Selecting the proper mechanical pressure gauge is crucial. Not just to gain accurate readings, but for safety purposes as well.
In this article, we take you on a deep dive into the purpose of mechanical pressure gauges, why it’s so important to use a multi-step process to select one that meets the standards for your use, and what that selection process entails.
A mechanical pressure gauge is a gauge that doesn’t use electronics. Its design is simple, yet tried-and-true, featuring a simple analog dial face with a glass cover. Its function is to measure the pressure of a vessel’s liquid or gas contents, also known as the process fluid.
Installing a pressure gauge on your industrial pressurized vessel is critical for maintaining safety in a cleaning or testing environment. If something is wrong with the vessel or its contents, the reading on the pressure gauge is one of the first clues for anyone working in the area that they may need to initiate a shutdown or perform some other safety measure.
Pressure gauge selection is just as important as the function of the gauge itself. The person making the selection must consider several different factors as they relate to the industrial application of the gauge.
Some of these factors include the accuracy of the gauge reading, the size of the dial, the case materials, and pressure ranges that adhere to ASME B40.100. These are all steps in the gauge selection process.
Without considering these factors, disaster is a foregone conclusion. For example, if the gauge that is chosen can’t stand up to certain temperatures or changes in temperature that the pressurized vessel often reaches, then it’s not a suitable choice.
Here’s another example. If the case materials of the pressure gauge aren’t compatible with the process media within the vessel, then they could corrode and need replacing in a short span of time. This is a waste of both time and the money spent on the gauge.
In the previous section, we mentioned that the pressure ranges on a mechanical pressure gauge should adhere to the limits set by ASME B40.100. But we didn’t explain what that term means.
ASME B40.100 is the American national standard for pressure analog pressure gauges. It is important to choose a gauge that adheres to ASME B40.100 to ensure that it is rated to withstand a certain range of pressure.
Having this standard is like having the industry stamp of approval. Without it, the gauge may not be safe to use on a pressurized vessel.
Below are the seven steps you should follow to properly select a pressure gauge.
1. Pressure Gauge Accuracy
The first metric you should look for in a mechanical pressure gauge is its accuracy.
For a mechanical pressure gauge, accuracy is defined as a percentage of the full-scale range. Pressure gauges are available with various ranges of accuracy, from ±0.25, ±0.50, ±1, ±1.5, and 2 to 2.5 percent.
Requirements for pressure gauge accuracy differ depending on the industry. For testing applications, the full-scale accuracy should be 0.25-0.10 percent. For critical processes, it should be 0.5 percent, and for general industrial processes, it should be 1 percent.
2. Dial Size
Dial size should be your second consideration when choosing a pressure gauge.
Pressure gauge dial sizes range from less than 1 inch to 16 inches in diameter. The size you choose will depend on factors like readability requirements and space limitations in the environment where the gauge will be located, as well as the required gauge accuracy.
Accuracies of 0.25 percent or 0.50 percent typically have dial sizes of 4.5 inches or larger, since more dial graduations are required.
3. Case Material
The material of the case surrounding the dial is extremely important to take into account. It should be a material that can withstand the environmental conditions of its surroundings and not corrode, melt, or become clouded with condensation.
Environmental considerations include ambient temperature, air-borne
particulate, condensation, humidity, water, and chemicals - all of which
can affect the gauge’s performance.
If the gauge will be exposed to liquid or humidity, for example, one should choose a gauge that is weatherproof or hermetically sealed to protect it from condensation and corrosion.
4. Process Media Compatibility With Wetted Parts
In the fourth step, you should ensure that the wetted parts of the pressure gauge, the Bourdon tube, and the socket are compatible with the process media. If the process media is not compatible with the wetted parts of the gauge, corrosion will occur.
Corrosion of gauge wetted parts will eventually cause gauge failure and could lead to safety issues with the pressurized vessel and its contents.
5. Gauge Connection Size
Step five should be to look at the gauge connection type and size. There are a variety of connections available, including NPT, DIN, JIS, BSP, and SAE.
Some things to consider when picking the correct type and size are the process pressures, gauge size and weight, space limitations, leak integrity, and past experience.
6. Gauge Connection Location
Location should always be a priority when choosing a pressure gauge. Depending on the size and shape of the pressurized vessel where you’re installing a pressure gauge, you’ll need a specific type of mount. This may inform the type, size, and weight of the gauge you choose, as well.
Pressure gauge mounts are available in the following configurations:
- Stem mount lower connect
- Wall/surface mount lower connect
- Panel mount back connect
- U-clamp flush mount back connect for panel mounting
- Front flange flush mount back connect for panel mounting
7. Pressure Ranges
Finally, consider the pressure ranges of the gauge.
ASME B40.100 recommends that the normal operating pressure ranges for a gauge be confined to 25-75 percent of the full scale. If pulsation is present in the process, the maximum operating gauge pressure should not exceed 50 percent of the full-scale range.
As you can see, proper gauge selection is important to maintaining safety, as well as ensuring the functionality of pressurized applications.
That’s why at PFC, we have the best gauge cleaning and testing capabilities, with special attention to quality and the meeting required standards. This way, you never have to worry about your pressure gauges turning into a liability. Contact us today.