This article was originally published on June 9, 2021, and was updated on March 4, 2024.
Pressure gauges play a critical role in your process applications. They accurately and reliably measure and monitor pressure to determine if process systems are working effectively and efficiently, or if you need to make system alterations or adjustments. This helps ensure the safety of your personnel, the efficiency of your processes and the quality of your products.
But what happens when your pressure gauges stop working? Your entire operation is at risk. That's why periodic instrument audits are good practice.
Ashcroft has been conducting comprehensive instrument audits for 10 years. As the product lead for process gauges, I see the results of these audits and can tell you why instruments fail in the first place. The good news is that most of these “instrument killers” we've identified can be prevented if you know the warning signs. In this article, you will learn the primary indicators that tell you your pressure gauge may be failing and the 6 most common pressure gauge problems and solutions that we found in our instrument audits.
When you are done reading, you will know what to look for and be prepared to address any of these issues ahead of time. Armed with this information, you will be able to keep your processes running safely, smoothly and effectively.
Early warning signs of pressure gauge failure
Like all instruments, pressure gauge maintenance is one of the keys to achieving and maintaining personnel safety, process efficiency and product quality. An instrument audit, for example, makes it easier for you to identify instrument issues and execute appropriate solutions before they become more significant or widespread problems. This helps save you time and money by preventing costly service work, unplanned downtime and equipment or process-based employee injuries.
Here's what we've found to be primary indicators of pressure gauge issues:
- Pointer flutter. The gauge pointer continually moves back and forth, making it difficult to read the measurement indicated.
- Unresponsive gauge. The pointer component does not move in response to changes in the operating pressure.
- Dented pointer. This a sign the gauge has been severely under or overpressure.
- Discoloration. Yellowing liquid in a liquid-filled gauge case usually indicates elevated ambient temperature at the gauge.
- Deformed or melted gauge window. This is also a sign of extreme elevated temperature.
- Black-coated window or dial. When the gauge window and dial are coated in a black powder causing a readability issue. This is typically the result of pulsation and/or vibration that causes fretting or wear of the gauge movement teeth
Each of these signs (among others) is an indicator of underlying gauge issues. If you can recognize them and understand their causes, you will be better prepared to diagnose and resolve problems that may occur in your process instruments.
Six most common pressure gauge problems and solutions
The key to overcoming problems with instruments in critical applications is to understand their causes. Below are some of the most common pressure gauge problems we have come across, including why they occur, what effects they have on the instrument and the overall operation or process, and how to resolve them.
1. Excessive Pulsation/Vibration
Problem. In processing equipment, surges in process pressure can lead to pulsation in gauges. These pulsations can cause poor gauge readability due to pointer flutter and decreased gauge integrity due to component damage.
Similar to pulsation, vibration can lead to pointer flutter and component damage in gauges. They can be classified into two categories: high-frequency/low-amplitude and low-frequency/high-amplitude. The former causes pointer flutter and centralized gauge movement gear teeth damage on the segment, while the latter causes widespread gear teeth damage across the segment and increased stress on the bourdon tube.
As a rule of thumb, if pulsations or vibrations trigger pointer movement of 5% or more of the full-scale range, you should take steps to reduce their generation or their effect on the instrument.
Solution. There are three common solutions for instrument problems stemming from excessive pulsation and vibration:
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Dampening the movement/tube. You can dampen the effect of pulsations/vibrations on the gauge by filling the case with silicone, glycerin or halocarbon that includes an integrated throttle screw. Also consider a dry gauge with a dampened movement, like the Ashcroft Duragauge with PLUS!™ performance - a dry gauge that works like a liquid-filled gauge dampening the effects of pulsation and vibration.
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Installing the instrument assembly away from the source. You can use a capillary line to mount the instrument further away from the source of the pulsation and vibration. Capillary is available in lengths from 1 foot to 100 feet.
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Restricting the flow of the process material. You can reduce pulsation to the instrument by integrating a pulsation dampener, throttle screw, steel needle valve or a diaphragm seal to dampen the flow of process material. These accessories dissipate pulsation before it reaches the instrument.
2. Low/High Temperatures
Problem. Instruments are rated for use in a specific temperature range. Using them in temperatures outside of this range can lead to significant damage, depending on their design and construction. For example:
- Dry gauges are typically rated for use in ambient temperatures below 200°F (93 °C). Above this temperature, they may experience dial discoloration, window discoloration (if acrylic) or gasket hardening. Process temperatures for dry gauges are typically rated for between -20°F (-20 °C) to 250 °F (121 °C).
- Liquid-filled gauges are typically rated for use in ambient temperatures up to 150 °F (66 °C). Above this temperature on a liquid-filled gauge, they may experience leaching of the gasket and O-ring material and discoloring of the fill liquid. Both extremely low and extremely high temperatures can also trigger accuracy issues in instruments. A standard dry gauge can experience slowed point response time in low temperatures.
Gauge accuracy is affected when the ambient gauge temperature exceeds the temperature at which it was calibrated. As a guide, if a gauge is calibrated at 68 °F (20 °C), accuracy will be affected by approximately 0.4% per 25 °F/13.9 °C.
Solution. There are several common solutions for instrument problems stemming from excessively high or excessively low temperatures:
- Mounting the instrument remotely
You can install the instrument away from the process with a capillary to protect it from high or low temperatures. A gauge pipe mounting bracket is a convenient available option when remotely mounting the gauge. Ashcroft® capillary is rated for temperatures of -300 °F to 750 °F (-184 °C to 399 °C). A simple 5-foot length of capillary between the instrument and the process is very effective at increasing low temperatures and decreasing high temperatures.
- Mounting the instrument directly
The Ashcroft® MicroTube™ or finned siphons are rigid devices mounted directly to the instrument and then to the process so there is no need to consider how to mount the instrument if it were remotely mounted. The MicroTube™ siphon has been engineered for process pressures to 5000 psi and process temperatures to 800 °F (427 °C). The finned siphon is rated for pressures to 3000 psi and process temperatures to 700 °F (371 °C). Both devices are good temperature dissipaters. - Incorporating a coil or pigtail siphon for steam applications
These siphons when attached to the instrument can curtail temperature in steam applications. A pigtail siphon is used for vertical mounting whereas a coil siphon is used for horizontal mounting. Before installation, the siphon loop needs to be filled with water. The water acts as a barrier to protect the instrument from the elevated temperature and the harmful effects of the water hammer, which is typical with steam applications.
3. Pressure Spikes
Problem. Pressure spikes have many causes, including water hammer, overly rapid valve actuation, equipment malfunction or process fluid freezing. Gauges subjected to these conditions often show signs of damage like a dented pointer, a ruptured or deformed tube, or a broken segment gear. This damage can lead to unresponsiveness to changes in process conditions or complete instrument failure, both of which can result in poor operation or performance in your process.
Pressure spikes or surges beyond the full-scale range of a gauge or overpressure can result in accuracy degradation, gauge failure or rupture of the bourdon tube.
Solution. There are many solutions if you experience instrument problems stemming from pressure spikes, including:
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Integrating an internal stop
You can integrate an internal stop/overload stop to increase the proof pressure of the gauge. This device typically increases proof pressure by an additional 20%.
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Installing a pressure limiting valve (PLV) or a gauge with high overpressure capability
This accessory device can be set to shut off at the full-scale range of the gauge. When process pressure falls below the full-scale gauge range pressure, the PLV will reset and allow process pressure to flow through the instrument. Another option to consider is a gauge with high overpressure capability like the Ashcroft T6500 with the XRA option. This gauge allows for overpressure up to 400% of the gauge range.
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Selecting a new, properly rated gauge
You should choose a new gauge that accommodates the maximum operating pressure. For optimal readability, the gauge pointer should normally operate at 12:00 on the dial face. If the normal operating pressure of the gauge is 50 psi, choose a full-scale range twice the operating range or 0/100 psi.
4. Instrument Clogging
Problem. Instruments installed in equipment for “dirty” processes—i.e., processes involving particulates, slurries and sludge—are highly susceptible to clogging. Process material can become stuck on the instrument’s inner surfaces as it flows through the system, which can hinder the operation of the instrument and the efficiency of the process.
Solution. Depending on the specific issue, there are a few options to choose from:
- If the instrument’s process connection is susceptible to process media buildup or blockage, you can prevent clogging by isolating the instrument from the process media using a diaphragm seal or isolation ring.
- When clogging of the diaphragm seal is a concern, consider an available flushing connection. It is designed to flush process media buildup in the seal. Attaching a valve to the flushing port is ideal to control process flow.
- For heavy slurries or sludge, consider an isolation ring. This 360-degree design for process flow makes clogging virtually impossible. To learn more, read When to Use a Diaphragm Seal vs. an Isolation Ring.
5. Instrument Corrosion
Problem. The wetted parts of an instrument must be compatible with the process material. Otherwise, the instrument may corrode during use, which can affect product and process quality. Under severe process conditions, process media that is not compatible with the wetted parts of the instrument will result in the eventual failure of the instrument causing the media to escape into the environment. This becomes a safety issue where operators can be injured or, in extremes, lose their lives.
Solution. If you want to avoid instrument problems stemming from corrosion, you should ensure the material for the instrument’s wetted parts is suitable for the process material’s composition, concentration and temperature. If it is not possible to choose a compatible wetted material, you can integrate a diaphragm seal/instrument isolator or isolation ring constructed from an appropriate material for the process. Refer to the Ashcroft® Material Selection & Corrosion Guide for process compatibility guidance.
6. Instrument Abuse
Problem. Instruments are delicate pieces of equipment. While integrating the right design elements and accessories can help protect them from damage during severe service applications, it cannot protect them against abuse, i.e., incorrect installation or usage. Installing or using instruments incorrectly can cause significant damage, which can lead to measurement error or component failure.
Solution. Always install, use and maintain your instruments properly. Installing NPT instruments requires the use of an open-ended wrench.
- Do not attempt to install and tighten the instrument using the instrument case. This often causes irreparable damage to the instrument.
- Do not use the instrument as a step ladder after it is installed as this presents safety issues. Not only can the instrument be damaged, but someone can get hurt.
- Inspect the instruments routinely for damage and performance.
Ready to learn more?
Now that you know the most common reasons why pressure gauges fail and the warning signs to look for, you are in a much better position to keep your people and processes safe and secure.
At Ashcroft, we are committed to helping customers select the right instruments for their specific needs. Contact us any time to talk to one of our industry experts or request a Critical Application Solutions Experts® (CASE®) audit for your company. Read 4 Important Benefits of Critical Application of Instrument Audits to learn more about it.
In the meantime, here are a few more articles that may be of interest to you.
- How To Identify Your Pressure Gauge and Get the Proper Replacement
- How Does Temperature Affect Pressure Gauge Performance?
- How Do I Select the Right Pressure Gauge Range?
- How Often Should I Check the Calibration of My Pressure Gauge?
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