1- Two-Pipe System
In this system, two pipes are provided. One pipe collects the foul soil and lavatory wastes, whereas the second pipe collects the unfoul water from the kitchen, bathrooms, house washings, rainwater etc. The soil pipes (pipes carrying the soil waste) are directly connected to the drain, whereas the waste pipes (pipes carrying unfoul water) are connected through the trapped gully. All the traps used in this system are fully ventilated.
2- One-Pipe System
In this system, only one main pipe is provided which collects both the foul soil waste as well as unfoul waste from the buildings. The main pipe is directly connected to the drainage system. If this system is provided in multi-storeyed buildings the lavatory blocks of various floors are so placed one over the other so that the wastewater discharged from the different units can be carried through short branch drains. All the traps of the W.C., basins sinks, etc. are fully ventilated and connected to the ventilation pipe. But all gully traps and waste pipes are completely dispensed with.
3- Single-Stack System
Fig. 24.23 illustrates this system. This is similar to the single pipe system, the only difference being that no ventilation is provided even in the traps too.
4- Single-Stack Partially Ventilated System
This system is in between the one pipe and single-stack system. In this system, only one pipe is provided to collect all types of wastewater foul as well as unfoul. A relief vent pipe is provided for ventilating only the water closet-traps.
Nowadays in modern multi-storeyed buildings, the one-pipe system is becoming popular due to its low cost. C.B.R.I. Roorkee, after doing extensive research on this system, has recommended it in modern buildings.
An analysis of this system showed that the flow from the applicant to the stack through the branch is momentarily halted at the sharp change of flow of direction. Sometimes a plug of water is formed immediately at the junction, which depends upon the rate of change of discharge and the size of the branch. This gives rise to unequal pressures at the seals, for the lower floors of the building and sometimes this breaks the water seals of the sanitary appliances. C.B.R.I has recommended the use of aerator and deaerator in the stack to increase its capacity.
The function of the aerator is to prevent the formation of the plugs of water in the vertical stack and to make a mixture of water and air of low specific gravity. The aerators are provided on every floor.
(a) For supply of water to various sanitary fittings.
(b) For the collection of wastewater from the sanitary fittings.
(c) For the collection of rainwater from the roofs, house and courtyard washings.
The fixing of sanitary appliances in the walls, floor and other places and their connected pipe works are to be done carefully for their proper functioning. Deaerators are provided at the foot of the stack to separate air and water to avoid excessive backpressure. Studies carried out by C.B.R.I. revealed that 100 mm dia. Stack with these fittings can be safely used up to 15 storeys, whereas a single stack system without these fittings can be used only up to 5 storeys.
The two-pipe system is costly as it requires much labour and material with antisyphonage pipe, as compared with the single stack system of plumbing. No antisyphonage pipe is required. The single stack system is becoming popular in modern building construction. The tests are done by C.B.R.I. on 5 storeyed building shows that there was no break of water seals.