For applications that may expose instrumentation (such as pressure gauges, pressure switches or pressure transmitters) to clogging or corrosion it is appropriate to isolate the instrument from the process.
The industry typically uses diaphragm seals or isolation rings to protect instrumentation against such conditions.
For example, in water and wastewater applications engineers may specify a diaphragm seal to protect an instrument against treatment chemicals such as sodium hypochlorite, sodium fluoride or chlorine. Diaphragm seals can be made in many different materials that are appropriate for the application.
For instance, if the instrument would be exposed to sodium hypochlorite it could be installed on a diaphragm seal made with tantalum, titanium or PVC materials that are more compatible with the process.
They may also specify isolation rings to protect against clogging from heavy waste slurries.
But can you remove a pressure instrument from an isolator when working in the field?
This article will explain the dangers of removing an instrument from an isolator and how you might do so safely.
Removing an Instrument from an Isolator
Diaphragm seals and isolation rings in principle operate the same. Instruments are attached creating a closed system. The filling process involves drawing a complete vacuum through a fill port and pumping in some form of transfer fluid (usually silicone or some other specialty fluid).
Once filled the instruments should be factory calibrated or calibrated by an authorized assembler as the impact of the isolator may shift the original calibration of the instrument.
After the instrument/isolator assembly is completed, it is ready to be installed. At this point the instrument should not be removed from the isolator assembly. In fact, even tampering with the positioning of the instrument as it is threaded onto the seal could impact the calibration of the assembly.
If the instrument is removed or tampered with it may need to be refilled and recalibrated (again by the manufacturer or an authorized assembler).
In the event that an instrument over time gets damaged or requires routine maintenance (recalibration or otherwise) the entire assembly should be removed and sent to a facility that can perform the work according to NIST standards.
Many diaphragm seal designs allow for removal of the instrument portion of the assembly while keeping the bottom housing installed in the pipe. This continuous duty design is very common; however, the process piping is exposed during this process and needs to be shut down.
For isolation rings this process can be very cumbersome as they are flanged (or threaded) in line with piping. This is the case particularly for larger rings that may require heavy duty equipment (such as cranes) to install and uninstall.
Once removed from the process the isolation ring (many times used for wastewater) would need to be properly cleaned and sanitized before being sent to the facility for calibration. This procedure is often labor-intensive and expensive.
As a general rule, you should avoid removing pressure instruments from an isolation ring without using a Safe Quick ReleaseTM (SQRTM) option.
Ashcroft Safe Quick Release™ (SQR™) Option
Ashcroft Safe Quick Release™ option is a dry break connector that allows an operator to remove an instrument from the isolation ring without losing the fill fluid. You won’t need to pull the piping apart as the release is built into the isolation ring. It’s offered as an option on all of our isolation rings.
Figure 1: Ashcroft Safe Quick Release Option
The Safe Quick Release™ option is becoming more common in many applications and is often a requirement in new plant constructions or additions to plants. Isolation rings an be configured with the SQR™ option because the amount of fill fluid in the overall system is more forgiving and can accommodate the repeated process of removal and reinstallation of the connector.
Diaphragm seals are much more sensitive and typically the process of removal and reinstallation would impact the performance of the instrument. The SQR™ option would not work well on a diaphragm seal assembly – thankfully the process of removal is typically easier for these designs than the inline isolation ring assemblies!
We don’t like to pressure you, but we have more information.
Now that you better understand the dangers behind removing a pressure instrument from a diaphragm seal or isolation ring assembly, you can help protect your instruments and keep your application running efficiently.
If you want more information on mounting accessories and assemblies, view our webinar about pressure instrument mounting assemblies or download our Complete Guide to Pressure Instrument Assembly.
We also have a few related blog articles that you may find are helpful:
If you want to learn about other pressure gauges, here are some other reviews:
- Why Use a Flushing Connection on a Diaphragm Seal?
- When to Use a Welded Instrument Assembly
- Best Practices for Installing Flanged Diaphragm Seals
- Isolation Ring Assemblies for the Water/Wastewater Industry that are Accurate and Reliable
Feel free to contact us with any questions or concerns. Our industry experts at Ashcroft can help answer your questions and get you back on track!
