plastic flushing cisterns for water closets and urinals

IS 7231: Scope & Key Specifications

Scope (Clause 3.0 - 3.5)

• Defines flushing cistern components, materials, and dimensions.
• Flush pipe diameters:
  • High-level cistern: 32 ± 1 mm internal diameter
  • Low-level cistern: 38 + 1 mm internal diameter
• Flush pipe thickness:
  • Steel: ≥ 1 mm
  • Lead: ≥ 3.5 mm
• HDPE and unplasticized PVC flush pipes:
  • HDPE outside diameter: 40 mm
  • PVC outside diameter: 40 mm (high-level), 50 mm (low-level)
• Pipe clips with rubber buffers recommended for high-level cisterns.
• No flush pipe needed for coupled cisterns.

Materials (Table 1, Clause 4)

Dual Flush Specification (Clause 7.5)

• Dual flush cistern capacity: 6/3 litres
• Full flush: 6 ± 0.5 litres
• Half flush: 3 ± 0.5 litres

Summary Diagram of Flush Pipe Dimensions

graph LR
    HL[High-Level Cistern Flush Pipe]
    LL[Low-Level Cistern Flush Pipe]
    HL -->|Internal Diameter 32 ± 1 mm| Pipe1[Flush Pipe]
    LL -->|Internal Diameter 38 + 1 mm| Pipe2[Flush Pipe]
    Pipe1 -->|Steel thickness ≥ 1 mm| SteelPipe1
    Pipe2 -->|Lead thickness ≥ 3.5 mm| LeadPipe2
    Pipe1 -->|HDPE OD 40 mm| HDPEPipe1
    Pipe2 -->|PVC OD 50

IS 7231 Key References & Specifications Summary

1. Referenced IS Standards for Materials & Components

2. Flush Pipe Specifications (Clause 3.5)

• Internal Diameter:
  • High-level cistern: 32 ± 1 mm
  • Low-level cistern: 38 + 1 mm
• Thickness:
  • Steel flush pipe: ≥ 1 mm
  • Lead flush pipe: ≥ 3.5 mm
• Plastic Pipes:
  • HDPE: Outside diameter 40 mm
  • Unplasticized PVC: 40 mm (high-level), 50 mm (low-level)
• Corrosion: Increase thickness in corrosive environments

3. Material Table for Flushing Cistern Components (Table 1, Clause 4)

IS 7231: Definitions & Key Specifications Summary

Clause 3.0 - 3.4:
Defines terms used in flushing cistern standards (not detailed here).

Flush Pipe Specifications (Clause 3.5 & Table 5.3)

• Pipe clips with rubber buffers are required for high-level cistern flush pipes.
• No flush pipe needed for coupled cisterns.

Materials for Components (Table 1)

Notes

• Thicknesses specified suit normal service; increase for corrosive environments.
• Referenced IS codes provide detailed material and dimensional standards.
• Testing includes material, construction, finish, discharge capacity, and rate (Clause 2.1).

flowchart LR
    A[Cistern] --> B[Flush Pipe]
    B --> C{Material}
    C -->|Steel| D[Thickness ≥ 1 mm]
    C -->|Lead| E[Thickness ≥ 3.5 mm]
    C -->|HDPE/PVC| F[Diameter as per cistern level]
    B --> G[Pipe Clip with Rubber Buffer (High

IS 7231: Key Materials Specifications & Tables

Flush Pipe Dimensions (Clause 3.5)

Note: Use thicker pipes in corrosive environments.

Table 1: Materials for Flushing Cistern Components (Clause 4)

Important Notes:

• Talc filler in polypropylene ≤ 20%.
• Pipes and components must conform to respective IS standards.
• Corrosion resistance is critical; select materials accordingly.

flowchart LR
    A[Cistern] -->|Material| B

IS 7231: Construction Requirements - Key Points

• Lot Conformance (Clause 3.1, E-3.1):
  A lot conforms if it meets conditions in E-3.1.1 and E-3.1.2.

• Inspection & Testing (Clause 2.1, E-2.1):
  All cisterns must be checked for:

  • Materials quality
  • Construction integrity
  • Surface finish
  • Discharge capacity test (7.5)
  • Discharge rate test (7.6)

• Acceptance Criteria (Clause 3.1.1, E-3.1.1):
  Number of cisterns failing any characteristic ≤ permissible failure number (see col 3, Table 2).

• Sampling Size (Clause 1.2, E-1.2):
  Number of cisterns sampled depends on lot size (col 1 & 2, Table 2).

Table 2 (Summary):

(Refer to IS 7231 Table 2 for exact values)

Testing Formulas (Discharge Capacity & Rate):

• Discharge Capacity, Q:
  [ Q = \frac{V}{t} ]
  Where:

  • (V) = Volume discharged (liters)
  • (t) = Time taken (seconds)

• Discharge Rate:
  Measured as liters per second (L/s) during test.

flowchart LR
    LotSize[Lot Size] --> SampleSize[Sample Size (Table 2)]
    SampleSize --> Inspection[Inspection & Tests]
    Inspection --> Acceptance[Acceptance Criteria]
    Acceptance --> Conformance[Lot Conforms if ≤ Max Failures]

Summary: Use Table 2 for sampling and allowable failures. Test all cisterns for materials, construction, finish, and discharge performance

IS 7231: Dimensions and Markings – Key Points

1. Markings (Clause 13.1 & 13.3)

• Manufacturer's name/trade-mark must be on the cistern body (inside or outside).
• Discharge capacity and operating instructions must be clearly marked.
• BIS Standard Mark usage is regulated under the Bureau of Indian Standards Act, 1986 (Clause 13.3.2).

2. Flush Pipe Dimensions (Clause 3.5)

• Pipe clip with rubber buffer required for high-level cistern flush pipes.
• No flush pipe needed for coupled cisterns.

3. Materials for Components (Table 1, Clause 4)

Summary Diagram: Flush Pipe Dimensions

flowchart LR
    A[Flush Pipe] --> B{Cistern Type}
    B --> C[High-level]
    B --> D[Low-level]
    C --> E[Internal Diameter: 32 ± 1 mm]
    C --> F[Steel Thickness ≥ 1 mm]
    C --> G[HDPE/UPVC OD: 40 mm]

IS 7231: Operational and Performance Requirements (Clause 7 & related)

Key Points from Clause 9.3 (Endurance Test)

• Sample Testing: Random flushing cistern samples must comply with:
  • Materials (Clause 4)
  • Construction (Clause 5)
  • Operational & Performance (Clause 7)
  • Special requirements (Clause 8)
• Endurance Test: Operate the cistern 3,000 times.
• Acceptance Criteria:
  • No damage or defects post-test.
  • All parts function satisfactorily.
  • If a valve replaces the siphon, no leakage at rated capacity during the test.

Sampling and Conformity (Annex E)

• Lot conformity is based on sampling per Annex E.
• The lot is accepted if it meets criteria in E-3.1.1 & E-3.1.2.

Impact Test (Annex D)

• Drop a 1 kg steel ball suspended from a 2.5 m wire.
• Release from 1 m horizontal distance.
• Impact point: 75 mm from bottom, centerline of cistern.
• Test at ambient or 27 ± 2°C if disputed.

Summary Table: Endurance Test Criteria

flowchart TD
    A[Sample cistern] --> B{Check conformity}
    B -->|Materials, Construction, Operational| C[Pass]
    B -->|Fail| D[Reject]
    C --> E[Operate 3000 times]
    E --> F{Damage or leakage?}
    F -->|No| G[Pass Endurance Test]
    F -->|Yes| D

This ensures flushing cisterns meet durability and performance standards per IS 7231.

IS 7231: Special Tests on Cisterns — Key Points

1. Tests Overview (Clauses 2.1 & 2.2)

• All cisterns undergo:
  • Material, construction, finish inspection
  • Discharge capacity test (7.5)
  • Discharge rate test (7.6)
• Sub-sample undergoes:
  • Distortion resistance test (8.1)
  • Dead load test (8.2)
  • Front thrust test (8.3)
  • Impact test (8.4)
• Sample size per Table 2 (not provided here)

2. Front Thrust Test (Clause 8.3 & Annex C)

• Apply 110 N horizontal thrust via a 150 mm diameter disc at the front center line.
• Duration: 5 minutes
• Disc face: Soft material to conform to cistern shell contour.
• While thrust is applied, check for satisfactory operation.

3. Distortion & Dead Load Tests (Annex B)

• Cistern fastened to solid background.
• Filled to marked water line.
• Tested under specified conditions (details in clauses 8.1 & 8.2).

Front Thrust Test Setup (Fig. 2 schematic)

flowchart LR
    A[Cistern Front] -->|Apply 110 N thrust| B[150 mm Diameter Disc]
    B -->|Soft facing conforms to shell| C[Cistern Shell]
    C -->|Check operation under load| D[Pass/Fail]

Summary Table: Front Thrust Test Parameters

This ensures cistern structural integrity under front loading conditions.

IS 7231 Testing Procedures: Key Points

Impact Test (Annex D - Clause 8.4)

• Suspend a 1 kg steel ball by a fine wire 2.5 m long.
• Release from a horizontal distance of 1 m directly in front of the cistern.
• Impact point: 75 mm from bottom, on the cistern centerline.
• Test temperature: Ambient or 27 ± 2°C if disputed.
• Purpose: Check for damage or cracks on impact.

Endurance Test (Clause 9.3)

• Random sample cistern tested for:
  • Materials (Clause 4)
  • Construction (Clause 5)
  • Operational/performance (Clause 7)
  • Special requirements (Clause 8)
• Operate the cistern 3,000 times continuously.
• Post-test: No damage or leakage (especially valves).
• Frequency: Every 6 months or after design/material changes.

Sampling & Conformity (Annex E)

• All cisterns undergo:
  • Material, construction, finish checks.
  • Discharge capacity and rate tests (Clauses 7.5 & 7.6).
• Sampling follows Annex E procedures for lot acceptance.

Summary Table: Testing Parameters

flowchart TD
    A[Start Testing] --> B{Impact Test}
    B -->|Pass| C[Endurance Test: 3000 cycles]
    B -->|Fail| D[Reject Batch]
    C -->|No Damage/Leakage| E[Conformity Confirmed]
    C -->|Damage/Leakage| D

This

IS 7231: Sampling and Criteria for Conformity

Key Points from IS 7231:

• Sampling:

  • Samples are selected from each lot separately (Clause E-1.1.1).
  • Testing is done to verify material, construction, operational, and special requirements (Clauses 9.3, 4, 5, 7, 8).

• Endurance Test (Clause 9.3):

  • Operate flushing cistern 3,000 times without damage or leakage.
  • Valve leakage check during operation at rated capacity.
  • Test done by recognized labs, repeated every 6 months or after design/manufacture changes.

• Impact Test (Annex D, Clause 8.4):

  • Release a 1 kg steel ball from 1 m horizontal distance, suspended by 2.5 m wire, impacting 75 mm above cistern bottom on centerline at ambient or 27 ± 2°C.

• Criteria for Conformity (Annex E, Clause 10):

  • Lot conformity judged based on sample tests meeting all specified requirements.

Summary Table: Sampling & Tests

flowchart TD
    A[Select Sample from Lot] --> B{Test for Material & Construction}
    B -->|Pass| C{Endurance Test (3000 cycles)}
    C -->|Pass| D{Impact Test}
    D -->|Pass| E[Lot Accepted]
    B -->|Fail| F[Lot Rejected]
    C -->|Fail| F
    D -->|Fail| F

Note: Always refer to Annex E for detailed sampling plans and acceptance criteria tables.

IS 7231: Supply Conditions - Key Points

• Clause 11 (Supply Conditions) mandates that all flushing cisterns must be inspected for:

  • Materials (Clause 4)
  • Construction (Clause 5)
  • Finish (Clause 6)
  • Discharge capacity test (Clause 7.5)
  • Discharge rate test (Clause 7.6)

• Clause 9.2 (Test for Discharge Rate): Ensures flushing cisterns meet required flow rates under specified conditions.

• Clause 9.3 (Endurance Test):

  • Random samples undergo 3000 operation cycles.
  • No damage or leakage allowed post-test.
  • Applies especially if valves replace siphons.

• Clause 3.5 (Flush Pipe Dimensions):

  Cistern Type	Internal Diameter (mm)	Pipe Thickness (mm)	Outside Diameter (mm) for HDPE/PVC
  High-level cistern	32 ± 1	Steel ≥ 1, Lead ≥ 3.5	HDPE: 40, UPVC: 40
  Low-level cistern	38 + 1	Same as above	HDPE: 40, UPVC: 50

• Material Specifications (Table 1):
  Components like cisterns, flush pipes, overflow pipes, siphons, and float valves must conform to relevant IS standards (e.g., IS 7328, IS 4984, IS 1239, IS 1703).

Summary Diagram of Supply Condition Checks

flowchart TD
  A[Supply of Flushing Cistern] --> B[Material Inspection (Clause 4)]
  B --> C[Construction Inspection (Clause 5)]
  C --> D[Finish Inspection (Clause 6)]
  D --> E[Discharge Capacity Test (Clause 7.5)]
  E --> F[Discharge Rate Test (Clause 7.6)]
  F --> G[Endurance Test (3000 cycles) (Clause 9.3)]
  G --> H{Pass?}
  H -- Yes --> I[Approved for Supply]
  H -- No --> J[

IS 7231: Operating Instructions for Flushing Cisterns (Key Points)

1. Components & Materials (Table 1)

2. Flush Pipe Dimensions (Clause 3.5)

• High-level cistern: Internal diameter = 32 ± 1 mm
• Low-level cistern: Internal diameter = 38 + 1 mm
• Steel flush pipe thickness ≥ 1 mm; Lead pipe thickness ≥ 3.5 mm
• HDPE/PVC pipes outside diameter: 40 mm (high-level), 50 mm (low-level)

3. Operating Instructions (Clause 12.2)

• For dual-flush cisterns with knob operation, follow specific instructions different from lever-operated cisterns (Clause 12.1.1 not applicable).
• Ensure all components per Table 1 and flush pipes per Clause 5.3 are included.

Summary Diagram: Flushing Cistern Components

graph TD
    A[Cistern Body] --> B[Flush Pipe]
    A --> C[Cover]
    A --> D[Chain]
    A --> E[Operating Mechanism/Lever]
    B --> F[Material: Steel/Lead/HDPE/PVC]
    E --> G[Material: Non-ferrous metal]

Note: For corrosive environments, increase pipe thickness beyond minimum values. Flush pipe clips with rubber buffers are mandatory for high-level cisterns to prevent damage.

IS 7231 - Marking and Labeling Key Points

Clause 13: Marking on Cisterns

• 13.1:
  Each cistern must be marked with:

  • Manufacturer's name or trademark (inside or outside body)
  • Discharge capacity (refer Clause 7.5)
  • Operating instructions (refer Clause 12)

• 13.3:
  Cisterns may bear the BIS Standard Mark on the body.

• 13.3.1:
  Marking with the Standard Mark is optional but must be on the cistern body.

• 13.3.2:
  Use of the Standard Mark is governed by the BIS Act, 1986 and related rules.
  License conditions for using the Standard Mark are provided by BIS.

Summary Table for Marking Requirements

Notes:

• Markings ensure traceability and user guidance.
• Standard Mark use requires BIS license compliance.
• Refer to BIS Act for legal provisions on marking.

flowchart TD
    A[Cistern] --> B[Mark Manufacturer's Name]
    A --> C[Mark Discharge Capacity]
    A --> D[Mark Operating Instructions]
    A --> E{Use BIS Standard Mark?}
    E -->|Yes| F[Mark BIS Standard Mark]
    E -->|No| G[No BIS Mark]

This ensures compliance with IS 7231 marking and labeling requirements.

IS 7231: List of Referred Indian Standards & Key Specifications

This standard references important IS codes related to materials and components used in plastic flushing cisterns:

Key Specifications for Flushing Cisterns (Clause 3.5 & Table 1)

• Flush Pipe Diameters:
  • High-level cistern: 32 ± 1 mm internal diameter
  • Low-level cistern: 38 + 1 mm internal diameter
• Pipe Thickness:
  • Steel: ≥ 1 mm
  • Lead: ≥ 3.5 mm
• Materials for Components:

IS 7231: Sampling Procedures and Criteria for Conformity

Key Points from the Code

• Sampling: Samples must be selected and tested from each lot separately (Clause E-1.1.1).
• Endurance Test (Clause 9.3):
  • Random sample checked for materials, construction, operation, and performance.
  • Operate flushing cistern 3,000 times.
  • No damage, defects, or leakage allowed post-test.
  • Test repeated every 6 months or after design/material changes.
• Impact Test (Annex D, Clause 8.4):
  • Drop a 1 kg steel ball suspended from a 2.5 m wire.
  • Release from 1 m horizontal distance.
  • Impact point: 75 mm from bottom, center line of cistern.
  • Test at ambient or 27 ± 2°C if disputed.
• Conformity Criteria (Annex E, Clause 10):
  • Lot accepted if samples meet all requirements.
  • Testing per Annex E sampling plan (details in IS 7231 Annex E).

Summary Table: Sampling and Testing

Mermaid Diagram: Sampling & Testing Flow

flowchart TD
    A[Select Sample from Lot] --> B{Check Material & Construction}
    B -- Pass --> C[Perform Endurance Test (3000 cycles)]
    B -- Fail --> F[Reject Lot]
    C -- Pass --> D[Perform Impact Test]
    C -- Fail --> F
    D -- Pass --> E[Accept Lot]
    D -- Fail --> F

Note: For detailed sampling sizes and acceptance numbers, refer to Annex E of IS 7231.