Why Use a Saddle Seal in Process Applications?

Saddle connections provide a cost-effective, adaptable and maintainable way to isolate pressure instrumentation from process media in demanding applications.

As one of several inline diaphragm seal designs, saddle connections can help address clogging, corrosion and temperature concerns at the same time, particularly in larger pipe sizes where traditional connection methods become less practical.

Read this article to learn why diaphragm seals with saddle connections may be used instead of threaded or flanged connections, how inline design influences clogging, cost and performance, and when a saddle seal is the preferred solution.

When would you use a saddle seal instead of a flanged or threaded connection?

You would use a saddle seal instead of a flanged or threaded connection when clogging risk, dead leg or installation complexity makes traditional connections less effective.

Threaded and flanged diaphragm seal assemblies are the most common connection types, but they often include pipe taps and lower housing cavities that allow particulate to accumulate. 

These assemblies generally consist of a top housing, diaphragm and lower housing, held together with clamping rings or welded/bonded construction. Because they normally connect to pipe taps and incorporate cavities in the lower housing, they are prone to material buildup that can impede seal performance over time.

While some threaded and flanged designs offer flushing ports to help clean these areas, flushing is a manual process and does not address the root cause of clogging.

What are inline connections?

Inline diaphragm seal designs sense pressure directly from the process flow without requiring pipe taps. Because the sensing element is relatively flush with the process piping, inline designs provide a less restrictive path from the process media to the diaphragm, reducing areas where material can accumulate.

Inline connections, like threaded and flanged connections, can feature a versatile assortment of materials for the wetted components. Common inline seal designs referenced by ASME standards, include:

• Flanged
• Threaded
• Socket weld
• Butt weld
• Saddle weld
• Clamped

Each inline design has advantages depending on pipe size, media and installation constraints.

What are saddle seals?

Saddle seals are inline diaphragm connections installed by cutting an opening in the pipe and welding a saddle body (contoured to match the pipe curvature and opening) directly to the pipe wall. A bolt pattern on the top of the saddle then allows the diaphragm seal assembly and instrument to be mounted using a filled ring assembly.

Saddle seals can only be used on pipe sizes 3 inches and larger, which naturally limits their use to larger piping systems.

Key characteristics of saddle seals include:

• Welded, inline installation
• Flush sensing relative to the pipe interior
• Compatibility with a wide range of metallic and elastomeric materials
• Reduced susceptibility to clogging and corrosion

Typical applications include:

• Water and wastewater piping
• Oil production
• Chemical manufacturing

Because saddle seals are available with a wide range of metallic and elastomeric materials and install flush with the process piping, they are well suited for applications where both clogging and corrosion are concerns. They also provide an easier alternative to installing new threaded or flanged pipe taps in existing systems.

How do saddle connections help manage temperature concerns?

Saddle seals can help protect instrumentation in applications where elevated process temperatures would otherwise damage gauges or switches.

Some process media must remain at elevated temperatures to stay pumpable. In these cases, installing a saddle seal with a temperature dissipation device allows the instrument to be protected from excessive heat while still minimizing clogging risk.

When selecting instruments for these applications, users should verify compatibility using the Diaphragm Seal Pressure & Temperature Min/Max Guide, which outlines allowable pressure spans and temperature limits for seal and instrument combinations.

What are the benefits of using a saddle seal over other inline design?

Of all the inline designs, (threaded, flanged or welded that are 3-inces and larger) saddle seals are often preferred because they use the least amount of material, particularly material that is wetted. Other in-line designs involve spool fixtures, and if an exotic material is required, the entire fixture must be made from that same material.

Metals such as Hastelloy, titanium or Monel can make these assemblies extremely expensive. Plus, inline fixtures are highly dimension-specific, which makes them difficult to replace with an alternative design.

Saddle seals, by contrast, use a relatively small metallic saddle body that fits into a machined opening in the pipe wall. The saddle is welded to the pipe, and the top housing/ring is then installed on this welded base. Regardless of pipe diameter, the size of the saddle and wetted components remains essentially the same.

Other inline designs installed between flanges, or as welded or threaded spools may require:

• Larger, fully wetted housings
• More material overall
• Exotic alloys throughout the entire fixture when corrosion resistance is required

As pipe size increases or material cost rises, the price gap between saddle seals and other inline designs becomes more significant. Saddle seals rely on a small, welded saddle body, meaning the size of the wetted components remains relatively constant regardless of pipe diameter.

When should a saddle seal be used instead of an isolation ring?

Saddle seals are often a better alternative than isolation rings as pipe sizes increase and installation or maintenance complexity becomes a concern.

Isolation rings are also inline isolators and are commonly used in heavy slurry applications such as wastewater treatment. While features like Safe Quick Release (SQR™) can simplify instrument removal, there are situations where the entire isolation ring must still be removed, increasing labor and cost.

Saddle seals offer advantages in these scenarios:

• Easier replacement by removing bolts, ring and top housing
• No need to dismantle or modify piping
• Lower cost and simpler handling in large pipe sizes

Saddle seals can also be advantageous for low-pressure ranges and low switch set points. Flexible diaphragm options, such as Viton®, allow greater diaphragm displacement, enabling inches-of-water ranges that are more difficult to achieve with isolation rings due to their larger fill fluid volume.

How do saddle connections compare to other gauge connection options?

Saddle connections offer a welded, inline alternative that balances clogging resistance, cost and maintainability in larger pipe sizes.

The table below compares common pressure isolation and connection designs. It also highlights where saddle seals fit relative to threaded, flanged and other inline options.

Figure 1: Pressure Isolation and Connection Types Comparison Chart

Ready to learn more?

Understanding how saddle seals compare to threaded, flanged and other inline designs helps ensure the right connection method is selected for each application.

The key thing to remember is saddle connections provide a cost effective and in some cases better performing solution for isolating instrumentation on larger pipe sizes when clogging and corrosion concerns are present.

For more information, you can read related articles below or contact us to answer specific questions. In the meantime, feel free to download our guide to learn about other pressure and temperature instruments for your applications.