Code of practice for ancillary structures in the sewerage system, Part II: Flushing tanks

IS 4111 Part 2 - Scope Summary

• Scope: Covers ancillary structures in sewerage systems, specifically guidance for design and construction of flushing tanks.
• Applicability: Intended for local bodies, public health engineering departments, and others involved in sewerage infrastructure.
• Purpose: Ensures uniformity and safety in flushing tank design.
• Rounding Off: Final test or analysis values should be rounded per IS 2-1960, maintaining the same significant figures as specified values.

Key Notes:

No explicit formulas or tables are provided in the scope section; refer to subsequent clauses for design specifics.

flowchart TD
    A[IS 4111 Part 2] --> B[Scope: Ancillary Sewerage Structures]
    B --> C[Flushing Tanks Design & Construction]
    B --> D[Users: Local Bodies, PHE Departments]
    B --> E[Rounding per IS 2-1960]

IS 4111 Part 2 — Definitions Overview

• Clause 2.0 specifies that all key terms used in the standard are defined to ensure clarity and uniform understanding.
• Definitions relate to ancillary structures in sewerage systems, particularly flushing tanks.
• The standard emphasizes rounding off test or calculation results per IS 2-1960, maintaining the same significant figures as specified values.

Key Points on Definitions:

• Definitions ensure consistency in interpretation of terms like flushing tanks, ancillary structures, and related components.
• No direct formulas or tables are provided under "Definitions"—this clause is primarily terminology-focused.
• For numerical values, always apply rounding rules from IS 2-1960 for compliance checks.

IS 2-1960 Rounding Summary:

If you need formulas or tables related to design or construction aspects, please specify the section or topic.

IS 4111 Part 2 - General Requirements Summary

This part of IS 4111 (1985) covers ancillary structures in sewerage systems, focusing on design and construction of flushing tanks.

Key Specifications:

• Scope: Guidance for local bodies, public health engineering, etc., on flushing tank design.
• Rounding Off: Final test or calculation values must be rounded as per IS 2:1960, maintaining the same number of significant digits as specified values.

Important Notes:

• The standard ensures uniformity and accuracy in measurements.
• Applies to ancillary sewerage structures ensuring proper function and durability.

Typical General Requirements (from engineering practice):

Rounding Off Rule (IS 2:1960):

• Round to same decimal places as specified value.
• Example: 3.14159 rounded to 3.14 if specified as 3.14.

flowchart TD
    A[Start: Design of Flushing Tank] --> B[Check IS 4111 Part 2 Requirements]
    B --> C[Apply Structural Design per IS 456]
    C --> D[Calculate Test Values]
    D --> E[Round off Values as per IS 2:1960]
    E --> F[Verify Compliance]
    F --> G[Construct Tank]

For detailed design, refer to IS 4111 Part 2 and related IS codes (IS 456, IS 875).

IS 4111 Part 2 - Design Considerations for Flushing Tanks

Key Points from Clause 4.2 and 3.1:

• Flushing Water Quantity & Velocity:
  • For pipes < 600 mm diameter, flushing water must fill at least half the bore over the sewer length.
  • Initial discharge velocity must exceed self-cleansing velocity to remove deposited solids.
  • Typical flushing water volume for 75-90 m sewer length:

• Flushing Tanks Location (Clause 3.1):
  • Provided where flow is insufficient for self-cleansing velocity.
  • Positioned at sewer heads or intermediate points.

Additional Notes:

• Self-cleansing velocity typically ranges 0.6 to 0.9 m/s in sewers.
• Flushing water head should generate velocity > self-cleansing velocity.
• Flushing tanks ensure solids do not settle, maintaining sewer efficiency.

flowchart LR
    A[Flushing Tank] --> B[Flush Water Discharge]
    B --> C{Pipe Diameter < 600 mm?}
    C -->|Yes| D[Flush water fills half bore length]
    D --> E[Velocity > Self-cleansing velocity]
    E --> F[Solids removed]
    C -->|No| G[Design per other standards]

This ensures effective sewer flushing per IS 4111 Part 2.

IS 4111 Part 2: General Specifications Summary

IS 4111 Part 2 covers ancillary structures in sewerage systems, focusing on flushing tanks design and construction.

Key Points:

• Purpose: Guidance for local bodies and public health engineering on flushing tanks.
• Rounding Off: Final test or analysis values must be rounded as per IS 2:1960, maintaining the same significant figures as specified.
• Definitions: Clause 2.0 provides essential terms related to sewerage ancillary structures.

Important Notes:

• The standard emphasizes proper design and construction to ensure functional and durable flushing tanks.
• No explicit formulas or tables are provided in the general clauses; these appear in specific parts or subsequent clauses.

IS 2:1960 Rounding Rule (Brief):

• Round off values to the same decimal places or significant figures as the standard's specified value.

flowchart LR
    A[Test/Analysis Result] --> B{Compare with Specified Value}
    B -->|Round off| C[Final Rounded Value]
    C --> D[Use for Compliance Check]

For detailed formulas or tables, refer to specific parts of IS 4111 related to structural design or material specifications.

IS 4111 Part 2: Methods of Flushing & Flushing Devices

1. Methods of Flushing (Clause 4.3)

• Special Flushing Tanks: Manually operated or automatic tanks at suitable sewer points.
• Controlled Surface Water Admission: Limited surface water allowed into sewer at required points.
• Flap Valve/Plug in Manholes: Wooden stop gates or flap valves to accumulate sewage, then release a flush.
• Fire Hose/Water Tanker: Used with consultation from fire/water authorities.

2. Quantity & Velocity of Flushing Water (Clause 4.2)

• Pipes <600 mm diameter: Flush water should fill at least half the pipe bore over the length to be flushed.
• Initial velocity must exceed self-cleansing velocity to remove solids.

3. Key Specification

• Ensure flushing velocity > self-cleansing velocity (typically 0.6 to 0.9 m/s).
• Flushing volume must cover half-bore length to mobilize deposits.

flowchart LR
    A[Flushing Methods] --> B[Special Flushing Tanks]
    A --> C[Controlled Surface Water]
    A --> D[Flap Valve / Stop Gate]
    A --> E[Fire Hose / Water Tanker]

This ensures effective sewer cleaning and prevents blockages.

IS 4111 Part 2 – Special Flushing Tanks (Clause 4.4)

Key Specifications:

• Types: Manually operated and automatic flushing tanks.
• Purpose: To ensure efficient flushing with controlled water volume.

Important Formulas & Design Parameters:

• Flushing Volume (V):
  Typically depends on the fixture type; for example, a standard WC requires about 6-9 liters per flush.

• Tank Capacity (C):
  [ C \geq V + \text{Allowance for supply delay} ]

• Water Supply Pipe Diameter:
  As per IS 1239 or IS 3589, usually 15 mm to 25 mm depending on flow rate.

Typical Table for Flushing Volume (Indicative):

Additional Notes:

• Automatic tanks must have reliable float valves to maintain water level.
• Manual tanks require a flushing handle or lever mechanism.
• Material: Usually PVC, HDPE, or GI as per durability and installation environment.

flowchart TD
    A[Water Supply] --> B[Flushing Tank]
    B --> C{Type of Tank}
    C --> D[Manual Operation]
    C --> E[Automatic Operation]
    D --> F[Flush Handle]
    E --> G[Float Valve Control]
    F & G --> H[Flush Outlet to Fixture]

For detailed dimensions and installation, refer to IS 4111 Part 2 Tables and drawings.

Manually Operated Flushing Tank (IS 4111 Part 2, Clause 4.4.1)

• Purpose: Stores water for a single flush of sewer; operates manually.
• Construction: Small chamber of masonry/concrete, similar to a manhole.
• Size: Enough volume to store flushing water once (depends on sewer flushing volume).
• Connection:
  • Pipe diameter = sewer diameter.
  • Slots at outlet for a wooden stop gate (manual operation).
• Overflow: Overflow pipe above max water depth to prevent flooding if gate isn't opened.
• Water Supply: Constant small flow from water supply, ensuring daily filling.

Key Specifications:

Typical volume calculation:

[ V = Q \times t ] Where:

• (V) = volume of flushing water (m³)
• (Q) = flow rate required for flushing (m³/s)
• (t) = duration of flush (s)

flowchart LR
    WaterSupply --> FlushingTank
    FlushingTank -->|Stop Gate| SewerManhole
    FlushingTank -->|Overflow Pipe| Drain

This simple schematic shows water supply filling the tank, manual gate releasing water to sewer, and overflow preventing flooding.

IS 4111 Part 2: Automatic Flushing Tank Key Points

1. Automatic Flushing Tank (Clause 4.4.2)

• Description: Resembles a manhole with a syphon at the bottom.
• Operation: Water supply fills the tank once daily; when full, the syphon activates, flushing water into the sewer.
• Flush quantity: Depends on sewer diameter (see Clause 4.2).

2. Syphon Specifications

• Type: Adam's Syphon (cast iron with trapped outlet).
• Diameter options: 65 mm, 80 mm, or 100 mm, based on sewer line size.

3. Design Considerations

• Water supply: Constant but regulated to fill tank once daily.
• Tank size: Enough to store flush volume as per sewer diameter.

4. Typical Syphon Flush Volume (Refer Clause 4.2)

Conceptual Operation Flow:

flowchart TD
    A[Water Supply] --> B[Flushing Tank]
    B --> C{Tank Full?}
    C -- No --> B
    C -- Yes --> D[Syphon activates]
    D --> E[Flush water into sewer]

Summary: Automatic flushing tanks use Adam’s syphon to discharge a preset volume of water once daily, sized according to sewer diameter, ensuring effective sewer flushing without manual operation.

IS 4111 Part 2: Period of Flushing & Flushing Water Specifications

Key Points:

• Period of Flushing:

  • Once every 24 hours (Clause 4.5).

• Flushing Water Quantity & Velocity (Clause 4.2):

  • For pipes < 600 mm diameter, flush water should fill at least half-bore of the sewer length or between flush points.
  • Initial velocity must exceed self-cleansing velocity (≥ 0.75 m/s) to remove deposits.

Approximate Flushing Water Quantity per 75-90 m length:

Additional Notes:

• Flushing tanks are required where gradients do not maintain self-cleansing velocity (Clause 3.1).
• Flushing ensures dislodging of solids like clay and mud, preventing clogging.

Formula for Self-Cleansing Velocity:

[ V_{sc} \geq 0.75 , m/s ]

Where:

• (V_{sc}) = velocity of flow in sewer pipe

flowchart LR
    A[Non-self-cleansing sewer section] --> B[Flushing Tank]
    B --> C[Flushing Water Release]
    C --> D[Velocity > 0.75 m/s]
    D --> E[Deposit Removal & Sewer Cleaning]

This summarizes the flushing requirements per IS 4111 Part 2 for maintaining sewer cleanliness.

IS 4111 Part 2 - Safeguards for Flushing Tanks

Key Specification (Clause 5.1)

• Physical Break/Air Gap:
  For automatic flushing tanks, a physical break (air gap) must exist between the water supply inlet and the maximum water level in the tank to prevent backflow contamination.

Typical Dimensions (From Fig. 2 - Automatic Flushing Tank)

• Water Inlet Air Gap: Minimum 30 mm
• Wall Thickness: One brick thick (approx. 100 mm)

Purpose

• Prevents contamination of potable water by sewage or stagnant water in the flushing tank.
• Ensures backflow prevention by maintaining an air gap.

Summary Table: Safeguard Requirements

Diagram: Automatic Flushing Tank Safeguard

flowchart TB
    A[Water Supply] -->|30 mm Air Gap| B[Water Inlet]
    B --> C[Flushing Tank]
    C --> D[Maximum Water Level]
    style B fill:#a2d5f2,stroke:#000,stroke-width:1px
    style D fill:#f9f,stroke:#333,stroke-width:1px

Note: Always ensure compliance with IS 4111 Part 2 for safe sewer flushing systems to avoid contamination risks.

IS 4111 (Part 2) - Safeguards for Automatic Flushing Tanks

Key Specification (Clause 5.1)

• Physical break (air gap) required between the water supply connection and the maximum water level in the automatic flushing tank.
• This prevents backflow contamination from the tank to the supply.

Typical Dimensions (From Fig. 2 & Clause 5.1)

• Water inlet pipe size: 30 mm diameter.
• Air gap: Minimum 30 mm vertical gap between water supply outlet and max water level.
• Wall thickness: One brick thick masonry wall around the tank.

Important Notes:

• The overflow pipe must be provided above max water level to prevent flooding.
• The connection pipe diameter to sewer should match sewer diameter.
• The tank should fill at least once daily by a regulated constant water supply.

Summary Table for Safeguards

flowchart TB
    A[Water Supply] -->|30 mm pipe| B[Air Gap (30 mm)]
    B --> C[Automatic Flushing Tank]
    C --> D[Overflow Pipe (above max water level)]
    C --> E[Sewer Connection (same diameter as sewer)]

This ensures no backflow contamination and proper operation of automatic flushing tanks as per IS 4111 (Part 2).