ASME B40.100 vs. EN 837: Understanding Pressure Gauge Standards
- Merit Instruments
- 6 days ago
- 10 min read
Selecting a pressure gauge involves more than choosing a pressure range, dial size, or connection. For many industrial applications, the gauge must also be appropriate for the applicable standards, specifications, operating environment, and customer requirements. Two standards frequently encountered in international pressure-gauge applications are ASME B40.100 and the EN 837 series.
Although both address pressure gauges, they are not simply interchangeable versions of the same standard. Their scope, terminology, requirements, and application should be considered when specifying instrumentation.
This guide provides an overview of the two standards and explains some of the factors that should be considered when selecting a pressure gauge for North American, European, or international applications.
Technical Update — August, 2026. This article has been reviewed and revised to reflect the current ASME B40.100 standard and the applicable EN 837 series. References to the former ASME B40.7 digital pressure-gauge standard have been updated because B40.7 was incorporated into ASME B40.100.
What Is ASME B40.100?
ASME B40.100, Pressure Gauges and Gauge Attachments, is an American National Standard developed by the American Society of Mechanical Engineers (ASME). The current edition is ASME B40.100-2022. ASME identifies this edition as a consolidation and revision of five previously separate standards:
ASME B40.1 — Pressure-Indicating Dial-Type Elastic-Element Gauges
ASME B40.2 — Diaphragm Seals
ASME B40.5 — Snubbers
ASME B40.6 — Pressure-Limiter Valves
ASME B40.7 — Pressure Digital Indicating Gauges
The consolidation means that information historically associated with ASME B40.7 for digital pressure gauges is now contained within B40.100. ASME B40.100 addresses areas including terminology, dimensions, construction, safety, performance, testing, installation considerations, and general recommendations for pressure gauges and associated gauge attachments.
Why this matters
Older specifications, catalogs, drawings, and procurement documents may still reference ASME B40.7 or other former B40 standards. That does not necessarily mean the specification is incorrect. It may simply reflect the standard under which the original product or specification was developed. For current product specifications, however, ASME B40.100-2022 is the appropriate current consolidated reference where applicable.
What Is the EN 837 Series?
EN 837 is a European series of standards covering pressure gauges.
The series addresses different types of pressure gauges rather than treating all pressure gauges under one document. For example, EN 837-1 addresses Bourdon-tube pressure gauges, vacuum gauges, and compound gauges. BSI currently identifies BS EN 837-1:1998 as current and under review. Its scope includes circular gauges from 40 to 250 mm nominal size and pressure ranges up to 1,600 bar, subject to the standard's stated applicability.
The EN 837 series should therefore be considered according to the particular gauge construction and application rather than simply referring to "EN 837" as though it were a single universal specification.
An important distinction
EN 837 is a series. The specific part should be identified when determining whether a particular gauge is covered. This is especially important when specifications involve different sensing technologies or gauge constructions.
ASME B40.100 and EN 837 Are Not Simply "Competing Standards"
It is tempting to ask:
"Which is better—ASME B40.100 or EN 837?"
That is generally the wrong question. A more useful question is:
"Which standard or specification is appropriate for this particular instrument, application, market, and customer requirement?"
ASME B40.100 is commonly encountered in North American applications, while EN 837 is commonly encountered in European and other markets where European standards are specified. However, the actual requirement for a project may be determined by:
Customer specifications
Equipment specifications
Project documentation
Industry requirements
Applicable regulations
Contract requirements
Installation location
Original equipment manufacturer requirements
Purchasing standards
Existing plant standards
A pressure gauge should therefore be evaluated against the actual project requirement, rather than assuming that a particular geographic market automatically determines the applicable standard.
Understanding Gauge Accuracy
Accuracy is one of the most important characteristics addressed by pressure-gauge standards, but accuracy should always be evaluated in the context of the applicable standard and gauge type.
When comparing gauges, it is important to understand whether the accuracy specification refers to:
Percent of span
Percent of reading
A defined accuracy grade
A manufacturer's stated accuracy under specified conditions
These specifications should not be assumed to be directly interchangeable. For example, an accuracy specification expressed as a percentage of span behaves differently from one expressed as a percentage of reading.
Example
For a 0–1,000 psi gauge:
±1.0% of span = ±10 psi across the applicable measurement range.
An instrument specified as:
±1.0% of reading
would have an error of approximately: ±5 psi at 500 psi assuming the specification applies under the stated conditions.
This distinction becomes increasingly important when selecting instruments for applications requiring higher measurement accuracy.
Pressure Range Selection
Pressure range is another area where the standard alone does not determine the correct instrument.
The selected range should consider:
Normal operating pressure
Minimum operating pressure
Maximum expected pressure
Pressure fluctuations
Pulsation
Pressure spikes
Overpressure conditions
Required resolution
Required accuracy
A gauge should not simply be selected because its maximum scale value exceeds the normal operating pressure. The complete pressure profile should be considered.
Example
A system normally operating at 100 psi may occasionally experience substantially higher transient pressures. In that situation, a gauge with a 0–100 psi range may not be appropriate even though 100 psi is the normal operating pressure.
The instrument's published operating-pressure and overpressure capabilities should be reviewed along with the expected process conditions.
Operating Pressure vs. Overpressure
These terms should not be confused.
Operating pressure
The pressure that the instrument is expected to measure during normal operation.
Overpressure
Pressure exceeding the instrument's normal operating conditions. An instrument may tolerate a temporary pressure above its normal operating range without damage, but that does not necessarily mean it should be operated continuously at that pressure.
The allowable operating pressure and overpressure capability should always be taken from the applicable product specification.
There is no single universal operating-pressure percentage that should be applied to every pressure gauge. Gauge construction, pressure fluctuations, gauge movement, sensing element, accuracy requirements, and manufacturer recommendations all influence appropriate range selection.
Bourdon Tube, Capsule and Other Sensing Elements
Pressure gauges use different sensing technologies depending on the pressure range and application.
Bourdon Tube
Bourdon-tube gauges are widely used for industrial pressure, vacuum and compound pressure measurement. The sensing element may be manufactured in different shapes and materials depending on the instrument design and pressure range.
Capsule
Capsule elements are commonly used for relatively low-pressure measurement, particularly for gases and other applications where high sensitivity at low pressure is required.
Diaphragm
Diaphragm elements can be useful where low-pressure measurement, chemical compatibility, contamination resistance, or isolation from the process is important.
The sensing element should therefore be selected according to the actual pressure range, process media, environmental conditions, and required performance.
Materials and Process Compatibility
The applicable standard does not eliminate the need for an application-specific material review.The pressure gauge must be compatible with the process medium and operating environment.
Important considerations include:
Process media
Concentration
Process temperature
Ambient temperature
Pressure
Corrosive characteristics
Contamination
Viscosity
Suspended solids
Potential crystallization or plugging
Stainless-steel construction is commonly selected for many industrial applications, but stainless steel should not automatically be assumed to be compatible with every process.
Where process compatibility is uncertain, the wetted materials should be reviewed against the actual process conditions.
When Is a Diaphragm Seal Appropriate?
A diaphragm seal can be used to isolate the pressure gauge from the process.
This can be useful when the process contains:
Corrosive materials
Viscous fluids
Slurries
Suspended solids
Materials that may crystallize
Materials that could damage or contaminate the sensing element
A diaphragm seal may also be appropriate where the process temperature or hygienic requirements make direct connection of the pressure gauge undesirable. The gauge and diaphragm seal should be considered as a complete measurement assembly.
The diaphragm material, fill fluid, process temperature, pressure, capillary arrangement, and mounting configuration can all affect the resulting measurement performance.
Pressure Pulsation and Vibration
Pressure gauges installed on pumps, compressors, hydraulic equipment, reciprocating machinery, or other dynamic systems may experience pressure pulsation and mechanical vibration. These conditions can affect gauge performance and service life.
Depending on the application, protective measures may include:
Pressure snubbers
Restrictors
Dampening
Liquid-filled gauges
Vibration-resistant gauge movements
Remote mounting
Appropriate process connections
Diaphragm seals
The appropriate solution depends on the characteristics of the pressure and mechanical environment. A liquid-filled gauge is not automatically the correct solution for every vibrating application, just as a dry gauge is not automatically unsuitable.The instrument should be selected based on the actual application.
Temperature Considerations
Pressure-gauge performance can be affected by both process and ambient temperature.
When selecting a gauge, consider:
Process temperature
Ambient temperature
Temperature variation
Heat transfer through the process connection
Gauge temperature limits
Effects of temperature on accuracy
Whether a siphon, diaphragm seal, capillary, or other protective arrangement is required
The maximum temperature of the process should not be confused with the maximum temperature that can safely be applied directly to the pressure gauge. Where elevated process temperatures are present, the complete installation should be evaluated.
Connections and Installation
Pressure gauges are available with numerous process connections and mounting configurations.
Common considerations include:
Connection size
Thread type
Connection location
Bottom or back connection
NPT
BSP
BSPT
Other application-specific connections
Direct or remote mounting
Thread standards should be clearly identified in the specification. For international applications, NPT and BSP-family threads should never be assumed to be interchangeable simply because they have similar nominal sizes. The connection type, thread form, pitch and sealing method should be confirmed before installation.
Safety and Pressure Relief
Pressure gauges installed in applications where failure could expose personnel or equipment to process pressure require appropriate consideration of gauge construction and installation.
Depending on the application, considerations may include:
Solid-front construction
Blowout protection
Pressure relief
Appropriate mounting
Isolation valves
Snubbers
Diaphragm seals
Remote mounting
Suitable gauge range
Applicable installation requirements
The appropriate safety configuration depends on the application and applicable specification. A pressure gauge should never be selected solely on the basis of its dial range.
What About Digital Pressure Gauges?
Digital pressure gauges require some additional considerations.
These may include:
Display resolution
Accuracy specification
Sensor technology
Temperature effects
Battery life
Power requirements
Data logging
Electrical outputs
Environmental protection
Hazardous-location certification, where applicable
Older specifications may reference ASME B40.7, which was the former standalone ASME standard for digital pressure indicating gauges. That standard has been incorporated into the current ASME B40.100 consolidated standard.
When reviewing an older specification, it is therefore important to determine whether the reference is historical or whether the customer requires compliance with a specific edition.
International Projects: Which Standard Should Be Specified?
International projects can become more complicated when the customer, equipment manufacturer, project location, and instrumentation supplier operate under different standards.
For example:
A North American equipment manufacturer may specify ASME B40.100 while the equipment is being installed in Europe.
Alternatively, a European equipment manufacturer may specify EN 837 for equipment being supplied to North America.
In these situations, the correct approach is not to assume that the local market automatically overrides the customer's specification.
Instead, determine:
Which standard is specified?
Which edition is referenced?
What type of gauge is being specified?
What requirements are actually applicable to the instrument?
Are there additional project or regulatory requirements?
Does the proposed instrument have documented evidence supporting the required specification?
This is particularly important for OEM and international projects.
Can an ASME-Compliant Gauge Be Used in an EN 837 Application?
Not necessarily. A gauge designed or documented to one standard should not automatically be represented as compliant with another standard simply because its construction appears similar. The same principle applies in reverse.
Where a customer specifically requires compliance with a particular standard, the supplier should verify the applicable product documentation and determine whether the proposed configuration actually satisfies that requirement. If compliance with a specific standard cannot be demonstrated, it is better to identify that limitation before quotation or purchase than to assume equivalence.
Standards vs. Regulations
An important distinction should also be made between standards and regulations.
ASME and EN standards provide technical requirements, specifications, terminology, test methods, or recommendations within their respective scopes.
Regulatory requirements may come from governments or regulatory authorities and can vary according to:
Country
Jurisdiction
Industry
Equipment type
Installation
Intended use
Compliance with a pressure-gauge standard does not automatically mean that the complete installation complies with every applicable regulatory requirement. Conversely, a regulatory requirement may reference a particular standard or require evidence of conformity to a specified technical standard. The complete application should therefore be evaluated.
What Should Be Included in a Pressure-Gauge Specification?
For a new project, the following information can help ensure that the instrument is correctly specified:
Instrument
Gauge type
Analog or digital
Dial size
Accuracy
Scale units
Pressure range
Vacuum or compound range, if applicable
Process
Process medium
Normal pressure
Maximum pressure
Pressure fluctuations
Process temperature
Potential contamination or plugging
Construction
Case material
Wetted materials
Lens material
Connection material
Connection size
Connection location
Environment
Ambient temperature
Vibration
Outdoor exposure
Water or washdown
Corrosive atmosphere
Hazardous location, where applicable
Protection
Liquid filling
Snubber
Diaphragm seal
Siphon
Isolation valve
Other protective accessories
Standards and Documentation
Required standard
Required edition
Calibration requirements
Certificates
Material documentation
Inspection requirements
Customer-specific specifications
Providing this information allows the instrument to be evaluated against the actual application, rather than simply matching a catalog number to a requested description.
Choosing Between ASME B40.100 and EN 837
There is no universal rule that says one standard should be selected over the other.
The appropriate standard will depend on the:
Product
Application
Customer
Project
Installation location
Contract requirements
Equipment specification
Applicable regulations
For international projects, it is particularly important to identify the required standard before the instrument is quoted or manufactured. If a customer specification references an older edition or former standard, the supplier should clarify whether the customer requires the historical specification or the current applicable standard.
When the Customer's Original Specification May Need Review
In some applications, the requested gauge specification may not fully address the actual operating environment.
For example, a specification may identify:
0–300 psi pressure gauge, stainless steel, 4-inch dial
but omit:
Pressure pulsation
Maximum pressure
Process temperature
Corrosive media
Vibration
Required accuracy
Hazardous-location requirements
Required documentation
In such circumstances, simply supplying the requested gauge may not provide the best technical solution. A technical review can identify missing application requirements and determine whether additional protection, different materials, a different sensing element, or a different instrument configuration is appropriate.
The objective should be to select an instrument that is suitable for the application—not simply to reproduce a part number from a specification.
Merit Instruments: Application-Focused Pressure Measurement
Merit Instruments approaches pressure instrumentation from an application perspective. When a project involves unusual process conditions, international specifications, difficult environments, or conflicting requirements, Merit can review the application and help determine an appropriate instrumentation solution.
This may include:
Pressure gauge selection
Digital pressure gauges
Data-logging pressure gauges
Pressure transmitters
Diaphragm seals
Snubbers
Siphons
Isolation valves
Custom configurations
OEM instrumentation
The goal is straightforward: Specify the instrument according to what the application actually requires.
Technical Reference Note
Standards change and individual products may be subject to additional requirements. Always verify the applicable standard, edition, product specification, and regulatory requirements for the specific application.
ASME currently identifies B40.100-2022 as the applicable consolidated pressure-gauge standard. The EN 837 series should be evaluated according to the specific part applicable to the gauge type.
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