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Above ground drainage part 1


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Above ground drainage to be done with

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Above ground drainage part 1

  1. 1. PART 1 Practice plumbing exams © 1
  2. 2. Above Ground Drainage Waste Pipe Connections:-  Where an appliance is installed it will need to connect to ‘suitable system of drainage’  This is done by installing a ‘waste’ fitting called a trap to the appliance & connecting it to the discharge pipe  Each type of appliance has a standard size of waste & trap, as follows: Practice plumbing exams © 2
  3. 3. Above Ground Drainage Type of appliance Waste fitting size (inches BSP) Discharge pipe & trap size (mm) Sinks, showers, baths, washing machines & trough urinals 1 ½ 40 Wash basins, bidets, drinking fountains & bowl urinals 1 ¼ 32 Stall & slab urinals 2 ½ 65 Practice plumbing exams © 3
  4. 4. Above Ground Drainage Waste Pipe Connections:-  Appliances such as sinks & baths use a combination overflow (o/f) & waste fitting (the o/f connects to the waste before the trap)  Appliances such as Belfast sinks, bidets & wash basins have an integral o/f so they need a ‘slotted’ waste  Some appliances such as showers have no o/f at all, & may use an ‘unslotted’ waste Practice plumbing exams © 4
  5. 5. Above Ground Drainage Traps:-  A trap is a fitting attached to the waste which is designed to retain a water seal between the appliance & the drain to stop smells coming back into the room  There are P, S, running, bottle, integral & resealing traps Practice plumbing exams © 5
  6. 6. Above Ground Drainage Traps:- For discharge pipes of less than 50 mm, the trap seal should be 75 mm  For discharge pipes above 50 mm, only a 50 mm seal is required  If the appliance is fitted with spray taps & has no plug (basin or shower), then a 50 mm trap seal may be used  Tubular traps are less prone to blockage than bottle traps  Resealing traps may be used where the seal could be lost  The trap to a WC is an integral part of the WC. It has a 50 mm deep seal & the outlet is approximately 100 mm in dia. Practice plumbing exams © 6
  7. 7. Above Ground Drainage Definitions:-  Branch pipe – is the name given to the near horizontal pipe into which several appliance can discharge. Should fall at about 1:50. Stack – is the name given to the large diameter vertical drain  Ventilation pipe – is the name given to the smaller diameter pipes which ensure atmospheric pressure is allowed to enter at the top of the appliance outlet. Smallest dia. is 25 mm, but if above 15 m’s long or serves 2 or more appliances dia. is 32 mm  Vent – where the drainage system is open to atmosphere (usually above the roof-line) Practice plumbing exams © 7
  8. 8. Above Ground Drainage Discharge Systems:- There are 4 types of discharge systems:- 1. Dual Pipe System  Oldest system - based on soil & waste fittings kept separate until below ground  Soil stack discharges via slow bend, with ventilation (or anti-siphon ) pipe connected to each appliance  Ventilation pipes & stacks venting above roof with cages to prevent birds/matter entering  Waste stack discharges to a common gully with ventilation pipes also fitted to each appliance  Waste appliance traps may be 38mm (1 1/2”) seal Practice plumbing exams © 8
  9. 9. Discharge Systems:- 2. Single Pipe Ventilated System  Has a single stack discharging via slow bend to drain  Stack vents above roof via cage  Waste fittings have 75mm deep seal traps  Ventilation pipe fitted to each discharge branch – not each appliance  Used where long individual branches are required  The ventilation pipe may have its own separate vent, or return back into the stack vent at the top Practice plumbing exams © 9
  10. 10. Discharge Systems:- 2. Single Pipe Ventilated branch System 1st floor Ground floor Roof line Cage(s) House drain Sink WC Bath Basin Ventilation pipe-work Main ventilation stack Branch ventilating pipe Practice plumbing exams © 10
  11. 11. Above Ground Drainage Discharge Systems:- 3. Single Pipe Ventilated Stack System  Similar to Ventilated System, but only the stack is ventilated (mainly because of compression)  None of the branch pipes are ventilated  Only suitable where appliances are closely grouped to the stack Practice plumbing exams © 11
  12. 12. Discharge Systems:- 3. Single Pipe Ventilated Stack System 1st floor Ground floor Roof line Cage(s) House drain Sink WC Bath Basin Ventilation pipe-work Main ventilation stack Practice plumbing exams © 12
  13. 13. Above Ground Drainage Discharge Systems:- 4. Single Stack System  By far the most common with domestic dwellings  No ventilation pipes because stack is large enough to prevent pressure fluctuations  All waste fittings have 75mm deep seal P traps  Main stack is 100mm minimum with slow radius bend at base  Each branch connection should not cause ‘cross- flow’ into other branches Practice plumbing exams © 13
  14. 14. Discharge Systems:- 4. Single Stack System Recommended sizes for all branch pipes 1st floor Ground floor Roof line Cage Sink WC Bath Basin Single large dia. stack Large radius bend 450 mm minimum Practice plumbing exams © 14
  15. 15. Above Ground Drainage Crossflow:-  Occurs when one branch pipe connecting to the stack ‘crosses over the stack’ to another branch on the opposite side  Any branch-pipe should be at least 200 mm below the centre- line of a WC branch (or above it)  All other sizes of branch must be above/below any opposite branch by the following amount:- Practice plumbing exams © 15
  16. 16. Above Ground Drainage Stack size Distance ‘X’ 75 mm 90 mm 100 mm 110 mm 150 mm 250 mm Small branch connection ‘X’ Main stack Crossflow:- Practice plumbing exams © 16
  17. 17. Above Ground Drainage Single Stack System:- The following guidelines should apply  All appliances should be closely grouped around the stack in accordance with the following table Appliance Maximum no. fitted Minimum pipe size (mm) Gradient (mm/m) WC 8 100 9 - 90 Wash basin 4 50 18 - 90 Bowl urinal 5 50 18 - 90 Stall urinal 6 65 18 - 90 Unvented discharge pipes serving more than one appliance Practice plumbing exams © 17
  18. 18. Above Ground Drainage Single Stack System:- • All appliance should be fitted with P traps with discharge pipe dia at least equal to trap size • Bends in branch & stack pipes avoided • Long radius bend fitted to base of stack • Lowest branch connection to stack is at least 450 mm above invert level of drain. If building over 3 storeys – increased to 750 mm • 100 mm stack for up to 3 storeys, 150 mm up to 20 storeys with 2 groups of appliances on each floor • Branch connections to join the stack at 45° or 25 mm radius for pipes up to 75 mm, & 50 mm radius for larger pipes Practice plumbing exams © 18
  19. 19. Above Ground Drainage Pipe size (mm) Maximum length (m) Gradient (mm/m) 32 1.7 18 - 80 40 3.0 18 - 90 50 4.0 18 - 90 100 6.0 Minimum 18 Branch connections Single Stack System:- Practice plumbing exams © 19
  20. 20. Above Ground Drainage Ventilation:-  Essential to allow air in & out of drainage systems to ensure atmospheric pressures e.g. if negative pressures inside pipe-work – trap seals may be lost  By allowing air through the system, any foul matter adhering to inside of pipe would soon dry & be washed away  Venting pipes prevents the build up of hazardous gasses such as methane Practice plumbing exams © 20
  21. 21. Above Ground Drainage Ventilation:-  Air enters the drain at low level (manholes etc.) & rises through the stack by convection currents  The termination of the stack should be in a position that dies not cause nuisance or health hazard  If vent within 3 m’s of window opening – vent should be 0.9 m’s higher  Every vent should be fitted with a domical cage to exclude birds nesting etc.  Vent may be reduced in houses up to 2 storeys but must be 75 mm minimum Practice plumbing exams © 21
  22. 22. Above Ground Drainage Ventilation:-  Discharge stacks may terminate with an ‘Air Admittance Valve’  These valves are designed to allow air into the stack but not out of  They must not be fitted to:-  drains which have a record of surcharging  drains which an interceptor fitted  Limited in number to:-  where 5 houses connect to same drain – head of drain to be conventional vent  or where >5 houses head of drain & every 6th vent Practice plumbing exams © 22
  23. 23. Above Ground Drainage Stub Stack:- A short 100 mm dia. discharge stack which is capped with rodding eye at the top, but connected to ventilated stack no more than 6 m’s away  This may be extended to 12 m’s where a group of appliances is fitted  Any WC connection should be no more than 1.5 m’s above invert & waste conns 2 m’s max. “Stubby Stack” Practice plumbing exams © 23
  24. 24. Stub Stack:- 6 m’s maximum To ventilated drain Rodding eye Basin WC WC 1.5 m’s max. Waste Connections 2 m’s max. 100 mm discharge stack Practice plumbing exams © 24