The pressure instrument mounting accessories you select to protect your instruments can help ensure safe and accurate measurements. In the water and wastewater industry, combining instruments with accessories like isolation rings, referred to as an assembly here, can prevent pump damage, clogging and other problems if designed properly.
So, how do you ensure the proper design of assemblies using isolation rings?
Many factors contribute to this. This article will cover the effects isolation rings can have on your water and wastewater application and how to design the assembly correctly.
Potential Equipment Problems in Water/Wastewater
Equipment used in water and wastewater applications is subject to particularly demanding operating conditions. Here are some of the many potential problems your instruments can face:
- 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.
Ashcroft offers a variety of specially engineered accessories available to help protect your pressure measurement equipment from damage. Diaphragm seals can help protect instruments from clogging and corrosion, pressure limiting valves can protect instruments from overpressure, and capillaries or siphons can help prevent heat damage.
Isolation rings can also help prevent your pressure gauge or switch from clogging by isolating the instrument from the process media and are frequently used in the water and wastewater industries to monitor and protect pumps.
However, designing a proper isolation ring assembly can be a challenge. How do isolation rings affect the design of an instrument accessory assembly? And why don’t we use goalposts as other manufacturers do? Let’s discuss instrument assemblies and the benefits of isolation rings in water/wastewater applications.
Proper Design of Instrument Assemblies
Selecting the right equipment for your application will impact installation, proper function and help avoid the possibility of future malfunctions and failures.
So, once you have your isolation ring, what ensures that your entire instrument assembly is designed properly? The first thing to consider is temperature error.
With pressure gauges 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.
The opposite occurs with pressure switches. 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 can mitigate these effects, as they are less susceptible to the thermal effects of fill fluid.
Because of these temperature effects just described, it is important to minimize the amount of fill volume in an isolation ring assembly.
Other manufacturers in the industry use a product called 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, so that only the minimum amount of fill is used to fill an assembly. This minimizes temperature error due to the expansion and contraction of fill fluid.
Figure 1 below demonstrates this effect: the assembly using a low-volume fitting reduced switch setpoint drift due to temperature by 36%.
Figure 1:
Creating a custom instrument assembly can consolidate all of your instrumentation into one platform. This is important because a single manufacturer puts it together, tests and calibrates the assembly as a single unit and ensures that the whole thing is working properly.
Sometimes the person that sells you the products isn’t an expert in gauges or switches or isn’t the manufacturer, so if something goes wrong with the product you won’t know who is at fault – the gauge manufacturer or isolation ring manufacturer. So, having all components 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.
- Smaller, compact instrument tees minimize the potential for breakage during shipment or construction at water treatment plants by decreasing torque/force on the pipe or isolation ring.
- Consider the 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. You can read more about compatible materials in our guide to Pressure and Temperature Instrumentation for Water and Wastewater Applications.
- Once your assembly is built, consider additional certifications you might want to secure. Calibration charts provide a traceable record of the assembly’s accuracy, while hydrostatic testing checks for any pressure decay caused by leaks.
- Finally, ensure that your instrument and isolation rings are compatible. Learn more about instrument assemblies on our blog.
We don’t like to pressure you, but we have more information.
Now that you better understand using isolation rings in the water and wastewater industry, you’re on your way to safer and more accurate applications. If you want more information, view our webinar to learn more about pressure instrument mounting assemblies.
You can also reach out to us with any questions or concerns. Our industry experts at Ashcroft can help you get back on track. Let us be your one-stop-shop for pressure instruments!