Diaphragm Valve Materials

Figure 1: A stainless steel, electrically actuated diaphragm valve

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Diaphragm valves are suitable for various applications, making proper material selection critical to ensure the chosen valve suits the specific application. For example, a diaphragm valve with a neoprene diaphragm can be suitable for wastewater applications but not oil and gas applications. This article provides guidance primarily on selecting materials for the diaphragm and the valve body, as these are the only valve components that contact the media flowing through the valve.

Diaphragm materials

When selecting material for the diaphragm valve's diaphragm, consider the following criteria:

• Temperature rating: Different materials can have vastly different temperature ratings. If the diaphragm is frequently exposed to temperatures outside its rating, it will quickly wear down.
• Flexibility: Diaphragm flexibility ranges from highly flexible to relatively stiff. For guidance on choosing this value, see the next section (Diaphragm flexibility—why it matters).
• Application/System media: As seen in Table 1, some diaphragm materials are well suited for particular applications or system media and not well suited for others. The media running through the system can likely decide which material to select for the diaphragm.

Table 1: Diaphragm valve selection criteria for the diaphragm

Material Temperature Rating Flexibility Applications EPDM -29 °C to 110 °C (-20 °F to 230 °F) High Handling acids, alkalis, alcohols, ozone resistance, steam sterilization PTFE (Teflon) -184 °C to 149 °C (-300 °F to 300 °F) Low due to stiffness Strong acids, alkalis, solvents, high sealing force applications Neoprene -29 °C to 93 °C (-20 °F to 200 °F) Moderate to High Wastewater pipelines, fluids with oils, acids, alkalis, petroleum, explosives, fertilizers Butyl rubber -20 °C to 120 °C (-4 °F to 248 °F) High Gaseous media, steam sterilization, acids, alkalis Nitrile rubber -26 °C to 57 °C (-14 °F to 134 °F) High Gasses, fuels, fats, oils, alcohols, petroleum (not with acetones, ketones, ozone) Natural rubber -40 °C to 57 °C (-40 °F to 134 °F) Very High Abrasives, dilute mineral acids, brewing Viton -29 °C to 149 °C (-20 °F to 300 °F) Moderate Most chemicals, solvents, oils (not ammonia, polar solvents)

Note: The values for flexibility (e.g., high or moderate) indicate the material's flexibility relative to the other materials in the table. Learn more about each material's chemical resistances in our chemical resistance of materials guide.

Diaphragm flexibility - why it matters

If the system parameters (e.g., temperature and media) allow for different diaphragm materials, selecting flexibility may be the next step toward choosing the most suitable material.

• High flexibility advantages: Highly flexible diaphragms are more responsive to low pressures, open and close faster, and provide tighter seals because they can better take the shape of the valve seat.
• Lower flexibility advantages: Diaphragms with lower flexibility typically have higher temperature and pressure resistance and are usually less porous, making them suitable for applications for which leak prevention is a top priority.

Diaphragm valve body materials

A diaphragm valve can be metal or plastic, indicating the material used for its body. Table 2 describes the most common material types and each material's most important properties.

Table 2: Diaphragm valve body material types

Body material Pressure rating (bar [psi]) Temperature rating Primary advantages Stainless steel diaphragm valve 10.3 - 413 (150 - 6,000) -157 to 427 °C (-250 to 800 °F) Corrosion resistance, durability, cleanliness PVC diaphragm valve 1.4 - 31 (20 - 450) Up to 60 °C (Up to 140 °F) Chemical resistance, lightweight, cost-effective Carbon steel diaphragm valve 10.3 - 172 (150 - 2,500) -29 to 427 °C (-20 to 800 °F) Strength, toughness, shock resistance Cast iron diaphragm valve 8.6 - 17.2 (125 - 250) Up to 232 °C (Up to 450 °F) Durability, cost-effectiveness, good vibration dampening

Other component materials

The two other primary components for a diaphragm valve are its stem and bonnet. The stem is typically made of stainless steel or plastic and the bonnet will likely be made of the same material as the valve body. Selecting the material is not as critical because the system's media will not interact with the bonnet or stem. When choosing between stainless steel or plastic for the stem, select stainless steel if the temperature around the stem will be 60 °C (140 °F) or higher.

Sanitary diaphragm valve is operated by remote control or manual operation through the handle of the driving device, and there are there standards of the driving device: normally closed type, normally open type, and pneumatic type.

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Sanitary diaphragm valve has the advantages of simple structure, beautiful shape, quick disassembly and assembly, flexible operation, small fluid resistance, and safe and reliable use, so it is suitable for chemical, petroleum, metallurgy, water heating, food, medicine, and other industries of water, gas, oil and corrosive medium control.

The pneumatic sanitary diaphragm valve is a special form of the cut-off valve, that appeared in the s. Its opening and closing parts are made of a piece of the soft material diaphragm, the valve body cavity, and cover cavity and drive parts separated, so it is called a pneumatic health diaphragm valve.

The most prominent feature of the pneumatic health diaphragm valve is the diaphragm to the lower body cavity and the upper cover cavity are separated, so that the valve stem, disc, and other parts located above the diaphragm are not subject to medium corrosion, eliminating the packing seal structure, and will not produce medium leakage.

Selection principles of the pneumatic sanitary diaphragm valve

The pneumatic sanitary diaphragm valve is a clamping class valve and is mainly used for opening and closing the pipeline. It has two main advantages: one is that the valve does not require a separate stem packing seal structure, while the diaphragm plays a role in stem sealing while cutting off the medium; the second is the flexibility of the diaphragm has a reliable closing performance, and it can even do a good cut off sewage.

Therefore, the operating mechanism and the media channel are completely separated, so that the pneumatic diaphragm valve can not only apply to the food industry and medical and health industry, but also be applicable to some difficult-to-transport mediums and the greater risk of the medium.

Usually, the selection of a diaphragm valve will be recommended in the requirements of strict sealing performance, mud medium, wear, light structure, and low-pressure cut-off (pressure difference is small) to the atmosphere a small amount of leakage, and abrasion of the medium.

Pneumatic sanitary diaphragm valves are characterized by a thin, hemispherical metal film clamped to the body as a barrier between stem and fluid, and the valve closure is achieved by pressing the disc against the seat through the stem head and metal film. The valve is opened by an internal spring that lifts the disc when the stem rises and disengages from contact with the film.

As the valve travel is equal to the film travel, so the valve features a much smaller lift than the general valve. To overcome resistance losses due to low lift, the seats and flow area are larger than normal valves to achieve greater flow.

Since the valve seat is large, the force is much greater than the normal valve to obtain sufficient sealing force on the disc because there is no direct contact between the stem and the disc. The disc does not move the stem away from the seat, so the valve is suitable for differential pressure unidirectional flow, and the medium is usually “under the seat”.However, large amounts of backflow should be avoided in service to avoid affecting valve closure. Generally speaking, the choice of the metal diaphragm valve is economical and effective in high-temperature and high-pressure environments.