Pressure gauges come in a number of different options, including range, materials and size. You can even customize the gauge dial.
Different dial sizes can suit your particular application and the location of your pressure gauge. So, what size pressure gauge is best for your application?
This question is often asked and does not always have a simple answer. This article will explore dial size and provide guidance for selecting the best gauge size for your application.
Gauge Readability
Gauge size and the ability to read the gauge go hand in hand. The larger the dial size the easier it is to read.
Figure 1: Operator Reading a Gauge
How accurately you need to read the pressure value on the gauge is another major factor in determining the minimum gauge size to use. To read a gauge to its stated accuracy, you need to be able to clearly see the minor divisions on the scale.
ASME B40.100 makes a minimum recommended gauge size (see Figure 2 below):
Figure 2: ASME B40.100 Minimum Recommended Gauge Size
Distance
The distance between the gauge and the operator reading it is the most important consideration in determining the size of the gauge. To examine how distance affects the readability of a gauge, we took a series of photographs of two gauges (a 6-inch dial size gauge and a 3½-inch dial size gauge) from 2 feet, and then in 2-foot increments up to 12 feet.
We measured the height of the gauge case at each distance and calculated what would be the apparent gauge height at each of the distances (Figure 3). The height is calculated as a percent of the height of the gauge at 2 feet. This should give a better frame of reference. For example, a 6-inch dial size gauge would appear to have a ~1-inch dial size at 12 feet.
Figure 3: Calculated Apparent Gauge Height
The following sequence of photos is used to illustrate the ability to read two different sizes of gauges side by side.
As you can see here, both the 6-in. and 3½-in. gauges can be easily read from 2 feet away:
6-in. 1009 and 3½-in. 1009 Gauges at distance of 2 feet
At 4 feet, both gauges are still easy to read:
6-in. 1009 and 3½-in. 1009 Gauges at distance of 4 feet
At 6 feet, both gauges are still easy to read (Note: picture resolution is not as good as eyesight):
6-in. 1009 and 3½-in. 1009 Gauges at distance of 6 feet
At 8 feet, it’s starting to get hard to read the scale on the 3½-in. gauge. The 6-in. gauge is still readable:
6-in. 1009 and 3½-in. 1009 Gauges at distance of 8 feet
At 10 feet, it is hard to read the numbers and the scale on the 3½-in. gauge. The 6-in. gauge is still readable:
6-in. 1009 and 3½-in. 1009 Gauges at distance of 10 feet
At 12 feet, the 3½-in. gauge cannot be read to its stated accuracy. The 6-in. gauge is still readable. If the gauge is used just for a reference, meaning the pointer is in the range of where it should be, then both gauges could be read at 12 feet:
6-in. 1009 and 3½-in. 1009 Gauges at distance of 12 feet
If the gauges were going to be used just as a reference, adding zone markings (Figure 4) to the dial would make it very easy for the user to read the gauges.
Figure 4: Zone Markings on a Dial
Comparing Dial Sizes
Cost is a factor as well, as a larger gauge costs more than a smaller gauge, so the project budget must be considered. The next set of photos compares common sizes of gauges.
This first photo compares a 4½-in. 1209 process gauge and 100 mm T6500 process gauge. As you can see, the 4½-in. 1209 gauge is much larger than the 100 mm T6500 gauge. In fact, the 4½-in. 1209 dial has 65% more surface area than the 100 mm T6500 dial.
It is important to note that with a gauge built to the ASME B40.100 standard, the size of the gauge is the dial diameter. An EN837-1 gauge size is the case diameter, not the dial. The 100 mm T6500 actually has a 3½-in. dial.
Comparison of a 4½-in. 1209 and 100 mm T6500
This second photo shows the 100 mm T6500 and a 3½-in. 1009 gauge. As you can see, they are the same size:
Comparison of 3½-in. 1009 and 100 mm T6500
This third photo is a comparison of a 6-in. 1379 process gauge and a 160 mm T6500 process gauge. As you can see, they are also the same size:
Comparison of 6-in. 1379 and 160 mm T6500
We don’t like to pressure you, but we have more information.
In summation, determining which size gauge is best for an application starts with understanding how accurately the measurement needs to be. If a high degree of accuracy is required, you’ll need a larger size gauge, and the measurement should be taken from a close distance to the gauge.
If the measurement is just a reference indication, a smaller gauge can be used, and it can be read from a further distance. Adding zone markings to the dial will greatly help when reading a gauge from a greater distance.
For more information on pressure gauges, check out some other articles we’ve written:
- How Can I Order Custom Dials for Pressure Gauges?
- 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?
Feel free to contact us today to talk to one of our industry experts and get all your measuring instrument questions answered.
You can also download our eBook to learn how to avoid pressure equipment failure: