DRAINAGE
House drainage is very essential system provide every building for proper drainage. Adequate arrangements are required to be made for quick collection, conveyance
and disposal of used water from the fittings without any risk to the health of
the occupants. It is also essential that the rain or storm water from the roof
and paved areas of building and the ground surface is suitably collected and
discharged without flooding the area. The term drainage or sewerage includes
the system of removal of sullage or waste water, soil water and storm water
from a building and conveying the same upto its ultimate point of treatment and
disposal.
Drainage below the ground:
This comprises of a system of underground house drain, inspection
chamber, main drain or sewer, manholes, ventilation shafts etc. provided for
conveying the sanitary sewage and storm water for final treatment or disposal.
1.Combined system: In this system the storm water is
completely mixed with the sanitary sewage and conveyed through a single drain or
sewer.
2. Separate system: In this system the storm water is not
allowed to get mixed with sanitary sewage. Two separate drains are provided,
one for sanitary sewage and other for drainage of storm water.
3. Partially combined system: In this system a part of storm water
run off from roofs, paved yards and street etc. is mixed with sanitary sewage
and conveyed through sewer and the remaining storm water is conveyed through
separate surface drains.
Drainage above the ground:
This consists of a system of vertical stacks, horizontal branches, floor
traps etc. provided for conveying sanitary sewage storm water etc. to the
underground drainage system for final disposal. This system is also known as
house or building drainage system.
TYPES OF PIPES
The pipes used in drainage system may be of cast iron, reinforced
concrete, pre stressed concrete, mild steel, wrought iron, asbestos, P.V.C. or
stone ware. For drainage work above ground, cast iron, asbestos cement or
P.V.C. pipes are generally used. The pipes may be jointed either with cement
mortar or lead. Stone ware pipes are commonly used for house drain. For sewers,
stone ware pipes, cement concrete pipes are normally used.
TRAPS
A trap is a fitting provided in a drainage system to prevent entry of
foul air or gases from the sewer or drain into the building. The barrier to the
passage of foul air is provided by the water seal in the trap. In its simplest
form a trap is merely a double bend or loop in the sanitary fitting, the depth
of water seal being the distance between the top of the first bend and the
bottom of the second. The deeper the seal the more efficient is the trap.
Depending upon the design of the trap, the depth of water seal vary from 40 mm
to 75 mm. The trap should always be fitted close to the waste or soil fitting
unless the trap from an integrated part of the fitting as in case of European
W.C.
Essentials of a good trap:
· It should maintain an efficient water
seal under all conditions of flow, both during the water flow as well as in the
absence of water flow.
· It should be self cleaning.
· It should not have any internal
projections, angles or contractions so as to permit unobstructed flow through
it.
· It should be provided with suitable
means of access for cleaning purpose.
Causes of loss or breaking of water
seal:
The primary object of providing a trap is lost, in case it is not
possible to retain its water seal. The water seal in a trap may break due to the
following causes:
· Evaporation of water in the trap
caused on account of not using the appliance for long time.
· Use of defective trap, defective
installation of trap or development of crack in trap after installation.
· Creation of partial vaccum caused due
to discharge of another fitting connected to the same stack leading to emptying
of the water of the seal by included siphonage.
· Build up of back pressure of sewer
gas in the drain forcing up the water of the trap seal.
· Due to capillary action caused by piece
of some porous material getting struck at the outlet of the trap in such a
manner that one end of the piece remains in water in water of the seal and the
other end of the piece remain hanging over the outlet.
TYPES OF TRAPS:
Traps can be made in different shapes and they are normally named after
the shape of the letter they resemble. Out of the different shapes, the trap
resembling the letter P, Q and S are more common. The traps are normally made
of cast iron and glazed stone ware. Depending upon the use and location, the
various types of traps can be broadly summarised under:
1.Floor trap or Nahani trap:
Trap provided in floors to collect used water from floors of bath room,
kitchen or washing floor etc. are known as floor traps or Nahani traps. This type
of trap is made of cast iron and it is provided with a removable grating on
top. The grating intercepts dust or other solid matter and prevents blockage of
trap. The depth of water seal of floor trap should not be less than 40 mm.
2. Gully trap:
Gully trap is a deep seal trap which is provided on the external face of
wall for disconnecting the waste water flowing from kitchen, bath, wash basin
& floors from the main drainage system. The deep water seal forms a barrier
for preventing the passage of foul air from house drain to inside of the
building. It is made of cast iron or glazed stoneware. The stoneware gully trap
has top square in plan where as the top of cast iron trap is normally circular.
It is fitted in a small masonry enclosure to meet the requirements of invent
levels of waste pipes discharging into the gully trap. Grating is provided on
top of the trap to intercept and retain all solid matter and prevent it from
flowing into the drain.
3. Intercepting trap:
This trap is provided at the junction of house drain and street sewer to
prevent entry of foul gases from sewer into the house drain. The intercepting
trap is thus provided to disconnect the house drain from the street sewer. The
trap is made of glazed stoneware and has a opening at top. The opening is kept
closed with a tight fitting plug which is taken out only during cleaning of the
trap. It has a deeper seal than normal traps not less than 100 mm.
4. Grease trap:
Grease traps are provided in large hotels, restaurants or other
industries producing large quantity of greasy waste with the primary aim of
removing the grease content of waste water before discharging the same into the
drain. If the greasy or oily matter is removed, being sticky in nature, it will
induce deposition of solids in the drain which can cause obstruction to the
flow of water in the drain and may finally result in blockage of drain. Grease
trap is a small masonry or cast iron chamber with a T or bent pipe to serve as
the outlet. The velocity of waste water flow gets reduced on entering the
grease trap and this results in separation of oily or greasy matter from the
waste water. The greasy matter appears as floating which is removed
periodically with the help of a mild steel tray.
5. Silt trap:
Silt traps are provided only in situations where the waste carries large
amount of silt, sand, coarse particles etc. It is a masonry chamber which
functions like grit chamber where the silt, sand etc. settle down before the
waste water is discharged into the drainage system.
SANITARY FITTINGS
The fittings or appliance used for collection and discharge of soil or
waster matter is termed as sanitary fittings. Different types of sanitary
fittings are normally made of ceramics, glazed fire clay, glazed fire clay,
glazed earthen ware or glazed chinaware. The fittings are so designed and
shaped that they have non-absorbent surface which can be cleaned easily.
1.Wash basin:
A wash basin is used for washing hands, face etc. It is made of porcelain
vitreous enamelled steel, or plastic and is available in various pattern and
sizes. The type of wash basin normally used in a house has an oval shaped bowl
with an overflow slot at top. The wash basin has a flat back and has provision
for making holes for installing one, two or even three taps. Normally two pillar
taps are provided one for cold water and the other for hot water. It has a
circular waste hole for draining out waste water from basin. A metallic stainer
is provided in the waste hole which is connected to a waste pipe either
directly or through a bottle trap for discharge of waste water into the floor
trap. The basin is normally mounted on 2 angle irons fixed in the wall. The top
of the wash basin should be kept at a height of about 75 to 80 cm from floor
level.
2. Sink:
Sink is commonly used in kitchens, hospitals and laboratories. Sink is
made of glazed fire clay, stainless steel, plastic, marble and R.C.C. Sink may
be made with or without overflow arrangement. In hospitals and laboratories
only vitreous sinks are preferred. It has a circular waste hole for fixing the
metallic stainer to which the waste pipe is attached for conveying the
discharge from sink to the floor trap. The kitchen sink is invariably provided
with a drain board.
3. Bath tub:
A shower is considered to be more efficient and hygienic means of taking
bath and as such is widely used in bathrooms by most of the people. However,
some people prefer to use bath tub as they find it to be more comfortable and
relaxing. Use of bath tub is restricted to certain class of hotels and private
residences. Bath tubs are made of enamelled steel, gel coated fibre glass,
reinforced resign, marble finishes etc. Bath tubs are provided with holes for
fixing hot and cold water connections and have provision for over flow and
waste water pipes.
4. Urinals:
Urinals fall under the category of soil appliance and as such the
discharge from urinals is connected to soil pipe either directly or through a
trap provided with gun metal or bass domed shaped removable grating. From
hygienic consideration it is desirable to provide glazed tiles on walls of
urinal preferably upto door height.
a. Bowl type:
This is one-piece construction with integral flushing box rim having 12
hole suitably distributed for proper flushing. The urinal has an outlet horn at
bottom for connecting to the trap and an outlet pipe. In another pattern of bowl
type urinal, the appliance has a porcelain trap inbuilt with the pan as a
single piece. In case number of urinals are required to be installed in a row,
it is necessary to provide vertical partition between two urinals from
consideration of privacy.
b. Slab or stall type:
This type of urinal is manufactured either as a single unit or as a range
of two or more units. In case of single unit the width of stall should not be
less than 75 cm. The flushing of urine is normally carried out through
automatic flushing cistern which operates at regular intervals of 10 to 15
minutes. The discharge from the series of stalls in a row is usually carried
through a glazed semi-circular drain which has a sharp fall towards the trap from
where it is discharged into the soil pipe.
5. Water closets:
Water closet is a sanitary appliance provided for collection and
discharge of human excreta into the soil pipe through a trap. The W.C. is
connected to a flushing cistern to flush the excreta from the pan. W.C. is made
of glazed earthen ware, fire clay or white vitreous chinaware. The types of
W.C.s commonly used are as under:
a. Indian or squatting type W.C.:
This type of W.C. is used in squatting position. The W.C. consists of two
pieces ..Porcelain pan and a Pors trap. The W.C. pan along with the trap is
fixed flush with the floor of W.C. Two foot rests are provided on either side
of the pan. The pan has inbuilt flushing rim having number of holes through
which the flushing water from the cistern is discharged. The flushing cistern
is normally kept 1.8 to 2 m above the floor level. The contents of the pan are
removed by the gravity flush of water.
When the pan and foot rests are made as integral single piece, the
appliance is termed as Orissa pattern. In this type while using the W.C. the
excreta does not fall directly into the trap and in case the flushing is not
proper, the matter remains stuck to the pan which is considered unhygienic.
b. European type W.C.:
This type of W.C. is used in sitting position over a plastic seat hinged
to the appliance. This is a pedestal type of appliance with the pan and trap in
a single piece. The pan is shaped in the form of a short inverted cone with an
almost vertical back and providing minimum fouling area. The main advantage is
that by virtue of the design of pan, the excreta falls almost directly on the
water in the trap and chances of the same getting struck to the sides of the
pan are less. The flushing rim of the pan is attached to the cistern which may
be of high level type or low level type for getting flushing water.
Flushing Cistern:
A Flushing cistern is used for storage and discharge of water for
flushing of contents from a W.C. or urinal. Cistern is made of cast iron,
vitreous china or pressed steel plates or plastic. The capacity of flushing
cistern varies from 10 to 15 litres. When the cistern is fixed at a height of
1.58 to 2 m from floor level it is termed as high level cistern. Indian type
W.C. is invariably provided with high level cistern made of cast iron. The
European type cistern made up of porcelain. The low level operates at a height
not more than 30 cm between top of pan and underside of cistern.
Flushing cistern are of three types:
1.Valveless siphonic type or Bell type
2. Valve fitted type or piston type
3. Automatic flushing type
The valve less type or bel type of flushing cistern is used only as high
level cistern whereas the piston type as well as automatic type can be used
both as high level as low level cistern.
The components of a bell type cistern which is most widely used for
Indian type W.C. are as under:
· A cast iron box having a stone
capacity of 10 to 15 litres.
· A central outlet stand pipe covered
by a bell or dome shaped cast iron vessel.
· A lever arrangement attached with a
long chain.
· A float valve with a float.
· Inlet, outlet and overflow pipes.
In this case the bell shaped vessel is connected to a chain through a
lever arrangement. The float valve provided with a ball float, closes the water
supply to the cistern as soon as the pre fixed level is reached.
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