Seal Materials Explained

Solenoid valves come in many materials, one of the most important factors to consider are the solenoid valve seal materials used as these need to be compatible i.e. resistant to the chemicals and pressure whilst offering the best sealing characteristics. Standard general purpose Brass solenoid valves are normally fitted with NBR elastomer seals suitable for most air, water applications but for more aggressive media or high pressure or temperature applications other compatible seal materials are readily available.

It is always wise to check with your chemical supplier for recommended compatible seal materials or ask technical support team.


Helpful Hint: Don't guess but either ask your chemical supplier or check what has been successfully used so far.

Aflas® (TFE/P)

Aflas® (TFE/P) Temperature range: between -10°C and +205°C (intermittent/compound specific between -20°C and +250°C), created from an exceptional Fluoroelastomer (FKM), which is resistant to steam, petroleum oils, amine corrosion inhibitors, and hydrogen sulphide.

Aflas® (TFE/P) has good resistance to:  Steam, Petroleum Oils, H2S


Butyl Rubber IIR , also known as Isobutylene-isoprene (IIR)

Butyl Rubber IIR is a synthetic rubber developed in the 1940’s. It has exceptionally low gas permeability making it ideal for inner tubes and high pressure/vacuum sealing applications. Very low resilience makes it suitable for shock and vibration damping. 

Excellent resistance to heat, ozone, and weathering, and also to dilute acids and alkali's.

Not suitable for use in mineral or petroleum based fluids.

Typical applications include diaphragms, gaskets, inner tubes, liners, O-rings, seals, speaker surrounds and bottle closures. Typical working temperature range: -50°C to +100°C


Carboxylated Nitrile (XNBR)

Carboxylated Nitrile (XNBR) Temperature range: between -55°C and +135°C, Applications: Carboxylated Nitrile (XNBR) oil seals are created from a low-temperature tolerant compound, also has an excellent abrasion resistance.

XNBR has good resistance to: Water, Petroleum Oils


ECO – Epichlorohydrin Rubber 

ECO – Epichlorohydrin Rubber properties similar to nitrile rubber but with better heat, oil and petrol resistance, low gas permeability, better low temperature flexibility than NBR, excellent resistance to acids, alkali's and ozone. Typical uses are in automotive fuel systems, bladders, diaphragms and rollers. Typical working temperature range: -35°C to +125°C

Poor compression set limits its use as a sealing material and its corrosive effect on metals can increase tooling costs and limit metal bonding applications.


EPDM (Ethylene Propylene Diene Monomer) 

EPDM rubber seals also known as Ethylene Propylene Diene Monomer are well suited for hot and drinking water, Steam, Freon refrigerant gas and Air due to its excellent resistance to heat to 120 degrees centigrade or 150 for steam.

EPDM has Good resistance to: Heat, Ozone, Oxidising Chemicals, Up to Medium concentration Acids, Alkali's, Fire proof hydraulic fluids, most Ketone's and Alcohols, sunlight, abrasion and tearing.

EPDM has Poor resistance to:Most oils and Fuels, Hydrocarbons, Aromatic and Aliphatic hydrocarbons, halogenated solvents and concentrated acids.


FKM Fluoroelastomer (Fluorocarbon) Viton® is a registered brand name of Dupont, also known as FKM and is a Fluoroelastomer.

FKM has excellent heat resistance to 150 degrees centigrade and is commonly used for hot water, acid, alkali, oils, hydrocarbons and salt solutions, many aggressive chemicals, diluted acids, weak alkali's, mineral oils, aliphatic and aromatic hydrocarbons, chlorinated hydrocarbons, sunlight and ozone.

FKM has Poor resistance to: Ketone's and Acetone.


FF-KM

FF-KM is an upgraded version of FKM lso known as Simriz a Perfluoroelastomer that has its pros and cons for example it can reach higher temperatures of around 250 degrees centigrade where as the original FKM can only reach 150 degrees centigrade which is still very high but if you need that extra 100 Celsius then FF-KM would be more effective for your situation, It is also highly resistant to a wide range of solvents and chemicals. FF-KM has a few main cons, which are the high price and the fact that it is extremely hard to mould. 

FF-KM has good resistance for: Almost all Solvents and Chemicals and excellent resistance to almost every thing far surpassing FKM

FF-KM reduced or fair resistance to halogenated refrigerants.


Fluorinated Ethylene

Fluorinated Ethylene – Propylene (FEP) Temperature range: between -55°C and +205°C (dependant on core material), Applications: FEP oil seals are an excellent option for static and slow intermittent dynamic applications. FEP is interfered by a poor memory at low temperatures. FEP is, however, very tough, a chemically inert polymer that has a spectacular working scope.

Fluorinated Ethylene is Resistant to: Majority of chemicals


Fluorosilicone (FVMQ)

Fluorosilicone (FVMQ) Temperature range: between -60°C and +180°C (intermittent/compound specific up to +200°C), Applications: Fluorosilicone (FVMQ) oil seals incorporate a good low and high-temperature persistence of Silicone (VMQ) and Fluorocarbon’s resistance to solvents, oil, and fuel. It also presents great resistance to gasoline and petroleum oils.

Fluorosilicone (FVMQ) has good resistance to: Gasoline, Petroleum Oils


HNBR (Hydrogenated Nitrile Butadine Rubber)

HNBR also known as HSN or Highly Saturated Nitrile Rubber has a high saturation of Butadiene carbon polymer giving higher thermal stability up to 150 degrees centigrade and improved chemical, dynamic loading and abrasion resistance over standard NBR.

HNBR has Good resistance to: motor oils, sour gas, amine oil mixtures, oxidised fuels, lubricating oils, mineral based hydraulic oil, animal and vegetable oil, diesel fuel, ozone, dilute acids and bases, new bio-oils, H2S Hydrgen Sulphide and C02 carbon dioxide.

HNBR has Poor resistance to: concentrated alkali's, esters, alkyl phosphate, ethers, halogenated solvents, ketone's, halogenated hydrocarbons, solvents and flames.


Hypalon is a chlorosulfonated polyethylene (CSPE) synthetic rubber (CSM)

CSM grades usually contain 20 - 45 percent chlorine which provides excellent resistance to chemicals, ozone, ultraviolet light, oxidising agents, dry heat up to 150 Centigrade, hot water, corrosive chemicals, low gas permeability, good electrical properties, low flammability and is an extremely durable waterproof elastomer designed for extreme use with white water rafts, containment suits and other outdoor equipment. It was a product of DuPont.

Poor/fair fuel resistance and its low temperature properties are generally limited, depending on the chlorine content of the CSM grade. Furthermore, its compression set is rather low.


NBR (Nitrile Buna Rubber)

NBR also known as Butadiene Acrylonitrile One of the most common seals found in solenoid valves and O-rings as it is suitable for most neutral fluids and gases. NBR can withstand ageing with heat very well up to temperatures to 80 degrees centigrade for long periods of time and for short times up to 100 Centigrade, it has good abrasion resistance but poor resistance to sunlight. NBR is most commonly used for Water, Air and different fuels and Oils. NBR has Good resistance to: Aliphatic Hydrocarbons, Petroleum, Fuels, Mineral Oil, Vegetable and Hydraulic Oil, Alcohol and many Acids. NBR has Poor resistance to: Ozone, Acetone, Methyl ethyl Ketone, Chlorinated Hydrocarbons, Ethers and Esters.


Neoprene (also known as CR or Chloroprene)

Neoprene was the first synthetic rubber developed for commercial use by DuPont in the early 1930's. Neoprene refers to a whole a group of synthetic rubbers that are produced by the polymerization of chloroprene. This process yields a large family of compounds with many different chemical and physical properties. Some of these neoprene compounds are used in the manufacture of o-rings and seals and some are used for other purposes (such as wet suits, electrical insulation and cell phone cases).

Neoprene has low gas permeation, good resistance to Freon and ammonia, resistant to flames, has excellent resistance to UV rays, ozone, oxygen and sunlight, tough, abrasion resistant and has a low compression set with an outstanding ability to adhere to metals.


Polyacrylate (ACM)

Polyacrylate (ACM) Temperature range: between -20°C and +150°C, Applications: Polyacrylate oil seals have superior high-temperature resistance than that of Nitrile. Therefore, they are ideal for high surface speed oil applications and are used in high-stress hydraulic applications, in which highly pressured compounds are exposed to wear. Polyurethane, however, presents a great high abrasion resistance qualities and high tensile strength.

Polyacrylate (ACM) has good resistance to: Freon, Petroleum Oils Polyurethane (AU) Temperature range: between -15°C and +85°C (intermittent/compound specific between -50°C and +100°C),

Polyurethane (AU) has good resistance to: Hydraulic Oils, Petroleum Oils


PTFE (Polytetrafluoroethylene) also known as Teflon® registered brand name of Dupont.

PTFE has excellent resistance to almost every fluid or gas and extreme temperatures to +230 degrees centigrade and is ideal for cryogenic applications down to -200 centigrade but as it is not an elastomer (elastic / rubbery) it can have limiting sealing properties.


Silicone (VMQ)

Silicone rubber withstands high beyond 150 degrees centigrade and low temperatures down to -60 degrees centigrade, but can harden and become brittle when heated with air.

Silicone has Good resistance to: Oil but not diesel, solvents, aniline alcohol, dilute acids or bases, benzene, toluene, gasoline.

Silicone has Poor resistance to: Hot air, steam over 150 C, strong acids and bases.



THERMOPLASTICS & ELASTOMER'S


ABS

Acrylonitrile Butadiene Styrene Class 32222 conforming to ASTM D3965 is a time-proven material. The smooth inner surface and superior resistance to deposit formation makes ABS drain, waste, and vent material ideal for residential and commercial sanitary systems. The residential DWV system can be exposed in service to a wide temperature span.

ABS-DWV has proven satisfactory for use from -40°F to 180°F. These temperature variations can occur due to ambient temperature or the discharge of hot liquids into the system.

ABS-DWV is very resistant to a wide variety of materials ranging from sewage to commercial household chemical formulations. ABS-DWV is joined by solvent cementing or threading and can easily be connected to steel, copper, or cast iron through the use of transition fittings.


CPVC — Chlorinated Polyvinyl Chloride

Class 23447 conforming to ASTM D1784, has physical properties at 73°F similar to those of PVC, and its chemical resistance is similar to or generally better than that of PVC.

CPVC, with a design stress of 2000 psi and maximum service temperature of 210°F, has proven to be an excellent material for hot corrosive liquids, hot or cold-water distribution, and similar applications above the temperature range of PVC. CPVC is joined by solvent cementing, threading or flanging.


PP (Polypropylene)

Polypropylene is a polyolefin, which is lightweight and generally high in chemical resistance. Although polypropylene is slightly lower in physical properties compared to PVC, it is chemically resistant to organic solvents as well as acids and alkalis.

Generally, polypropylene should not be used in contact with strong oxidizing acids, chlorinated hydrocarbons, and aromatics. With a design stress of 1000 psi at 73° F, polypropylene has gained wide acceptance where its resistance to sulphur bearing compounds is particularly useful in salt water disposal lines, crude oil piping, and low pressure gas gathering systems. Polypropylene has also proved to be an excellent material for laboratory and industrial drainage where mixtures of acids, bases, and solvents are involved. Polypropylene is joined by the heat fusion process, threading or flanging. At 180°F, or when threaded, PP should be used for drainage only at a pressure not exceeding 20 psi.


PVC — Polyvinyl Chloride Class 12454 conforming to ASTM D1784.

PVC is the most frequently specified of all thermoplastic materials. It has been used successfully for over 40 years in such areas as chemical processing, industrial plating, chilled water distribution, de-ionised water lines, chemical drainage, and irrigation systems. PVC is characterised by high physical properties and resistance to corrosion and chemical attack by acids, alkali’s, salt solutions, and many other chemicals.

It is attacked, however, by polar solvents such as ketone's, some chlorinated Hydrocarbons and aromatics. The maximum service temperature of PVC is 140°F. With a design stress of 2000 psi, PVC has the highest long-term hydro-static strength at 73°F of any of the major thermoplastics being used for piping systems. PVC is joined by solvent cementing, threading, or flanging.


Polyvinylidene Fluoride

is a strong, tough and abrasion resistant fluorocarbon material. It resists distortion and retains most of its strength to 280°F. It is chemically resistant to most acids, bases, and organic solvents and is ideally suited for handling wet or dry chlorine, bromine and other halogens. No other solid thermoplastic piping components can approach the combination of strength, chemical resistance and working temperatures of PVDF. PVDF is joined by the heat fusion process, threading or flanging.


POLYCHLOROPRENE (CR)

Polychloroprenes were one of the first synthetic rubbers developed. Polychloroprene is an all-purpose polymer with many desirable characteristics and features high resiliency with low compression set, flame resistance, and is animal and vegetable oil resistant.

Polychloroprene is principally recommended for food and beverage service. Generally, Polychloroprene is not affected by moderate chemicals, fats, greases, and many oils and solvents. 

Polychloroprene is attacked by strong oxidizing acids, most chlorinated solvents, esters, ketone's, aromatic hydrocarbons and hydraulic fluids. Polychloroprene has a moderate temperature range of -20°F to 160°F.


GRAPHITE 

Graphite is the packing and seal material of choice for most fire-rated products, primarily because of its high temperature rating of approximately 2000°F. Graphite has excellent chemical resistance, can retain compressibility at all temperatures and has a low coefficient of friction.

Graphite is not recommended for use in strong oxidizing atmospheres.



METALS USED IN VALVES & FITTINGS


COPPER

Among the most important properties of wrot copper materials are their thermal and electrical conductivity, corrosion resistance, wear resistance, and ductility. Wrot copper performs well in high temperature applications and is easily joined by soldering or brazing. Wrot copper is exclusively used for fittings.


BRONZE 

One of the first alloys developed in the bronze age is generally accepted as the industry standard for pressure-rated bronze valves and fittings. Bronze has a higher strength than pure copper, is easily cast, has improved machine-ability, and is very easily joined by soldering or brazing. Bronze is very resistant to pitting corrosion, with general resistance to most chemicals less than that of pure copper.


SILICONE BRONZE 

Silicone bronze has the ductility of copper but much more strength. The corrosion resistance of silicon bronze is equal to or greater than that of copper. Commonly used as stem material in pressure-rated valves, silicon bronze has greater resistance to stress corrosion cracking than common brasses.


ALUMINIUM BRONZE 

The most widely accepted disc material used in butterfly valves, aluminium bronze is heat treatable and has the strength of steel. Formation of an aluminium oxide layer on exposed surfaces makes this metal very corrosion resistant. 

Not recommended for high pH wet systems.


BRASS

Generally, brass has good corrosion resistance. 

Susceptible to de-zincification in specific applications; excellent machine-ability. Primary uses for wrot brass are for ball valve stems and balls, and iron valve stems. A forging grade of brass is used in ball valve bodies and end pieces.


GRAY IRON

An alloy of iron, carbon and silicon, Gray iron is easily cast, and has good pressure tightness in the as-cast condition. Gray iron has excellent dampening properties and is easily machined. It is standard material for bodies and bonnets of Class 125 and 250 iron body valves. Gray iron has corrosion resistance that is better than steel in certain environments.


DUCTILE IRON

Ductile iron has composition similar to Gray iron. Special treatment modifies metallurgical structure, which yields higher mechanical properties; some grades are heat-treated to improve ductility. Ductile iron has the strength properties of steel using similar casting techniques to that of Gray iron.


CARBON STEEL

Carbon steel has very good mechanical properties and is resistant to stress corrosion and sulphides. Carbon steel has high and low temperature strength, is very tough and has excellent fatigue strength. Mainly used in gate, globe, and check valves for applications up to 850°F, and in one-, two-, and three-piece ball valves.


3% NICKEL IRON

3% Nickel iron has improved corrosion resistance over Gray and ductile iron. Higher temperature corrosion resistance and mechanical properties. Very resistant to oxidizing atmospheres.


NICKEL-PLATED DUCTILE IRON

Nickel coatings have received wide acceptance for use in chemical processing. These coatings have very high tensile strength, 50 to 225 psi. To some extent, the hardness of a material is indicative of its resistance to abrasion and wear characteristics. Nickel plating is widely specified as a disc coating for butterfly valves.400 SERIES


STAINLESS STEEL 

An alloy of iron, carbon, and chromium, 400 series stainless steel is normally magnetic due to its martensitic structure and iron content. It is resistant to high temperature oxidation and has improved physical and mechanical properties over carbon steel. Most 400 series stainless steels are heat-treatable. The most common applications in valves are for stem material in butterfly valves and back-seat bushings and wedges in cast steel valves.


316 STAINLESS STEEL

An alloy of iron, carbon, nickel, and chromium, 316 stainless steel is non-magnetic with more ductility than 400SS. Austinetic in structure, 316 stainless steel has very good corrosion resistance to a wide range of environments, is not susceptible to stress corrosion cracking and is not affected by heat treatment. Most common uses in valves are stem, body and ball materials.


630 STAINLESS STEEL

630 stainless steel is a martensitic precipitation/age hardening stainless steel, offering high strength and hardness. 630 SS withstands corrosive attack better than any of the 400 series stainless steels, and in most conditions its corrosion resistance closely approaches that of 300 series stainless steel. 630 SS is primarily used as a stem material for butterfly and ball valves.


For more information click here for seal and metal chemical compatibility guide.