Product list
2. Principles of waste water discharge
cause compression of air, and overpres- sures and underpressures will be created. These must be kept within limits. Steps must also be taken to prevent excessive overpressures or underpressures created by hydraulic sealing, whereby little or no air can pass over or through a flowing mass of water. The principles and stipula- tions for the removal of waste water are based upon these assumptions. Having dealt with general construction principles,
In houses and other residential properties waste water and rainwater must be collected separately and led to the exterior of the building, or at least up to the location of a discharge construction for the rainwater. It is important in removing waste water that the pipework empties thoroughly, that any soil is carried along by the water and that no waste water or sewer gases enter the building via the trap. Discharges will
this chapter goes on to discuss the waste water system from the fitting to the building boundary. Requirements and problems are examined and solutions suggested.
fitting
baseline
diameter of
external diameter connecting pipe in PVC and PE
reduced external diameter for wall and floor piping
discharge l/s trap
(pipe type)
(mm)
(mm)
(mm) 1)
mouthwash unit drinking fontain leakage removal overflow hopper hand washbasin washbasin
0
40
32
32
2.1 General design principles
0,5
50
40
In order to prevent traps being emptied by suction or pressure, overpressures and underpressures must not exceed 300 Pa (30 mm water column). Air must be able to escape from the system (venting) and to enter the system (admittance). A ventilated discharge pipe is used for this purpose. Good practice is to create a primary discharge system extending the discharge stack above roof level (see illustration 2.1). This system allows air to continually enter and vent from the main sewer. In the case of a secondary discharge system, each fitting or branch pipe is connected to a separa- te ventilation system. A secondary dis- charge system may be taken through the roof or connected to a primary discharge system prior to this being taken through the roof (illustration 2.2). An unavoidably long branch pipe may give rise to pro- blems in a primary system. The section of the branch pipe furthest from the stack may then be connected to a restricted secondary discharge pipe. This may either be led directly through the roof or connected to the stack or to the primary discharge stack. This may be referred to as a circulating or end discharge system (illustration 2.3). In this case an internal air admittance vent on the end of the branch pipe may be useful. However these can only admit air to the system, not release it. Where overpressure occurs in the system a membrane is pressed closed, otherwise sewer stench would enter the room. The air admittance surface area must be as close as possible to the cross sectional area of the collection stack. For ease of maintenance the air admittance vent must be fitted in accessible place
shower without tray bidet automatic washing machine domestic dishwasher urinal footbath kitchen sink (single or double)
0,75
63
(HDPE)
slop sink
40
or 75
50
bath
shower with tray
1,0
(PVC)
sink with capacity over 30 l Toilet
2,0
-
110
90
siphonic closet
2,5
-
110
90
bedpan sluice floor drain 32 mm
0,5
-
50
40 50 50
40 mm 50 mm 70 mm 100 mm
0,75
- - - -
63/75 63/75
1,0 1,5 2,0
75
- -
110
1) reduction permissible if • total length of connecting pipework is no more than 3,5 m. • length of wall-mounted pipe (horizontal) is no more than 0,5 m and only a single vertical element is not longer than 1,5 m.
15 20 25 30 40 50
10
9 8 7 6 5 4
Illus. 1.2 Baseline discharge, required
diameter for traps and (reduced) connecting pipework for a variety of fittings.
3,5
3
2 2,5
1,5
1,0 0,9 0,8 0,7 0,6 0,5 0,4
Q o can be read off for different values of p in illustration 1.3 if the sum of Q ¡ is known. Q o may never be lower than the highest value for baseline discharge rates.
1 1,5
2 3 4 5 6 7 8 910
15
20 30 40 50 70 100 150 200 300 400500 700 1000
Q i (sum of baseline discharge (l/s) Q o may never be less than the largest of the baseline discharges
Illus. 1.3. Relationship between Q o , p and Q i . Example: Calculated using table in 2 gives Q i = 52 l/s Office (p = 0,7) hence Q o = 5 l/s
Illus. 2.1 Principles of the primary discharge system.
8
9
Made with FlippingBook Annual report