What is the maximum allowed water absorption for the vitreous china material?

The water absorption shall not be more than 0.5 percent of the dry mass of the test piece (Clause 3.1).

What are the standard nominal flushing capacities specified in this code?

The standard specifies capacities of 5, 6.3, 7.5, 9, 10, 11, 12.5 and 15 litres (Clause 6.1).

How is the resistance to crazing (fine cracking of the glaze) tested?

The cistern is subjected to a crazing test by heating it in a steam autoclave or oven and then immediately plunging it into water, to check for formation of cracks (Clause 9.3).

What is the minimum required flushing rate for a 10-litre cistern?

For a 10-litre capacity cistern, the minimum average rate of discharge must be 2.2 litres per second (Table 2).

IS 7742 Part 1

: 1991

Flushing cisterns for water closets and urinals, Part 1: Plastic flushing cisterns (First Revision)

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This standard specifies the requirements for materials, dimensions, construction, and flushing performance of vitreous china flushing cisterns. It covers various capacities for use with water closets and urinals, and details the test methods to verify quality, durability, and functional efficiency.

Specifies requirements for plastic flushing cisterns used with water closets and urinals.

Quick Reference Values

Maximum Water Absorption0.5 percent by mass

Minimum Average Flushing Rate (10 Litre Cistern)2.2 litres/second

Crazing Test Temperature130 ± 5 °C

Maximum Noise Level for Ball Valve Operation30 dB(A)

Standard Flushing Capacities5, 6.3, 7.5, 9, 10, 11, 12.5 and 15 litres

Practical Notes

Vitreous china offers superior stain resistance and hygiene compared to plastic cisterns, but is significantly heavier and more susceptible to impact damage.

Ensure the internal fittings (float valve and syphon mechanism) also conform to their respective IS codes (IS 1703, IS 8931) as they are critical for the cistern's performance and water efficiency.

This standard predates modern dual-flush systems; while it covers various single-flush capacities, newer water-saving fixtures may be governed by more recent standards or manufacturer specifications.