Diaphragm Seal Selection Guide
Engineer-focused guidance on when to use diaphragm seals, how to select materials, and how to avoid response and stability issues in pressure and DP measurement.
What Is a Diaphragm Seal?
A diaphragm seal isolates the pressure measuring instrument from the process media. Pressure is transmitted via a fill fluid to the sensing element, protecting it from extreme temperature, corrosion, clogging, or hygiene-related constraints.
When Diaphragm Seals Are Required
Selection Logic (What Engineers Must Decide)
Seal type:
Threaded, flanged, clamp-type, or inline—selected by process connection and maintenance access.
Diaphragm material:
SS, Hastelloy, Monel, PTFE-coated, or special alloys—based on media compatibility.
Fill fluid:
Selected for temperature range and ambient conditions to avoid expansion errors.
Capillary use:
Required when remote mounting is needed, but increases response time and temperature sensitivity.
Capillary Length & Temperature Effects
- Capillaries allow remote mounting but introduce additional fill fluid volume. As ambient temperature changes, the fill fluid expands or contracts, which can affect zero and response time.
- Keep capillary length as short as possible
- Avoid routing near hot equipment or direct sunlight
- Use temperature-compensated systems where required
Common Seal Selection Mistakes
- Ignoring media compatibility → diaphragm corrosion or coating failure
- Overusing capillaries when not required → slow response
- Wrong fill fluid for temperature range → zero drift
- Poor mounting orientation → trapped gas or solids
Spec Checklist (Share Before Ordering)
- Process media name and concentration
- Operating pressure and temperature (min/max)
- Connection type and size
- Need for remote mounting (capillary length)
- Ambient temperature conditions
- Providing complete data upfront avoids repeat selection errors and site rework.
