Sewer Appurtenances | Trappings used in Sewers
Sewer Appurtenances are those structures of the sewerage system which are thus constructed at suitable interval and other locations along a sewer line. These are to assist in efficient operation and also maintenance of the system.
Following are important sewer appurtenances
- Catch Basins
- Clean Outs
- Drop Manholes
- Flushing Tanks
- Grease and Oil Traps
- Inverted Siphons
- Storm Regulators
An inlet is a device meant to admit the storm water or surface wash and therefore convey it into a storm or combined sewer. Inlets are thus not necessary for the separate sewers. Therefore, Inlets are of 3 types –
- curb inlet or vertical inlet
- gutter inlet or horizontal inlet
- combination inlet
Maximum spacing between inlets on a straight road thus 30 m is recommended. Inlets, also located at street intersections and so placed that cross walks will not be flooded. Therefore street corners are avoided for this purpose. These are connected to near by manholes however through pipelines.
2. Catch Basins or Catchpits
A catch basin or a catchpit is a special type of inlet, in which a basin provided which allows grit, sand, debris etc. flowing in with storm water, settle out. The outlet is usually trapped to prevent escape of odours from the sewers and to retain floating matter. The settled matter is taken out periodically.
3. Clean Outs
A clean out is an inclined pipe with its one end connected to the underground sewer line and the other end brought up to ground level, with a proper cover at the top. They are meant for cleaning out the lateral sewers and provided instead of manholes.
A manhole is a masonry or RCC chamber constructed on the alignment of a sewer for providing access to the sewer. Its purpose is to provide access for inspection, testing, cleaning and removal of obstruction from the sewer line. It is helpful in changing the direction or alignment or both.
Classification of Manholes on the basis of depth are as –
- Shallow Manholes (0.75 to 0.9 m depth, also termed as inspection chamber)
- Normal Manholes (1.5 m depth, cross section varies 0.8 to 1 m by 1 to 1.2 m)
- Deep Manholes (deeper than 1.5 m, its component parts includes access shaft, working chamber, invert, side walls, steps or ladder, top cover)
5. Drop Manhole
A drop manhole is a special type of manhole on a sewer line which is constructed to provide a connection between a high level branch sewer to a low level main sewer. When a branch sewer enters a manhole by more than 0.5 to 0.6 m above the main sewer, the sewage is not allowed to fall directly into the manhole. This is to avoid the possibilities of sewage being thrown on persons entering in the working chamber of manhole. Instead, the sewage of the the branch sewer is brought in the manhole of the main sewer either by inclined pipe or through a down pipe. In the former case, it is termed as ramp, while in the latter case it is referred as a drop manhole.
Lampholes are special openings, constructed to join a hole in the sewer and the ground, for the purpose of lowering a lamp inside the sewer. A lamphole may consists of either a vertical concrete or stoneware pipe connected to the sewer through a Tee-junction. A manhole cover with suitable supporting frame is therefore provided on its top, to take up the load of the traffic. It is thus constructed where the construction of manhole is difficult.
7. Flushing Tanks used in Sewer Appurtenances
A flushing tank is a device or arrangement which holds water and then throws it into the sewer for the purpose of flushing it. It can be operated either manually or automatically. Sewer laid on flat gradients may not produce self cleansing velocity and also may get blocked frequently. Thus they can be cleaned with the help of such flushing tanks.
Flushing may be achieved by 2 methods
(i) Hand operated flushing operation
(ii) Automatic flushing tanks
8. Grease and Oil Traps used in Sewer Appurtenances
Grease and Oil Traps are those sewer appurtenances which are specially built chambers on the sewers to exclude grease and oil from sewage before they enter the sewer line. Such traps are located near those sources, such as automobile repair workshop, garages, kitchens of restaurant / hotels, oil and grease industries.
9. Inverted Siphons used in Sewer Appurtenances
When a sewer line dips below the hydraulic gradient line, it is called an inverted siphon. The purpose is to carry the sewer under the obstruction such as – roadway, railway, stream, river etc. and regain elevation as much as possible. The sewage in it flows under pressure which is greater than atmospheric. Most appropriate name of this is depressed sewer.
10. Storm Regulators
Storm Regulators are the sewer appurtenances which constructed for combined sewerage system, so as to permit the diversion of storm water when the discharge exceeds the certain value. The excess water is thus diverted to a natural stream or river.
Following are 3 types of Storm Regulator:
(i) Over flow or side flow weirs
(ii) Leaping weirs
(iii) Siphon spillways