flush valves and fittings for water closets and urinals
1981 Edition

IS 9758 defines the nominal sizes for flush valves as 15 mm, 25 mm, and 32 mm, where the nominal size corresponds to the bore diameter of the supply pipe connected to the valve. The outlet diameters for these valves are 20 mm for 15 mm nominal size, 32 mm for 25 mm, and 40 mm for 32 mm. The threading conforms to IS 2643 (Part I) - 1975 to ensure interoperability with plumbing systems.

Flush valve bodies must be constructed from cast brass or die-cast brass complying with Grade 3 of IS 292-1961 and IS 1264-1965. Flush pipes may be made from steel tubes with vitreous enamel or hot-dip galvanizing, PVC, HDPE, or lead, adhering to respective IS standards such as IS 3972, IS 2629, IS 4985, IS 4984, and IS 404. Washers should be rubber as per IS 4346, springs from phosphor bronze or stainless steel per IS 7608 and IS 4454. Stop valves are also cast brass per IS 292. The external surface of the valve body must be polished bright and chromium plated to at least service grade 3 according to IS 4827-1968, providing corrosion resistance and a high-quality finish, while concealed parts are exempt from plating.

Per IS 9758, flush valves are required to discharge volumes of either 5 or 10 litres with a tolerance of ±0.5 litre. The discharge rate test, conducted following IS 774-1971, specifies that an average of 5 litres ±0.5 litres should be flushed within 3 seconds, maintaining consistent flushing force throughout. Additional testing includes hydraulic pressure endurance and longevity testing to confirm durability and performance.

IS 9758 mandates that flush valves must withstand a hydraulic pressure test of 2 MPa (20 bar) for 2 minutes without leakage or sweating. The operational pressure range for reliable functioning is between 0.15 MPa and 0.5 MPa, ensuring safe performance under typical domestic water supply pressures with an adequate safety margin verified by the pressure test.

Flush valves should bear permanent, legible markings that include the manufacturer's name or trademark and the valve’s nominal size. Additionally, products may carry the ISI Certification Mark, which signifies compliance with Indian Standards and is granted under the Indian Standards Institution (Certification Marks) Act. This mark indicates that production adheres to stringent quality control and testing procedures. Manufacturers must hold a valid license to use the ISI mark.