Following are the various equipment and devices used for clearing sewers: 1. Portable Pump-Set 2. Sectioned Sewer Rods 3. Flexible Sewer Rod 4. Ferret Used in Conjunction with a Fire Hose 5. Sewer Cleaning Bucket Machine 6. Rodding Machine with Flexible Sewer Rods 7. Dredger 8. Scraper 9. Hydraulically Propelled Devices.
Device # 1. Portable Pump-Set:
This device is used in situations where sewers are blocked completely and sewage has accumulated in manholes, for pumping the collected sewage out to tackle the sewage blockage. These pumps should be of non-clogging type, preferably on four wheel trailers for the largest size and should be provided with a self-priming unit to save time and effort.
Device # 2. Sectioned Sewer Rods:
These rods are used for cleaning small sewers. These may be bamboo or teak wood or light metal usually about 10 m long at the end of which is a coupling which remains intact in the sewer but can be easily disjointed in the manhole. Sections of the rods are pushed down the sewer until the obstruction is reached and dislodged.
The front or the advancing end of the sewer rod is usually fitted with a cutting edge to cut and remove the obstruction. These rods are also used in locating the obstruction from either manhole in case the particular portion of the sewer is to be repaired/exposed.
Device # 3. Flexible Sewer Rod:
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This is made by sandwiching a manila rope between bamboo strips and tying at short intervals. The flexible rod is first introduced from one manhole to the other, its end being connected to a thicker rope when dragged down the sewer, draws out sand and detritus into the downstream manhole. The flexible sewer rod is used in routine sewer cleaning works.
Device # 4. Ferret Used in Conjunction with a Fire Hose:
This is used for breaking and removing sand stoppages. The high velocity jet stream, of water is used from the hose-connected to the fire-hydrant towards upstream and downstream sides of the sewer. The forward stream loosens the accumulated debris ahead of the tool and the rear jets of the ferret admit water to wash the sand back downstream, where it can be removed from the manhole manually.
Device # 5. Sewer Cleaning Bucket Machine:
This machine consists of two powered winches with cables in between. In cleaning a section of the sewer, the winches are centred over two adjacent manholes. To get the cable from one winch to the other, it is necessary to thread the cable through the sewer line by means of sewer rods.
The cable from the drum of each winch is fastened to the barrel on each end of an expansion sewer bucket fitted with closing device, so that the bucket can be pulled in either direction by the machine on the appropriate end. The bucket is pulled into the loosened. Material in the sewer until the operator feels that it is loaded with debris.
The motor is then thrown out of gear and the opposite winch is put into action. When the reverse pull is started, the bucket automatically closes and the dirt is deposited in a truck of sewer cleaning. trailer. This operation is repeated until the line is clear. This machine is also used along with other scraping instruments for loosening sludge banks of detritus or cutting roots and removing obstructions from the sewer line.
Device # 6. Rodding Machine with Flexible Sewer Rods:
This machine consists of a flexible rod to which cleaning tools are attached. The flexible rod consists of a series of steel rods with screw couplings. The flexible rod is guided through the manhole by a vent pipe. The machine rotates the rod with the tool attached to one end.
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The rotating rod is thrust into the bent pipe manually with clamps with long handles holding the rod near the coupling. The rod is pulled in and out in quick succession when the tool is engaging the obstruction, so as to dislodge or loosen it. When the obstruction is cleared, the rod is pulled out by means of clamps keeping the rod rotating to facilitate quick and easy removal.
Device # 7. Dredger:
For cleaning the larger manholes, dredgers are used. It consists of a crane and a pulley, with the help of which a grab bucket is lowered. This scrapes the bottom deposits and brings it to the ground, where the bucket opens and the silt is automatically dropped into truck or trailer. The dredger cannot clean the corner deposits of the manhole.
Device # 8. Scraper:
For larger dia sewers more than 750 dia scraper is used for cleaning the sewers. It consists of an assembly of wooden planks of slightly smaller size than the sewer to be cleaned. If the scraper cannot be lowered through the manhole opening, it has to be assembled inside the manhole. The scraper chain, being attached to a control chain in the manhole, where it is lowered, is then connected to a winch on the next downstream man-hole by means of chains.
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The winch is then revolved to push the debris ahead of the scraper. The heading up of the flow behind the scraper will also assist in pushing it in the forward direction. This ensures that the bottom and the sides of the sewer are cleaned thoroughly. The scraped debris is manually removed from the manhole.
Device # 9. Hydraulically Propelled Devices:
The device take advantage of the force of impended water to effectively clear sewers. Efficiency depends on the hydraulic principle that an increase in velocity in a moving stream is accompanied by a greatly increased ability to more entrained material. The transporting capacity of water varies as the sixth power of its velocity.
Following are the various hydraulically propelled devices used in the cleaning of sewers:
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(a) Flush Bags:
This is the most effective tool for cleaning portions of sewers, where rods cannot be used. The flush bag is a canvas bag or rubber bag equipped with a fire hose coupler at one end and a reducer at the other end. The flusher is connected to the fire hose and placed in the downstream end from the point where a choke is located.
The bag is allowed to fill up until it expands and seals the sewer. The upstream pressure built up due to this damming effect breaks loose the obstruction. Care should be taken in using this device, otherwise due to high pressure the sewage may flow back into the hose connections or break the pipes or its joints.
(b) Sewer Balls:
These are simple elastic pneumatic type rubber Bail balls which can be blown up to varying degrees of inflation. These are available in sizes from 150 to 750 mm dia when fully inflated. While using in cleaning a sewer, the ball is first inflated and then wrapped in a canvas cloth, the edges of which are sewed together.
A trail line, little longer than the distance between the manholes, is attached securely to the covering. The size of the ball and the covering shall be such as to fit fairly snugly into the sewer. Immediately the ball is thrust into the sewer, sewage commences to back up in the manhole and continue to rise until such time as its pressure is great enough to force sewage under the ball and moving it down stream through the pipe.
Acting as a compressible floating plug, it affords enough obstruction, so that a continuous high velocity jet spurts under and to some extent around the ball, thereby sluicing all the movable material ahead to the next manhole.
If the ball encounters an obstruction which is immovable, the ball merely indents to the necessary degree and moves forward. Bricks, stones, bottles, loose metal parts, broken pieces of pipes, graval, sand, settled sludge are easily moved ahead. When the ball stops momentarily, a pull on the trial line is usually sufficient to set it in motion again.
A wooden ball, also called a sewer pill, can be used for this purpose, specially for cleaning large outfall sewers. This pill is dropped into the sewer and owing to its buoyant action rolls along the invert of the sewer. The obstruction caused by it to the flow produces a vigorous scouring action along the invert and the sides which has the effect of removing the growths and the deposits from the sewers.
(c) Sewer Scooter:
This method is the improved version of the scraper and consists of the two jacks, a controlling rope and the scooter with a light fitting shield. In contrast to the scraper, the scooter completely stops any flow of sewage. The scooter attached to the control rope, is lowered into the manhole and then into the downstream sewer line.
The downstream manhole jack is lowered into place from the road and the upper manhole jack set across the top of the manhole. When the scooter is introduced, it stops the flow of sewage thus building up a head behind the shield. The resulting pressure causes the scooter to move through the sewer until it accumulates enough debris to stop its movement.
The head is then allowed to build upto 1.0 m approx, before the control rope is pulled, causing the shield to fold back and allowing the accumulated sewage to gush in the downstream, flushing the debris ahead to the next manhole from where it is removed.
The control rope is released, clearing the shield against the sewage and causing the scooter to advance again until the debris stops its movement. This process is repeated till the scooter reaches the downstream manhole, where it may be taken out or allowed to continue through the next sewer section.