Cast Copper Alloy Screw Down Bib Taps And Stop Valves for Water Services

IS 781: Scope Overview

IS 781 primarily covers dimensions and tolerances for metric screw threads (e.g., M20 × 1.5, M24 × 1.5). Key points from the scope and related clauses:

• Thread Length (R): Includes any cut-back under the hexagon.
• Core Diameter (K): Values refer to the core diameter of the thread.
• Face-to-Face Diameters (U, V): These diameters are measured face to face.
• Packing Face Dimension (F): Refers to the packing face dimension on the component.

Key Definitions (Clause 2.0)

• Standardizes terminology related to threads, dimensions, and tolerances for metric screws.

Sampling and Acceptance (Clause 10.1, Appendix A)

• Specifies sampling scale and conformity criteria for quality acceptance of threaded parts.
• Ensures consistent quality control during manufacturing.

Typical Thread Dimension Table (Example for M20 × 1.5)

Note: Exact values depend on thread class and tolerance.

flowchart LR
    A[Thread Nominal Size] --> B[Pitch (P)]
    B --> C[Core Diameter (K)]
    B --> D[Thread Length (R)]
    B --> E[Face-to-Face Diameter (U, V)]
    E --> F[Packing Face Dimension (F)]

For detailed dimensions and tolerances, refer directly to IS 781 tables and appendices.

IS 781: Definitions & Key Specifications

• Thread Designation (e.g., M20 × 1.5):

  • M = Metric thread
  • 20 = Nominal diameter in mm
  • 1.5 = Pitch in mm

• Notes on Dimensions:

  • R = Length of thread including cut back under hexagon
  • K = Core diameter (used for stress calculations)
  • U, V = Face-to-face diameters (important for wrench size)
  • F = Packing face dimension

• Quality Checks (Clause 2.1):
  Items must be verified for:

  • Material
  • Workmanship
  • Construction
  • Finish
  • Dimensions
  • Minimum mass

• Rounding Off (Clause 0.3):
  Final test values should be rounded per IS 2-1960, maintaining the same significant figures as specified.

Example: Thread Dimension Table (Simplified)

flowchart TD
    A[Select Thread Size] --> B[Check Material & Workmanship]
    B --> C[Verify Dimensions (R, K, U, V, F)]
    C --> D{Pass All Checks?}
    D -- Yes --> E[Accept Item]
    D -- No --> F[Reject Item]

This ensures compliance with IS 781 definitions and quality standards.

IS 781: Designation and Nominal Sizes - Key Points

• Designation Format:
  Example: M 20 × 1.5

  • M = Metric thread
  • 20 = Nominal diameter in mm
  • 1.5 = Pitch of thread in mm

• Nominal Size Definition (Clause 3.3):
  Nominal sizes correspond to the nominal bore of the socket or pipe outlet where the bib tap or stop valve is fitted.

• Minimum Bore (Clause 6.7.1):
  For non-threaded ends, minimum bore dimension is given by K in Table 2.

Table Extract: Dimensions for Washer Plate and Stop Valves (Selected Sizes)

Notes on Dimensions:

• R includes any thread cutback under the hexagon.
• K refers to core diameter (minimum bore for non-threaded ends).
• U and V are face-to-face diameters.
• F is the packing face dimension.

Summary

IS 781: Materials for Bib Taps and Stop Valves (Clause 4.1)

Minimum Finished Mass (kg) of Bib Taps & Stop Valves (Clause 7.1)

IS 781: Dimensions and Tolerances (Clause 5.1 & Table 2 Summary)

Key Points:

• Dimensions are in millimeters.
• Thread sizes for nuts follow standard metric threads, e.g., M20 × 1.5, M24 × 1.5.
• Dimension R includes cut back under hexagon (if any).
• K refers to core diameter (minimum bore for non-threaded ends).
• Dimensions U and V are face-to-face diameters.
• Dimension F is the packing face.

Sample Dimensions for Bib Taps and Stop Valves (Nominal Size 15 mm):

Notes on Tolerances:

• Tolerances are implicit in the minimum values given.
• Packing face (F) and bore (K) critical for sealing and fitting.
• Thread dimensions per standard metric thread specifications.

Visual Summary (Mermaid Diagram):

graph LR
  A[Overall Length (A)] --> B[Width (B)]
  B --> G[Minor Diameter (G)]
  G --> Đ[Diameter (Đ)]
  Đ --> E[Thickness (E)]
  E --> F[Packing Face (F)]
  F --> K[Thread Size (K)]
  K --> R[Thread Length (R)]
  R --> U[Face to Face Diameter (U)]
  U --> V[Face to Face Diameter (V)]

For detailed design, refer to **Table 2 in Clause

IS 781: Construction and Workmanship - Key Points

1. Inspection Criteria (Clause 2.1 & A-2.1)

• Items must be checked for:
  • Material
  • Workmanship
  • Construction
  • Finish
  • Dimensions
  • Minimum mass
• Any failure in these renders the item defective.

2. Sampling & Acceptance (Clause 2.1.1 & A-2.1.1)

• Lot acceptance depends on the number of defective items ≤ acceptance number from Table 4.
• Sampling is done randomly.

3. Materials for Components (Clause 4.1 & Table 1)

4. Thread & Dimension Notes (Clause 1.5)

• Length of thread includes cut back under hexagon.
• K values refer to core diameter.
• U and V diameters are face-to-face.
• F dimension is packing face.

Summary Diagram: Inspection & Material Flow

flowchart TD
    A[Start: Item Selection] --> B[Material Check]
    B --> C[Workmanship & Construction Check]
    C --> D[Dimension & Mass Check]
    D --> E{Defective?}
    E -- No --> F[Accept Item]
    E -- Yes --> G[Reject Item]
    F --> H[Sampling & Lot Acceptance]
    G --> H

**Use this as a checklist for quality

IS 781: Minimum Finished Mass for Bib Taps and Stop Valves (Clause 7.1)

The minimum finished mass ensures durability and quality compliance for taps and valves.

Key Table: Minimum Finished Mass (kg)

Additional Specifications:

• Hexagonal shoulders are mandatory on inlet ends of taps and both ends of stop valves.
• Square or hexagonal shoulders on all bonnets.
• Dimensions across flats for shoulders are as per Table 2 of IS 781.
• Thread length includes cut back under hexagon (if any).

This ensures mechanical strength and compatibility with standard fittings.

If needed, I can provide dimensions for hexagonal shoulders or thread details as per IS 781.

IS 781 - Finish: Key Specifications and Minimum Finished Mass

Minimum Finished Mass (Clause 7.1, Table 3)

Additional Notes:

• Thread Length (R) includes any cut back under hexagon.
• K values refer to core diameter.
• U and V diameters are face-to-face dimensions.
• F dimension is the packing face.
• For compliance, values are rounded per IS 2-1960 rounding rules.

Quality Check (Clause 2.1):

• Items must be inspected for material, workmanship, construction, finish, dimensions, and minimum mass.
• Failure in any aspect renders the item defective.

This table and notes ensure taps and valves meet minimum mass and finish standards for durability and quality.

IS 781: Hydraulic Test Key Points

Hydraulic Test Pressure (Clauses 1.5 & 9.1)

• Test Pressure: Minimum 2.0 MPa (20 bar) internal hydraulic pressure.
• Duration: Maintain pressure for at least 2 minutes.
• Acceptance: No leakage or sweating allowed during the test.

Procedure

• Test every bib tap and stop valve in the closed position.
• Ensure all components are assembled.
• Use a calibrated pressure gauge for accuracy.

Relevant Dimensions (Clause 5.1, Table 2)

• Dimensions and tolerances of bib taps and stop valves components like washer plates, nuts, threaded parts are specified.

Summary

• Use 2 MPa hydraulic pressure for testing.
• Hold pressure for 2 minutes.
• No leakage or sweating allowed.
• Follow dimensional tolerances for components to ensure proper fit and sealing.

flowchart TD
    A[Assemble Bib Tap/Stop Valve] --> B[Close Valve]
    B --> C[Apply Hydraulic

IS 781 - Sampling and Criteria for Conformity (Clause 10.1 & Appendix A)

Key Points:

• Lot conformity: A lot is accepted if defective items ≤ acceptance number (Col 3, Table 4).
• Sampling size depends on lot size (Col 1 & 2, Table 4).
• Random sampling methods should be used.

Table 4: Scale of Sampling and Criteria for Conformity

Usage:

• Select sample size based on lot size.
• Count defective items in sample.
• If defective ≤ acceptance number, accept the lot.
• Otherwise, reject.

flowchart TD
    A[Start: Define Lot Size] --> B{Lot Size?}
    B -->|Up to 150| C[Sample Size=8, Accept=0]
    B -->|151-300| D[Sample Size=13, Accept=0]
    B -->|301-500| E[Sample Size=20, Accept=1]
    B -->|501-1000| F[Sample Size=32, Accept=2]
    B -->|1001-3000| G[Sample Size=50, Accept=3]
    B -->|3001+| H[Sample Size=80, Accept=5]
    C --> I[Inspect sample]
    D --> I
    E --> I
    F --> I
    G --> I
    H --> I
    I --> J{Defects ≤ Acceptance Number?}
    J -->|Yes| K[Accept Lot]
    J -->

IS 781: Sampling and Criteria for Acceptance

Key Points from Clause 10.1 & Appendix A:

• Lot conformity: A lot is accepted if the number of defective items in the sample ≤ acceptance number (Col 3, Table 4).
• Sampling size depends on lot size (Cols 1 & 2, Table 4).
• Random sampling methods should be used.

Table 4: Scale of Sampling and Criteria for Conformity

Summary:

• Sample size increases with lot size.
• Acceptance number defines max defective items allowed.
• Use random sampling to select items.
• If defective items ≤ acceptance number → lot accepted.
• Sub-sample size is for further detailed testing if required.

flowchart TD
    A[Start: Identify Lot Size] --> B[Determine Sample Size (Table 4)]
    B --> C[Randomly Select Sample]
    C --> D[Count Defective Items]
    D --> E{Defective ≤ Acceptance Number?}
    E -- Yes --> F[Accept Lot]
    E -- No --> G[Reject Lot]

This ensures quality control by statistically verifying conformity with IS 781 standards.