Skip to main content

Working of two sewer appurtenances

Short answer

Manholes allow worker access for inspection and cleaning; sewage flows through a half-round channel, and benching prevents solids settling. Catch basins collect silt and grit from storm water by reducing velocity; heavy particles settle in the sump, and a hooded outlet traps floating matter and provides a water seal.

Describe with neat sketches the working of any two sewer appurtenances that are usually provided on any sewer line.

Two commonly provided appurtenances are the manhole and the catch basin (or street inlet). Their working is explained below.

1. Manhole

A manhole is a vertical chamber built over a sewer to let a worker go down for inspection, cleaning and repair.

      ___ cover
     |   |
     | S |   shaft with steps
     | H |
    /  A  \
   |Inlet  |
   |--->===|---> Outlet
   |_______|
   Half-round channel

Working: the sewage from the inlet sewer flows through a half-round channel built in the base to the outlet sewer without splashing; side benching sloped to the channel stops solids from settling. The cast iron cover also ventilates the sewer. When a blockage occurs, workers enter and remove it or insert rods from the manhole. Manholes are provided at changes of direction, gradient and size, at junctions and every 30-90 m in straight length.

2. Catch basin

A catch basin is a small chamber with a silt pit below the level of outlet, provided at the inlet of a storm or combined sewer.

   Street inlet
        |
     ___v___
    |       |  <- cover
    |       |_ outlet to sewer (hooded)
    |_______|
    silt/grit settles here

Working: storm water enters from the street inlet and falls in the chamber. Its velocity is reduced, so heavy silt, sand, grit and rubbish settle to the bottom pit, and only the clear water flows out through the outlet pipe which is higher than the bottom and often has a hood or elbow dipping under water to hold back floating matter and foul gas (water seal). The deposit is removed periodically by hand or by a bucket. This protects the sewer from silting and blockage.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Sanitary Engineering chapter 4 questions →