Question

The minimum grade for the drains of 10 cm diameter should be:

• A. 1.00%
• B. 0.50%
• C. 0.20%
  (D) 0.10%
• D.

Hint:

A simple rule of thumb for minimum sewer grades is that the slope is inversely proportional to the diameter. Smaller pipes need steeper slopes. For a 10 cm (4") pipe, a grade of 1 in 500 (0.2%) is a good value to remember.

Answer 1

The Correct Option is C

Step 1: Grasp the principle of minimum drain gradient.Drains and sewers are installed with a slope (gradient) to facilitate wastewater flow by gravity. This slope is critical for establishing a "self-cleansing velocity" (generally between 0.6 to 0.9 m/s) that prevents solid waste from accumulating and obstructing the pipe.
Step 2: Articulate the standard guideline for minimum gradient.The necessary minimum gradient is determined by the pipe's diameter and its internal surface texture. Pipes with smaller diameters require a steeper slope than larger pipes to achieve the self-cleansing velocity. For a drain with a small diameter, such as 10 cm (or 4 inches), drainage and plumbing regulations typically recommend a minimum gradient of 0.20% to 0.25%. A 0.20% gradient signifies a drop of 0.20 meters for every 100 meters of pipe length.