In the industrial production process, valves are the core components for controlling the transportation of media, and the sealing performance is the “lifeline” for the stable operation of the valves. Once the valve sealing fails, not only will there be a production interruption, but it may also trigger a chain reaction of risks.
There are three direct hazards of valve sealing failure, each of which can cause significant losses to the enterprise.
After clearly defining the working conditions, it is necessary to select an appropriate sealing material from the mainstream ones. Currently, the commonly used valve sealing materials in the industrial field include four types, each with clear characteristics, applicable scenarios and usage restrictions, which need to be precisely distinguished.
Nitrile Butadiene Rubber is a highly cost-effective general-purpose sealing material, with core characteristics focusing on “practicality” and “economy”: excellent oil resistance, capable of withstanding common oil-based media such as mineral oil and hydraulic oil; low cost, suitable for large-scale procurement; and good elasticity, able to closely adhere to the sealing surface, providing stable sealing effect under low-pressure conditions.
From the perspective of applicable valves, Nitrile Butadiene Rubber sealing is mainly used in hydraulic valves, fuel system valves, especially suitable for pipelines transporting non-corrosive media such as diesel and lubricating oil. For example, the reversing valves in machine tool hydraulic systems and the fuel pipe valves in automobiles mostly use Nitrile Butadiene Rubber sealing.
However, its usage restrictions are also clear: it is not resistant to high temperatures, when the medium temperature exceeds 80℃, the rubber will accelerate aging, harden and lose elasticity; it also does not resist strong oxidants, if it comes into contact with strong oxidizing media such as nitric acid and hydrogen peroxide, the sealing surface will be corroded and damaged, and therefore must not be used in chemical corrosion-intensive working conditions valves.
Fluororubber is an “all-rounder” for dealing with complex working conditions, with core characteristics being a wide range of temperature resistance (-20℃~200℃), not hardening easily in low-temperature environments, and not aging easily in high-temperature environments; at the same time, it has strong corrosion resistance, can withstand strong acids, strong bases, and most organic solvents , with chemical stability far exceeding Nitrile Butadiene Rubber.
From the perspective of applicable valves, fluororubber sealing is mainly used in corrosion-resistant valves in the chemical industry and high-temperature working conditions. For example, acid and alkali transportation valves in chemical enterprises, high-temperature dye control valves in printing and dyeing factories, and low-pressure steam valves in steam pipelines, are all suitable for using fluororubber sealing.
However, it also has obvious limitations: not resistant to low temperatures, when the medium temperature is lower than -20℃, fluororubber will harden and crack, unable to achieve effective sealing, therefore cannot be used in low-temperature cold storage, liquid natural gas transportation and other low-temperature working condition valves; at the same time, it is more expensive, 3-5 times that of Nitrile Butadiene Rubber, if the working conditions are simple , using fluororubber will cause cost waste.
Polytetrafluoroethylene (commonly known as “Teflon”) is the “corrosion-resistant champion” among sealing materials, with core characteristics being an “extreme condition buster”: it has extremely strong chemical inertness and can withstand all inorganic acids, organic acids, bases, and organic solvents, and is hailed as the “plastic king”; at the same time, it has outstanding resistance to extremely high temperatures, with a long-term use temperature exceeding 260°C, and can withstand temperatures above 300°C for short periods, and does not release harmful substances at high temperatures.
It is highly precise for valve scenarios: one is for valves with strong corrosive media, such as concentrated nitric acid transfer valves in chemical enterprises and acid wastewater treatment valves in electroplating plants; the other is for food-grade valves, as polytetrafluoroethylene complies with food contact material safety standards (such as FDA certification), does not contaminate food, and is suitable for use in beverage production line valves, dairy product storage tank valves, etc.
However, it also has usage restrictions: it becomes brittle at low temperatures, and when the temperature is below -18°C, polytetrafluoroethylene loses its toughness and is prone to fracture under external force impact, thus not suitable for low-temperature conditions; at the same time, the processing of the sealing surface requires high standards, and the flatness error of the sealing surface must be within 0.01mm, otherwise, due to poor sealing, there will be slight leakage, and a professional processing technique must be combined.
Graphite (especially flexible graphite and expanding graphite) is a “special material” for handling high-temperature and high-pressure conditions. Its core characteristics are the ability to withstand extremely high temperatures (long-term use temperature > 600°C, short-term up to 1000°C or above), and it does not burn or deform at high temperatures; it also has strong resistance to high pressure, can withstand pressures of 10 MPa or more, and the sealing surface is not prone to deformation under high pressure; in addition, it is resistant to wear and is suitable for conditions where the medium contains trace particles
The valves it is suitable for are mainly high-temperature and high-pressure valves, typical scenarios include: main steam valves in power plants (medium temperature above 400°C, pressure above 10 MPa), high-temperature smoke gas valves in metallurgical enterprises, and molten glass transfer valves in glass factories. These valves have extremely high requirements for the sealing material’s temperature and pressure resistance, and graphite is the only non-metallic sealing material that can meet these requirements.
The usage restrictions of graphite need to be carefully focused on: it is not resistant to strong oxidizing media. If it comes into contact with strong oxidizing substances such as concentrated nitric acid or chlorine gas, graphite will be oxidized into carbon dioxide, causing the seal to fail. Therefore, it must not be used in high-oxidizing media pipeline valves; at the same time, it needs to be combined with a metal framework to enhance strength. Pure graphite sealing pieces have low strength and are prone to cracking during installation, so in practical applications, a stainless steel or copper framework must be combined to enhance structural strength.
| Seal Material | Core Characteristics | Suitable Valves & Scenarios | Usage Taboos |
| Nitrile Rubber (NBR) | – Oil-resistant- Low cost- Good elasticity (low-pressure sealing) | – Hydraulic valves, fuel system valves- Non-corrosive media (diesel, lubricating oil) | – Temp >80℃: Ages/hardens- Not resistant to strong oxidizers (nitric acid, H₂O₂) |
| Fluororubber (FKM) | – Temp range: -20℃~200℃- Corrosion-resistant (acids, alkalis)- High stability | – Chemical industry corrosion-resistant valves, high-temp valves (steam, dye liquor) | – Temp < -20℃: Hardens/cracks- High cost (3~5x NBR) |
| PTFE (Teflon) | – Chemically inert (resists most media)- Temp >260℃ (long-term)- Food-safe | – Strong corrosive media valves (acid/alkali)- Food-grade valves (beverage, dairy) | – Temp < -18℃: Brittle- Sealing surface flatness ≤0.01mm required |
| Graphite (Flexible/Expanded) | – Temp >600℃ (long-term)- Pressure >10MPa- Wear-resistant | – High-temp/high-pressure valves (power station steam, metallurgy flue gas) | – Not resistant to strong oxidizers (nitric acid, Cl₂)- Needs metal skeleton |
Even if the working conditions and material characteristics are clear, there may still be “traps” in the selection process due to details being overlooked. Mastering the following three professional tips can further improve the accuracy of the selection and avoid later failures.
Many people think that “in the same working conditions, all valves can use the same sealing material”, which is a typical misconception. In fact, even if the working parameters are the same, different types of valves have different sealing structures and stress conditions, and thus have different requirements for sealing materials.
For example, in a low-pressure water system working condition (medium is tap water, temperature 25°C, pressure 0.6 MPa): the sealing surface of the ball valve is point contact between the ball and the valve seat, requiring a sealing material with good elasticity, which can be selected as nitrile rubber; the sealing surface of the gate valve is plane contact, with a large stress area, which can be selected as a less expensive natural rubber; while the sealing surface of the butterfly valve is ring-shaped contact between the butterfly plate and the valve seat, requiring the material to have certain wear resistance, which can be selected as chloroprene rubber. If “one-size-fits-all” is adopted and all are made of nitrile rubber, although it can seal, it will increase the wear rate of the valve’s seal and shorten the replacement cycle.
Sealing materials all have a fixed “aging cycle”, that is, after a period of use, due to aging, wear, and other factors, the sealing performance will decline. If the seal fails before replacement, it is likely to cause production disruptions or safety risks. Therefore, when selecting materials, it is necessary to pay attention to the aging cycle of the materials and plan the replacement time in advance.
The aging cycles of different materials vary significantly: Nitrile rubber has an aging cycle of about 1-2 years at room temperature (25°C), and it will be shortened to 6-8 months at high temperature (60°C); Fluorine rubber has an aging cycle of about 3-5 years at room temperature and about 1-2 years at high temperature (150°C); Polytetrafluoroethylene and graphite have longer aging cycles, which can be used for 5-8 years at room temperature and about 3-5 years at high temperature.
It is recommended to ask the supplier to provide the “aging life curve” of the material and, based on the actual working temperature and pressure, calculate the specific replacement period and incorporate it into the equipment maintenance plan to avoid sudden failure due to seal aging.
“Materials are labeled as resistant to a certain medium, but they fail quickly in actual use.” This situation is often due to the lack of actual compatibility tests. Therefore, when selecting materials, it is necessary to require the supplier to provide a “compatibility report” of the sealing material with the medium to verify the stability of the material in actual working conditions.
The compatibility report should include key information: the specific composition of the test medium , the test temperature (consistent with the actual working temperature), test pressure, test duration (at least 72 hours), and the changes in material performance after the test.
For example, when using fluorine rubber sealing for “20% hydrochloric acid solution” conditions, the supplier must provide a report proving that in 20% hydrochloric acid, 50°C, and 1 MPa pressure, after 72 hours of immersion, the weight change rate is <1%, the hardness change is <5 Shore A, and there are no corrosion marks on the seal surface. If the supplier cannot provide the report, it is necessary to be cautious and avoid seal failure due to compatibility issues.
As long as you follow this selection logic, you can extend the valve seal life by more than 50%, not only reducing the frequency of seal replacement, but also reducing maintenance costs, and avoiding production disruptions and safety risks caused by seal failure.
If you are still unsure how to select, you can provide the specific working conditions of the valve (medium composition, temperature range, pressure grade, valve type), and we will provide you with a customized sealing material recommendation plan to make the valve seal truly “long-lasting and reliable”.
