Flushing Cistern for Water Closets and Urinals (Other Than Plastic Cisterns)
2004 Edition

IS 774 specifies the following materials for flushing cistern parts:

• Cistern bodies can be made from cast iron (Grade FG 150 as per IS 210), vitreous china (IS 2556 Part 1), or enamelled pressed steel (IS 513 and IS 1239 Part 1).
• Flush pipes may be constructed from hot-dip galvanized steel tubes (IS 1239 Part 1), lead pipes (IS 404 Part 1), copper alloy tubes (IS 407 or IS 2501), HDPE, or unplasticized PVC.
• Covers should be fabricated from the same material as the cistern body.
• Chains are made from hot-dip galvanized steel wire or corrosion-resistant non-ferrous metals.
• Overflow pipes use non-ferrous metals, HDPE, or unplasticized PVC to prevent corrosion.
• Siphon parts are constructed from cast iron/vitreous china (Grade FG 150 or above) or plastics like HDPE, GRP, or ABS.
• Levers are cast iron or corrosion-resistant non-ferrous metals.
• Float valves conform to IS 1703, IS 12234, or IS 13049.
• Bolts, nuts, coupling nuts, and lock-nuts are made from hot-dip galvanized steel, non-ferrous metals, malleable iron, or injection-moulded HDPE/PVC.

Materials not explicitly stated should be mutually agreed upon between manufacturer and purchaser to ensure durability and compliance.

IS 774 categorizes flushing cisterns based on their vertical position relative to the top of the pan:

• High-level cisterns are installed at a minimum height of 1250 mm above the pan, utilizing gravity to generate sufficient flushing velocity.
• Low-level cisterns are positioned at heights not exceeding 300 mm above the pan; however, for Orissa or squatting pans, the minimum is set at 700 mm to maintain effective flushing.

This distinction influences the flushing mechanism and installation design, with high-level cisterns relying on gravity-induced siphonic action and low-level cisterns dependent on direct water flow.

IS 774 defines discharge volume requirements as follows:

• Single-flush cisterns must deliver either 5 ± 0.5 litres or 10 ± 0.5 litres per flush depending on their capacity.
• Dual-flush cisterns provide two flush volumes:
  • For 10/5 litre capacity: full flush of 10 ± 0.5 litres and half flush of 5 ± 0.5 litres.
  • For 6/3 litre capacity: full flush of 6 ± 0.5 litres and half flush of 3 ± 0.5 litres.

These specifications ensure water-efficient operation while maintaining adequate flushing performance.

Flush pipes must meet these criteria:

• Internal diameter: 32 ± 1 mm for high-level cisterns and 38 ± 1 mm for low-level cisterns.
• Material thickness: minimum 1 mm for steel pipes and 3.5 mm for lead pipes.
• HDPE or unplasticized PVC flush pipes should have outside diameters of 40 mm (high-level) and 50 mm (low-level).
• Flush pipes must connect securely and airtight to the cistern outlet via a coupling nut; plastic components must match materials.
• Cistern outlet diameters must be at least 32 mm for high-level and 38 mm for low-level cisterns, with screw threads conforming to 1½" size per IS 2643.
• The outlet length from bottom surface to outlet end must be 37 ± 2 mm.
• Flush pipes should be detachable with watertight and airtight joints.
• For lead pipes, copper alloy coupling nuts and tailpieces at least 60 mm long are required.
• Flush pipe length for testing is 1250 mm (high-level, steel, 32 mm ID) and 300 mm (low-level, steel, 38 mm ID).

No flush pipe is necessary for coupled cisterns. These requirements ensure a leak-proof, durable, and corrosion-resistant connection.

IS 774 requires the following major tests:

1. Endurance Test (Clause 8.3): A randomly selected cistern, compliant in materials, construction, and performance, must operate through 3,000 continuous flush cycles without damage or leakage. Valves, if used, must show zero leakage at rated capacity.

2. Discharge Capacity Test (Clause 8.1): The volume of water discharged during flushing is measured and must meet the rated capacity stated for the cistern.

3. Discharge Rate Test (Clause 8.2): The water flow rate must achieve specific volumes within defined times (e.g., 6 ± 0.5 litres in 6 seconds for 10-litre cisterns).

These tests collectively ensure reliable operation, water efficiency, and mechanical integrity of flushing cisterns.