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This article was originally published on August 30, 2021, and updated on December 2, 2024.
Your pressure gauge performs an important role in your application by providing pressure measurement which allows for precise system monitoring and control. However, your entire process can come to an abrupt halt if it stops working. And, if you replace it with the wrong gauge, it can cost you time, money and the safety of your personnel.
Replacing your pressure gauge with the most suitable match will ensure that your process can keep operating safely and efficiently. But how can you identify your existing gauge and obtain the proper replacement? At Ashcroft, our product and sales teams are confronted with this question almost every day, so this article will outline the many ways to identify your gauge and find a suitable replacement.
When you're done reading, you'll have a better understanding of what you need to know about your pressure gauge before you replace it. Plus, you will have links to other resources that can help you get the best option for your needs.
Not all pressure gauges are the same.
Unlike a vehicle’s VIN (Vehicle Identification Number), which provides complete product details, pressure gauges often only indicate the manufacturer, brand, or model family. That's because these instruments are made up of many components, some of which are incorporated within the device.
When you call your pressure gauge manufacturer for a replacement, you may think providing a product photo or a brief description will suffice. However, the reality is you will often be asked to identify specific aspects of the gauge to ensure you get the correct gauge.
What you will need to order the right pressure gauge replacement.
Here are the common questions our team will ask to ensure the new gauge is a suitable replacement for your application. Of course, these aren’t all the factors to consider, but it’s a useful guide to get you started.
1. What is the case material of your pressure gauge?
Gauge cases, also known as enclosures or housings, are typically made from materials like black-painted aluminum, stainless steel, phenolic, plastic, brass, or other materials that meet specific industry standards or requirements. Although brass was once the preferred choice for marine applications due to its durability, the rising costs have led to the use of alternative materials. For instance, 316L stainless steel is commonly used for chemical, food and beverage, and sanitary applications.
The structural design of the case is also important. Does it have a solid front or an open front? A solid front includes an integral wall behind the dial face, while an open front does not. Most gauges are used for general pressure measurement and do not need a solid front. However, a solid front provides extra safety for the operator and a sturdier enclosure in case of extreme pressure spikes that could rupture the gauge system.
In such cases, the excess pressure is expelled from the back of the gauge case, away from the operator. Solid-front gauges are often used in refineries and chemical plants where there is a greater concern for process media.
2. Does your pressure gauge require vibration and pulsation protection?
An often overlooked feature is whether the gauge is liquid-filled or equipped with a dampening feature. Liquid-filled and direct-drive gauges can reduce the impact of vibrations, while a throttling plug or screw minimizes pressure fluctuations, both protecting the measuring instrument.
To determine if these features are present, check for a solid fill plug and a visible level of fill fluid, which should typically cover more than 90% of the dial. Liquid filling helps prevent excessive wear on the gauge movement, which can otherwise lead to inaccurate readings and higher maintenance repair or replacement costs. You also want to ensure the fill fluid is compatible with the process media; common options include glycerin, silicone, or halocarbon.
To check for a throttling plug or screw, look into the process port. This feature helps prevent process pulsation from affecting the gauge.
3. Does your application involve corrosion?
To replace a gauge that is used in a harsh environment and at risk of damage from corrosion, you will need to confirm that the wetted material of the pressure system is fully compatible with your process media. Often, the pressure system’s wetted materials are printed on the dial face and/or on the gauge socket. Use our Material Selection & Corrosion Guide to help in your selection process.
4. How important is pressure gauge accuracy?
For your gauge to function correctly, it must adhere to specific accuracy standards, typically ASME B40.100 or EN 837-01. These standards determine the number of dial graduations and figure intervals.
Examine the face of your gauge. How many graduations and figure intervals does it have? This information is crucial for confirming the gauge's accuracy. Keep in mind that more graduations and figure intervals indicate higher accuracy.
Additionally, test gauges often feature a mirror band along the dial's edge and a precise "knife-edge" pointer.
5. What is the connection size of your current pressure gauge?
Pressure gauges offer a wide variety of pressure connections, such as NPT, DIN, BSP, JIS and more. The most common standard used in the United States is NPT (National Pipe Thread). You will need to know the thread type to ensure proper installation and prevent potential damage due to galling or cross-threading.
As a rule, the size of the gauge dial is a guide to understanding the common pressure connection size. Economical gauges with 1 ½ to 3 ½ in. dials typically offer 1/8 NPT to 1/4 NPT, while 4 ½ in. or larger dial sizes offer 1/4 NPT to 1/2 NPT.
Models identified as process gauges have dial sizes of 4 ½ in. and larger, and are commonly supplied with a 1/2 NPT that supports the instrument.
6. Where is the mounting location on your instrument?
Is it lower or back/rear connected, or does it have a special orientation such as 3 o’clock (left), 9 o’clock (right) or 12 o’clock (top)? And, are there potential space restrictions that will impede installation?
When replacing your gauge, these are your mounting options:
• Stem mount: offered with a lower, center-back or lower-back connect
• Wall/surface mount: offered with a lower or lower-back connect
• Panel mount: offered with a center-back or lower-back connect
• U-clamp flush (panel) mount: offered with a center-back or lower-back connect
• Front flange flush (panel) mount: offered with a center-back or lower-back connect
7. What is the pressure range of your dial?
You will need to confirm the dial pressure range and units of measure of your gauge. This should also help identify the accuracy as mentioned in step 3. When replacing the gauge, consider that ASME B40.100 recommends normal operating pressure be confined to 25% to 75% of the selected range. However, in the event of pulsation, the maximum recommended operating pressure should not exceed 50% of the full-scale range.
Other considerations when replacing a pressure gauge.
When replacing a gauge, don't just focus on getting the same one. Many people aren't familiar with all the details of the product and your current gauge might have been chosen incorrectly with insufficient guidance. Plus, you may not know the particulars of the original gauge if you didn't purchase it, or if it was sold to you by a distributor or another party.
Finally, remember to always buy new instruments, not used ones. Used instruments can be unreliable and may contain contaminants, posing risks to your processes and costing you money or downtime.
While no manufacturer can guarantee a perfect match, following these guidelines can help you choose more confidently.
Ready to learn more?
Now that you know more about finding the gauge you need and ensuring you get the right replacement, do your due diligence and make sure you are working with a trusted industry expert to find the best options for your application.
Feel free to contact an Ashcroft product expert and get all your pressure gauge questions answered. If you want to learn more about pressure gauges, here are a few other articles that may interest you:
- How Do I Select the Right Pressure Gauge Range?
- Choosing the Right Pressure Gauge Dial Size
- How Often Should I Check the Calibration of My Pressure Gauge?
- How Does Temperature Affect Pressure Gauge Performance?
- Why Did My Pressure Equipment Fail? 6 Instrument Killers
- How Much Do Mechanical Pressure Gauges Cost?
In the meantime, check out our pressure gauge selection tool to help you find the best instrument for your needs.
