A chemical seal (diaphragm seal) serves as a critical barrier in pressure measurement systems to protect against corrosive, high‑temperature, high‑viscosity, and crystallizing media. Choosing the right chemical seal not only extends instrument life but also ensures process safety and measurement accuracy. How do you select the most suitable chemical seal for your application? This guide outlines the key selection considerations from five aspects.
1. Diaphragm Material – Select According to the Chemical Properties of the Medium
The diaphragm material of a chemical seal directly determines how long the entire sealing system will last in a specific chemical environment. The first step in selection is to clearly identify the composition, concentration, and temperature of the process medium.
• 316L Stainless Steel: Suitable for water, oil, weak acids/bases, and most organic solvents. Offers the best cost‑performance ratio and is the first choice for conventional applications.
• Hastelloy C‑276: Resists chloride ions, wet chlorine, sulfuric acid, hydrochloric acid, and other highly corrosive media. Ideal for harsh environments such as seawater and bleach solutions.
• Monel 400: Particularly suitable for hydrofluoric acid and high‑temperature concentrated caustic solutions. Indispensable in fluorochemical and caustic soda plants.
• Tantalum: Used for extreme corrosive conditions like boiling hydrochloric acid and concentrated nitric acid. High cost, only used in special processes.
• PTFE‑Coated Diaphragm: When the medium has strong adhesion or metallic materials still lack corrosion resistance, PTFE provides excellent chemical inertness and non‑stick properties.
2. Fill Fluid – Match the Process Temperature Range
• Standard silicone oil: –40°C to 150°C (general purpose)
• High‑temperature silicone oil / fluorinated oil: up to 400°C
• Low‑temperature silicone oil: down to –70°C
• Food‑grade: FDA‑compliant, for pharmaceutical/food applications
3. Pressure and Vacuum Risks
• For conventional positive pressure, select according to the flange rating (e.g., Class 150 ≤ 20 bar, Class 300 ≤ 50 bar).
• If the process involves vacuum or negative pressure, a fully welded diaphragm or a diaphragm with a support ring is mandatory, and the manufacturer must be explicitly informed.
4. Process Connection and Flange Compatibility
• Confirm the standard system: ANSI, DIN, JIS, or GB
• Specify parameters: Pressure rating, nominal diameter, sealing face type (RF, RTJ, etc.)
• For hygienic applications: Flush‑welded diaphragm with surface finish Ra ≤ 0.4 μm
5. Special Industry and Compliance Certifications
• Export to the EU: CE, ATEX (explosion protection)
• International explosion protection: IECEx
• Sour oil/gas fields: NACE MR0175
• Oxygen service: Strict degreasing and non‑flammable fill fluid
---About Us
As a professional diaphragm seal manufacturer, WINNERS recommends that before selecting a chemical seal, you should clearly determine the following in order: medium composition and concentration, operating/ambient temperature range, normal/maximum/minimum pressure (indicate whether vacuum is involved), flange standard and dimensions, as well as any industry certification requirements. Proper selection can significantly improve measurement stability and the overall value of your equipment throughout its lifecycle.
For a chemical seal selection data sheet or consultation on specific applications, please feel free to contact us.
Post time: Apr-03-2026