Topic 4
I. Sanitary drainage system
The design of a sanitary pipe work system should be able to carry away the foul water with the minimum amount of pipe work from the building quickly and smoothly.
The code of practices allow the following design and practices:
- Single stack system for residential buildings up to 6 storeys
- Ventilated stack system for buildings up to 30 storeys
- Fully ventilated system for buildings up to 6 storeys with 7 storeys or more
The maximum distant from the discharge stack to the discharge pipe of the furthest or last appliance should be of 2.5m and the maximum nos. of discharge pipes connected to the discharge stack should be 2. There should be a minimum of 225mm between the discharge pipe and the cross vent connection points. The uppermost main discharge stack (open roof top) should be installed at a minimum distant of 3m away from any window or opening adjoining the building. The main discharge stack should be at least 150mm throughout the whole length.
The sanitary appliances and fittings connected to the sanitary drainage system are:
Water closet pan, flushing cistern, urinal, flush valve, automatic flushing devices, bidet, special sanitary appliances subjected to approval from PUB, floor trap and floor waste.
The urinal and floor traps need to be vented to prevent water siphoning. The purpose of venting the floor trap is to prevent the water siphoning so that a water trap or seal is formed at the bottom of the floor trap. Water seal or trap is to prevent foul smell and insects from entering the building through the sanitary drainage system.
Generally, there are 2 types of sanitary appliances connecting to the soil waste drainage system. They are:
Soil sanitary appliances – For the reception and discharge of excretory matters. Examples are: WC, urinal and bidet.
Soil sanitary appliances should have at least one trap with a water seal of not less than 50mm before connecting to a separate branch drain-line to an inspection chamber at level 1 or to a discharge pipe on upper story level.
Waste sanitary appliances – For the reception and discharge of water for cleaning or culinary purposes. Examples are: Sink, basin, bath and shower.
Sources – From SIM University – School of Science and Technology note
Further details – Refer to the local Sanitary Plumbing System, code of practice on sewerage and sanitary works, 2000
II. Domestic water supply system
There are 3 modes of water supply for a building based on local requirements:
- The level of highest fitting below 125m reduced level with direct water supply
- The level of highest fitting above 125m reduced level but below 137m reduced level with indirect water supply through high level storage tank
- The level of highest fitting above 137m reduced level with indirect water supply through low level with pumping (transfer pump and tank) to high level tanks
The storage capacity of the high level tank should be sized to be equivalent to the one day’s water requirement. If the storage capacity is more than 5,000 litres, the tank shall be compartmentalised with balancing pipe and valve so that each tank is able to be isolated for cleaning and inspection without interfering with the supply of water. For tall building, fittings should not be subjected to pressures greater than 35m head. For water tank, the overflow pipe should have an internal diameter larger than that of the inlet pipe. The overflowing level of the overflow pipe should be below the invert of the inlet pipe at a vertical distance of not less than the diameter of the overflow pipe. A warning alarm will be activated when the water reaches a level of not less than 50mm below the invert of the overflow pipe. Storage tank shall have a water line set at a vertical distance of not less than 25mm below the warning alarm level. The pump should be powered by the emergency power source switchboard.
Sources from the SIM university – School of Science and Technology note and for further details, refer to the CP48 Code of Practice for Water Services
Domestic water supply storage and water transfer tanks:
- Both are installed with ball float valves and water sensor electrodes for high rise building.
The ball float valve is to control the amount of water entering the tank to prevent water from overflowing from the overflow outlet.
2. The water sensor electrodes which are installed in the water tank and are connected via the cables to the float relays are used to activate the domestic transfer pump when water level falls below the set level and cut off the pump when the water level rises to the required level.
3. The water sensor electrodes and relays are also used to cut off the pump when the water level is below the low or above the high set level points to prevent the pump from running dry and water from overflowing from the overflowing outlet.
Facilities Maintenance Knowledge 