The working temperature of the sanitary diaphragm valve is mainly limited by the diaphragm material and the valve body lining material, which are the two most crucial factors. Additionally, it is closely related to the sealing material, the working medium, and the pressure-temperature grade. 

1. The most crucial factor: Diaphragm material 

The diaphragm is an elastic sealing component that directly comes into contact with the medium. Its heat resistance directly determines the maximum operating temperature of the valve. The applicable temperature ranges for different diaphragm materials vary significantly: 

EPDM (Ethylene Propylene Diene Monomer rubber): Operating temperature range -40℃ to 120℃, with some models capable of reaching 150℃. This is the most commonly used diaphragm material, offering high cost-effectiveness and excellent steam resistance. 

Silicone rubber (VMQ/SI): Operating temperature range -20℃ to 150℃, with excellent resistance to both high and low temperatures. 

PTFE (Polytetrafluoroethylene): Operating temperature range -10℃ to 180℃, some models can reach up to 200℃. It has the strongest resistance to chemical corrosion and is highly resistant to high temperatures. 

FKM/FPM (fluorine rubber): Operating temperature range -10℃ to 150℃, some models can reach up to 200℃. Resistant to oil and strong corrosive media. 

FFKM (Perfluoroelastomer): Can reach 200℃, which is the highest temperature resistance level, but it is very costly. 

NBR (Nitrile Butadiene Rubber): Operating temperature range -10℃ to 85℃. Resistant to oils, but has a relatively low temperature resistance. 

CR (Chloroprene Rubber): Applicable temperature range: -10℃ ~ 85℃. Resistant to animal and vegetable oils, but has a relatively low temperature resistance. 

The general temperature range for sanitary diaphragm valves is -30℃ to 150℃. By selecting special diaphragm materials (such as PTFE, FFKM), the temperature range can be extended to 180℃ to 200℃. 

II. Second factor: Valve body lining material 

The valve body lining and the diaphragm together form the sealing pair. The temperature resistance performance of the lining material also limits the upper limit of the working temperature: 

EPDM lining: Temperature resistance ≤ 150℃ 

PTFE lining: Temperature resistance ≤ 180℃ (even higher) 

Rubber lining: Generally ≤ 120℃ 

Furthermore, the lining process itself is also subject to manufacturing constraints - the larger the area of the lining, the greater the difficulty of the process. This is also one of the reasons why diaphragm valves are generally not used for pipe diameters larger than DN200. 

III. Other Influencing Factors 

Sealing components (such as O-rings, etc.) materials 

The O-rings at the valve stem seal, flange seal, etc. also have temperature limitations. For example, EPDM O-rings generally cannot exceed 150℃, while PTFE-coated or FFKM O-rings can withstand higher temperatures. Sealing components are often the weakest link in terms of temperature and are often overlooked. 

2. The influence of the working medium 

The same type of diaphragm material has different temperature resistance capabilities in different media. For example, the EPDM diaphragm can withstand 150℃ in steam, but in some highly oxidizing media, it may only be able to withstand 120℃. The corrosiveness and oxidizing nature of the medium will accelerate the aging of the diaphragm, thereby reducing the actual usable temperature. 

3. Coupling relationship between pressure and temperature (P-T scale) 

This is extremely important: The higher the temperature, the lower the allowable working pressure. For example, a diaphragm valve with a nominal PN10 specification might only be able to withstand 0.6 MPa at 120℃, while at normal temperature it can withstand 1.0 MPa. When selecting the model, one must consult the pressure-temperature comparison table simultaneously. One cannot just consider the temperature or just the pressure. 

4. Valve body material (Stainless steel 304/316L) 

The stainless steel itself can withstand temperatures of several hundred degrees Celsius, far exceeding the actual working temperature of the diaphragm valve. Therefore, the material of the valve body is generally not a limiting factor. However, in extremely high-temperature (above 200°C) conditions, the creep and strength attenuation of the stainless steel need to be considered. 

5. Operating Method and Frequent Opening and Closing 

The frictional heat generated by frequent switching or by pneumatic/electric actuators can cause the local temperature of the diaphragm to rise. The actual working temperature may be higher than the temperature of the medium. If this situation persists for a long time, it will accelerate the aging of the diaphragm. 

✅ Summary sentence 

The upper limit of the working temperature of a sanitary diaphragm valve is essentially determined by the material with the lowest temperature resistance among the "diaphragm material, liner material, and sealing element material". It is also subject to the constraints of the medium type and pressure-temperature grade. When selecting the model, the diaphragm material should be the primary consideration, and then the matching of the sealing element and P-T grade should be verified.