What's the Difference Between ASME B40.100 and EN 837-1?

ASME B40.100 and EN 837-1 are two widely recognized standards for mechanical pressure gauges. Both establish requirements that help manufacturers produce instruments with consistent performance, but they differ in their scope, preferred measurement units, accuracy classifications, and gauge sizing conventions.

ASME B40.100 is an American standard covering pressure gauges and related accessories, while EN 837-1 is a European standard specifically addressing Bourdon tube pressure gauges. Understanding these differences can help engineers and operators select pressure gauges that meet their application requirements.

Ashcroft® manufactures pressure gauges for applications around the world, including instruments designed to meet applicable ASME and EN requirements.

In this article, you'll learn:

• What ASME B40.100 and EN 837-1 cover.
• How the standards differ in measurement units and accuracy classifications.
• Why gauge sizing conventions matter when selecting a pressure gauge.
• How to compare pressure gauges manufactured to different standards.

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

ASME B40.100 and EN 837-1 establish requirements for pressure-indicating instruments, but they cover different types of gauges and related components.

What is ASME B40.100?

ASME B40.100 is a standard developed by the American Society of Mechanical Engineers (ASME) that addresses pressure gauges and gauge attachments.

The standard covers several types of pressure measurement instruments and accessories, including:

• Mechanical pressure gauges: Instruments with elastic sensing elements, such as the Ashcroft® 1209 pressure gauge.
• Diaphragm seals: Devices that isolate the instrument's sensing element from process media to help prevent damage.
• Snubbers: Accessories used to reduce the effects of sudden pressure changes and pulsation.
• Pressure limiting valves: Devices designed to limit the pressure reaching an instrument to a specified value.
• Digital pressure gauges: Instruments that provide pressure readings on an electronic display.

These requirements help manufacturers evaluate instrument design, performance and suitability for different operating conditions.

What is EN 837-1?

EN 837-1 is a European standard developed by the European Committee for Standardization (CEN). It establishes requirements for Bourdon tube pressure gauges.

The standard applies to Bourdon tube instruments used to measure:

• Positive gauge pressure: Pressure above atmospheric pressure.
• Vacuum: Pressure below atmospheric pressure.
• Compound pressure: Both positive gauge pressure and vacuum.

EN 837-1 also includes requirements for performance approval testing and production testing.

Although both standards address mechanical pressure measurement, EN 837-1 focuses specifically on Bourdon tube gauges, while ASME B40.100 covers a broader range of instruments and accessories.

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

The three primary differences between ASME B40.100 and EN 837-1 are their preferred measurement units, accuracy classifications and gauge sizing conventions.

1. How do the preferred measurement units differ?

ASME B40.100 commonly uses US customary units, while EN 837-1 generally uses metric units.

For example:

• ASME B40.100: Pressure in pounds per square inch (psi), gauge dial sizes in inches, and commonly NPT process connections.
• EN 837-1: Pressure in bar, gauge sizes in millimeters, and commonly metric process connections.

When selecting a pressure gauge, make sure the pressure units, connection type, and instrument dimensions are compatible with your system.

2. How do pressure gauge accuracy classifications differ?

Both standards express pressure gauge accuracy as a percentage of the instrument's span. However, ASME B40.100 includes accuracy grades with different tolerances across sections of the scale, while EN 837-1 uses accuracy classes that apply across the entire scale.

ASME B40.100 uses accuracy grades ranging from 4A through D.

• Grades 1A through 4A: Accuracy is defined as a ± percentage of span across the entire gauge scale.
• Grades A through D: Accuracy is defined across three sections of the gauge scale: the lower quarter, middle half, and upper quarter.

For Grades A through C, the allowable error is lower in the middle half of the scale than at either end.

Figure 1. ASME B40.100 accuracy grades and allowable error across the gauge scale

EN 837-1 defines accuracy classes as a ± percentage of span across the entire gauge scale.

For example, a Class 1.0 gauge has an allowable indication error of ±1% of its span.

Figure 2. EN 837-1 accuracy classes and allowable error across the gauge scale

Both standards provide accuracy classifications to help users select an instrument that meets their measurement requirements.

When comparing gauges, consider not only the stated accuracy grade or class but also where the instrument will typically operate within its pressure range.

3. How do pressure gauge sizing conventions differ?

ASME B40.100 and EN 837-1 use different conventions for identifying pressure gauge size. This can affect the actual diameter of the dial and how easily an operator can read the instrument.

• ASME B40.100: Gauge size is generally identified by the nominal diameter of the dial, expressed in inches.
• EN 837-1: Gauge size is identified by the nominal case size, expressed in millimeters.

A larger dial typically makes pressure readings easier to see from a distance. However, gauges with similar overall dimensions may have different dial sizes depending on their design.

The following Ashcroft pressure gauge examples illustrate these differences.

How do ASME and EN pressure gauge sizes compare?

Comparing pressure gauges manufactured using different sizing conventions helps demonstrate why nominal gauge size and actual dial diameter are not always the same.

4½-inch 1209 vs. 100 mm T6500 pressure gauge

The 4½-inch Ashcroft® 1209 process gauge has a larger dial than the 100 mm Ashcroft® T6500 process gauge.

The original comparison shows that the 1209's 4½-inch dial has approximately 65% more surface area than the 3½-inch dial of the T6500.

This additional dial area can improve readability, particularly when the instrument must be viewed from a distance.

Figure 3. Comparison of the 4½-inch Ashcroft 1209 and 100 mm Ashcroft® T6500 pressure gauges

3½-inch 1009 vs. 100 mm T6500 pressure gauge

The 3½-inch Ashcroft® 1009 pressure gauge and 100 mm Ashcroft® T6500 pressure gauge have approximately the same overall dimensions.

This example demonstrates how instruments identified using different sizing conventions can be similar in physical size.

Figure 4. Comparison of the 3½-inch Ashcroft 1009 and 100 mm Ashcroft® T6500 pressure gauges

6-inch 1379 vs. 160 mm T6500 pressure gauge

The 6-inch Ashcroft® 1379 process gauge and 160 mm Ashcroft® T6500 process gauge are also similar in overall size.

As with the previous example, the nominal gauge sizes are expressed differently, but the physical dimensions are comparable.

Figure 5. Comparison of the 6-inch Ashcroft 1379 and 160 mm Ashcroft® T6500 pressure gauges

These examples demonstrate why it's important to review actual dial and case dimensions when selecting or replacing a pressure gauge, particularly when working with instruments manufactured to different standards.

Why do ASME B40.100 and EN 837-1 matter when selecting a pressure gauge?

ASME B40.100 and EN 837-1 provide established requirements that help engineers and operators evaluate pressure gauge performance and design.

Although both standards address pressure measurement, understanding their differences can help you:

• Confirm measurement requirements: Select the appropriate pressure units and accuracy classification.
• Check installation compatibility: Verify process connections and instrument dimensions.
• Evaluate readability: Choose a dial size appropriate for the operator's viewing distance.
• Meet applicable requirements: Identify which standard is specified for your equipment, facility or application.

Neither standard is automatically the better choice for every application. The appropriate standard depends on your system requirements, operating conditions and applicable specifications.

What should you remember about ASME B40.100 and EN 837-1?

ASME B40.100 and EN 837-1 both support consistent pressure gauge performance, but they differ in scope, measurement conventions, accuracy classifications and sizing.

The most important consideration is choosing a pressure gauge that meets your application's requirements, regardless of which standard is referenced.

Understanding these differences can help you compare instruments more effectively and avoid potential issues with readability, installation and measurement performance.

Ready to learn more?

Understanding pressure gauge standards is one part of selecting the right instrument for your process. Check out the additional resources below for additional information. Contact us anytime and a product expert can answer any specific questions you may have. In the meantime, download our guide to learn how to avoid common mistakes when choosing a pressure gauge.