RRB ALP Plumber Trade — Complete CBT-2 Study Guide

• Common pipe materials: GI (Galvanized Iron — durable, used for both water supply, being gradually replaced in new construction), PVC/CPVC (Poly Vinyl Chloride/Chlorinated PVC — corrosion-resistant, lightweight, CPVC rated for hot water unlike standard PVC), PPR (Polypropylene Random copolymer — good heat resistance, joined by heat-fusion for leak-proof joints). • Pipe fittings (elbows, tees, couplings, reducers, unions) allow pipes to change direction, branch, connect different sizes, or be joined/disconnected for maintenance — correct fitting selection ensures proper flow and easy future serviceability. • Pipe joining methods vary by material: Threaded joints (for GI pipe, using pipe wrenches and thread sealant/tape), Solvent cement welding (for PVC, chemically fuses the joint), Heat fusion (for PPR, melts and fuses pipe ends together for a monolithic joint). • Pipe layout must maintain proper slope for drainage lines (gravity-flow, typically a minimum fall of about 1:40 to 1:60 depending on pipe size/code) to ensure waste flows away without stagnation, while supply lines are pressurized and don't require gravity slope.

• Water supply systems can be Direct (mains pressure feeds fixtures directly) or Indirect/tank-fed (water stored in an overhead/underground tank, then pumped/gravity-fed to fixtures) — tank systems provide a buffer against mains supply interruptions. • Overhead tank systems rely on gravity for water pressure at fixtures — pressure depends on the height difference between the tank and the fixture (higher tank = more pressure at lower fixtures). • Booster pumps increase water pressure where mains/gravity pressure alone is insufficient (e.g. upper floors of a tall building) — must be sized correctly to avoid excessive pressure damaging fixtures or insufficient pressure at peak demand. • Backflow prevention devices (check valves, air gaps) prevent contaminated water from flowing backward into the clean water supply system — a critical health/safety measure, especially where a supply line could ever connect to a non-potable source.

• A trap (P-trap or S-trap) is a curved section of pipe below a fixture (sink, toilet) that retains a small amount of water, forming a seal that blocks sewer gases from entering the building through the drain — a dry trap (from long non-use) allows sewer gas to escape into the room. • Venting system allows air to enter the drainage system, preventing trap seals from being siphoned out by the vacuum effect of water flowing through the drain pipes, and allowing sewer gases to vent safely to the outside atmosphere rather than into the building. • Soil pipes carry waste from toilets (containing solid human waste); Waste pipes carry waste from sinks/basins/baths (without solid waste) — some plumbing codes distinguish and route these separately, others combine them into a single stack. • Fixture units are a standard way to express the load a given fixture places on the drainage system, used to correctly size drain pipes for the combined load of all fixtures connected to them.

• Valve types: Gate valve (fully open or fully closed, minimal flow resistance when open, NOT suited for throttling/partial flow control since partial opening causes erosion damage to the gate), Globe valve (good for throttling/regulating flow, higher pressure drop than a gate valve even fully open), Ball valve (quick quarter-turn operation, good sealing, common for general shut-off duty), Check valve (allows flow in ONE direction only, preventing backflow). • Centrifugal pumps (most common for water supply) convert the rotational kinetic energy of an impeller into pressure/flow — suited for moderate-to-high flow rates at moderate heads (pressure). • Priming (filling the pump casing and suction pipe with water before starting) is essential for most centrifugal pumps to operate — an unprimed centrifugal pump cannot draw water on its own since it needs liquid present to generate the centrifugal force that creates flow. • Pump cavitation (formation and violent collapse of vapor bubbles within the pump due to locally low pressure) causes noise, vibration, and can seriously damage impeller surfaces over time — usually caused by insufficient suction pressure (Net Positive Suction Head) available at the pump inlet.