Selecting the right process connection for your pressure gauge, switch, or transmitter may seem like a small decision—but it can make the difference between a reliable installation and one that leaks, fails, or requires costly rework.
With so many connection options available, it’s easy to feel uncertain about which one is the best fit for your application. That’s where Ashcroft can help. With over a century of experience in pressure instrument manufacturing, we’ve guided countless customers through their connection challenges.
Read this article to learn why process connections matter, the different types available, what they’re best suited for and how to select the right one for your system.
What is the primary function of process connections on pressure and temperature measurement instruments?
Process connections are the interfaces that attach a pressure or temperature instrument to the process system. They are used on pressure gauges, pressure sensors, switches (pressure and temperature), thermometers, diaphragm seals and more.
From the list below, you can see that these connections do more than simply “attaching” an instrument to the process. They also:
- Provide a secure seal. The connection ensures no process fluid leaks from the system, even at high pressures.
- Ensure measurement accuracy. A proper fit prevents stresses that could distort readings.
- Extend instrument life. Correct connections reduce vibration damage and wear from over-tightening.
- Support safety. A reliable seal protects operators from leaks of hazardous gases, steam, or chemicals.
Without the right process connection, even the most advanced instrument cannot perform reliably.
How many types of process connections are there?
There are numerous types of process connections used worldwide, and each one is designed to meet specific industry requirements. While the full list is extensive, let’s focus on three common categories:
- Threaded. These are the most widely used, particularly in North America, because they are versatile and cost-effective. They include:
- National Pipe Thread (NPT)
- British Standard Pipe Tapered (BSPT)
- British Standard Pipe Parallel (BSPP)
- Japanese Industrial Standard (JIS)
- Unified National Fine (UNF) flare fittings
- Society of Automotive Engineers (SAE) straight threads
- Tube stub fittings. Threaded connections are versatile and cost-effective but may require sealants or O-rings depending on the design.
- Tri-Clamp (sanitary). These clamp-style fittings are common in the food, beverage, and pharmaceutical industries. They eliminate threads that could trap bacteria. Instead, they use a smooth gasketed clamp that is easy to disassemble for cleaning, preventing contamination, and making them ideal for hygienic applications
- DIN (Deutsches Institut für Normung). These fittings are widely used in European process equipment and are standardized for chemical and pharmaceutical plants. They have a smooth design and gasket sealing that makes them reliable and easy to service.
- Flanged. These are larger, bolted connections with gaskets. They are most often used in power plants, petrochemical facilities and high-pressure piping systems where strength and sealing integrity are critical.
- Welded. These connections provide a permanent, permanent, leak-free attachment in systems that don’t require disassembly. They are commonly used in nuclear, chemical and high-pressure steam systems where safety and reliability are a priority.
An important distinction between the threaded and the non-threaded option is risk management. The threaded designs are best for the majority of general applications in oil & gas and HVAC systems, for example. On the other hand, non-threaded, Tri-Clamp and DIN connections minimize the possibility of leaks, contamination, or fatigue failure that can occur in food and beverage or pharmaceutical applications where cleanliness, safety, or long-term reliability is critical.
Figure 1: Process Connection Comparison Chart
What are the features and benefits of threaded process connections?
As you learned above, threaded connections are the most popular process connection type, especially in North America. They come in two main forms: tapered and straight.
Tapered threads (NPT, BSPT). Seal by wedging together with PTFE tape or compound. They’re simple, low-cost, and widely available, making them common in oil and gas, HVAC, water treatment, and general industrial piping. Their limits: threads deform with use, sealant is required, and instrument orientation can be tricky.
Straight threads (UNF, SAE, BSPP/G-thread). Seal with an O-ring, gasket, or washer instead of the threads. They’re reusable, easier to orient, and provide excellent sealing in high-pressure or high-purity applications such as aerospace, hydraulics, and semiconductor systems.
Both designs are widely used—tapered for cost and availability, straight for performance and reusability. Here’s a quick comparison of the most common threaded connections:
Figure 2: Threaded Process Connection Types
Remember, not every application is suited to threads. Non-threaded connections (shown in the Process Connection Comparison Chart), such as tri-clamp, DIN, flanged and welded, are used where hygiene, safety or long-term reliability matter most. Those designs eliminate the drawbacks of threads by reducing leak paths, improving cleanliness, or creating permanent seals.
Why are specific connection types used in different industries?
The choice of process connection is closely aligned with the specific demands and operating environments of each industry. In other words, each industry’s priorities, whether it’s hygiene, vibration resistance, high pressure or cost efficiency, will drive the choice of connection.
Here are a few examples:
Oil & Gas/Petrochemical companies often use NPT and BSPT connections because they’re simple, inexpensive, and well-suited for threaded piping systems found in refineries, pipelines, and tank farms. Straight threads (like SAE) are also used in high-pressure hydraulic systems supporting drilling and lifting equipment.
Pharmaceuticals, food and beverage markets avoid threaded connections because they create crevices where bacteria can grow. Instead, sanitary connections like tri-clamps are required. These allow for easy disassembly and cleaning, ensuring compliance with FDA and EHEDG hygiene standards.
Chemical and power plants tend to use flanged or welded connections in high-pressure steam, corrosive chemical processes, or hazardous service because they provide maximum sealing and durability.
Hydraulics and mobile equipment industries focus more on SAE straight threads and UNF flare fittings for heavy equipment, construction machinery and defense vehicles. These industries prioritize vibration resistance and the ability to handle pressures above 3,000 psi without leakage.
Automotive and aerospace manufacturers like UNF flare fittings and military-spec connections because of their durability under extreme vibration and temperature changes. For example, 37° flare fittings are found in aircraft hydraulic systems and even in race cars, where reliability under stress is critical.
Global markets require threaded options beyond NPT, so BSPP and G-thread connections dominate in Europe, Asia, and international markets where O-ring sealing is preferred.
Ready to learn more?
With a clearer understanding of why process connections are among the most important factors in ensuring accurate, safe and reliable pressure and temperature measurement, you are better equipped to assess your options. The connection you choose directly impacts sealing performance, service life and compliance with industry standards. This knowledge enables you to make confident choices that will keep your systems running safely and efficiently.
If you have questions, contact us to speak to a product expert who can guide you to the best solution for your needs. In the meantime, here are a few relevant articles that may interest you:
- Why Use TriClamp Fittings for Hygienic Applications
- Product Review: 1032 and 1033 Sanitary Pressure Gauges
- Choosing a Pressure Switch: 5 Factors to Consider
- How to Identify the Best Pressure Gauge Replacement
Contact us to speak with one of our industry experts and get all your pressure gauge questions answered.
