Tradesman — Plumbing — Technical Education / Plumber — KWA — 2016 — Official Paper — Kerala PSC PYQ Practice with Answers

Correct answer (Option C):\nA reflux valve, also known as a check valve or non-return valve, is automatically operated and permits water to flow in only one direction. It is installed at intervals in long pipelines and on the delivery side of pumps to completely prevent the backflow of water and protect the pumping machinery from back pressure when the pump stops working. Option C is correct.\n\nWhy others are wrong:\nOption A (Gate valve) is used to control or shut off the flow of water entirely but does not automatically prevent backflow. Option B (Mud valve) is used to drain out collected silt from basins. Option D (Pressure relief valve) opens to release water when a preset pressure limit is exceeded to prevent pipe bursts.\n\nStudy tip:\nReflux valves are crucial components in rising mains to prevent water hammer and reverse rotation of pumps.

Correct answer (Option A):\nThe dead-end system, also known as the tree system, is highly suitable for old towns or cities that have grown organically and irregularly without any pre-planned road layout. It consists of a main line from which sub-mains branch off, terminating in dead ends. Option A is correct.\n\nWhy others are wrong:\nOption B (Grid Iron System) is suitable for well-planned rectangular or grid-pattern cities. Option C (Radial System) splits the area into zones where water is pumped to a central reservoir and distributed radially outward. Option D (Ring System) encircles the entire area with main lines and is suited for planned circular or rectangular towns.\n\nStudy tip:\nWhile cheap and simple to design, the major drawback of the dead-end system is the accumulation of stagnant water at the terminal dead ends, which requires periodic flushing.

Correct answer (Option C):\nAccording to Indian Standards, IS 1536 specifies the strict technical specifications for centrifugally cast (commonly known as spun iron) pressure pipes intended for water, gas, and sewage transportation. Option C is correct.\n\nWhy others are wrong:\nOptions A, B, and D do not correspond to the standards governing centrifugally cast iron pressure pipes for water supply networks; IS 1537, for example, applies to vertically cast iron pressure pipes.\n\nRemember:\nSpun iron pipes are widely preferred over standard cast iron pipes due to their superior tensile strength, uniformity in wall thickness, and higher durability.

Correct answer (Option B):\nA union is a specific type of pipe fitting designed in such a way that it allows two pipes to be connected and disconnected cleanly without causing any physical rotation or disturbance to the remaining network. This feature makes it highly ideal for quick maintenance, dismantling, and replacement tasks. Option B is correct.\n\nWhy others are wrong:\nOption A (Elbow) is used to alter the directional flow of the pipe by 90° or 45°. Option C (Reducer) alters the diameter to connect a larger pipe to a smaller one. Option D (Cap) is explicitly used to seal off the dead end of a male-threaded pipe.\n\nStudy tip:\nUnions are highly essential when connecting rigid pipelines to appliances like water heaters or pumps that require periodic servicing.

Correct answer (Option C):\nThe biggest structural disadvantage of Galvanized Iron (GI) pipes is their high vulnerability to chemical corrosion when conveying highly acidic or alkaline water. Over time, corrosive water eats away at the internal protective zinc layer, accelerating corrosion and leading to scale buildup. Option C is correct.\n\nWhy others are wrong:\nOptions A and B highlight real practical advantages of utilizing threaded GI pipes. Option D describes the fundamental purpose of the protective galvanization process itself, which is a key advantage rather than a functional drawback.\n\nRemember:\nDue to chemical vulnerability and subsequent scale formation, GI pipes are progressively being replaced by PVC, CPVC, and multi-layered composite pipes for indoor domestic water delivery lines.