Introduction: Why Material Choice Matters for WRAS Approved Valves
The material from which a WRAS approved valve is manufactured is one of the most fundamental aspects of its specification. In potable water systems, valve materials are not simply an engineering choice based on strength, cost, and machinability — they have direct implications for water quality, regulatory compliance, service life, and suitability for specific applications. WRAS approval for a valve confirms that the wetted materials — those in direct contact with the drinking water — have been independently tested and verified not to contaminate the water supply, in compliance with BS 6920.
However, not all WRAS approved materials are equal in every application. Different body materials, seat materials, and seal materials offer different combinations of corrosion resistance, pressure rating, temperature resistance, chemical compatibility, and cost. Selecting the wrong WRAS approved valve material for a particular application can result in premature valve failure, increased maintenance costs, or in the worst case, a water quality problem that compromises the safety of the potable water supply.
This guide provides a comprehensive overview of the key materials used in WRAS approved valves — including brass (DZR and standard), gunmetal, cast iron, stainless steel, and engineering polymers — examining the advantages, limitations, and ideal applications for each material, as well as the seat and seal materials commonly used in WRAS approved valve construction.
DZR Brass: The Standard Material for WRAS Approved Valves in the UK
DZR (dezincification-resistant) brass is by far the most widely used body material for WRAS approved valves in the UK potable water industry. Standard brass is an alloy of copper (typically 60-65%) and zinc (typically 35-40%), offering excellent machinability, good pressure resistance, and ease of joining by soldering, compression fitting, or threading. However, standard brass is susceptible to dezincification in certain water conditions — particularly in soft, slightly acidic water, stagnant water, or hot water — where the zinc is selectively leached from the alloy, leaving a porous, mechanically weak copper structure.
DZR brass addresses this weakness by incorporating a small addition of arsenic (typically 0.02-0.06%) that inhibits the dezincification mechanism. This makes DZR brass suitable for use in the full range of UK water conditions, including the soft, acidic water found in parts of Scotland, Wales, and the North of England, as well as the hard chalky water of the South East. WRAS approved DZR brass valves must comply with BS EN 12165 or equivalent standards for the brass material, as well as BS 6920 for WRAS approval of the wetted components.
In the UK, WRAS approved ball valves, gate valves, globe valves, check valves, pressure reducing valves, strainers, and most other valve types for standard cold and hot water applications are typically manufactured from DZR brass. The combination of cost-effectiveness, wide availability, ease of installation with standard fittings, and proven long-term performance in UK water conditions makes DZR brass the default material choice for most WRAS approved valve applications.
One important consideration with DZR brass WRAS approved valves is to ensure that the brass used is genuinely dezincification-resistant and not simply standard brass marketed as DZR. Reputable WRAS approved valve manufacturers will provide material certification confirming DZR compliance. This is particularly important when sourcing WRAS approved valves from overseas suppliers, where standard brass (which does not meet the UK's DZR requirement) may be used.
Gunmetal: Enhanced Corrosion Resistance for Demanding Applications
Gunmetal (also known as red brass) is an alloy of copper, tin, and zinc, typically in proportions of approximately 85% copper, 5% tin, 5% zinc, and 5% lead (or in lead-free grades, with antimony or bismuth replacing the lead). The much lower zinc content of gunmetal compared to standard brass makes it inherently more resistant to dezincification, while the addition of tin enhances its resistance to corrosion in water containing dissolved oxygen.
WRAS approved gunmetal valves are widely specified for applications where enhanced corrosion resistance is required: systems with particularly soft or aggressive water chemistry; older pipework systems where the water contains dissolved gases or impurities that could attack standard brass; and applications involving hot water recirculation, where the combination of elevated temperature and dissolved oxygen can accelerate corrosion of standard brass. WRAS approved gunmetal gate valves and check valves are the traditional specification for water distribution systems in the UK water industry and are widely used by water companies and mechanical contractors.
The main limitations of gunmetal compared to DZR brass are its higher cost and its tendency to have a rougher internal surface finish due to the casting process typically used to manufacture gunmetal valves. For WRAS approved valve applications where internal surface smoothness is important (such as food and beverage applications), machined DZR brass or stainless steel WRAS approved valves are generally preferred.
Stainless Steel: Premium Corrosion Resistance and Food-Grade Performance
Stainless steel WRAS approved valves offer the highest level of corrosion resistance of any metallic valve material commonly used in potable water systems. Stainless steel is an iron-based alloy containing at least 10.5% chromium, which forms a passive oxide layer on the surface that protects the steel from corrosion. In potable water applications, WRAS approved stainless steel valves are typically manufactured from Grade 304 (1.4301) or Grade 316 (1.4401) stainless steel, with Grade 316 offering superior corrosion resistance due to the addition of 2-3% molybdenum.
WRAS approved stainless steel ball valves, butterfly valves, check valves, and pressure reducing valves are specified where the water conditions or application requirements exceed what DZR brass can reliably deliver. Key applications include: coastal and marine locations where the water contains elevated chloride levels; systems using demineralised, softened, or RO-purified water, where the low ion content of the water can be corrosive to brass; food and beverage production facilities where food-grade materials are required; pharmaceutical and laboratory water systems; and systems handling chemically treated water containing corrosion inhibitors or other additives incompatible with brass.
The principal advantage of WRAS approved stainless steel valves is their combination of high corrosion resistance, mechanical strength, hygienic surface finish, and compatibility with a wide range of chemicals. The principal limitations are higher cost compared to brass and, in some grades, susceptibility to crevice corrosion and pitting in stagnant water with elevated chloride levels. For applications requiring maximum corrosion resistance in chloride-containing water, Grade 316L stainless steel WRAS approved valves are preferred.
WRAS approved stainless steel valves are available in the same range of configurations as brass valves: ball valves, butterfly valves, check valves, gate valves, strainers, pressure reducing valves, solenoid valves, and expansion bellows. Connection types include threaded (BSP), press-fit, compression, and flanged, making stainless steel WRAS approved valves compatible with all standard pipework systems used in the UK.
Cast Iron: Large-Bore Valves for Distribution and Industrial Applications
Cast iron is used primarily for large-bore WRAS approved valves in water distribution, fire fighting, and industrial applications. Cast iron offers high compressive strength, excellent pressure resistance, and the ability to be cast into complex shapes — making it well suited for large flanged gate valves, butterfly valves, and check valves that would be impractical or uneconomical to manufacture in brass or stainless steel at sizes above 2 inches or DN50.
WRAS approved cast iron valves are most commonly encountered in the following applications: water utility distribution mains (buried gate valves and butterfly valves for zone isolation); large commercial and industrial cold water storage and distribution systems; fire hydrant and fire suppression supply lines; large process water supply systems; and pumping station and booster set installations. In these applications, the ability of cast iron to be manufactured in large sizes at relatively low cost makes it the practical choice.
The main limitation of cast iron WRAS approved valves in potable water applications is their susceptibility to internal corrosion over time, particularly in aggressive water conditions. To address this, WRAS approved ductile iron (spheroidal graphite iron) valves are used in preference to grey cast iron where higher strength and better corrosion resistance are required. Internal epoxy lining of cast iron WRAS approved valves provides a protective barrier between the iron body and the water, significantly extending service life and maintaining water quality by preventing iron contamination of the water supply.
WRAS approved ductile iron butterfly valves with EPDM liners are one of the most widely used large-bore valve types in UK water distribution and commercial building services. The EPDM liner provides both a WRAS approved potable water contact surface and the valve seat, while the ductile iron body provides the mechanical strength and pressure resistance. This combination offers excellent value for large-bore WRAS approved valve applications.
Engineering Polymers: Lightweight, Corrosion-Free WRAS Approved Valves
Engineering polymers including PVC-u (unplasticised polyvinyl chloride), CPVC (chlorinated polyvinyl chloride), PP (polypropylene), PVDF (polyvinylidene fluoride), and glass-filled nylon are used for WRAS approved valve bodies in applications where metal valves would be susceptible to corrosion, where weight is a concern, or where cost is a priority.
PVC-u WRAS approved valves are the most widely used polymer valve type in UK water supply, distribution, and treatment applications. PVC-u offers good resistance to chlorine-disinfected water, mild acids, and alkalis, and is unaffected by dezincification. WRAS approved PVC-u ball valves, butterfly valves, and gate valves are used in water treatment plant, irrigation systems, chemical dosing systems, and low-pressure distribution systems where their light weight and corrosion resistance are advantages. However, PVC-u has a lower pressure and temperature rating than metal valves and becomes brittle at low temperatures, so it is not suitable for all applications.
CPVC WRAS approved valves are similar to PVC-u but with improved high-temperature resistance, making them suitable for hot water applications up to around 80-90°C. CPVC WRAS approved valves are used in hot water distribution systems in buildings where corrosion of metal valves is a concern, and in process water systems in the chemical and food industries.
PVDF WRAS approved valves offer the highest chemical resistance of any polymer valve material and are used in ultra-pure water systems, pharmaceutical applications, and chemical dosing systems where standard PVC-u or metal valves would be attacked by the process fluid. PVDF WRAS approved valves are significantly more expensive than PVC-u but offer superior performance in demanding chemical environments.
Glass-filled nylon (polyamide) WRAS approved valves are widely used for domestic appliance connections, small solenoid valve bodies, and service valves where their lightweight, corrosion-resistant construction, and low cost are advantages. They are not suitable for applications requiring high pressure or elevated temperature, but are well suited for low-pressure domestic and light commercial applications.
WRAS Approved Valve Seat and Seal Materials
The seat and seal materials used in WRAS approved valves are as important as the body material for determining the valve's performance, service life, and suitability for specific applications. The most commonly used seal and seat materials in WRAS approved valves are PTFE, EPDM, NBR, and silicone, each with distinct performance characteristics.
PTFE (polytetrafluoroethylene) is the most widely used seat material in WRAS approved ball valves. PTFE seats offer low friction, excellent chemical resistance, a wide temperature range (-200°C to +260°C), and a smooth, non-stick surface that resists scale adhesion and microbial colonisation. PTFE is WRAS approved for potable water contact and is compatible with virtually all water chemistry conditions encountered in UK potable water systems. Full-bore WRAS approved ball valves with PTFE seats are the standard isolation valve in UK water systems.
EPDM (ethylene propylene diene monomer) is the preferred seal and diaphragm material for WRAS approved valves in hot water, chlorinated water, and outdoor applications. EPDM is resistant to hot water, steam (to 120°C), ozone, UV radiation, and chlorine at the concentrations used in UK potable water disinfection. WRAS approved butterfly valves, check valves, and pressure reducing valves typically use EPDM seats and seals. EPDM is not compatible with oils, fuels, or aromatic solvents, but these are not encountered in standard potable water applications.
NBR (nitrile butadiene rubber) is used in WRAS approved valves for cold water applications where oil resistance is required (for example, in compressed air systems that may contain oil mist). NBR is less suitable than EPDM for hot water, high-chlorine, or outdoor applications where ozone exposure is a concern. NBR seals in WRAS approved valves should be replaced with EPDM where the valve is used in hot water or high-chlorine service.
Silicone seals are used in WRAS approved valves for food-grade applications and for applications requiring very wide temperature range. Silicone is WRAS approved for potable water contact and is FDA-compliant, making it suitable for food-contact water applications. However, silicone has lower tensile strength than EPDM and is less resistant to abrasion, so it is not used in high-cycle or abrasive service applications.
Selecting the Correct WRAS Approved Valve Material for Your Application
The selection of the correct WRAS approved valve material for a specific application should be based on a systematic assessment of the following factors: water temperature (cold water, hot water, steam, or chilled water); water chemistry (hardness, pH, chloride content, dissolved gases, chemical treatment); operating pressure; operating environment (internal, external, coastal, industrial); required service life; hygiene requirements (food-grade, pharmaceutical, laboratory); chemical compatibility (CIP, chemical dosing, cleaning agents); and cost.
For standard cold and hot water applications in domestic, commercial, and industrial buildings with UK mains water supply, DZR brass WRAS approved valves are the appropriate first choice. For hard water areas with aggressive water chemistry, DZR brass remains the standard choice with gunmetal as an upgrade for critical applications. For coastal or industrial applications with elevated chloride levels, stainless steel 316 WRAS approved valves provide the best long-term performance. For food and beverage, pharmaceutical, or laboratory applications, stainless steel 316 with EPDM or PTFE seals is the preferred specification. For large-bore distribution and industrial applications, ductile iron WRAS approved valves with EPDM liners provide the most cost-effective solution.
Conclusion: Material Knowledge Is the Foundation of WRAS Valve Specification
Understanding the properties and limitations of WRAS approved valve materials is fundamental to specifying valve systems that deliver long-term performance, regulatory compliance, and value for money in potable water applications. Whether you are specifying a standard DZR brass ball valve for a domestic installation, a stainless steel solenoid valve for a food production facility, or an epoxy-lined ductile iron butterfly valve for a large commercial water distribution system, the material choice determines the valve's suitability for the application and its long-term reliability.
At Wras Valves, our range of WRAS approved valves encompasses all the key material types described in this guide: DZR brass, gunmetal, stainless steel, ductile iron, and engineering polymer valve bodies, with PTFE, EPDM, NBR, and silicone seat and seal options. All our WRAS approved valves carry current WRAS approval and are manufactured from materials tested to BS 6920 for potable water contact. Our technical team can help you select the right material combination for your specific application. Browse our full range online or contact us for material-specific technical guidance.