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Your pressure gauge performs an important role in your application, and if it stops working then your entire process can come to an abrupt halt. 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 do you identify your existing gauge and the replacement you should buy?
Our product and sales teams hear this question almost every day, so this article will outline the many ways to identify your gauge and find a suitable replacement.
Not All Pressure Gauges Are the Same
Unlike a vehicle’s VIN (Vendor Identification Number), which provides complete product detail, a pressure gauge frequently offers no more than referencing the manufacturer, brand or family model. You will soon find that they consist of numerous elements, though some are hidden inside the instrument.
Just as your favorite coffee stands out from the rest, you will find that your gauge is not just a gauge. Though the customer may offer a product photo or limited description, this isn’t enough. I usually need to ask a few questions to properly source a replacement.
7 Steps for Identifying Your Pressure Gauge
I’ve helped customers with their pressure instrument concerns for years, and the gauge selection process I use can help find them the proper gauge that will perform over a long time and keep their businesses operating.
Let’s discuss what questions to ask and the information needed for identifying your gauge.
I go through these steps to help identify the gauge customers have, ensure it’s sufficient for what they’re using it for, and then suggest a suitable replacement. Of course, these aren’t all the factors to consider, but it’s a useful guide to get you started.
1. Case (Enclosure/Housing)
What material is it? Gauge cases are typically available in black-painted aluminum, stainless steel, phenolic, plastic, brass, or another material for meeting an industry specification and/or requirement.
In the past, brass was highly preferred as it is extremely resilient for marine applications, though rising costs influenced its replacement by alternative materials.
Additionally, 316L stainless steel has become a common requirement for chemical, food and beverage, and sanitary installations.
Next is the case’s structural design. Does it have a solid front or open front? This pertains to whether the gauge does (solid) or doesn’t (open) have an integral wall incorporated into the case behind the dial face.
Most gauges do not require a solid front as most are for general pressure measurement, yet it offers additional operator safety and a more rugged enclosure if there are extreme pressure spikes that can lead to the rupturing of the gauge system.
The overpressure is projected out of the back of the gauge case and directed away from the operator. Solid-front gauges are common within refineries and chemical plants where there is a heightened concern for process media.
2. Vibration and Pulsation Protection
Another feature often overlooked is whether the gauge is liquid-filled and/or has a throttling device. Why are these important? Each protects the measuring instrument; liquid fill dampens the effects of vibration, whereas a throttle plug/screw dampens pressure fluctuations.
How do you know if these are present? Liquid fill can be verified if the gauge has a solid fill plug and a discernable level of fill fluid typically covering >90% of the dial. Liquid fill protects the gauge movement from excessive wear that otherwise would lead to inaccurate readings and an increase in repair/replacement costs.
Be sure that the selected fill fluid is compatible with the process media – the most common fill fluids are glycerin, silicone or halocarbon.
You can see if a unit has a throttling plug/screw installed by looking into the process port; this feature is used to keep process pulsation from affecting the gauge.
3. Contamination Control
To replace your gauge, be sure to confirm that the wetted material of the pressure system is fully compatible with your process media.
Our corrosion guide can assist in your selection process.
Often, the pressure system’s wetted materials are printed on the dial face and/or on the gauge socket.
4. Accuracy
Check the gauge face (dial) of your gauge. How many graduations and figure intervals are there? This will help verify gauge accuracy.
Most gauges meet either ASME B40.100 or EN 837-01 – both standards guide the number of dial graduations and figure intervals.
Remember, a greater number of graduations/figure intervals means higher instrument accuracy.
Also, units with a mirror band running along the dial’s edge are typical of test gauges, and they will also have a fine “knife-edge” pointer.
5. Connection Size
You will soon realize that pressure gauges offer a wide variety of pressure connections. The most common standard for the U.S. is NPT (National Pipe Thread). You should 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. Connection Location
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, 9 or 12 o’clock? Additionally, you should be aware of space restrictions that will limit installation.
When replacing your gauge, consider these mounting options:
- Stem mount: offered with a lower-connect gauge
- Wall/surface mount: offered with a lower-connect gauge
- Panel mount: offered with a back-connect gauge
- U-clamp flush mount: offered with a back-connect (panel mount installations) gauge
- Front flange flush mount: offered with a back-connect (for panel installations) gauge
7. Pressure Ranges
Confirm the dial pressure range and units of measure of your gauge. This should also help identify the accuracy as mentioned under 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.
Considerations When Replacing a Gauge
When seeking a gauge replacement, obtaining the same instrument should not be your only consideration.
Many people don’t know the ins and outs of the product. Your gauge may have been specified incorrectly or you could have received improper guidance when you made your purchase.
Not every customer knows what gauge was originally ordered, either. They may not have ordered it - a distributor or other third party could have sold it to them.
Make sure you buy new and not used instruments. Questionable instrument reliability/integrity and contaminants can present a serious risk to your processes and cost you money or downtime.
My suggested gauge for the customer is the closest I can get to satisfy the application. No reputable pressure instrument manufacturer can tell you with 100% certainty that their recommended replacement gauge is a perfect match, but you should be more confident when following a set guideline.
We don’t like to pressure you, but we have more information.
Now that you know more about identifying a gauge and finding 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 us today to talk to one of our industry experts here at Ashcroft and get all your pressure gauge questions answered. We can help you find the right replacement gauge.
If you want to learn more about pressure gauges, read some other articles we’ve posted on the subject:
- 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?
And learn how to avoid pressure equipment failure in our eBook: