Pipes & Cisterns | Time & Work Aptitude Practice | Kuriloo

Fundamental Principles

Inlet Pipe vs. Outlet Pipe

An inlet pipe fills a reservoir (positive work/efficiency), while an outlet pipe drains fluid out of the reservoir (negative work/efficiency).

Net Flow Rate Equation

If an inlet fills a tank in 'x' hours and an outlet empties it in 'y' hours, the combined net filling rate per hour when both run at once is: (1/x) - (1/y).

Essential Formulation Tips

If the net hourly output calculation returns a negative value, it means the reservoir is draining rather than filling.
Always ensure that the total capacity volume unit remains completely uniform when matching different pipe sizes.

Shortcut Execution Techniques

Find the LCM of the filling and emptying timelines to establish a fixed capacity for the tank in liters. This lets you quickly add and subtract whole-number flow rates.

Contextual Inquiries (FAQs)

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Example Breakdown: Simultaneous Flow Balancing

Standard fluid mechanics setup verifying signs across multi-directional systems.

Problem QueryPipe A fills a storage tank in 10 hours, while Pipe B empties the same tank in 15 hours. Calculate the total time required to fill the tank from empty if both pipes are opened simultaneously.

Step-By-Step Solution Path

Step 1: Find the LCM of 10 and 15 to establish total tank capacity: 30 units (liters).

Step 2: Calculate individual hourly flow rates: Pipe A = +3 units/hour; Pipe B = -2 units/hour.

Step 3: Combine the flow rates to find the net hourly balance: +3 + (-2) = +1 unit/hour.

Step 4: Divide total capacity by net hourly flow: 30 units / 1 unit per hour = 30 hours.

Analytical Hint: Treat the outlet pipe as a source of negative work to determine the net hourly filling rate.

Pipes & Cisterns Practice Set 1

10 questions analyzing multi-valve arrays, structural leaks, and changing flow intervals.

Q1. A cistern has a leak that can empty it completely in 8 hours. An inlet pipe fills it at 6 liters per minute. If the cistern is full, and the inlet is opened, it now takes 12 hours to empty. Find the total capacity of the cistern.

Q2. Two inlet pipes can fill a reservoir in 4 hours and 6 hours respectively. How long will it take to fill the reservoir if both open at once?