20.05.2026

How To Select the Right Diaphragm Pump Material

Selecting the right diaphragm pump materials is key to a reliable, long-lasting and contamination-free pump operation. We explain what to look for when choosing materials and highlight the most important and commonly used materials.

Designing a tailor-made diaphragm pump for your application is like putting together a jigsaw puzzle: every piece must fit to create the right solution. A crucial piece is the material selection as it determines the pump’s lifetime, safety, and performance. But what should you consider when selecting diaphragm pump materials, and why?

Using the Right Diaphragm Pump Materials Is Crucial for Most Applications

Diaphragm pumps consist of three main components: pump head, housing, and motor. To provide the ideal configuration, KNF uses a modular system which offers a variety of material, motor, mechanical, and connection options. These custom adaptations are essential because diaphragm pumps are used across a wide range of industries, each with its own specific requirements that influence the pump’s required performance, reliability, safety, and service life.

In each case, selecting the right diaphragm pump material is crucial to prevent damage to the pump, ensure a leak-tight operation and avoid contamination. However, choosing the right material can be complex, and various factors must be considered.

The Five Most Important Criteria for Selecting the Right Diaphragm Pump Material

All pump head components, including diaphragms, valves, connection and intermediate plates, come in contact with the transferred media. Therefore, the materials used for these parts must be tailored to the specific application. Five key factors should be considered.

Chemical Compatibility

Each media has distinct characteristics and may, for example, contain oil, or be highly reactive or corrosive. The diaphragm pump material must be chemically compatible with the transferred media. Choosing the wrong material can lead to serious issues, such as

•    Swelling of valves and other components due to chemical reactions
•    Permanent damage like cracks or ruptures caused by corrosion
•    Hazardous leaks or contamination
•    Reduced service life, increased maintenance, and higher downtime costs

Material Cost and Availability

Material cost and availability are decisive factors in selecting diaphragm pump materials. While high-performance materials may offer optimal results, they are often costly. Especially large-scale or cost-sensitive applications must find a balance between performance and affordability. For example:

Non-critical or short-term applications may use standard materials that offer adequate performance
Critical or regulated environments require premium materials to meet stringent standards

Choosing economically viable materials that meet technical requirements helps reduce unnecessary costs, avoids over-engineering, shortens lead times, simplifies sourcing, and eases maintenance.

Mechanical Properties

Diaphragm gas and liquid pumps are continuously subjected to pressure forces due to

•    The constant up-and-down movement of the diaphragm
•    Generated vacuum and pressure conditions
•    Transferred media that may be abrasive or contain sharp particles
•    External pressure fluctuations or spikes

The pump material must withstand these stresses while maintaining (depending on the component) its elasticity or rigidity, shape, tensile strength, and resistance to abrasion and tearing, even in 24/7 operations. If these properties are compromised, it can result in leakage, reduced diaphragm movement, and diminished pump performance and efficiency.

Regulatory Requirements

Industries such as pharmaceuticals, chemicals, food and beverage, and medical applications impose strict safety, hygiene, and quality standards to prevent contamination. Materials must comply with these regulations, which vary by country or region and may include:

•    Various explosion-proof classifications
•    FDA compliance
•    RoHS or REACH regulations
•    NSF certification

Additionally, material certificates, also known as material test reports or acceptance tests, may be required. These documents specify the mechanical and chemical properties of the material, batch or heat number, and applicable standards. Non-compliance can lead to legal issues or product recalls.

Temperature Resistance

The temperature to which the pump is exposed plays a crucial role in its performance, safety, and reliability. High temperatures can compromise material stability, leading to softening, deformation, or even melting. Hot media may also cause steam and condensation inside the pump, resulting in expansion, fatigue or warping. When hot media, especially liquids, are transferred, they may reach temperatures near or above their boiling point, especially under vacuum conditions. This can result in steam formation inside the pump, which increases internal pressure and may cause the material to expand, fatigue, or warp. In contrast, when handling hot gases, temperature fluctuations can lead to condensation forming inside the pump. This condensate can accumulate on internal surfaces, potentially degrading materials over time and affecting leak-tightness and chemical compatibility. Low temperatures on the other hand can make materials brittle and prone to cracking. Each scenario poses risks to pump integrity.

To ensure long-term thermal stability and resilience, the following factors need to be considered:

• The temperature of the transferred media, e.g. hot gases or heated liquids
• The operating environment’s temperature range, including heating or cooling cycles
• Ambient air temperature fluctuations affecting the pump, media and system
• The impact of vacuum conditions, such as changes in the boiling point of liquids

Common Materials Used in Diaphragm Pumps

To ensure reliable and safe pump performance, the materials used must be tailored to the specific requirements of the application and media. While diaphragm liquid pumps often demand high chemical resistance, diaphragm gas pumps may have high requirements in terms of cleanliness and tightness. KNF’s modular system enables the selection of various material options for the pump head components, including the head plate, diaphragm, O-rings, connection and intermediate plates, valves, and seals. These materials fall into three main categories: elastomers, thermoplastics, and metals.

With KNF’s modular system, each part that comes in contact with the media can be customized with different material options to ensure chemical resistance, leak-tightness and contamination-free operation of the pump. This includes the head plate (1), diaphragm (2, 7), o-ring (3), connection (4) and intermediate (6) plate, valves (5), and housing (8).

Elastomers are dimensionally stable yet elastically deformable plastics. Their flexibility and ability to return to their original shape make them ideal for diaphragms, seals and valves. Common elastomers used in diaphragm pumps include:

EPDM (ethylene propylene diene monomer): A versatile synthetic rubber offering excellent resistance to water, steam, and mild chemicals. However, it is not suitable for oils or hydrocarbons. EPDM is flexible, cost-effective, durable, and highly wear-resistant. It is an ideal solution for applications that require a long service life such as industrial cleaning and disinfection systems, agriculture or pharmaceutical processes. A thin layer of PTFE can be coated onto an EPDM diaphragm to impart chemical and temperature resistance, while retaining the flexibility required of the diaphragm.
FFKM / FFPM (perfluoroelastomer): Perfluoroelastomer is characterized by a fully fluorinated polymer structure and combines the chemical resistance of PTFE with the elastic properties of rubber. Available in various grades, FFKM is the most resistant elastomer to aggressive media and offers high thermal stability which makes it ideal for demanding applications such as semiconductor manufacturing or pharmaceutical processes.
FKM (fluoroelastomer): Contains less fluorine than FFKM but still offers high chemical resistance and temperature tolerance up to 200 °C. As a more cost-effective alternative compared to FFKM, it is well suited for valves and used in less extreme environments like pharmaceutical and medical devices, laboratory and analytical equipment, or industrial manufacturing.

A standard NMP 830.1.2 diaphragm gas pump from KNF is designed with EPDM diaphragm, valves and sealings. EPDM is a cost-effective and durable material ensuring the reliability of the pump. FKM and PTFE material options are available upon request.

Thermoplastics are moldable plastics that soften when heated and solidify when cooled, a process that can be repeated, making them recyclable. They offer a high strength-to-weight ratio, durability, chemical resistance, and cost-effectiveness. However, they are generally unsuitable for extreme temperatures. They are used in pump heads and valves, and are categorized as high-performance thermoplastics (PEEK, PPS), engineering thermoplastics (PPA, PET) and standard thermoplastics (PP, PVC). Common examples used for diaphragm pumps include:

PPS (Polyphenylene Sulfide): PPS is a high-performance thermoplastic with high temperature stability, good chemical resistance against many acids and bases, is corrosion resistant and offers good dimensional stability.
PTFE (polytetrafluoroethylene): PTFE provides very good chemical and temperature resistance but is a rather stiff material. It is suitable for medical and pharmaceutical applications, food and beverage operations, chemical and petrochemical processing and the semiconductor industry. Full PTFE parts are used for the transfer of hot gases up to 240 °C or for chemically aggressive gases that would attack EPDM, such as ozone, fluorides, and chlorides.
PEEK (Polyether Ether Ketone): Key characteristics include a high mechanical strength, wear resistance, and durability. It also provides very good resistance to heat and chemicals, making it ideal for high-pressure, high-temperature, and demanding applications. PEEK is costly but highly effective.
PVDF (Polyvinylidene Fluoride): A high-performance thermoplastic with good chemical resistance, high purity, mechanical strength, and abrasion resistance. PVDF is a cost-effective solution for high-volume production.

Note: PTFE is often grouped with thermoplastics but is technically categorized as an elastomer.

Liquids tend to be more aggressive than gases. That’s why it is essential that diaphragm liquid pumps use chemical resistant materials. For its NF 25 pump solution, for example, KNF offers PEEK and PVDF as pump head material options.

Metals are primarily used for pump housings, head and intermediate plates, as well as structural components. Some diaphragm pumps, especially large process pumps, also use metal for their valves. Their properties make metals suitable for regulated or demanding environments such as pharmaceutical or chemical applications. Common metals for diaphragm pumps include:

Aluminum: A lightweight metal with good heat conductivity, suitable for non-corrosive media. It is cost-effective but not ideal for humid gases unless anodized for humidity resistance. Aluminum is moldable and machinable and often used for compressors.
Stainless steel:An iron-based alloy containing chromium, which provides high corrosion resistance and chemical durability. It is hygienic, easy to clean, machinable, and capable of withstanding high pressures and temperatures.

Different material properties and compositions must be matched to the characteristics of the transferred media and the specific application requirements. Only by considering all relevant factors can the optimal pump solution be developed, ensuring the required performance, reliability and safety.

Gas pumps like the N 922 ST from KNF are designed with stainless steel head parts to ensure the safe handling of aggressive gases. This pump series is also available as Ex- and ATEX-models making it ideal for emission monitoring applications.

How To Approach Diaphragm Pump Material Selection

Selecting the right material for a diaphragm pump can be complex. A structured approach is essential to achieve the best technological and economic solution. The following factors should be considered during the selection process:

Required application parameters such as flow rate, pressure or vacuum requirements
Chemical compatibility
Mechanical and thermal requirements such as temperature range
Conditions of the operating environment
Regulatory compliance needs
Material costs and availability

KNF experts bring extensive experience in pump design and support customers throughout the entire selection process. This may even include a chemical resistance kit to ensure compatibility of diaphragm liquid pumps. With KNF’s modular system, each of the more than 100 standard pump types for gas and liquid handling can be customized to meet specific requirements, material selection being one of the key elements in this process. KNF offers a wide range of materials, many of which are listed above. Even more specialized options such as gold-plated or high-tech polymers like PCTFE are available. On request, special cleaning and coatings are also available.

Contact your KNF expert today to find your customized diaphragm pump!

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