Hydraulic components
Quality spare parts and plumbing materials
Not just electric pumps and valves: hydraulic material is made up of many components that play a fundamental role within a plumbing or thermo-hydraulic system. Hydraulic filters, tanks, manifolds, flanges, manometers, etc. must be chosen with care by evaluating their reliability and functionality. From the materials to the construction technologies, each piece has elements that affect the performance and longevity of a plant.
Plumbing materials: how to choose the right ones
Two components with the same dimensions and the same nominal pressure can have very different service lives depending on the material they are made from. Corrosion, scaling, release of substances into the water and incompatibility between metals are the most frequent causes of failures and unplanned maintenance. Here are the criteria and materials you need to know.
Selection criteria
The first criterion is the fluid. Drinking water requires materials suitable for food contact and, in Italy, compliant with D.M. 174/2004 and D.Lgs. 18/2023. Heating water may contain additives or glycol. Aggressive water, rich in chlorides or very soft, puts less resistant metals under severe strain. Next come operating temperature and pressure, which determine the component’s PN rating and the choice of seals. Finally, consider compatibility between different metals: pairing materials with very different electrochemical potentials, such as galvanised steel with copper or brass, promotes galvanic corrosion. In these cases, dielectric unions are used or a single material is chosen for the entire section.
AISI 304 and AISI 316 stainless steel
Stainless steel is the benchmark material for high-quality plumbing components: it resists corrosion, is chemically inert and retains its properties over time. AISI 304 is suitable for most drinking water and process water applications. AISI 316, thanks to its molybdenum content, offers superior resistance to chlorides and is the right choice for aggressive water, chlorinated water and swimming pools. An electropolished finish makes the surface even smoother and more uniform, reducing bacterial adhesion and limescale deposits. Find out more in our [guide to drinking water valves].
Brass
Brass is widely used in fittings, manifolds and valves because it is easy to machine, has good mechanical strength and is cost-effective. For drinking water, it is important to choose dezincification-resistant (DZR) and low-lead brasses, increasingly required by the new European rules. With very soft or aggressive water, conventional brass can lose zinc and become porous over time.
Carbon steel, galvanised steel and cast iron
Carbon steel is used mainly for flanges and closed-circuit heating systems, where dissolved oxygen is limited. Galvanised steel is inexpensive but not recommended for domestic hot water, and must be kept separate from copper and brass. Cast iron, particularly ductile iron, is common in large diameters and water mains, usually with an epoxy coating to protect it from corrosion.
Seals and elastomers: EPDM, NBR, PTFE
A system’s tightness also depends on the materials used for its seals. EPDM is the standard for hot and cold water and for drinking water, but is not compatible with oils and hydrocarbons. NBR resists oils and fuels well but is less suitable for hot water. PTFE is chemically inert and withstands high temperatures; it is used in flat gaskets, valve seats and sealing tape.
Which material to choose: quick guide by application
For drinking water, the safest choice is AISI 304 stainless steel, or low-lead DZR brass for fittings and manifolds in residential and commercial installations, always with EPDM seals certified for food contact.
For swimming pools, chlorinated and aggressive water, AISI 316 stainless steel is preferable, as it better resists chlorides. In these environments, conventional brass and carbon steel tend to degrade quickly.
For closed-circuit heating systems, carbon steel and brass can also be used, because the low oxygen content limits corrosion. Seals must withstand the operating temperatures and any additives in the water.
For booster sets and water lifting, stainless steel manifolds and fittings ensure pressure resistance, hygiene and durability, especially when the water is intended for human consumption.
For water mains and large diameters, flanges and components in epoxy-coated ductile iron are often used, or stainless steel for the most demanding applications.
For non-potable cold water, such as fire protection systems, galvanised steel remains a cost-effective option, provided it is not directly coupled with copper, brass or stainless steel.
What to look for in each component family
For fittings and flanges, check the material, threading or drilling according to the standard (for example EN 1092-1 for flanges) and the PN rating. In manifolds, the body material must be consistent with the rest of the system: stainless steel is ideal for booster sets and drinking water applications. In flexible hoses, what matters is the stainless steel outer braid and the inner core, which for drinking water must be food-grade EPDM. For expansion vessels, distinguish between models for heating and models for domestic water, in which the water is only in contact with a certified membrane. For filters, assess the body and cartridge material according to water quality. For pressure gauges, a stainless steel case and glycerine filling ensure stable readings even with vibrations and water hammer.
Frequently asked questions about plumbing materials
What is the best material for a plumbing system?
There is no single best material: it depends on the fluid, temperature, pressure and water quality. For drinking water and the most demanding applications, AISI 304 or 316 stainless steel offers the best combination of durability, hygiene and corrosion resistance. Low-lead DZR brass remains an excellent solution for fittings and manifolds in residential and commercial installations.
Can stainless steel and brass components be connected in the same system?
Stainless steel and brass have relatively close electrochemical potentials and generally coexist without problems in plumbing installations. The risk of galvanic corrosion is higher when galvanised or carbon steel is coupled with copper, brass or stainless steel. In these cases, dielectric fittings are recommended.
What is the difference between AISI 304 and AISI 316?
Both are austenitic stainless steels, but AISI 316 contains molybdenum, which increases its resistance to chloride corrosion. It is therefore preferable for swimming pools, chlorinated water, marine environments and particularly aggressive water. For drinking water under normal conditions, AISI 304 is generally sufficient.
Which materials are suitable for drinking water?
In Italy, suitable materials are those included in the positive lists of D.M. 174/2004 and compliant with the migration limits, now made stricter by D.Lgs. 18/2023, which transposes European Directive 2020/2184. In practice: stainless steel, low-lead brasses, and certified plastics and seals. Always check the Declaration of Conformity and any certifications (ACS, DVGW, WRAS, NSF/ANSI 61).
Looking for other plumbing materials? Also discover our hydraulic valves and hydraulic pumps, selected with the same quality criteria.