If you work in any industry where you need pressure instrument assemblies mounted on diaphragm seals, fluctuations in ambient temperature can affect the accuracy of your pressure instrumentation, especially in low-pressure systems. To help minimize temperature fluctuations and improve the accuracy of your instrument readings, we recommend keeping the fill fluid volume as low as possible using a low-volume tee fitting in your diaphragm seal assembly.
As an industry leader in pressure and temperature instrumentation since 1852, Ashcroft developed a series of Understanding the Basics articles that cover common process industry topics and terms. If you are new to manufacturing or process applications or just want a refresher, this is a great place to start.
Read this article to learn the basics of low-volume t-fittings, including what they are, how they work and the benefits of using them as part of your assembly for these types of applications.
Why use a low-volume tee fitting?
Errors in pressure instrument readings can occur when ambient temperature changes cause the expansion or contraction of the fill fluid in a pressure instrument. The impact of this error on the instrument's accuracy is influenced by various factors including the expansion rate of the fill, the diaphragm's flexibility, how much the fill volume changes with temperature, and the pressure range of the instrument.
Note: Although a change in the internal fill volume in the assembly is not a function of the instrument pressure range, the final percent error does depend on the range. Therefore, low-pressure range gauges will have higher errors than high-pressure range gauges.
How a low-volume T-fitting can help with instrument errors.
If you want to eliminate or reduce temperature-related inaccuracies in pressure instrument measurements, using low-volume tee fitting can help. Use this device in your diaphragm seal assembly and it will decrease the overall fill volume in the assembly and reduce the impact of temperature fluctuations on your instrument. It's important to note that traditional tee fittings do not provide the same advantages as low-volume fittings.
The use of compact tees or cross fittings reduces the internal volume of the assembly and reduces the temperature error of the instrument(s) attached. Ashcroft® diaphragm seal assemblies feature a low-volume design as a standard option.
Tip: To optimize your instrument setup, it's best to reduce the number of fittings and ensure uniformity in connection sizes (such as all ½ NPT or all ¼ NPT).
Benefits of a low-volume tee fitting in a diaphragm seal assembly
When you attach multiple instruments to a single diaphragm seal, it is important to enhance the efficiency of the assembly to achieve the most reliable and precise instrumentation possible. That means designing the assembly to minimize:
- Potential leak paths
- The total weight of the assembly, focusing on load-bearing points
- The effects of daily use with pulsation, vibration and temperature fluctuations
- Fill volume within the assembly
Placing an instrument on a tee fitting ensures that its weight is evenly distributed over the diaphragm seal connection port, which will reduce the risk of damage during transportation. Using a tee fitting also requires less fill fluid. This helps improve the assembly's temperature accuracy during operation.
Figure 1. Instrument assembly with tee fitting using a pressure gauge and switch.
Go beyond the basics.
Now that you know a little more about low-volume tee fittings and how they work, you may want to get some more in-depth information on diaphragm seal assemblies. Here are a few related articles for your reference.
- What is a Diaphragm Seal?
- What Factors Affect Diaphragm Seal Performance?
- What is the Right Pressure Instrument Assembly for My Application?
Feel free to contact us with any questions or concerns. In the meantime, download our guide to learn more about selecting an instrument assembly solution for your specific needs. 