Lesson Notes By Weeks and Term v3 - Senior Secondary 3
Methods of laying pipes
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Methods of laying pipes
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Subject: Plumbing And Pipe Fitting
Class: Senior Secondary 3
Term: 3rd Term
Week: 1
Theme: Methods Of Drainage System And Procedures For Laying Pipes
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Lists methods of setting out trenches for laying pipes. List various methods for laying vitrified and iron spigot. Practically carry out laying of PVC pipes and spigot end as bestos pipes.
Setting out a trench accurately is the first critical step in pipe laying. It involves marking the exact line and depth for the trench to ensure the pipe follows the desired alignment and gradient. 2.1.
1. Tools for Setting Out: Measuring Tape: For measuring lengths and depths.
Pegs/Stakes: To mark points along the trench line.
String/Line: To connect pegs and define the trench's alignment.
Spirit Level: To check horizontal alignment and gradient.
Plumb Bob: To establish vertical lines (e.g., for transferring points).
Boning Rods (Sight Rails): Used in conjunction with a boning rod (T-shaped stick) to establish and check the trench invert level (bottom of the trench) at a consistent gradient. Two sight rails are set up at known levels, and a third 'boning rod' is used to check the level along the trench.
Chalk/Paint: For marking lines on the ground. 2.1.
2. Setting Out Methods: a.
Centreline Method (for Straight Runs): Application: Ideal for long, straight sections of pipe.
Procedure: Determine the starting and end points of the pipe run. Drive pegs into the ground at these points, marking the centreline of the proposed trench. Stretch a tight string line between the pegs, representing the exact centreline of the pipe. Measure outwards from the string line on both sides (half the trench width) to mark the edges of the trench. Drive additional pegs or mark with chalk/paint. Use a spirit level and boning rods (or a dumpy level/laser level if available) to establish the correct gradient along the trench centreline before excavation begins. This is typically done by setting up sight rails above the trench at known heights, then using a boning rod to ensure the trench bottom (invert level) is dug to the correct depth relative to the sight rail. b.
Offset Method (for Curves or Obstacles): Application: Used when the pipe run is curved, or when there are obstacles that prevent direct stringing along the centreline.
Procedure: Establish a clear reference line (baseline) parallel to the proposed pipe centreline, at a known, fixed distance (offset) from it. This baseline should be free of obstructions. Mark points along this baseline. From each point on the baseline, measure perpendicular distances (offsets) to locate corresponding points on the pipe centreline. Connect these marked points on the ground to outline the pipe trench. This method allows for accurate alignment even when the direct path is obstructed. c. Batter Rails Method (for Depth and Gradient Control): Application: Primarily used to control the depth and gradient of the trench bottom (invert level) precisely, especially for drainage and sewer lines.
Procedure: Set up pairs of pegs (batter rails) perpendicular to the trench line at regular intervals, typically 3-5 meters apart. Nail horizontal cross-pieces (battens) to these pegs, ensuring they are perfectly level across the trench. Establish a reference level (datum) and calculate the required height of the battens above the invert level of the pipe. Use a sight rail (or boning rod) that is a specific length (e.g., 2 meters) and has a T-piece. The top of the T-piece aligns with the underside of the battens, and the bottom of the sight rail rests on the desired invert level of the trench. Excavators can then use the sight rail to check the depth as they dig, ensuring a consistent gradient.
Example (Nigerian Context): When laying a domestic sewage line from a pit latrine to a soak-away, ensuring a constant fall (gradient) of 1:60 or 1:80 is crucial for waste flow. Batter rails help achieve this precision over varying ground levels common in many Nigerian compounds. Insert spun yarn/tarred rope (oakum) into the socket, packing it tightly. Use a pouring gate (collar) around the spigot to hold molten lead. Pour molten lead evenly into the joint. Once cooled, use a caulking iron and hammer to compress the lead, ensuring a tight seal.
5. Jointing (Rubber Gasket Push-fit): Clean socket and spigot ends. Insert the rubber gasket correctly into the socket groove. Apply approved lubricant to the spigot end and the gasket. Using a pipe puller or crowbar, push the spigot end firmly and squarely into the socket until the insertion mark on the spigot aligns with the socket face.
6. Anchoring: For pressure mains, thrust blocks (concrete blocks) are often used at bends, tees, and caps to resist forces from water pressure.
7. Testing and Backfilling: Conduct hydrostatic pressure tests for water mains. Backfill carefully, compacting layers. 2.2.
3. Laying PVC Pipes Characteristics: Lightweight, corrosion-resistant, flexible, smooth bore (low friction), easy to cut and join. Widely used in Nigeria for both pressure (water supply) and non-pressure (drainage, ventilation) applications.
Jointing Methods: Solvent Cement Welding (for pressure pipes and fittings): A chemical fusion process where solvent cement dissolves the PVC surfaces, allowing them to fuse together when joined. Rubber Ring Push-fit Joints (for drainage and non-pressure applications): Similar to VCP/CI, a rubber ring in the socket provides a flexible, watertight seal. Laying Procedure (Solvent Cement Jointing):
1. Trench and Bedding: Trench should be clean, free of sharp objects. A minimum of 100-150mm of fine granular bedding (sand) is ideal for cushioning.
2. Pipe Preparation: Cut pipe to desired length using a fine-toothed saw or pipe cutter. Ensure cut is square. Chamfer (bevel) the outside edge of the spigot end to aid insertion. Clean both the spigot and the inside of the socket thoroughly with a clean, dry cloth to remove dirt, grease, or moisture. Apply PVC primer (if specified by manufacturer) to both surfaces.
3. Solvent Cement Application: Apply a liberal, even coat of solvent cement to the outside of the spigot end (cover entire surface to be inserted). Immediately apply a thinner, even coat to the inside of the socket.
4. Joint Assembly: Immediately (while cement is wet) push the spigot fully into the socket with a slight twisting motion to ensure even spread of cement. Hold the joint firmly for 15-30 seconds to prevent the pipe from pushing out. Wipe off any excess cement from the joint exterior.
5. Curing: Allow sufficient curing time (minutes to hours, depending on temperature, humidity, and pipe size) before handling or pressure testing. Do not stress the joint during curing.
6. Support and Anchoring: Ensure proper pipe support. For exposed pipes, use hangers/clips. For buried pressure pipes, thrust blocks may be needed at bends.
7. Testing and Backfilling: Conduct pressure tests for water mains. Backfill carefully, compacting selected fine material around the pipe first. 2.2.
4. Laying Asbestos Cement (AC)
Spigot and Socket Pipes Disclaimer: While AC pipes were historically used for water supply and drainage, they pose significant health risks due to asbestos fibres when disturbed. Modern plumbing practices in Nigeria increasingly favour safer alternatives like PVC, HDPE, and ductile iron. If encountered or if this objective must be covered, extreme caution and safety protocols (PPE, dust suppression) are paramount.
Characteristics: Lightweight, corrosion-resistant, relatively brittle.
Jointing Methods: Flexible Push-fit Couplings (e.g., Gibault, Simplex couplings): These use rubber gaskets and metal sleeves/bolts to create a mechanical, watertight, flexible joint. The pipe ends are plain-ended, and the coupling provides the joint. (The objective mentions "spigot end asbestos pipes," which implies a spigot-and-socket type, making rubber ring push-fit the likely method, similar to other spigot-and-socket pipes, but with specialized AC gaskets). * Laying Procedure (Spigot and Socket with Rubber Ring):
1. Safety First: Ensure all personnel wear appropriate Personal Protective Equipment (PPE), including respirators, gloves, and protective clothing. Minimize dust generation. Avoid cutting or drilling AC pipes if possible.
2. Trench and Bedding: Similar to other pipes, a stable, well-prepared trench with adequate bedding (sand) is required. 3. *Pipe General principles for laying pipes include: proper trenching, suitable bedding, careful handling, correct jointing, precise alignment and gradient, and thorough backfilling. 2.2.
1. Laying Vitrified Clay Pipes (VCP)
Characteristics: VCP are heavy, brittle, corrosion-resistant, and commonly used for non-pressure drainage and sewerage systems due to their strength and chemical resistance. They are typically spigot and socket pipes.
Jointing Methods: Cement Mortar Joints (Traditional): A mixture of cement, sand, and water is packed into the annular space between the spigot and socket. Requires curing.
Flexible Push-fit Joints (Rubber Ring): A rubber ring (O-ring) is inserted into the socket, and the spigot end is pushed in, creating a flexible, watertight seal.
Laying Procedure:
1. Trench Preparation: Ensure trench bottom is firm, at the correct grade, and free of debris.
2. Bedding: Provide a suitable bedding material (e.g., 100-150mm of well-compacted sand, gravel, or fine crushed stone). For larger pipes or poor ground, concrete bedding may be required. Create recesses (snug holes) in the bedding for the pipe sockets to ensure the barrel of the pipe rests evenly.
3. Pipe Placement: Start laying from the lowest point (downstream) with the socket facing upstream. Carefully lower each pipe into the trench using ropes or machinery.
4. Alignment and Gradient: Ensure pipes are correctly aligned (straight in line and level across) and at the specified gradient using sight rails and spirit levels.
5. Jointing (Cement Mortar): Clean spigot and socket ends thoroughly. Place a spun yarn or tarred rope into the annular space to centralize the pipe and prevent mortar from entering the pipe. Fill the remaining annular space with stiff cement mortar, ensuring it is tightly packed and finished with a smooth bevel at 45 degrees. Allow adequate curing time (days) before backfilling to prevent disturbance.
6. Jointing (Flexible Rubber Ring): Clean spigot and socket. Ensure rubber ring is correctly seated in the socket groove. Lubricate the spigot end and the rubber ring with approved lubricant. Push the spigot firmly into the socket, ensuring it's fully seated and the joint is concentric.
7. Haunching/Surrounding: After jointing, pack selected granular material or concrete around the sides of the pipe (haunching) to provide lateral support and transfer loads from above. For critical installations, a full concrete surround may be used.
8. Testing: Perform leakage tests (e.g., water test) before backfilling.
9. Backfilling: Carefully backfill the trench in layers (e.g., 150-300mm), compacting each layer to avoid damage to the pipes. Initial backfill should be fine, selected material around and over the pipe barrel, free of large stones. 2.2.
2. Laying Cast Iron Spigot and Socket Pipes Characteristics: Strong, durable, resistant to high pressure, used for water supply mains and heavy-duty drainage. Also typically spigot and socket.
Jointing Methods: Caulked Lead Joints (Traditional): Molten lead is poured into the annular space and then hammered (caulked) to form a watertight, rigid seal. This is labor-intensive and less common now. Rubber Gasket Push-fit Joints (Tyton, Lok-Ring, etc.): A modern, efficient method where a shaped rubber gasket (Tyton gasket) is fitted into the socket, and the spigot is lubricated and pushed in to form a flexible, watertight seal.
Laying Procedure:
1. Trench and Bedding: Similar to VCP, robust bedding is essential due to the weight of CI pipes. Socket recesses in the bedding are crucial.
2. Pipe Placement: Lay pipes from the lowest point with sockets facing upstream. Use lifting equipment due to pipe weight.
3. Alignment and Gradient: Maintain accurate alignment and gradient.
4. Jointing (Caulked Lead - Historical context): Clean joint ends. Insert spun yarn/tarred rope (oakum) into the socket, packing it tightly. Use a pouring gate (collar) around the spigot to hold molten lead. Pour molten lead evenly into the joint. Once cooled, use a caulking iron and hammer to compress the lead, ensuring a tight seal.
5. Jointing (Rubber Gasket Push-fit): Clean socket and spigot ends. Insert the rubber gasket correctly into the socket groove. Apply approved lubricant to the spigot end and the gasket. * Using a pipe puller or crowbar, push the spigot the coupling provides the joint. (The objective mentions "spigot end asbestos pipes," which implies a spigot-and-socket type, making rubber ring push-fit the likely method, similar to other spigot-and-socket pipes, but with specialized AC gaskets). Laying Procedure (Spigot and Socket with Rubber Ring):
1. Safety First: Ensure all personnel wear appropriate Personal Protective Equipment (PPE), including respirators, gloves, and protective clothing. Minimize dust generation. Avoid cutting or drilling AC pipes if possible.
2. Trench and Bedding: Similar to other pipes, a stable, well-prepared trench with adequate bedding (sand) is required.
3. Pipe Placement: Carefully lower pipes into the trench using mechanical means if available, to minimize handling and potential breakage.
4. Alignment and Gradient: Maintain precise alignment and gradient.
5. Jointing (Rubber Ring): Clean spigot and socket ends thoroughly. Inspect the rubber ring gasket for damage and seat it correctly in the socket groove. Apply approved non-toxic lubricant to the spigot end and the rubber gasket. * Push the spigot end firmly and squarely into the socket until it is fully seated. Mechanical aids might be needed for larger pipes.
6. Anchoring: Provide thrust blocks for pressure mains at bends and fittings.
7. Testing and Backfilling: Conduct pressure tests. Backfill carefully, using fine material around the pipe to prevent damage. Do not compact aggressively directly over the pipe.
Community Water Supply and Sanitation Projects (SDG 6): Knowledge of pipe laying methods is directly applied in establishing and maintaining community boreholes, water treatment plants, and distribution networks in Nigerian towns and villages. Proper laying prevents contamination, reduces water loss through leaks, and ensures a reliable supply of potable water, directly impacting public health and economic development. For drainage, correct pipe laying prevents stagnant water bodies, mosquito breeding, and the spread of waterborne diseases like cholera and typhoid, common challenges in many Nigerian communities. Building Construction and Real Estate Development: Every residential, commercial, or industrial building in Nigeria requires plumbing for water supply and waste disposal. Skilled plumbers who can correctly set out trenches and lay pipes are in high demand in the construction industry. This knowledge translates into direct employment opportunities for students in building houses, offices, hospitals, and schools, contributing significantly to the national infrastructure development and job creation.
Irrigation Systems for Agriculture: In Nigeria's agricultural sector, efficient irrigation systems are vital for food security. Laying pipes for drip irrigation or sprinkler systems requires similar skills in trenching, pipe joining (often PVC or HDPE), and maintaining appropriate gradients or pressure ratings. This knowledge can be applied to establish and maintain irrigation infrastructure on farms, leading to increased crop yields and improved livelihoods for farmers.