Drainage: Above ground

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Definition

• Above ground

– System of pipework required to carry waste fluids

and quasifluids away from appliances (e.g. sink,

washing machine, shower, toilet etc.) to

underground system

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Drainage terminology

• definitions

Waste water – sinks, showers, dishwashers etc.

Soil water – toilets.

Foul water – both waste and soil water.

Surface water – rainwater from roofs, roads etc.

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Functions of pipework

• Convey fluids or quasi-fluids from a to b.

• Control leakage inwards or outwards.

• Resist deposits of solids.

• Resist blockages.

• Resist abrasion by grit (scouring) esp. road drains.

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Functions of pipework.

• Resist corrosion by acid/alkali.

sulphate – bog/ chlorine – seawater.

• Accommodate pressure – internal/external.

– eliminate undue build up of gases.

• Allow access for maintenance

• Cost.

• Safety – asbestos link to lung cancer.

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Above Ground Water Drainage

Two main types

1. Single stack system 2. Two-pipe system

1.Single stack

• Most commonly used

• Soil and waste water discharge into a single pipe or stack

• Efficient working of the system is dependant on all branches (connections) being as short as possible and closely grouped on the stack

• Each appliance should be connected separately to the stack

• Stack should be vertical

• observe regulations for the diameter, length, fall and connections to the stack

Regulations for Single Stack

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Drainage

above

ground:

external

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Typical bathroom layout

Door

SVP

Design features • System should be

ventilated at every house or if the branch is longer than 6m.

• Access points should be placed at changes in invert level.

• Curves (where unavoidable) should have as large a radius as possible.

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cage

Min

900 mm

Above

Opening

If less

Than 3 m

From nearest

opening

Less than 3 m

Min . Centre line

Radius 200mm 100 mm min.

diameter

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Two-pipe System

• Older system is simple and effective.

• It has a soil pipe for the w.c. and a separate waste pipe for wash hand basins and baths.

• Allows flexibility in the placement of appliances but it is costly due to the amount of pipework.

Traps

• Trap is used at the connection of each appliance to the wastewater drainage system.

• Its purpose is to prevent foul odours entering the house.

• Trap is simply a water-sealed bend in the pipe work.

Traps A trap is used at the connection of each

appliance to the wastewater drainage system (e.g. sink). The purpose of the trap is to prevent foul smelling air entering the building.

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P’ trap Depth

of

seal

Water seal

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Traps

‘S’ trap

Water seal

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Traps Bottle trap

‘P’ outlet

Detachable bowl

Depth

of

seal

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When an appliance is emptied, the water flows away through the trap. However, the last portion of water is left behind in the trap creating a seal until the appliance is next used

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Plug

New water

Old water

Plug removed

Old water

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New water

forms seal.

Traps

How it Works

Siphonage

• The regulations with regards to size and placement of pipes in extremely important because of siphonage

• Siphonage is a difference in air pressure that creates suction.

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Siphonage

Self-siphonage

• Caused by the flow of water in the waste branch running full bore (across the entire diameter)and unsealing the trap by symphonic action

Induced siphonage

• The flow of passing water down the stack can cause suction in the waste pipe of the appliance, therefore unsealing the trap

Back Pressure/Compression

• Caused when the rate of flow of foul water is reduced suddenly due to a small radius bend

• Air then forces (by compression) the water in the trap back up into the appliances, breaking the seals