIEN TS

Choice of gradients should be such as to maintain self-cleansing velocity under normal discharge conditions.

To achieve a satisfactory installation, diameter and gradient should be adequate for the maximum flow and

competent supervision should be provided to ensure a high standard of pipe quality, laying, jointing and

workmanship. This is particularly important when pipes are laid to flat gradients.

The following guidelines on gradients should be observed.

(a) For flows of less than 1 L/ s, pipes not exceeding 100mm nominal bore at gradients not flatter than 1:40 have proved satisfactory.

(b) Where the peak flow is more than 1 L/ s, a 100mm nominal bore pipe may be laid at a gradient not

flatter than 1 : 80 , provided that at least one W C is connected.

(c) 150mm nominal bore pipe maybe laid at a gradient not flatter than 1:150, provided that at least five

WCs are connected.

(d) Experience has shown that for gradients flatter than those given in items (a) to (c), a high standard of

design and workmanship is necessary if blockages are to be minimised. W here this has been achieved,

gradients of 1:130 for 100mm nominal bore pipes and 1: 200 for 150mm nominal bore pipes have

been used successfully.

Where the available fall is less than that necessary to achieve the recommended gradient, increasing the pipe

diameter particularly at low flows is not a satisfactory solution. It will lead to a reduction in velocity and depth

of flow and an increase in the tendency for deposits to accumulate in the pipes.

Where it is expected that a drain may be affected by settlement, the selected gradient should be such as to

ensure that a satisfactory fall will be maintained.

Research has shown that high velocities of sewage flow arising from steep gradients do not cause increased

erosion of pipes or deposition of solids. In such situations drains should be laid at gradients which are the

most economical in excavation and cost. High velocities can, however, cause excessive turbulence at bendsand manholes and lead to fouling. W here this occurs it can be mitigated for example by using long radius or

sealed access fittings.



Hydraulic Performance

Various roughness values (k or K s) for drain pipe are suggested by the industry, the commonest being 1.5mm,

0.6mm and 0.06mm. BS EN 752-4: 1998 recommends k values for foul and combined drains and sewers in

average condition of I.5mm and 0.6mm depending on the velocity of flow. W hilst it recommends k 0.6mm for

surface water. The smooth bore of PVCu drain and the infrequent joints result in lower turbulence and

increased hydraulic performance. Consequently Hydraulic Research Ltd in their ‘TabIes for the Hydraulic

Design of Pipes and Sewers’ recommend Ks 0.06mm for PVCu pipe with ring seal sockets at six to nine metre

intervals.

Flow Rate Gra phs

The flow rate graphs on the following pages are for full bore flow and although public and trunk sewers are

often designed to run full during periods of calculated peak loading, it is recommended that estate drainage

and drains close to buildings should be designed to run part full. Therefore, a proportional depth should be

selected to allow for additions to the system, however, to ensure that trap seals are retained, foul drains and

sewers should not exceed 0.75 proportional depth.

When considering the flow rate one should remember that a pipe flowing half full would discharge half the

full bore capacity at the full bore velocity, however, there is no direct relationship between other proportional

depths.

Pipe sizing

Foul drains

The generally accepted method of sizing foul drains serving individual or small groups of buildings is the

discharge unit method. Discharge units for various sanitary appliances discharging to System III discharge

pipes are given in table 1.01.

Surface Water Drains

The drain should be sized to provide sufficient storage as protection against flooding and surcharge from

storms of predetermined intensities and frequencies.

For calculating the run off from roofs, and paved areas of up to 2000 m2 use the formula

Q = Ae x IF x RI

3600

Q = run off in litres per second

Ae = effective area in m2

IF = Impermeability factor

(The worst instance is covered using a factor of 1.0 see BSEN 752-4 for further information)

RI = rainfall intensity (use 50mm/ hr for paved areas and 75mm/ hr for roofs)

1 .04 Conver ting Discharge Units to Flow ra tes (I/ s)

Discharge units are figures used for calculation purposes only and are not related to the discharge rates

quoted in product standards. The method attributes discharge units for the sanitary appliances, which can be

converted to the flow (in litres per second) by using the formula below.

Q = k DU

The quantity of water (Q)

The frequency factor (k)

The square root ( )The sum of all the discharge units (DU)



BANANA GRAPH

DIAGRAM SHO W IN G PROPORTION AL DEPTH

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Fig. 1

Velocity

Discharge

Proportional Velocity and Discharge

Proportional Depth

Proportional DepthdD

D

d



Tab le 1. 01 System IIIDischarge Units

Applia nce Litres per second

Wash Hand Basin, Bidet 0.3Kitchen Sink 1.3Dishwasher Domestic 0.2Domestic Washing Machine up to 6kg 0.6Commercial Washing Machine up to 12kg 1.2Bath 1.3Shower Tray without plug 0.4

Shower Tray with plug 1.3Bowl Urinal 0.4Urinal Stall 0.2 (i)Water Closet 6.0 litres 1.2-1.7 (ii) (iii)Water Closet 7.5 litres 1.4-1.8 (ii) (iv)Water Closet 9.0 litres 1.6-2.0 (ii) (iv)i. per personii . with siphon flush cistern onlyii i. since January 2001 this is the maximum flush allowed for a newly installed WC suiteiv. only use to replace the same size siphon

Table 1 .02 Frequency of use of appliance k

dependent upon the type of buildingIntermittent use, dwelling, guesthouse, office 0.5Frequent use, hospital, school, restaurant, hotel 0 .7Congested use, toilets and showers open to the public 1.0Special use, laboratory buildings 1.2

Appliance Discharge Units

Kitchen Sink 1.3Domestic Washing Machine up to 6kg 0.6Bath 1.3

Water Closet 6.0 litres 1.2-1.7Wash Hand Basin 0.3TOTAL for one tw o bed terraced houses 5 .2TO TAL for thirty-four two bed terraced houses 176 .8

Intermittent use factor 0 .5

Ex ample of Calcula ting Proportional Flow Using The Flow Rate Graphs

We wish to discharge to foul water drains from thirty-four two bed terraced houses containing.

Q = k DU Q = 0.5 176.8 DU transposes to a flow rate of 6.65 l/ s

The flow rate graphs on the following pages are for full bore flow. W hen pipes are designed for less than fullcapacity, the proportions of velocity, discharges and depths are shown on the banana graph.

The Hydraulic Research Tables state that for a velocity of approximately 0 .75m/ s we would select a Ks0.6mm for

PVCu pipe in a normal slimed condition.

Reading from the Ks 0.6 graph we find that a 110mm diameter pipe flowing full bore will carry 8.0 l/ s at0.84m/ s when laid at a gradient of 1.65.

Refer to the banana graph to see that where the proportional depth line of 0.7 strikes the discharge line we have areading of 0.86 on the bottom of the banana graph. Therefore a proportional discharge factor of 0.86 x 8.0 l/ s(the full bore flow) = 6.88 l/ sWhere the proportional depth line of 0.7 strikes the velocity line we have a reading of 1 .11 on the proportionalvelocity and discharge line of the bottom of the banana graph. Therefore a proportional velocity factor of 1.11 x0.84 m/ s (the full bore flow) = 0.93 m/ s

110mm dia. pipe laid at 1:65 will carry 6.88 l/ s flowing at a speed of 0.93 m/ s.



2000

1000

10

9

8

7

6

5

10 40 100 500

Gradient 1 : x

1000

100

Discharge rate of PVCu drain/ sewer pipes in the nominal range from 110 to 630 for different gradients based on aroughness height of 0.06mm. Suitable for PVCu pipe with ring seal sockets at 6-9m intervals

Discharge litres/s (runn

ing full)



Gradient 1 : x

2000

1000

10

10 100 1000

100

D

ischarge litres/s (running full)

Ks 1.5mm only required for UPV-C sewers in a poor slimed condition.



1.05 DESIGN INFORMATION

General layout

The layout of drains should comply with the relevant Buildings Regulations and British Standard Codes of Practice listed

previously under ‘Design of Drainage Systems’. The following is intended as a guide only. The layout of any drainage system

should be as simple as practicable. The following detailed design considerations apply to all drains.

A drainage system must be planned and laid in such a manner that effluent is conveyed from the house to the sewer, cesspool or

other places of disposal as speedily as possible and without causing an unacceptable nuisance, or danger to health. Drains must

be constructed so as to be as far as possible self-cleansing and so reduce the risk of blockages of a minimum, whilst adequate

mans of access must be provided for the purpose of inspection, testing and clearing should an obstruction take place. Drainsmust be watertight to prevent pollution of the surrounding ground by soil wastes, and adequate ventilation is essential.

Principles to be Observed in the Design of a Drainage System

The following are the main points which must be considered in designing a drainage system:-

1. Pipes to be laid at such a gradient as to ensure a self-cleansing velocity. See section 1.03

2. Pipes to be of sufficient size to cope effectively with the maximum load to be carried. See section 1.03

3. Efficient mans of ventilation to be provided and maintained. See following pa ges

4. Adequate means of access to be provided. See next web page

5. Length of branch drains to be kept to a minimum and all junctions to be made in the direction

of the flow. See Tab le 1 .0 3

6. Pipes to have watertight joints. See section 6.0 4 - 6 .06

7. Every part of the drainage system to be adequately supported. See section 6.08

8. So far as circumstances wi ll permit, drains should not pass under buildings. See section 8.13

9. Drains to be laid as far as possible in straight lines between points where access is provided

10. Drains not to be laid in close proximity to trees owing to the possibi lity of damage being caused by roots.



Access to drains

The Hunter Underground range offers many different types of components for gaining access to drains: 230mm diameterShallow and 450mm diameter full height Inspection Chambers, Sealed Rodding Access Fittings, Manhole Bases, Gullies and,within traditional manholes, Channel and Sealed Access Fittings.

Full details of these products are given in Section 2 (page 17). Access is required to drainage installations for testing, inspection,maintenance and the removal of debris. Access to drains allowing rodding in both directions can be provided by eithermanholes, or pre-formed inspection chambers, and by some access fittings. Rodding eyes provide access in only one direction.Every section of drain or sewer should be accessible without entering buildings.

Siting of access points

Access should be provided at the following points:

a). on or near the head of each drain run

b). at a change of gradient or alignment

c). at a change of pipe size

d). at a junction (see note 1) or at a bend (see note 3)

e). at drainage fittings such as intercepting traps or anti-flood valves

Notes:

1. Where a branch joins a main pipe without an inspection chamber or manhole at the junction, access should be providedon the branch within 12m of the junction.

2. Deep inspection chambers may restrict the use of trenchless technology equipment and should not be used in highways orother high use areas when excavation for repairs would be unacceptable.

3. On drains, bends with an angle of not more than 45 ˚ may be used outside inspection chambers. W here bends occuroutside manholes and inspection chambers, this may restrict access for CCTV surveys.

The table below indicates the recommended maximum distances between access points. These are based on manual cleaningtechniques, consequently where only remotely operated and automatic equipment will be used for maintenance (e.g. jetting), thespacing may be increased.

Table 1.0 3

Distance from: To access To access To junction To inspection To manholefitting Type 1 fitting Type 2 or branch chamber and inspection

shallower chamber deeperHunter 230mm than 1.2m than 1.2mShallow Accesschamber

Start of external drain* 12m 12m _ 22m 45m

Rodding eye (DS670) 22m 22m 22m 45m 45m

Access fitting Type (1) _ _ 12m 22m 22m

min. 150mm dia.

Access fitting Type (2) _ _ 45m 22m 45mmin. 225mm dia.

Inspection chamber

shallower than 1.2m 22m 45m 22m 45m 45m

Manhole & inspection _ _ _ 45m 90 (Up to 200m

chamber deeper for man-entry

than 1.2m size drains and

sewers - see

BS EN 752-3:19 97

* Note: Soil stack or ground floor appliance



Access fittings

Access fittings Type 1 and 2 are drain fi ttings that have an opening on to the pipe, which is widened into a small chamber capableof being fitted with a cover. The chamber should preferably be the same size as the drain pipe but should not be less than 100mmdiameter. An example of a type 1 access fitting is Hunter ’s access pipe DS309, or access junction DS680 which can be installedwithin a chamber with a cover at ground level to provide a sealed drainage system. An example of a type 2 access fitting isHunter’s shallow access chamber DS71 Risers DS72 and Frame and cover DS69.

The diagram below illustrates principals taken from the taken on the previous page. Hunter ’s rest bend (DS663) must always beused at the base of a soil stack with a type 1 or 2 access fitting within twelve metres because British Standard 752.3: 1994 states‘every drain and sewer length should be accessible for maintenance and cleaning without the need to enter buildings’. However,should the property owner need to unblock the underground drain within the property’s curtilage an access fitting at the bottom ofthe soil and vent pipe will allow a set of drain rods to be passed easily through to Hunter ’s shallow access chamber where any

debris can be removed.

Ventilation of the underground drainage system

All drainage systems need adequate ventilation to the open air in order to reduce the build-up of toxic or explosive gases in the

system, and to equalise air pressure when effluent flows through a pipe.

In order to ensure the drainage system is ventilated by a flow of air, a vent pipe or soil and vent stack should be provided at:

1) the head of each main drain

2) a drain fitted with an intercepting trap

3) any drain subject to surcharge

Access pipe S309

Rest bend

DS663

Type 2. Shallow access chamber base (DS71)

Shown with 2 no. raising pieces (DS72)

Bedding/ backfill

material to Appendix

A of BS5955

Bedding/

backfill

materials

Main drain



Ventilation cont-

Ventilating pipes open to outside air should finish at least 900mm above any opening into the building within 3 metres, and shouldbe finished with a vent cowl.

All inlets entering a foul water or combined drainage system must be trapped with a sufficient depth of seal to prevent syphonage.This includes all yard gullies, rainwater and surface water inlets. Drains carrying surface water only do not usually need traps.

Inspection chambers, access and manhole sizing

The depth of any inspection chamber or manhole is determined by its minimum internal dimensions, since there must be adequateaccess or entry for rodding and maintenance.

Minimum dimensions for rodding points, access fittings,and inspection chambers (non man-entry)

Table 1.0 4

Recommended dimensions for rodding eyes, access fittings and inspection chambers (non man-entry)

Rodding point - - Preferably same size - Same size as pipework4

as drain but not less

than DN100

Access fitting2 0.6 or less, except 150 x 10 0 150 Same size as access Same size as access

Type (1 ) where si tuated fi tti ng4 fitting4

See Table NB.1 in chamber

Access fitting2 0.6 or less, except 225 x 10 0 225 Same size as access Same size as access

Type (2) where situated fitting4 fitting4

See Table NB.1 in chamber

Inspection chamber3 0.6 or less 225 x 100 190 for drains - Min 190

shallow up to DN 150

1.2 or less 450 x 450 450 Min 430 x 430 Min 430

Inspection chamber4 G reater than 1 .2 450 x 4505 450 5 Max 300 x 300 Max 350

deep

Type of access Depth to invert from

cover level Rectangular length Circular diameter Rectangular length Circular diameter

and width and width

(m) (mm) (mm) (mm) (mm)

The depth restriction isimposed because of thelimited access affordedand is based on theability to manipulate astopper at arms lengthfrom the surface

Restricted to inspectionand remotely operatedequipment - nopersonnel entry

Restricted to inspectionand remotely operatedequipment - nopersonnel entry. Maxsize imposed to prevent

personnel entry.

Minimum nominal internal dimensions1 Clear opening Remarks

Notes: 1 These sizes apply to straight-through pipes, larger sizes may be required for turning chambers or chamberswith several side branches.

2 Fitting wi th a removable cover that permits access into the pipe, either from surface level or from withina chamber.

3 Chamber with a removable cover constructed on a drain or sewer that provides access from surface levelonly, but does not permit entry of a person (BS EN 752-1).

4 The clear opening may be reduced by 20mm in order to provide proper support for the cover and frame.

5 It may not be possible to gain access to side branches. The upper part of the chamber may be reduced to a

minimum of 300 x 300 or 350 dia. to form a shaft.

Hunter Plastics Limited only manufacture preformed inspection chambers that provide access from ground level, but do not permitentry of a person (non-man entry). Hunter does manufacture products that can be used within manholes that accommodate manentry, such as channel pipe, channel bends and Type 1 access pipe and junctions. For the recommended dimensions of thesemanholes refer to Table N B3: BSEN 752:3 . 1997.



SVP SVPSVP SVP SVP SVP

IC

IC

IC IC

BIG BIG BIG BIG BIG BIG

RWP RWP RWP RWP RWP RWP

SAC SAC SAC

RP

SAC

ICBIG BIG

BIG BIG

BIG BIG

BG BGTG TG TG TGIC IC IC

TYPICAL DRAIN LAYOUTS

SEPARATE SYSTEM

COMBINED SYSTEM

This diagram shows the variety of ways Hunter drainage products can be utilised to make the same connections.

KEY

Trapped Gully TGRodding Point RPInspection Chamber ICShallow Access Chamber SACSoil Vent Pipe SVPBack Inlet Gully BIGBottle Gully BGRainwater Pipe RP

Drainage layouts shown are for

guidance purposes only. All

drainage schemes should

comply with local authorityrequirements.



1.06 RODDING POINT SYSTEM

Head of Drain Access

Rodding points eliminate the need for the majority of conventional manholes. However, there are obviously certain cases wherethese are unavoidable or are required by local building control regulations.

Using the standard range of Hunter fittings, various combinations of rodding points may be formed - a number of these areillustrated in the next few pages.

By using this method of installation considerable savings may be made over the traditional form of manhole construction.

The Ramped Rodding detail shows a method of using the DS22 sealed plate access point in the DS3 square hopper. However,the DS22 can be directly solvent welded onto the pipe end.

The following details provide a vandal-proof access but should only be situated in paths or borders, as the DS22 or DS670 arenot designed for heavy loads.

DS670

110mm Rodding Point

Rodding Point SystemShallow Rodding Point

Rodding Point SystemRodding Point for Deeper Inverts

DS670

DS208

DS211

DS211

DS557

DS676



DS22 sealed plate solvent welded tosquare hopper DS3

110mm pipe to suit length

Rodding Point SystemRamped Rodding Point

Rodding Point System45 ˚ Swept Junctions areused for blind connectionson drain runs

DS331

DS678

Blind connection to 110mm drain (plan view)

45 ˚ bend DS331

45 ˚ branch DS678

45 ˚ bend DS331 or DS676

Suitable backfill material



Rodding Point System

MAIN SEWER

SURFACE WATER DRAIN

MH

MH

MH

MHMH

MHMH MH MH MH MH

MH

SVP SVP SVP SVP SVP

MAIN SEWER

SURFACE WATER DRAIN

MH

MH

MH

MH

RP

MH

RP RP RP RP RP

SVP SVP SVP SVP SVP

RW GullyRW Gully

RW GullyRW Gully

RW GullyRW Gully

RW GullyRW Gully

The lay outs below illustrate the savings that m ay be mad e using the Rodding Point System.

TRADITIONAL SYSTEM WITH MAN HOLES

Using a traditional manhole system extra time and labour costs are spent on unnecessary excavation and installation. Manholesrequire either precast concrete rings or a concrete base with a engineering brick chamber to be constructed, then drainagechannel needs to be haunched and covers and frames need to be set in position.

Rodding Point System

Using the rodding point system deep excavation is not required. Swept 135 ˚ junctions are installed on the drain branches andthe main drain run with rodding points fitted at ground level. An inspection chamber or manhole must be fitted in the system toallow debris to be removed from the system. Otherwise, eliminating extra time and labour costs on unnecessary excavation andinstallation makes savings.

du calculation for house connection

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