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IS 7742:1991 Part 1 is the Indian Standard (BIS) for flushing cisterns for water closets and urinals, part 1: plastic flushing cisterns (first revision). 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.
BIM-relevant code. See the BIM Hub for ISO 19650, IFC, and LOD/LOIN frameworks used alongside it.
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.
Consolidated list per BIS. For the text of each amendment, refer to the BIS portal link above.
plasticpvchdpepolypropylene
International Equivalents
Similar International Standards
BS EN 14055:2010+A1:2015BSI (British Standards Institution), UK / CEN (European Committee for Standardization), Europe
HighCurrent
WC and urinal flushing cisterns
Specifies constructional and performance requirements for plastic and ceramic WC cisterns.
AS 1172.2:2014Standards Australia, Australia
HighCurrent
Water closets (WCs), Part 2: Cisterns
Covers requirements for cisterns for use with WCs, with a strong focus on water efficiency.
ASME A112.19.5-2017 / CSA B45.15-17ASME (American Society of Mechanical Engineers), USA / CSA (Canadian Standards Association), Canada
MediumCurrent
Flush-ing devices for water closets and urinals
Covers all flushing devices including gravity cisterns, but also pressure-assist and flushometer types.
SS 379:1996Enterprise Singapore, Singapore
MediumCurrent
Specification for flushing cisterns and flush pipes for water closets
Specifies requirements for flushing cisterns, but is older and more aligned with former British Standards.
Key Differences
≠IS 7742:1991 permits large single flush volumes up to 10 litres, reflecting older water use norms. Modern international standards like BS EN 14055 and AS 1172.2 mandate significantly lower volumes (e.g., 6/3 litre or 4.5/3 litre dual flush) to conserve water.
≠The mechanical endurance requirement in IS 7742 is 50,000 cycles for the flushing mechanism, whereas BS EN 14055 requires 200,000 cycles, indicating a four-fold increase in durability expectation in the European standard.
≠BS EN 14055 includes specific clauses and classifications for acoustic performance (noise levels during filling), a parameter not addressed in IS 7742:1991.
≠International standards provide more detailed and stringent requirements for backflow prevention in the inlet valve (e.g., specifying air gap types like AUK1) to protect potable water supplies, compared to the more general provisions in the Indian standard.
Key Similarities
≈All standards mandate fundamental performance tests, including the water tightness of the cistern body, the seal of the flush valve to prevent leaks into the pan, and the functionality of the overflow.
≈Both the IS code and its international counterparts specify that plastic materials used must be resistant to corrosion, household cleaning agents, and be opaque to light to prevent algae growth.
≈IS 7742 and international standards require the cistern to be clearly and permanently marked with essential information, such as the manufacturer's name/trademark and a water level line.
≈All standards specify that the inlet valve mechanism must reliably shut off water flow at the prescribed level and withstand specified static water pressures without failure or leakage.
Parameter Comparison
Parameter
IS Value
International
Source
Flush Volume (Nominal Single Flush)
10, 7.5, or 5 litres
Class 1: 6 litres; Class 2: 4 to 5 litres
BS EN 14055:2010+A1:2015
Endurance Test (Flushing Mechanism)
50,000 cycles
200,000 cycles
BS EN 14055:2010+A1:2015
Endurance Test (Inlet Valve)
10,000 cycles
80,000 cycles
BS EN 14055:2010+A1:2015
Overflow Discharge Capacity
≥ 0.3 L/s at 50 mm head
≥ 0.4 L/s (at manufacturer-specified head)
BS EN 14055:2010+A1:2015
Flush Valve Seal Leakage Test
No visible leakage after 15 minutes.
Max. 200 ml leakage over a 2-hour period.
AS 1172.2:2014
Minimum Wall Thickness (Cistern Body)
2.0 mm
Not specified (performance-based; must pass strength/impact tests)
BS EN 14055:2010+A1:2015
Operating Force (Flush Activation)
Not to exceed 30 N for push-button.
Not to exceed 20 N for push-button; 5 N for lever.
BS EN 14055:2010+A1:2015
⚠ Verify details from original standards before use
Key Values5
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
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).