How To Select Suitable Membrane Materials To Ensure Their Chemical Compatibility

Choosing the right diaphragm material to ensure chemical compatibility is the most critical step in diaphragm valve selection. The diaphragm is

the only moving part of the valve that is in continuous contact with the medium. Incorrect material selection can lead to diaphragm swelling,

hardening, cracking, or degradation, causing internal or external leaks, and even media contamination.

The following are systematic material selection steps and key points:

I. Chemical Compatibility Characteristics of Mainstream Diaphragm Materials

EPDM (Ethylene Propylene Diene Monomer)

EPDM exhibits excellent resistance to polarity, water, dilute acids and alkalis, and ozone aging. It is suitable for common media such as water,

dilute acids and alkalis, alcohols, ketones, and CIP cleaning fluids. However, it is not resistant to oils or hydrocarbon solvents and is strictly

prohibited from use in environments with mineral oil, gasoline, aromatic hydrocarbons (benzene, toluene), and concentrated strong acids. The

standard operating temperature range is -10℃ to 80℃, with a maximum of 120℃.

PTFE (Polytetrafluoroethylene)

PTFE is resistant to almost all chemical media and is the preferred material for strong acids, strong alkalis, organic solvents, oxidants, and

high-temperature media. The only drawback is its inability to withstand molten alkali metals and high-temperature fluorine gases. PTFE material

itself is relatively rigid, and an auxiliary elastic layer (such as a composite diaphragm) is usually required for sealing. Its temperature range is wide,

from -30℃ to 180℃.

FKM/FPM (Fluororubber)

Fluororubber is known for its resistance to oils, hydrocarbons, high temperatures, and strong oxidants, making it suitable for mineral oils, fuel oils,

aromatic hydrocarbons, and halogenated hydrocarbons. However, it is not resistant to low-molecular-weight esters (such as ethyl acetate),

ketones (such as acetone), and amines. Its operating temperature range is -20℃ to 200℃.

NBR (Nitrile Butadiene Rubber)

NBR has excellent oil and hydrocarbon resistance and is commonly used for mineral oils, diesel oils, and hydraulic oils. However, it is not resistant

to strong acids, strong alkalis, ketones, and has poor ozone resistance. Its applicable temperature range is -20℃ to 80℃.

Hypalon (Chlorosulfonated Polyethylene)

Hypalon exhibits good resistance to strong acids, strong oxidants (such as concentrated sulfuric acid, nitric acid, and chromic acid), and ozone,

but is not resistant to hydrocarbons, esters, and ketone solvents. The operating temperature range is -20℃ to 100℃.

Silicone Rubber (VMQ)

Silicone rubber possesses excellent high and low temperature resistance (-50℃ to 200℃), is soft, and has good physiological inertness, making

it suitable for food, pharmaceutical, and high-temperature clean environments. However, its chemical resistance is poor; it is not resistant to oils,

steam, or concentrated acids.

II. Material Selection Considerations under Special Process Conditions

In sanitary applications (pharmaceuticals, food), the diaphragm material must comply with standards such as FDA 21 CFR 177.2600 and USP Class

Commonly used materials include FDA-approved EPDM and PTFE+EPDM composite diaphragms.

For applications involving aseptic processes (CIP online cleaning, SIP online sterilization), materials capable of withstanding high-temperature

steam must be selected. PTFE+EPDM composite membranes can simultaneously meet the requirements for corrosion resistance and steam

sterilization resistance, while pure EPDM membranes are not recommended for high-temperature steam environments.

When the medium contains oils or hydrocarbons, EPDM must be avoided (it will swell severely in the presence of oil); FKM or NBR should be

selected instead.

For strong oxidizing agents (such as concentrated sulfuric acid, nitric acid, chlorine, sodium hypochlorite), PTFE and Hypalon are more reliable

choices; EPDM and NBR are easily oxidized and degraded.

In ultrapure water or high-purity media applications, materials with low exudation properties should be selected, typically PTFE or modified PTFE,

to avoid ionic contamination.

III. Correspondence between Media Type and Membrane Material

For inorganic acids (dilute), such as dilute sulfuric acid and hydrochloric acid, EPDM or PTFE can be used; NBR should be avoided.

For concentrated inorganic acids, such as 98% sulfuric acid and concentrated nitric acid, PTFE should be the first choice, with Hypalon as an

alternative. EPDM and NBR are strictly prohibited.

For alkaline solutions, such as sodium hydroxide and potassium hydroxide solutions, both EPDM and PTFE can be used; NBR and FKM are not

recommended.

For organic solvents, such as acetone, ethanol, and toluene, PTFE is the most reliable choice. For hydrocarbon solvents, FKM can also be used;

however, EPDM is not resistant to most organic solvents and should be avoided.

For mineral oils, such as hydraulic oil and lubricating oil, FKM or NBR should be used; PTFE can also be considered, but EPDM is strictly prohibited.

For oxidants, such as sodium hypochlorite and ozone, both PTFE and Hypalon can be used; EPDM and NBR are not suitable.

For water and steam, especially in purified water or steam applications, a PTFE+EPDM composite membrane is the best choice. EPDM can also

be used for water media if the temperature does not exceed 80℃; NBR is not resistant to steam and is not suitable.

For food and beverages, such as juices and dairy products, FDA-certified EPDM or PTFE+EPDM composite diaphragms should be selected,

avoiding the use of ordinary industrial-grade materials.

IV. Core Principles for Selecting Diaphragm Materials

Accurate selection of diaphragm materials requires following these steps:

First, fully identify the chemical composition of the medium, including the main medium, cleaning agents, disinfectants, and any potential

impurities. Special attention should be paid to whether the medium contains oils, aromatic hydrocarbons, strong oxidants, or polar solvents.

Second, compare the chemical compatibility data with the chemical corrosion resistance table provided by the valve manufacturer, confirming the

compatibility of the material with the medium item by item. For mixed media, the "most stringent" component should be used as the evaluation

basis.

Third, fully consider the effects of temperature and pressure. Chemical compatibility decreases significantly with increasing temperature; selection

must be based on compatibility at the highest process temperature. Simultaneously, pressure fluctuations accelerate diaphragm fatigue;

composite diaphragms may be necessary to improve reliability.

Fourth, assess the specific requirements of the process, such as hygiene certification, aseptic processes, and frequent opening and closing. For

highly corrosive media and applications requiring frequent operation, PTFE+EPDM composite diaphragms are ideal, providing both the chemical

resistance of PTFE and the elasticity of EPDM to ensure a tight seal.

Finally, rely on the supplier's actual test data. Material formulations vary between manufacturers; before final selection, it is recommended to

provide the diaphragm valve supplier with complete information on the media composition, concentration, temperature, pressure, and process

requirements, and obtain a written compatibility confirmation from the supplier.

In summary, the essence of selecting diaphragm materials is finding a balance between chemical compatibility, temperature resistance, elastic

sealing capability, and specific process requirements. For most highly corrosive media, PTFE+EPDM composite diaphragms are widely used due

to their combination of corrosion resistance and sealing reliability; for non-corrosive or weakly corrosive media, EPDM dominates due to its good

cost-effectiveness and versatility; and for oil-containing and hydrocarbon-containing media, FKM is the best choice.