What’s the Right Pressure Instrument Mounting Assembly for Me?
Options for pressure instrument mounting assemblies can seem overwhelming. There are endless combinations and products, each with its own configurations depending on how you’re using them.
So, how can you get the proper assemblies to suit your project’s needs? How do you start looking in the first place?
There are a few factors to consider when researching pressure instrument mounting assemblies. All of them can help protect your equipment and ensure successful processes. This article will focus on five of the top considerations when choosing the right assemblies.
What Pressure Instrument Mounting Assemblies Do You Need?
You may have started searching and found a variety of pressure instrument mounting assembly variations, so how can you find the right ones for you? You should start by asking what you’re hoping to accomplish and what your project needs to be efficient and accurate. These are just a few of the main considerations to keep in mind before you buy:
1. Minimize Temperature Error
If you need help preventing or reducing temperature reading errors, there are a few solutions. Low-volume street fittings will reduce the overall fill volume inside the assembly, minimizing the impact of thermal expansion of the fill fluid on the accuracy of the assembly. Typical street fittings are not low volume. When selecting a street fitting, look for a fitting that minimizes internal volume. Ashcroft’s instrument tee used in assemblies comes standard with a low volume design.
You should also minimize the number of fittings used and make sure that all of your instrument connections are the same size (e.g., all ½ NPT or all ¼ NPT). Temperature error is also minimized by using compact instrument tees or cross fittings. This eliminates the need for “goalpost” configurations, which are bulky, expensive, and prone to damage.
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. With elevated process temperature, consider a siphon specifically designed to reduce temperature. Some siphons can reduce the process temperature to the instrument(s) from 800 degrees F/427C to less than 150F/66C.
Another way to dissipate process temperature is with a minimal length of the capillary. A simple 6-inch length of capillary line is capable of reducing process temperature to the instrument(s) with elevated temperatures from 750 degrees F/300C to less than 100 degrees F/38C.
2. Select Proper Ranges
Multiple-instrument assemblies, specifically gauge/switch combinations, work best when the nominal instrument ranges are similar. When assembling multiple instruments, select ranges that are as close together as possible. Ideally, the operating range of the gauge pointer should be mid-scale of the full-scale pressure range. In some scenarios, this might not be possible. For example, an assembly might need to actuate a switch at very low pressures relative to the pressure range on an indicating instrument.
In cases like this, ensure that the lower-pressure instrument has a proof pressure that exceeds the indicated range of the other instrument, or use a pressure limiting device or PLV (pressure limiting valve) to protect it.
3. Select the Right Fill Fluid
What Mounting Assembly Options Are Available?
The labeling and identification of various mounting assembly options vary between manufacturers in the industry and there isn’t a standard identification system.
At Ashcroft, our Assembly Coding Guide is a comprehensive resource describing each of our mounting variations. It includes depictions of assemblies, easy lookup by orientation and connection size, and instructions for correctly coding and ordering mounting assemblies.
Once you've selected what you need, consider the following options:
Instrument Welded to Isolators: Instrument welding creates a tamper and leak-proof assembly and is used when absolute leak integrity is critical for the safe operation of your process. Welded surfaces must be of like materials. Instruments attached directly to isolators can be welded, and assemblies with capillaries or siphons can be welded at each connection. Certain fittings (e.g. tees, nipples) cannot be welded, nor can snubbers, dampeners, or PLVs.
Tamper Evident Sealant: Tampering with fittings can disrupt the fill fluid inside an assembly, causing instruments to read inaccurately or create unwanted shifts in setpoints. A brightly colored, tamper-evident sealant applied at each threaded joint in an assembly signals to an operator that they should not adjust these fittings and can serve as a quick diagnostic check if accuracy issues do arise.
Elbow for Vertical Piping: When instruments are installed onto vertical pipe runs, consider using an elbow installed at an isolator for better readability of the instruments.
Installation constraints sometimes need custom configurations that aren’t covered by standard assembly offerings. You may require longer fittings, angled connectors or special instrument orientations to ensure that the instruments are readable, and the assembly doesn’t interfere with nearby equipment.
For assemblies not included in our guide, you can always reach out to Ashcroft for assistance setting up a custom pressure instrument mounting assembly to perfectly suit your needs.
We don’t like to pressure you, but we have more information.
Now that you have an idea of what instrument assemblies are available and what they can be used for, you can find the right solution for your application. If you want more information, view our webinar to learn more about pressure instrument mounting assemblies.
Also, feel free to read some of our related articles:
- When to Use a Welded Instrument Assembly
- Isolation Ring Assemblies for the Water/Wastewater Industry that are Accurate and Reliable
- Best Practices for Installing Flanged Diaphragm Seals
You can always reach out to us with any questions or concerns. Our industry experts at Ashcroft can help you get back on track.
About Eric Deoliveira, Product Marketing Leader
Eric Deoliveira is a Product Marketing Leader at Ashcroft, Inc. He is currently responsible for pressure gauges, sanitary gauges, high-purity gauges, diaphragm seals and isolation rings. He’s been with Ashcroft since 2015 and spent 3 years as a Product Support Engineer for Mechanical Temperature before transitioning into the Product Manager role. Eric enjoys coming up with solutions for customer problems and introducing new products to satisfy the needs of the market. When not working on his products, he is out golfing in the summer and skiing in the winter.