WBCHSE HS Vocational Plumbing cheat sheet

Plumbing is the trade of installing, maintaining and repairing pipes, fittings and fixtures that convey water, gas and wastes; it is governed in India by the National Building Code and IS 1200 measurement rules.

Water flows by gravity from higher to lower head; 1 m of static head equals about 9.81 kPa, and a 10 m head produces roughly 98 kPa (about 1 kg/cm²) at the outlet.

Flow rate through a pipe follows Q = A × V; a 15 mm nominal bore pipe at 1.5 m/s carries roughly 0.26 L/s, so pipe sizing must be checked against fixture demand, not assumed.

Personal protective equipment for plumbing work: safety helmet, goggles, gloves, steel-toe boots, ear plugs when cutting with a grinder, and a dust mask when chasing walls or cutting AC sheet.

Before any excavation, confirm the location of underground electric cables and gas lines; hand-dig within 1 m of marked services, and shore trenches deeper than 1.5 m.

Electrical safety: use 230 V hand tools only through an RCCB/ELCB of 30 mA sensitivity; portable tools on wet floors require 110 V site supply or double insulation.

Confined-space entry into a manhole or sump requires gas testing for oxygen (19.5–23.5%), hydrogen sulphide and methane, plus a standby person and a retrieval harness.

Soldering and gas-cutting require a fire watch; keep a dry-powder extinguisher within 5 m and never use water on live electrical or burning solvent-based adhesives.

First aid for a blowlamp burn: cool with clean running water for at least 10 minutes, do not burst blisters, and cover with a sterile non-stick dressing before referral.

GI (galvanised iron) pipe is specified by nominal bore (15, 20, 25, 32, 40, 50 mm and above) and by 'medium' or 'heavy' class wall thickness; it is joined by threaded sockets and is used for exposed cold-water lines.

PVC-U pipe is for cold water and drainage only; its service temperature limit is about 60 °C, so it is not used on hot-water lines.

CPVC handles hot water up to about 93 °C at rated pressure and is joined with solvent cement; it must not be threaded.

uPVC SWR (soil, waste, rain) pipe is used for above-ground drainage; fittings are named by angle - 87.5°, 45°, 22.5° bends - because 90° bends are made as 87.5° to preserve the socket wall.

Copper tube is graded by wall thickness (Type L, M, K in imperial practice) and joined by capillary solder fittings, compression fittings or press fittings; it is used for hot water and medical gas lines.

Asbestos-cement and lead pipes are legacy materials; they are not installed new and must be handled as hazardous waste when removed.

Ductile iron (DI) pipe with cement lining is used for underground water mains because of its strength and corrosion resistance; joints are push-on (Tyton) or flanged.

Rubber ring (push-fit) joints on SWR pipe rely on a lubricated EPDM gasket, allow thermal movement, and must be inserted to the marked depth line on the spigot.

Material selection rule: match the pipe to the medium, temperature and pressure - GI for exposed cold water, CPVC for hot water, uPVC for drainage, DI for buried mains.

A pipe wrench grips by serrated jaws that bite harder as torque increases; it is used on threaded pipe and fittings, never on chrome-plated or plastic fittings.

A chain wrench or strap wrench is used on polished pipe and large plastic fittings where jaw marks are unacceptable.

A pipe vice holds pipe for cutting and threading; the pipe should be clamped close to the cut and rotated to bring the cut line near the jaws.

A wheel-type pipe cutter scores and severs metal pipe; the cutter wheel is tightened a quarter-turn per revolution to avoid burring and wheel damage.

A ratchet die stock with BSPT dies cuts external threads; standard pipe threads are 1:16 taper (about 55° thread angle) so the joint tightens and seals as it is made up.

A threading die must be lubricated with cutting oil, and the stock reversed a half-turn periodically to break chips.

A flaring tool makes 45° flares for copper tube flare fittings; a swaging tool expands tube ends for soldered slip joints.

A plumb bob and spirit level (600 mm for general work, 1 m for long runs) check verticality and fall; drainage falls are typically 1:40 to 1:80 for 100 mm pipe.

A pressure testing pump with a calibrated gauge is used to hydrostatically test installations; a manometer or U-tube measures low pressures and drain-line gradients.

BSP thread sizes: 15 mm (1/2") pipe carries a thread of about 20.9 mm outside diameter; 20 mm (3/4") about 26.4 mm; 25 mm (1") about 33.2 mm.

Thread engagement rule: 15 mm pipe takes roughly 8–10 full threads, and fittings should leave 2–3 threads exposed after make-up.

A union allows a pipe run to be dismantled without cutting; it is installed at the fixture connection or at a valve for maintenance access.

An eccentric reducer is installed flat-side-up on horizontal runs to avoid air pockets, and flat-side-down where condensate or sediment must drain.

A Y-branch (45°) is preferred over a tee on drainage stacks to promote smooth flow and reduce blockage; tees are used for vent connections.

Pipe support spacing: GI pipe up to 25 mm is supported at about 2.0–2.5 m intervals, larger sizes at 3 m; supports must not be spaced so far that the pipe sags and holds water.

Allowance for thermal expansion of pipe is about 0.012 mm per metre per °C for steel; a 10 m steel run heated 50 °C expands roughly 6 mm, requiring an expansion loop or offset.

Bending rule: the minimum bend radius for copper tube is about 3–4 times the outside diameter when annealed, and much larger when hard-drawn.

When joining dissimilar metals, use a dielectric union or isolating bush to prevent galvanic corrosion between copper and GI.

Solvent cement jointing of uPVC/CPVC: cut square, deburr, clean with primer, apply cement to both surfaces, insert with a quarter-turn, hold 30 seconds and allow 24 hours before pressure testing.

Screwed GI joints are sealed with PTFE tape (2–3 turns in the direction of thread) or jointing compound; tape is wound clockwise on a right-hand thread so it is not unwound during make-up.

Soldered copper capillary joints need clean, fluxed surfaces, a heat source applied away from the fitting mouth, and solder drawn in by capillary action until a fillet appears.

Compression fittings seal by an olive (ferrule) crushed onto the tube; they must be tightened about 1–1.5 turns past finger-tight and are not reusable indefinitely.

Flanged joints use a gasket matched to the medium (rubber, CAF, spiral wound) and bolts tightened in a cross pattern in stages to avoid uneven gasket loading.

Drainage pipe installation requires a continuous fall in the direction of flow, with 100 mm pipe laid at about 1:60 to 1:80 and 50 mm branch waste at about 1:40.

Hydrostatic test: fill the installation, expel air, pressurise to 1.5 times working pressure (or as specified) and hold for at least 1 hour; a drop in gauge with no visible leak indicates trapped air or a leak.

Every fixture trap must have a water seal of 50–75 mm, and the trap must be accessible through a screwed cap for cleaning.

Vertical stacks must be carried up full bore as a vent above the highest fixture connection and terminated with a cowl or wire mesh at least 0.6 m above the roof.

A water closet requires a flush volume of about 6 L in modern dual-flush cisterns (full flush 6 L, reduced flush 3 L); older single-flush cisterns use 9–10 L.

Wash basin, sink and urinal waste pipes are 32–50 mm; a WC soil connection is 100 mm; a floor trap is 50–75 mm with a 50 mm seal.

The soil stack carries WC discharge, the waste stack carries sink and basin discharge, and the vent stack equalises pressure; a combined system uses one stack for both.

Two-pipe drainage systems separate soil and waste water; a one-pipe system collects both in one stack with each fixture individually trapped and vented.

Drainage gradients: 50 mm pipe 1:40, 75 mm 1:60, 100 mm 1:80, 150 mm 1:100 - steeper than this causes liquid to run ahead of solids.

A gully trap receives waste from kitchen and bathroom and includes a water seal; it must be placed outside the building and connected to the drain through a inspection chamber.

An inspection chamber is provided at every change of direction, at junctions, and at intervals not exceeding about 15 m on straight runs for access and rodding.

A manhole is required at the connection to the public sewer and at intervals of about 30 m on straight runs; it has steps and a cover rated for the traffic load above.

Anti-siphonage: a vent pipe or an air admittance valve prevents trap seals being siphoned by pressure fluctuations in the stack.

A direct (upfeed) system supplies fixtures from the mains pressure; an indirect (downfeed) system pumps to an overhead tank and distributes by gravity.

Overhead tank capacity rule of thumb: 100–150 L per person per day for domestic use; the tank should hold at least one day's demand and be sized to the number of occupants.

Tank outlet must be at least 50 mm above the tank floor and fitted with a strainer; the tank needs an overflow, a washout, a vent and a lockable cover.

A float valve (ball cock) controls filling; its inlet should discharge above the overflow level with an air gap to prevent backflow.

Static head at a fixture equals the vertical height from the tank water level to the fixture outlet; 1 m of head gives about 9.81 kPa, and 10 m gives about 98 kPa.

Minimum residual pressure at a fixture is typically 20–30 kPa; excessive pressure above about 500 kPa requires a pressure-reducing valve.

Water demand for a dwelling is estimated from fixture units: a WC about 3 fixture units, a wash basin 1, a sink 2, a shower 2 - total fixture units size the supply pipe.

A sump and booster pump set is used where mains pressure is inadequate; the pump must be protected by a dry-run cut-out and a non-return valve on the suction line.

Storage tanks must be cleaned and disinfected periodically; chlorination at about 1–2 mg/L free chlorine with 30 minutes contact time is a common disinfection dose.

A visible leak is located by isolating sections with valves; a pressure gauge on an isolated section that loses pressure indicates a leak within that section.

A concealed leak in a wall or floor often shows as damp patches, paint blistering, a jump in the water meter with all taps closed, or sound transmitted through the pipe.

Acoustic leak detection uses a listening stick or electronic ground microphone to find the loudest leak noise; it works best at night when background noise is low.

A water meter test: close all outlets, note the meter reading, wait 15–30 minutes, and re-read - any movement indicates an undetected leak or a passing float valve.

Frozen or burst pipe repair sequence: shut off supply, drain the section, cut out the damaged part, and fit a slip coupling or repair clamp with new gaskets.

A leaking threaded joint is repaired by dismantling, cleaning old tape or compound, re-taping with 2–3 turns of PTFE and remaking; over-tightening splits sockets.

A running WC is usually a perished flush valve washer or a faulty ball cock; a dye test in the cistern shows whether water passes into the pan.

A blocked drain is cleared with a plunger for a local trap, a drain snake or rod for a branch, and a high-pressure jetter for a main; jetting pressure for uPVC should not exceed about 100 bar.

Preventive maintenance schedule: inspect tanks and clean every 6 months, test backflow devices annually, exercise isolating valves every 6 months, and check exposed pipe supports yearly.

Measurement of plumbing work follows IS 1200 (Part 19 for water supply, drainage and sanitary fittings); pipe lengths are measured along the centre line of the pipe, including fittings but excluding the pipe inside the fitting.

Pipe work is measured in running metres by nominal bore, and fittings are counted separately by type and size; deductions are made for openings above the specified area.

A rate analysis for a pipe run = cost of pipe per metre + cost of fittings apportioned per metre + labour + wastage + contractor's overhead and profit.

Wastage allowance in estimates is typically 2–5% on pipe and 5–10% on fittings and consumables such as solvent cement and PTFE tape.

Labour output for GI pipe work is roughly 6–10 m per plumber per day for exposed runs; concealed and chase work is slower and must be priced higher.

A bill of quantities (BOQ) lists item description, unit, quantity and rate; the tender is compared on total amount, but rates must be checked for unbalanced pricing.

A bar bending schedule is not used in plumbing; instead a pipe schedule lists size, material, length, fittings and support spacing for each run.

Variation orders must be recorded in writing with quantity, rate and approval before the work is executed, otherwise the contractor may not be paid.

Retention money is typically 5–10% of each bill and is released after the defect liability period, usually 6–12 months after completion.

A plumbing contractor must register for GST if annual turnover exceeds the threshold (₹20 lakh for services in most states), and must hold a trade licence and, where required, a PWD or municipal contractor registration.

A simple break-even calculation: fixed monthly costs ÷ (average job price − variable cost per job) = number of jobs needed per month to break even.

A quotation must state scope, materials with brand and grade, rate, taxes, payment terms, warranty period and exclusions; verbal estimates are not enforceable.

Working capital for a plumbing business covers wages, material purchases and tools before payment is received; 30–60 days of operating cost is a common minimum.

Statutory obligations for a small contractor include EPF and ESI for eligible employees, labour licence where required, and payment of minimum wages.

A job card or work order records site address, scope, materials issued, labour hours and customer signature; it is the primary evidence for billing and disputes.

Customer-handling rule: confirm the complaint, quote before starting, protect the work area, test after repair, and leave a written bill with a warranty note.

Employability skills valued in plumbing: reading drawings and specifications, measuring accurately, safe work habits, teamwork, and clear spoken and written communication with clients.

Digital tools used by plumbing enterprises include WhatsApp for job scheduling, UPI for collection, and simple spreadsheet or app-based billing for GST invoices.

Workshop sequence for a threaded joint: measure and mark, cut with a pipe cutter, ream the burr, clamp in a vice, cut threads with a die stock, test-fit the fitting, apply PTFE tape and make up.

Reaming after cutting removes the internal burr that would otherwise raise flow resistance and trap sediment; the reamer is turned clockwise with light pressure.

A cutting list is prepared before fabrication, grouping identical lengths to minimise waste; each piece is marked with its position number to match the drawing.

A simple project such as a wash-basin connection includes: supply pipe with stop cock, 15 mm connection to the tap, 32 mm waste pipe, P-trap with 50 mm seal, and connection to the floor trap.

Testing after fabrication: blank off open ends, fill with water, apply test pressure, inspect all joints, and record the test on a signed test certificate.

Isometric drawings of plumbing installations use standard symbols: circle with cross for a floor trap, square for a tank, dashed line for concealed pipe, and arrow for flow direction.

Workshop safety check before starting: inspect tool handles for cracks, check that the grinder guard is in place, confirm the fire extinguisher is charged, and clear the work area of trip hazards.

Final inspection checklist: pipe alignment and level, support spacing, correct fall on drainage, trap seals present, all joints leak-free, and identification of valves and tanks.