Direct answer · August 2026
What is the difference between gunmetal Class-1 and Class-2 valves?
Per IS 778, Class-1 gunmetal valves are hydrostatically tested to 15 kg/cm2 on the body and 10 kg/cm2 on the seat. Class-2 valves are tested to 24 kg/cm2 body and 16 kg/cm2 seat — for higher-pressure water, fire, and compressed air lines. Both use gunmetal IS 318 LTB-2 bodies with BSP screwed ends, sizes 15 mm to 100 mm. Supreme Valves India manufactures ISI marked Class-1 and Class-2 gunmetal gate valves from Ahmedabad.
Gunmetal Class-1 vs Class-2 Valve Guide (IS 778)
Technical guide · Supreme Valves India · August 2026
Gunmetal (leaded tin bronze to IS 318 Grade LTB-2) gate valves are specified daily on plumbing, fire, HVAC, and utility tenders across India. The pressure class — Class-1 or Class-2 per IS 778 — determines hydrostatic test levels and whether the valve suits normal water service or higher-pressure lines. This guide explains the difference for buyers, contractors, and consultants sourcing ISI marked gunmetal valves.
What is gunmetal?
Gunmetal is a copper-tin-zinc-lead alloy cast to IS 318 LTB-2. It is corrosion-resistant, pressure-tight, and widely used for potable water and general-service valve bodies in India. Supreme Valves gunmetal gate valves use gunmetal body and wedge, high tensile brass stem (IS 6912), and cast iron hand wheel (IS 210 FG 200) with BSP screwed female ends.
Class-1 vs Class-2 test pressures (IS 778)
| Test | Class-1 | Class-2 |
|---|---|---|
| Body hydrostatic test | 15 kg/cm2 (1.5 MPa) | 24 kg/cm2 (2.4 MPa) |
| Seat / back seat test | 10 kg/cm2 (1.0 MPa) | 16 kg/cm2 (1.6 MPa) |
| Typical working service | Plumbing, potable water, HVAC, low-pressure air | Fire mains, higher-pressure water and air |
| Size range | 15 mm to 100 mm (1/2 inch to 4 inch) | Same |
| End connection | BSP screwed female (standard) | BSP screwed female (standard) |
When to specify Class-1
- Domestic and building water supply distribution
- Low-pressure compressed air in workshops and utilities
- HVAC chilled and hot water branches where working pressure stays well below 10 kg/cm2
- General plumbing tenders referencing IS 778 Class-1
When to specify Class-2
- Fire hydrant and fire water ring mains with higher static head
- Compressed air lines with higher operating pressure
- Project specifications explicitly calling IS 778 Class-2
- Surge-prone lines where additional test margin is required
ISI marking and documentation
ISI marked gunmetal gate valves carry Bureau of Indian Standards certification to IS 778. Each lot should include hydrostatic test certificates showing body and seat test pressures for the class ordered, plus material/test documentation for gunmetal body and brass stem. For export orders, the same ISI marked product is supplied with English-language test reports.
Indicative pricing note
Class-2 gunmetal gate valves are typically priced higher than Class-1 for the same size due to heavier casting sections and higher test requirements. Indicative ex-works range for ISI marked gunmetal gate valves from Supreme Valves India is approximately INR 350 for 15 mm Class-1 up to INR 9,500 for 100 mm Class-2 — send size, class, and quantity for firm pricing.
Frequently asked questions
What standard covers gunmetal Class-1 and Class-2 valves?
IS 778 for copper-alloy gate, globe, and check valves. Gunmetal body grade is IS 318 LTB-2. ISI marking confirms BIS certification.
What are Class-1 test pressures?
Body test 1.5 MPa (15 kg/cm2); seat and back seat 1.0 MPa (10 kg/cm2).
What are Class-2 test pressures?
Body test 2.4 MPa (24 kg/cm2); seat and back seat 1.6 MPa (16 kg/cm2).
When should I specify Class-2 over Class-1?
When working pressure or surge conditions approach Class-1 limits — fire mains, higher-pressure compressed air, or project specs mandating Class-2.
Are BSP and NPT interchangeable on gunmetal valves?
No. Standard IS 778 gunmetal valves have BSP screwed female ends. Use adaptors or specify NPT at enquiry if pipework is NPT.
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Send valve type, size, material grade, class, quantity, and destination. Engineering response within 24 hours.
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