Note on Sanitary

1. Chapter - 4
Sewer Appurtenances
Prepared by: Rashna Pandit

2. Presentation Outline
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4.1. Necessity of sewer appurtenances
4.2. Construction of sewer appurtenances- (location , function and construction)
4.2.1. Manhole
4.2.2. Drop manhole
4.2.3. Street inlets
4.2.4. Catch basin
4.2.5. Flushing device
4.2.6. Inverted siphon
4.2.7. Ventilating shaft
4.2.8. Water closet
4.2.9. Trap
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Sewer Appurtenances are those structures or devices in sewerage
system which is constructed at suitable interval and locations along a sewer
line, to assist in the efficient operation or proper functioning and maintenance
of the system.
Following are the important sewer appurtenances:
Manhole
Drop manhole
Street inlets
Catch basin
Flushing device
Inverted siphon
Ventilating shaft
Trap
Sewer Appurtenances

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Sewer Appurtenances

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4.2. Construction of sewer appurtenances- (location ,
function and construction)
4.2.1 Manhole
Objectives of providing Manhole:
➢ To provide manual access for inspection, cleaning
,testing etc in sewer.
➢ To allow joining of sewer lines in case of changing in
directions or at level or both.
➢ To lay sewer in convenient length and to achieve the
ventilation of sewers.
Location of Manhole:
They are provided at the centerline of the sewer and
at every bend, junctions, and every change of gradient
, direction and size and at other convenient locations.

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Construction of manhole
Top cover and frame
➢ Depth of frame is 20-25 cm and width is 10cm. The clear cover of the
opening should be at least 50 cm. The top cover with frame weights 90-270
kg.
Access Shaft
➢ The upper portion of the manhole is called the access shaft which
provides an access to the working chamber. Its size is 0.6m X0.75m for
rectangular and 0.6 to 0.75m diameter for circular manhole.
Working Chamber
➢ It is the lower portion of the manhole, which provides working space
and should have minimum 0.9m X 1.2m for rectangular and 1.2m diameter
for circular manhole.

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Construction of manhole
Bottom or Invert or Benching
➢ The bottom of the manhole is made of concrete bed of 150- 300 mm
thick and top slope of 1:6 towards the centre and called benching which
may be semi- circular or U-shaped.
Steps or Ladder
➢ It is the CI or steel steps provided for all deep manholes and made of and
placed 30 cm apart vertically for up and down.
Classification of Manhole
➢ Shallow manhole= depth 0.75m -0.9m
➢ Normal or medium manhole= depth 1.5m
➢ Deep manhole= depth greater than 1.5m

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• It is a special type of manhole used to
connect a branch sewer entering from
a high level to low-level main sewer.
• The main purpose of the drop manhole
is to avoid splashing of sewage on the
man working in manhole.
Drop manhole

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Lamp hole
• It consists of a vertical shaft of 20-30 cm
diameter connected to the sewer and the
top opening is covered by CI or RCC cover.

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Street inlets
Street inlets are the devices or opening in the street
constructed to intercept the storm water and surface
wash along the street and to convey it into the sewer.
Types of Street Inlets.
➢ Curb Inlet: It consists of a vertical opening with a CI
or street bar grating on the curb.
➢ Gutter Inlet: It consists of a horizontal opening with
CI or steel bar grating directly on the gutter to catch
large quantity of water
➢ Combined Inlet: It is the combination of curb and
gutter inlet.

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Catch Basin (Catch pit)
It is a RCC or masontry chamber constructed below
the street inlets to prevent the flow of girt, sand or
debris to the sewer.
➢ It has depth of 600 to 750 mm may be square
,rectangular or square of dimension 600- 900mm.
➢ After entering the water the sand , girt etc
settles down in the pit and only water enter s the
outlet pipe.
➢ The outlet pipe is fixed about 60 cm above the
bottom with trap to prevent from out coming of
odour.

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Flushing tank
➢ To reduce clogging of sewer due to various obstructions.
➢ It supplies water so as to flush the obstructions present in the sewer.
➢ It consists of flushing chamber used to store water to flush the clogged
sewer.
➢ It is of two types: Manually operated and automatically operated.
➢ In manually operated type, water is stored to certain level and opened
when desired.

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Automatic Flushing tank
Fig: Automatic Flushing Tank

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Automatic Flushing tank

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Sand, grease and oil trap
➢ Sewage from hotels, restaurants, kitchen,
automobile work-shop, garage and industries
contains grease are restricted by this.
➢ So, to trap and check them a structure is
constructed at the entrance of sewer is called sand,
grease and oil trap.
➢ It consists of a smaller tank or RCC or masonry
with or without baffle walls and a grating for inlet
and a outlet pipe to sewer.
➢ These traps are cleaned regularly for proper
functioning.

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Inverted siphon
➢ In areas having depression in the ground, the
lower level of the sewer is depressed below the
road, canals, etc and called depression sewer also
called Inverted Siphon.
➢ A true siphon flows full with the flow line above
the HGL , and therefore flows under less than
atmospheric pressure
➢ but inverted siphon flows full with the flow line
below the HGL and, therefore, flows under greater
than atmospheric pressure.
➢ It consists of an inlet and outlet chamber with
cover and three pipes of different sizes laid in
parallel to each other.

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Ventilating Shaft
During decomposition of organic matters within the sewer
the foul gases is produced and causes harm to human
health as well reduce the life of sewers by corroding the
sewers.
 So, to overcome the above negative impacts and to
help free flow of sewage with relief pressure, the
ventilation is provided to the sewer lines at every 80 m-
300 m to provide fresh air to the worker in the Manhole.
 In open areas ventilation is connected with manhole
cover but in crowded areas air tight ventilating shaft
with concrete base is provided.

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Sewer outlet
➢ Storm water or the treated water may be discharged to the small steams
or large water bodies through sewer outlet.
➢ It consists of simple concrete head wall and apron to prevent corrosion.
➢ Sewer discharging into large bodies of water are usually extended beyond
the banks into fairly deep water where dispersion and diffusion will aid in
mixing sewage with the surrounding water.
➢ A masonry head structure is made at the bank and a CI pipe is laid out to
discharge into river.

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