Maharashtra SSC Plumber (General) Pre-Voc/NSQF flashcards

38 cards. Read the term and the definition here. The deck at the top of this page is optional.

Confined space oxygen range

Safe entry range for oxygen in a confined space is 19.5 to 23.5 percent by volume. Below or above this, entry is prohibited until ventilation and retesting confirm safety.

RCCB sensitivity for wet work

A 30 mA residual current circuit breaker protects users of portable tools in wet areas by tripping on small earth leakage currents, reducing the risk of fatal electric shock.

Permissible H2S exposure limit

The 8-hour time-weighted permissible exposure limit for hydrogen sulphide is 10 ppm. Because smell is lost at higher concentrations, atmosphere testing, not odour, must decide entry.

Trench shoring depth rule

Excavations deeper than 1.5 metres require shoring, sloping or a trench box. Ladders for escape must extend one metre above the edge and be placed at intervals.

Hacksaw teeth per inch choice

Use 18 teeth per inch for thick cast iron and steel, 24 for general mild steel pipe, and 32 for thin copper and PVC. At least three teeth should span the wall.

Pipe cutter tightening rule

Tighten the cutter wheel about a quarter turn per revolution around the pipe. Over-tightening burrs the edge, work-hardens copper and can cause splitting during flaring.

Pipe wrench grip direction

A Stillson pipe wrench grips and turns in one direction only. Position it so the pull is towards the operator and the pipe sits mid-jaw to avoid crushing.

Deburring after cutting

Internal and external burrs must be removed with a half-round file or deburring tool. Burrs reduce bore, create turbulence, trap scale and damage compression olives and push-fit seals.

Vernier calliper least count

For a metric vernier with 1 mm main divisions and 50 vernier divisions, least count equals 1 divided by 50, which is 0.02 mm. Used to measure pipe wall and spigot sizes.

BSPT taper ratio

British Standard Pipe Taper threads have a taper of 1 in 16. They seal on the threads themselves, normally with jointing compound, unlike parallel threads that need a washer.

Pressure gauge mid-scale rule

Select a test gauge so the expected test pressure falls between one and two times mid-scale. A 0 to 16 bar gauge suits a 10 bar hydrostatic test.

PVC-U temperature limit

Unplasticised PVC handles cold water only, with a practical upper limit near 45 degrees Celsius. For hot water lines, CPVC or copper is used instead.

Solvent cement curing time

After applying solvent cement, push the pipe with a quarter turn, hold about 30 seconds, and allow roughly 24 hours before pressure testing to reach full joint strength.

Galvanic corrosion prevention

When copper and galvanised steel touch in the presence of water, the less noble metal corrodes. A dielectric union or plastic-lined fitting breaks the electrical contact between them.

PTFE tape winding direction

PTFE tape is wound clockwise for right-hand threads, in the direction of tightening, so it stays in place. It suits threaded joints only and is not a thread repair.

Union fitting purpose

A union allows a line to be dismantled without cutting pipe. It is placed immediately upstream of taps, pumps, meters and valves to simplify maintenance and replacement.

Compression olive tightening

Tighten the compression nut hand-tight plus one to one and a half turns. Over-tightening crushes or splits the olive, causing leaks that cannot be cured by further tightening.

Flange bolt tightening pattern

Bolts on a flanged joint are tightened in a criss-cross star pattern in two or three stages. This compresses the gasket evenly and prevents the flanges from cocking.

Dual flush cistern volumes

A dual-flush cistern delivers about 6 litres on full flush and 3 litres on reduced flush. Older single-flush cisterns typically use 9 to 10 litres per flush.

Minimum trap water seal

Water closets and traps require a minimum 50 mm water seal to resist sewer gas. A 75 mm seal is used where siphonage risk is higher on long branches.

Flushometer pressure requirement

Flush valves need a minimum dynamic supply pressure near 1 bar and adequate flow. They are unsuitable on low-pressure gravity systems fed from a small overhead tank.

Geyser pressure relief valve

An electric water heater must have a pressure-relief valve on the cold inlet. The thermostat is usually set at 60 to 65 degrees Celsius to limit scaling and scald risk.

Fixture unit method

Each fixture is assigned fixture units, for example WC 6, sink 2 and basin 1. Branch and main sizes are then read from the fixture-unit to diameter table.

Static head to pressure

Ten metres of static head equals about 1 bar. A tank 10 metres above a tap gives roughly 1 bar at the outlet before friction losses in the pipe run.

Water supply velocity limit

Cold water velocity is kept between 1.5 and 2.0 metres per second and hot water below 1.2. Higher velocities cause noise, erosion and excessive pressure loss.

Per capita water demand

Indian urban domestic demand is commonly taken as 135 litres per capita per day. Add allowances for gardens, leakage and fire reserve when sizing tanks.

Soil pipe gradient rule

A 100 mm soil pipe is laid at about 1 in 60 to 1 in 100, roughly 1 to 1.7 percent. Flatter gradients allow solids to settle and block the drain.

Vent stack sizing rule

The vent stack diameter must be at least half the soil stack diameter and never smaller than 32 mm. A 100 mm soil stack therefore needs a 50 mm vent.

Inspection chamber spacing

Inspection chambers are placed at changes of direction greater than 45 degrees, at junctions, and at maximum spacing of about 45 metres for 100 mm drains.

Hydrostatic test pressure

Water lines are tested at 1.5 times working pressure or 10 bar minimum, whichever is higher, held for one hour with no visible leak or pressure drop.

Drainage air test

Plug all openings, apply 38 mm water gauge air pressure, and hold for three minutes. A steady reading confirms the drainage line is free of leaks.

First-angle projection layout

In first-angle projection the view seen from the front is placed above the plan. Third-angle projection, common in building drawings, places the plan above the front view.

Dimension line placement

Dimension lines are drawn outside the object between extension lines, with arrowheads at each end. Dimensions are never given to hidden lines or repeated unnecessarily.

Centre-line estimation method

Wall length is taken along the centre line and multiplied by breadth and height. Junction overlaps are counted once, making the method quick for symmetrical plans.

Opening deduction rule

No deduction is made for openings up to 0.1 square metre. Between 0.1 and 0.5 square metre, deduct 50 percent. Above 0.5 square metre, deduct the full area.

Rainwater harvesting yield

Harvestable volume equals roof area in square metres multiplied by annual rainfall in millimetres, then by a runoff coefficient of about 0.8 to 0.9 for tiled roofs.

Dripping tap water loss

A tap dripping once per second wastes roughly 10 to 15 litres per day. Repairing washers early saves water and prevents damp damage to walls and floors.

Digital meter leak alert

A smart water meter flags a leak when continuous flow above about 20 litres per hour is recorded overnight, when no fixture should be drawing water.