What's the difference between ASME B40.100 and EN 837-1?

In another Ashcroft® Understanding the Basics article titled, What is a Pressure Gauge? you learn that manufacturers of pressure gauges must follow certain global standards to ensure all of these instruments function the same way.  The standards that we are referring to are ASME B40.100 and EN 837-1. 

As a global leader in pressure instrumentation, Ashcroft is often asked which of these manufacturing standards we follow for our pressure gauges. The answer is both, and the reason is simple. 

This article will provide you with a brief overview of ASME B40.100 and EN 837-1 standards, what they cover, their similarities and their differences.  Whether you are new to the world of pressure gauges, or you are looking for a quick refresher on the subject, you will gain a deeper understanding of these global standards after reading this piece.   

You will also find additional resources that may interest you when you are ready to go beyond the basics of pressure gauges. 

What do ASME B40.100 and EN 837-1 standards cover?

ASME B40.100 and EN 837-1 are both standards followed by pressure gauge manufacturers so operators have a dependable visual of what is going on inside the process. Each of these standards has important similarities and differences:  

1. The American Society of Mechanical Engineers (ASME) developed the ASME B40.1 standard. It is used for pressure gauges and gauge attachments.  

The ASME B40.1 standard covers:

• Mechanical pressure indicating instruments. Products like the Ashcroft® 1209 dial gauge with elastic sensing element.
• Diaphragm seals. Isolates the instrument's sensing element to protect it from getting damaged.
• Snubbers. Used to protect pressure instruments from sudden pressure increases or fluctuations.
• Pressure limiting valves. Designed to protect sensitive instrumentation by limiting pressure up to a specific set value.
• Digital gauges.  Pressure-indicating instruments with digital display.

2. The European Committee for Standardization developed the EN 837-1. This is geared to various pressure gauges and sensing elements:

• Bourdon tube indicating pressure gauges. 
• Vacuum gauges.
• Combined vacuum and pressure gauges (compound gauges).

This standard includes performance approval test methods and production testing methods.

What are the differences between ASME B40.100 and EN-837-1?

The three primary differences between the ASME B40.100 and the EN-837-1 are their preferred units of measure, accuracy and dial sizes. 

1.    Preferred units of measure.

• ASME B40.1 preferred units of pressure are psi, size in inches and process connections with NPT threads.
• EN837-1 preferred units of pressure are bar, size in millimeters and process connections with metric threads.

2.    Accuracy.

ASME B40.100 uses accuracy grades from 4A to D (see chart below).  

• For Grades 1A through 4A, the accuracy is defined as a ± % of span over the entire span of the gauge.
• For Grades A through D, the accuracy is defined as ± % of span in 3 different sections of the span: the lower ¼  scale, the middle ½ of the scale and the upper ¼ of the scale.  

Figure 1. ASME B40.100 accuracy chart.

EN837-1 accuracy classes are defined as a ± % of span over the entire span of the gauge (see chart below).

Figure 2: EN837-1 accuracy chart. 

3.    Gauge size.

Gauge size will determine your operator's ability to read the gauge at a specified distance. The larger the dial size the easier it is to read.

• AMSE B40.100 defines gauge size by the diameter of the dial size in inches.
• EN837-1 defines gauge size by the diameter of the case.

The image below compares the 4½-in. Ashcroft®1209 process gauge and the 100 mm Ashcroft® T6500 process gauge. As you can see, the 4½-in. dial on the 1209 gauge is much larger with 65% more surface area than the 100 mm T6500 gauge with a 3½-in. dial.

Figure 3: Comparison of a 4½-in. 1209 and 100 mm T6500.

The next image shows the 100 mm Ashcroft® T6500 process gauge and a 3½-in. Ashcroft®1009 gauge, both of which are the same size. 

Figure 4.  Comparison of 3½-in. 1009 and 100 mm T6500.

The final image compares a 6-in. Ashcroft® 1379 process gauge and a 160 mm T6500 process gauge, which are also the same size.

Figure 5.  Comparison of 6-in. 1379 and 160 mm T6500.

Ready to go beyond the basics?

Now that you have a better understanding of ASME B40.100 and EN 837-1 and why these standards are important for your products and process, you may want to dig a little deeper. To get you started, here are a few additional articles you may find interesting:

• What is a Pressure Gauge?
• 6 Reasons Pressure Gauges Fail
• Best Pressure Gauges with Overpressure protection
• Choosing the Right Pressure Gauge Dial Size

Or, to speak with someone directly, feel free to contact one of our product experts with any questions you have.

In the meantime, download our e-book to learn how to select the right pressure gauge for your process.