This article was originally published on October 18th, 2021 by John Varkonda and was updated on April 24, 2024, by Dean Moyer.
Anyone working in the water/wastewater industry knows just how important it is to maintain accurate and reliable pressure measurements throughout the process. Without the proper instrumentation to do the job, your operation is at risk for pump damage, clogging and other issues that could bring the entire system to a halt.
At Ashcroft, it is our business to know the challenges you may encounter to keep your operation running safely and effectively and to provide solutions that will address your specific needs. In fact, in my 30 years of experience, I have seen just about everything that can go wrong (and right) in water/wastewater applications.
In this article, you will get an overview of common water/wastewater application issues, and learn how the proper instrumentation, including isolation rings and accessories, can help you prevent these issues from happening to you. Throughout the article, you will also see links to additional resources that you can use as a reference to answer other questions you may have. Let's get started.
How isolation rings and accessories can keep your process flowing
Water/wastewater applications are harsh and corrosive. To maintain safe operations, durable and dependable pressure instruments are essential. It is also critical to protect those instruments from damage caused by the challenging conditions and corrosive substances present in the process. That's where isolation rings and accessories come in.
Isolation rings are specifically designed to help prevent your pressure gauge, switch or transmitter from clogging by isolating the instrument(s) from the process media. They are frequently used in water and wastewater applications to protect the instruments that are used to monitor and keep pumps from getting damaged.
Together, the pressure instrument, isolation ring and other protective accessories are assembled and mounted to your process to help prevent any of the following issues from occurring in your system:
- Clogging. Suspended solids, especially in sludge, can accumulate inside pressure instruments and cause them to fail.
- Corrosion. Water, sludge and treatment chemicals can corrode metal components resulting in instrument failure.
- Overpressure. Pressure line spikes and “water hammer” may introduce pressure beyond the operating range of the instrument and cause damage.
- Vibration. System machinery can cause vibration, which can result in pressure gauge “pointer flutter” and internal pressure gauge wear.
- Pulsation. In-line pumps cause pulsation in the pressure line, which can cause pointer flutter and internal pressure gauge wear. It can also result in Bourdon tube fatigue or rupture.
- Temperature. Pressure media at high temperatures will affect the elastic element inside the instrument resulting in decreased accuracy. Changes in ambient temperature can also impact the accuracy and operation of isolated pressure-measuring instruments.
There are numerous other accessories are also specially engineered to help protect instruments from these damaging application issues. Diaphragm seals, for example, can help protect them from clogging and corrosion, pressure-limiting valves can prevent overpressure, and capillary lines or siphons can help prevent heat damage.
How temperature affects design instrument assemblies.
Designing a proper isolation ring assembly can be a challenge. Selecting the right equipment for your application will impact installation and proper function and help avoid the possibility of future malfunctions and failures. When selecting the instruments, the first thing to consider is temperature error. Here's why:
- When pressure gauges are attached to seals or isolation rings, thermal expansion of the fill fluid causes a small pressure building inside the sealed portion of the assembly. This increase in pressure results in a positive offset in the reading on the instrument. The lower the instrument range, the greater the percent error of this offset will be.
- With pressure switches, the opposite is true. As temperature increases, the buildup of pressure decreases the amount of pressure needed to actuate the switch, decreasing the setpoint with increasing temperatures.
- Digital products like the Ashcroft® 2274 Digital Pressure Gauge with switch outputs are less susceptible to the thermal effects of fill fluid.
Because of these factors, it is important to minimize the amount of fill volume in an isolation ring assembly.
Some manufacturers use a "goalpost" to mount multiple instruments on an isolation ring or diaphragm seal. However, the large internal volume of these “goalpost” fittings introduces an additional (and unnecessary) temperature error.
At Ashcroft, we use custom-made low-volume fittings with narrow internal diameters, which only require the minimum amount of fill for an assembly. This minimizes temperature error due to the expansion and contraction of fill fluid. Figure 1 below demonstrates how the assembly using a low-volume fitting reduced the switch setpoint drift by 36% due to temperature.
Figure 1:Switch/Isolation Ring Setpoint vs. Temperature.
Creating a custom instrument assembly can help you consolidate all of your instrumentation into one platform. Using a single manufacturer who can provide all the components, assemble, test and calibrate the assembly as a single unit, and ensure that the whole thing is working properly has many benefits. This is especially true if you are confident the manufacturer is a trusted and reliable source for high-quality, cost-effective instruments.
If the person selling you the products isn’t an expert in gauges or switches or isn’t the manufacturer, you have little recourse if something goes wrong to know who is at fault. However, having all components made and assembled by the same manufacturer can streamline troubleshooting.
Tips for Instrument Assembly Design.
When designing your assembly:
- Minimize the number of fittings used to build assemblies. Ashcroft does that by using custom fittings made to match the existing connections supplied with our instrumentation.
- Don’t mix and match connection sizes. keeping it consistent minimizes the need for additional fittings.
- Decrease torque/force on the pipe or isolation ring. Smaller, compact instrument tees minimize the potential for breakage during shipment or construction at water treatment plants.
- Choose the correct orientation and fit of connections. How do you want it to fit into your system? Allow for the presence of other valves/piping around the assembly so they don’t interfere with electrical connections, valves, flow meters, etc. We provide dimensional drawings and 3D models for customers so they can ensure proper fit.
- Think about the different connections on gauges. Elbows help when putting in vertical piping so that instruments can be read upright. Consider using connections other than the common lower process connection (6 o’clock) on gauges.
- Be mindful of material compatibility and what the isolation ring will be exposed to. Make sure the proper materials are selected to extend the life of your products.
- Consider additional certifications. Calibration certs provide a traceable record of the assembly’s accuracy, while hydrostatic testing checks for any pressure decay caused by leaks.
- Go beyond 6 o’clock process connections. Ashcroft offers 3 o’clock, 9 o’clock & 12 o’clock positions for optional process connection locations to ensure the instrument is in an upright position.
- Install isolation valves upstream of the instrument/seal assembly for hydrostatic overpressure test at start up to protect the instruments from the high overpressure procedure.
- Use compatible materials. Ensure that your instrument and isolation rings are compatible.
Ready to learn more?
Now that you better understand how to use isolation rings in the water and wastewater industry, you’re well on your way to ensuring safer and more accurate applications. To dig a little deeper, check out these additional resources:
- The Expert Guide to Instrument Assemblies (Webinar)
- How to Optimize Water & Wastewater Monitoring Instruments
Feel free to reach out to us with any questions or concerns. Our industry experts can help you get back on track. In the meantime, you can read more about compatible materials in our guide to Pressure and Temperature Instrumentation for Water and Wastewater Applications.