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Above ground drainage part 2

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Above ground drainage part 2

  1. 1. PART 2 Practice plumbing exams © www.practiceplumbingexams.com
  2. 2. IN THIS SLIDE SHOW  Trap Seal Loss  Mechanical Disposal Units  Pipe Sizing of A. G. Drainage  Soundness test  Performance Testing  Eaves Guttering  Calculation of Roof Area  rain water pipes Practice plumbing exams © www.practiceplumbingexams.com
  3. 3. Above Ground Drainage Trap Seal Loss:-  If the seal in a trap is lost, nasty smells will enter into the building; this means the seal should be maintained at all times.  Trap seal may be lost due to leakage or evaporation  following faults may also be the reason for loss of trap seal apparent:- Practice plumbing exams © www.practiceplumbingexams.com
  4. 4. Above Ground Drainage Trap Seal Loss – Wavering out:- • Caused by the effect of wind passing over the top of a vent & bringing about pressure fluctuations within the stack • Pressure variations will eventually pull the trap seal into the stack Corrective action:-  Fit air admittance valve below roof-line  Install re-sealing trap  Ensure air is admitted to drain/stack at ground level Practice plumbing exams © www.practiceplumbingexams.com
  5. 5. Above Ground Drainage Trap Seal Loss – Compression:- • Generally occurs in high rise buildings where the discharged water compresses air at the base of the stack & forces out the trap seal in the nearest trap by generating air pressures greater than atmospheric Corrective action:-  Ensure long radius bend fitted at base of stack  No branch connections within 450 mm of invert  Fit vent pipe to stack Practice plumbing exams © www.practiceplumbingexams.com
  6. 6. Above Ground Drainage Trap Seal Loss –Induced syphonage:- • Caused when two of more appliances connected to same branch pipe & upper appliance is emptied to form a solid ‘plug’ of water in branch • This then forms a vacuum to suck out the trap seal out of the adjacent trap Corrective action:-  Fit ventilation pipes  Fit larger branch pipe  Fit re-sealing trap Practice plumbing exams © www.practiceplumbingexams.com
  7. 7. Above Ground Drainage Trap Seal Loss – Self Syphonage:- • Caused by funnel shaped basins which when emptied form a solid plug of water in the discharge pipe • Again this causes a vacuum in the pipe setting up a syphon Corrective action:-  Fit larger branch pipe  Fit re-sealing trap Practice plumbing exams © www.practiceplumbingexams.com
  8. 8. Above Ground Drainage Re-sealing traps:- • A trap designed to maintain its seal should a partial vacuum be created in the waste discharge pipe • Various designs available • One incorporates an anti-vacuum valve which opens under vacuum conditions • Another retains a larger volume of water so that when the syphon is broken, a reserve chamber of water is retained to form an adequate seal Practice plumbing exams © www.practiceplumbingexams.com
  9. 9. Above Ground Drainage Mechanical Disposal Units:- 1. Food Waste Disposal Units:  Mechanical device fitted under special sink bowl & is attached to 50 mm dia. waste fitting. This macerates (cuts into pulp) kitchen waste & water which is then pumped to discharge & into drain  Special sink unit is required, and separate trap fitted after unit to maintain seal  To be supplied via un-switched fused spur, so that electric supply is always maintained to unit Practice plumbing exams © www.practiceplumbingexams.com
  10. 10. Above Ground Drainage Mechanical Disposal Units:- 2. WC Macerators:  Packaged unit designed to pump the effluent from a WC (& can take other waste from basins etc.)  Fitted behind WC, it consists of macerator & pump to remove solid matter up to 4 metres vertically & 50 metres horizontally via a small 19 mm bore discharge pipe  May only be installed if another WC discharges into gravity system in case of electrical failure  Vertical rise must precede any horizontal run  Macerator to be supplied via un-switched fused spur Practice plumbing exams © www.practiceplumbingexams.com
  11. 11. Above Ground Drainage Pipe Sizing of A. G. Drainage:- • The size of the main vertical discharge stack will depend upon the amount of appliances connected & the type of building, & the following guidelines should apply: •This is a rough guide :  100mm diameter single stack without ventilation pipes for buildings up to 3 storeys  100mm diameter single stack with 50mm ventilation pipe (ventilated stack system) up to 12 storeys  150mm diameter single stack with ventilation pipe up to 24 storeys Practice plumbing exams © www.practiceplumbingexams.com
  12. 12. Above Ground Drainage Pipe Sizing of A. G. Drainage:- • Discharge Unit Method 1. Take the number of appliances (baths, basins etc.) & multiply by the units on the table for the area of use 2. Add these unit values together 3. Check on the table for size of vertical stack 4. If discharge passes through a horizontal pipe or drain, use the next table to determine the size & fall of the drain 5. Remember that the stack size will be the minimum size of drain! Practice plumbing exams © www.practiceplumbingexams.com
  13. 13. Above Ground Drainage Sanitary Appliance Domestic Use Commercial Use Congested Use e.g. Schools 9 litre WC 7 14 27 7.5 litre WC 6 12 24 6 litre WC 6 11 23 Sink 7 13 26 Wash basin 1 3 5 Bath 7 17 17 Washing machine 3 18 18 Discharge Unit Values:- Practice plumbing exams © www.practiceplumbingexams.com
  14. 14. Above Ground Drainage Internal Bore (mm) Maximum Discharge Units 50 10 65 60 75 200 90 350 100 750 125 2500 150 5500 Table 1. Maximum number of Discharge Units For Vertical Stacks:- Practice plumbing exams © www.practiceplumbingexams.com
  15. 15. Above Ground Drainage Internal Bore (mm) 1 in 111 1 in 45 1 in 22 32 - 1 1 40 - 2 8 50 - 10 26 65 - 35 95 75 - 100 230 90 120 230 460 100 230 430 1050 125 780 1500 3000 150 2000 3500 7500 Table 2. Maximum number of Discharge Units for Horizontal Pipes or Drains:- Gradient Practice plumbing exams © www.practiceplumbingexams.com
  16. 16. Above Ground Drainage Generally speaking the system should be inspected & tested at the beginning and end of each installation There are two tests to be carried out:- 1. Soundness Testing – where an air test is made to the system 2. Performance Testing – where a test is made to see how well the system performs Practice plumbing exams © www.practiceplumbingexams.com
  17. 17. Above Ground Drainage Soundness test (air test):- • Insert testing bags or expandable plugs into each end of the test • Cover the plugs with water to seal • Ensure all traps are full • Attach pump & manometer to one end & pump air pressure to 38 mm • Isolate pump & leave for 3 minutes • If a leak exists – locate via leak detection fluid, repair & re-test Practice plumbing exams © www.practiceplumbingexams.com
  18. 18. Above Ground Drainage Performance Testing:- • Each of the following tests should be carried 3 times to ensure at least 25 mm seal remains in every trap (checked by dipstick)  Test for self siphonage - fill every appliance to overflowing & remove plugs, then check seals  Test for induced siphonage – fill several upstream appliances & discharge simultaneously, then check downstream sealsPractice plumbing exams © www.practiceplumbingexams.com
  19. 19. Above Ground Drainage Performance Testing:- Test for siphonage & compression in stacks – a selection of appliances (as indicated in table) to be discharged simultaneously fro highest floor(s), this giving worst possible conditions Example:- A 7 storey block of flats has 2 sanitary appliances of each type on each floor (i.e. 2 baths, 2 sinks). The amount & kind of appliance to be discharged will be: 2 x 7 = 14 of each kind of appliance From the table – 1 WC, 2 sinks & 1 basin should be discharged from the top floor Practice plumbing exams © www.practiceplumbingexams.com
  20. 20. Performance Testing in Discharge Stacks Type of Building No. of each appliance on stack WC Sink Basin Domestic 1 – 9 1 1 1 Domestic 10 – 24 1 2 1 Domestic 25 – 35 1 3 2 Domestic 36 – 50 2 3 2 Domestic 51 - 65 2 4 2 Commercial 1 – 9 1 – 2 - 1 – 2 Commercial 10 – 18 1 – 2 - 2 – 3 Commercial 19 – 26 2 – 3 - 2 – 3 Commercial 27 – 50 2 – 3 - 3 – 4 Commercial 51 – 78 3 – 4 - 4 Commercial 79 - 100 3 - 4 - 5 Practice plumbing exams © www.practiceplumbingexams.com
  21. 21. Above Ground Drainage Eaves Guttering:-  Eaves guttering may be fixed at the edge of a pitched roof to receive & remove the rainwater run-off  Guttering was made from Asbestos, Cast iron & Galvanised steel; but is now usually made in Plastics  There are many different sizes, colours & styles – 75 to 150 mm & ½ round, Ogee, Square-line etc. Practice plumbing exams © www.practiceplumbingexams.com
  22. 22. Above Ground Drainage Eaves Guttering:- Installation -  Always allow for expansion/contraction  Minimum gradient of 1:600  Fix brackets equidistant but no more than 1 metre apart  Obtain “line of brackets” by stringing from each end  The size of the gutter will depend upon the pitch & the area to be drained & the following table may be helpful in this respect:- Practice plumbing exams © www.practiceplumbingexams.com
  23. 23. Above Ground Drainage Roof Pitch Effective Area (m²) Flat Plan area 30° Plan area x 1.15 45° Plan area x 1.4 60° Plan area x 2.0 70° to vertical Elevation area x 0.5 Calculation of Roof Area:- Practice plumbing exams © www.practiceplumbingexams.com
  24. 24. Above Ground Drainage Eaves Guttering:- Example – If the plan area of a 45° pitched roof measures 6 x 4 metres, the effective area will be = 6 x 4 x 1.4 = 33.6 m² Once the effective area has been determined, the gutter size may be found by use of the following table:- Practice plumbing exams © www.practiceplumbingexams.com
  25. 25. Above Ground Drainage Max effective area (m²) Gutter size (mm) Outlet size (mm) Flow capacity (litres/s) 18 75 50 0.38 37 100 63 0.78 53 115 63 1.11 65 125 75 1.37 103 150 89 2.16 Half round gutter size (outlet at one end) Practice plumbing exams © www.practiceplumbingexams.com
  26. 26. Above Ground Drainage Rainwater Pipes:- • Are the pipes which convey the water collected down to the drain at ground level • In most cases run externally with simple spigot & socket joints • Again, room to be left for expansion/contraction • Fix vertically by using plumb bob • Rainwater pipes should discharge to a Storm Water Sewer (if available) via gully or back inlet gully • If only a Combined system is available, the down-pipe may discharge into this via trapped gully Practice plumbing exams © www.practiceplumbingexams.com
  27. 27. Performance Testing in Discharge Stacks Type of Building No. of each appliance on stack WC Sink Basin Domestic Domestic Domestic Domestic Domestic Commercial Commercial Commercial Commercial Commercial Commercial Practice plumbing exams © www.practiceplumbingexams.com
  28. 28. Above Ground Drainage Pipe Sizing Exercise 1. You are asked to design an above ground drainage system for some office accommodation based on the information below. 1. What size of single stack would you recommend? 2. What size of below ground drain would you recommend. 3. At what fall should this drain be laid at? 12 WC’s - 7 1/2 litre flush 18 Wash basins 2 Sinks WC’s - 12 x 12 = 144 Basins - 18 x 3 = 54 Sink - 2 x 13 = 26 total = 224 therefore 90 mm stack sufficient 90 mm drain @ 1 in 45 fallPractice plumbing exams © www.practiceplumbingexams.com
  29. 29. Above Ground Drainage Pipe Sizing Exercise 2. You are asked to design an above ground drainage system for a school based on the information below. 1. What size of single stack would you recommend? 2. What size of below ground drain would you recommend. 3. At what fall should this drain be laid at? 24 WC’s - 7 1/2 litre flush 26 Wash basins 4 Sinks 1 Washing machine WC’s - 24 x 24 = 576 Basins - 26 x 5 = 130 Sinks 4 x 26 = 104 W/Machine - 1 x 18 = 18 total = 828 therefore 125 mm stack sufficient According to tables a 100 mm drain @ 1 in 22 fall would be sufficient, however the drain should not be of lesser dia. Than the stack. So a 125 mm drain @ 1 in 45 should be installed. Practice plumbing exams © www.practiceplumbingexams.com

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