Pressure Gauges and Gauge Attachments

A N A M E R I C A N N A T I O N A L S T A N D A R D

ASME B40.100-2022

(Revision of ASME B40.100-2013)

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ASME B40.100-2022

(Revision of ASME B40.100-2013)

Pressure Gauges and Gauge Attachments

AN AMERICAN NATIONAL STANDARD

Two Park Avenue • New York, NY • 10016 USA

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Date of Issuance: December 15, 2022

This Standard will be revised when the Society approves the issuance of a new edition.

This codeor standardwas developedunder procedures accredited asmeeting the criteria for AmericanNational Standards. The standards committee that approved the code or standard was balanced to ensure that individuals from competent and concerned interests had an opportunity to participate. The proposed code or standard was made available for public review and comment, which provided an opportunity for additional public input from industry, academia, regulatory agencies, and the public-at-large.

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No part of this document may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher.

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Copyright © 2022 by

THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS

All rights reserved Printed in U.S.A.

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CONTENTS

Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi

Committee Roster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Correspondence With the B40 Committee . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

Section 1 Scope, References, Definitions

1-1 Scope

1-2 References

1-3 Definitions

Section 2 Gauges: Pressure-Indicating Dial Type — Elastic Element

2-1 Pressure Gauges, General

2-2 General Recommendations

2-3 Safety

2-4 Cleanliness

2-5 Pressure Gauge Testing

2-6 Ordering Parameters and Related Standards

Section 3 Diaphragm Seals

3-1 Diaphragm Seals, General

Section 4 Snubbers

4-1 Purpose

4-2 General

4-3 Safety

4-4 Testing

Section 5 Pressure Limiter Valves

5-1 General

5-2 Construction

5-3 Selection of Pressure Limiter Valves

5-4 Installation

5-5 Safety

5-6 Reuse of Pressure Limiter Valves

5-7 Testing

Mandatory Appendices

I Test Procedures Used to Measure New Gauge Performance

II Gauges Used on Regulators

III Supplemental Requirements — Naval Applications

IV Snubbers for Naval Applications

Figures

1-3-1 Elastic Elements iii

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1-3-2 Cases

1-3-3 Cases/Mounting

1-3-4 Example of a Retard Gauge

1-3-5 Example of a Suppressed Scale Gauge

2-1-1 Basic Pressure Terms

2-1-2 Typical Pressure Gauge Components (C-Type Bourdon Tube Illustrated)

2-2.3.1.5-1 Recommended Case and Mounting Dimensions

2-5.2.4.3-1 Hysteresis and Offset Error

3-1.2.2.1-1 Upper Housing, Continuous Duty

3-1.2.2.3-1 Upper Housing, Noncontinuous Duty

3-1.2.2.4-1 Upper Housing, Removable (With Capsule Assembly)

3-1.2.2.4-2 Upper Housing, Removable

3-1.2.2.5-1 Upper Housing, Nonremovable

3-1.2.2.6-1 Upper Housing, Flush Flanged

3-1.2.2.8-1 Upper Housing, Inserted Flange

3-1.2.2.9-1 Upper Housing, Flanged Seal

3-1.2.6-1 Lower Housing

3-1.2.7-1 Fastening Methods

3-1.2.10.2-1 Flanged Seal

3-1.2.10.3-1 Threaded Seal

3-1.2.10.3-2 Flanged Seal With Sleeve

3-1.2.10.3-3 Butt Weld Seal

3-1.2.10.3-4 Socket Weld Seal

3-1.2.10.3-5 Welded Seal Saddle

3-1.2.10.5-1 In-Line Seal (Crevice Free)

3-1.2.11.1-1 Flushing Ring

3-1.2.14-1 Gauge Isolator

3-1.8.2-1 Sealed Setting

3-1.8.2-2 Fill Setting

4-2.3.1-1 Fixed Orifice

4-2.3.2-1 Needle Valve

4-2.3.3-1 Porous Metal

4-2.3.4-1 Felt Plug — Fluid Filled

4-2.3.5-1 Piston

4-4.5.2-1 Test Setup

4-4.5.2-2 Typical Input Surge

4-4.5.3-1 Desirable Snubber Output

5-2.1-1 Piston Type

5-2.2-1 Diaphragm Type

5-2.3-1 Relief Valve Type

5-2.4-1 Bellows Type

III-3.3.1.1-1 Case Design

III-3.3.2.2-1 O-Ring Union Assembly

III-3.3.5-1 O-Ring Union Nut/Threaded End Detail

III-6.9-1 Load Test iv

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IV-3.1.1-1 O-Ring Union Nut/Threaded End Detail

IV-4.5.2.1-1 Suggested Dampening Test Setup

Tables

2-2.2-1 Positive Pressure Ranges

2-2.2-2 Compound Pressure Ranges

2-2.3.2.1-1 Definitions of Pressure Various Units

2-2.4-1 Accuracy Grades/Classes and Recommended Number of Test Points

2-4.2-1 Cleanliness Levels

2-6.2-1 Conversion Factors

I-2.3-1 Proof Pressure Testing Specifications

I-2.4.1-1 Fatigue Testing Cycle Requirements

I-2.7.1-1 Vibration Test Amplitudes

I-3-1 Types and Number of Gauges to Be Tested

I-3-2 Selection of Gauges for Testing

II-3.3-1 Ranges

III-3.2-1 Positive Pressure Range Designators

III-3.2-2 Compound Pressure Range Designators

III-3.2-3 Refrigerant Pressure Gauge Designators

III-3.2-4 Retard Pressure Gauge Designators

III-3.2-5 Caisson Pressure Range Designators

III-3.3.5-1 Pressure Connection Requirements and Applications

III-3.3.6-1 Gauge Connection Positions

III-5.2.1.1-1 Inspection Requirements

III-6.10-1 Stem-Mounted Gauge Vibration

III-6.14-1 Conditions for Pressure Integrity Testing

III-7.2.1-1 Part Identifying Number (PIN)

III-8.4-1 Oxygen Service Ranges

IV-4.2.1-1 Qualification and Conformance Inspections

IV-4.2.2.3-1 AQL for Nonconformities

IV-4.5.1-1 Steady-State Transmission Pressures

IV-4.5.3.3-1 Temperature Cycle

IV-4.5.4.1-1 Vibratory Displacement Criteria v

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FOREWORD

ASME Standards Committee B40 is comprised of a group of volunteers representing pressure gauge users, manu-facturers, governmental agencies, testing laboratories, and other standard-producing bodies. All are convinced that national standards such as this serve not only to provide product performance and configuration guidelines but also to inform and assist both those who specify and the users regarding the science of pressure gauge production, application, and use. The standards are vehicles by which the Committee as a body can transmit to users the benefits of their combined knowledge and experience as regards the proper and safe use of pressure gauges.

The use of this Standard is entirely voluntary and shall in noway preclude themanufacturer or use of products that do not conform.NeitherASMEnor theB40Committeeassumes responsibility for theeffectsof observanceornonobservance of recommendations made herein.

The 2005 edition, which was approved on September 19, 2005, was issued to include Nonmandatory Appendix C on

Supplemental Requirements to B40.100.

The 2013 revision,whichwas approved on June 18, 2013,was issued to clarifywording in the B40.1 body document as well as in Nonmandatory Appendix C, now designated as Mandatory Appendix III. Nonmandatory Appendix A was also rewritten to include new gauge performance criteria, and it was designated as Mandatory Appendix I. Nonmandatory Appendix B was designated as Mandatory Appendix II.

The 2022 revisionwas issued to consolidate the previously combined ASMEB40 standards: ASMEB40.1, ASMEB40.2, ASMEB40.5, and ASMEB40.6, nowdesignated as Sections 1 through 4, respectively. ASMEB40.7 has been removed from this Standard andwill be revised and incorporated into ASMEB40.300. All appendices are now grouped at the end of this Standard. Definitions and references have been consolidated and moved to the beginning of the standard along with a comprehensivescopeof theoverall standard. Followingapprovalby theASMEB40StandardsCommittee,ASMEB40.100- 2022 was approved by the American National Standards Institute on June 6, 2022.

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ASME B40 COMMITTEE

Specifications for Pressure and Vacuum Gauges

(The following is the roster of the Committee at the time of approval of this Standard.)

STANDARDS COMMITTEE OFFICERS

P. Reed, Chair

K. Gross, Vice Chair A. Guzman, Secretary

STANDARDS COMMITTEE PERSONNEL

J. Conti, Consultant K. Gross, WIKA Instrument LP R. E. Honer, Jr., Perma-Cal® Industries M. F. Lancaster, NOSHOK, Inc.

P. Reed, Ashcroft

J. W. Weiss, Weiss Instruments, Inc.

R. A. Weissner, Consultant Z. Kaiser, Emerson Automation Solutions M. Nylin, Alternate, WIKA Instrument LP J. M. Payne, Alternate, Ashcroft vii

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CORRESPONDENCE WITH THE B40 COMMITTEE

General. ASME codes and standards are developed and maintained by committees with the intent to represent the consensus of concerned interests. Users of ASME codes and standards may correspond with the committees to propose revisions or cases, report errata, or request interpretations. Correspondence for this Standard should be sent to the staff secretary noted on the committee’s web page, accessible at https://go.asme.org/B40committee.

Revisions and Errata. The committee processes revisions to this Standard on a periodic basis to incorporate changes that appear necessary or desirable as demonstrated by the experience gained from the application of the Standard.

Approved revisions will be published in the next edition of the Standard.

In addition, the committee may post errata on the committee web page. Errata become effective on the date posted.

Users can register on the committee web page to receive e-mail notifications of posted errata.

This Standard is always open for comment, and the committee welcomes proposals for revisions. Such proposals should be as specific as possible, citing the paragraph number(s), the proposedwording, and a detailed description of the reasons for the proposal, including any pertinent background information and supporting documentation.

Cases

(a) The most common applications for cases are

(1) to permit early implementation of a revision based on an urgent need

(2) to provide alternative requirements

(3) to allow users to gain experience with alternative or potential additional requirements prior to incorporation directly into the Standard

(4) to permit the use of a new material or process

(b) Users are cautioned that not all jurisdictions or owners automatically accept cases. Cases are not to be considered as approving, recommending, certifying, or endorsing any proprietary or specific design, or as limiting in any way the freedom of manufacturers, constructors, or owners to choose any method of design or any form of construction that conforms to the Standard.

(c) Aproposed case shall bewrittenas aquestion andreply in the same format asexisting cases. Theproposal shall also include the following information:

(1) a statement of need and background information

(2) the urgency of the case (e.g., the case concerns a project that is underway or imminent)

(3) the Standard and the paragraph, figure, or table number(s)

(4) the edition(s) of the Standard to which the proposed case applies

(d) A case is effective for use when the public review process has been completed and it is approved by the cognizant supervisory board. Approved cases are posted on the committee web page.

Interpretations. The committee does not issue interpretations for this Standard.

Committee Meetings. The B40 Standards Committee regularly holds meetings that are open to the public. Persons wishing to attend anymeeting should contact the secretary of the committee. Information on future committeemeetings can be found on the committee web page at https://go.asme.org/B40committee.

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Section 1 Scope, References, Definitions

1-1 SCOPE

This Standard covers analog, dial-type gauges, which, using elastic elements, mechanically sense pressure and indicate it by means of a pointer moving over a grad-uated scale.

It also includes the following attachments installed between the pressure source and gauge(s): diaphragm seals, snubbers, and pressure limiting valves.

This Standard does not include gauges of special config-uration designed for specific applications, edge reading, deadweight or piston gauges, other gauges not using an elastic element to sense pressure, diaphragm actuated pressure instruments that employ mechanical linkages to transmit the applied pressure, other attachments such as siphons, electric contacts, and gauge isolation valves or other separation devices designed to protect the pressure element assembly.

1-2 REFERENCES

Other standards and specifications relating to pressure gauges and their performance requirements follow. The edition bearing the latest date of issuance shall be used.

3-A 63-04, Sanitary Fittings Publisher: 3-A Sanitary Standards, Inc., 6888 Elm Street, Suite 2D, McLean, VA 22101 (www.3-a.org)

ANSI Z26.1, Safety Glazing Materials for Glazing Motor Vehicles and Motor Vehicle Equipment Operating on Land Highways — Safety Standard

Publisher: SAE International, 400 Commonwealth Drive, Warrendale, PA 15096 (www.sae.org)

ASME B1.13M, Metric Screw Threads: M Profile ASME B1.20.1, Pipe Threads, General Purpose (Inch) ASME B1.20.3, Dryseal Pipe Threads (Inch) ASME B16.5, Pipe Flanges and Flanged Fittings: NPS 1∕2 Through NPS 24, Metric/Inch Standard

ASME B16.9, Factory-MadeWrought Buttwelding Fittings ASME B16.11, Forged Fittings, Socket-Welding and Threaded

ASME B31.3, Process Piping ASME BPE, Bioprocessing Equipment ASME BPVC VIII-1, Rules for Construction of Pressure Vessels Division 1

ASME PTC 19.2, Pressure Measurement: Instruments and Apparatus Supplement

Publisher: The American Society of Mechanical Engineers (ASME), Two Park Avenue, New York, NY 10016-5990 (www.asme.org)

ASTM C1048, Standard Specification for Heat-Strength-ened and Fully Tempered Flat Glass

ASTM C1422, Standard Specification for Chemically Strengthened Flat Glass

ASTM G93, Standard Guide for Cleanliness Levels and Cleaning Methods for Materials and Equipment Used in Oxygen-Enriched Environments

Publisher: American Society for Testing and Materials (ASTM International), 100 Barr Harbor Drive, P.O.

Box C700, West Conshohocken, PA 19428-2959

CGA E-4, Standard for Gas Pressure Regulators CGA G-4.1, Cleaning of Equipment for Oxygen Service Publisher: Compressed Gas Association (CGA), 14501 George Carter Way, Suite 103, Chantilly, VA 20151 (www.cganet.com)

EN837-1, PressureGaugesPart 1: BourdonTubePressure Gauge — Dimensions, Metrology, Requirements, and Testing

Publisher: European Committee for Standardization (CEN), Avenue Marnix 17, B-1000, Brussels, Belgium (www.cen.eu)

IEC 60529, Degrees of Protection Provided by Enclosure (IP Code)

Publisher: International Electrotechnical Commission (IEC), 3, rue de Varembé, Case Postale 131, CH-1211, Genèva 20, Switzerland/Suisse (www.iec.ch)

ISA RP2.1, Manometer Tables Publisher: International Society of Automation (ISA), 67 T.W. Alexander Drive, P.O. Box 12277, Research Triangle Park, NC 27709 (www.isa.org)

ISO 15001, Anaesthetic and respiratory equipment — Compatibility with oxygen

Publisher: International Organization for Standardization (ISO), Central Secretariat, ChemindeBlandonnet8,Case Postale 401, 1214 Vernier, Geneva, Switzerland (www.iso.org)

ASME B40.100-2022

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FED-STD-H28, Screw-Thread Standards for Federal Services. Defense Industrial Supply Center, 700 Robbins Avenue, Philadelphia, PA 19111-5096

NBS Monograph No. 8, Mercury Barometers and Manometers, National Bureau of Standards, Depart-ment of Commerce

NBS Monograph No. 65, Reduction of Data for Piston Gauge PressureMeasurement, National Bureau of Stan-dards, Department of Commerce

Publisher: Federal specification available from: Superin-tendent of Documents, U.S. Government Publishing Office (GPO), 732 N. Capitol Street, NW, Washington, DC 20401 (www.gpo.gov)

NIST.gov, 2017, “Non-NIST International Organizations and Programs” from https://www.nist.gov/iaao/non-nist-international-organizations-and-programs

SAE J906, Automotive Safety Glazing Manual Publisher: SAE International, 400 Commonwealth Drive, Warrendale, PA 15096 (www.sae.org)

UL 404, Standard for Gauges, Indicating Pressure, for Compressed Gas Service. Underwriters Laboratories Inc. (UL), 333 Pfingsten Road, Northbrook, IL 60062- 2096 (www.ul.com)

Publisher:UnderwritersLaboratories Inc. (UL), 333Pfing-sten Road, Northbrook, IL 60062-2096 (www.ul.com)

1-3 DEFINITIONS

The following definitions are provided to ensure under-standing of select terms used in this Standard:

absolute pressure: see pressure, absolute.

absolute pressure gauge: see gauge, absolute pressure.

acceleration of gravity: the acceleration of a body in free fall under the influence of earth's gravity expressed as the rate of increase of velocity per unit of time and assigned the standard value of 980.665 centimeters per second per second — also called g.

accuracy: the conformity of a gauge indication to an accepted standardor true value. Accuracy is thedifference (error) between the true value and the gauge indication expressed as a percent of the gauge span. It is the combined effects of method, observer, apparatus, and en-vironment. Accuracy error includeshysteresis and repeat-ability errors, but not friction error (mechanical gauges only, see friction error). It is determined under specific conditions (see Table 2-2.4-1).

adjustment: the process of graduating the pressure scale or adjusting themechanism to cause the gauge to indicate within specified accuracy limits.

ambient pressure: see pressure, ambient.

baffle wall: in a pressure gauge, the wall between the Bourdon tube and dial. The baffle wall should have a minimal number of openings. These openings shall be less than 5% of the area of the baffle wall.

bar: a metric pressure unit equal to approximately 14.50 psi.

bellows: a thin-walled, convoluted elastic pressure-sensing element (see Figure 1-3-1).

Bourdon tube: a tubular elastic pressure-sensing element.

May have a “C,” helical, spiral, or other form (see Figure 1-3-1).

brazing: a metal joining process wherein coalescence is produced by use of nonferrous filler metal having a melting point above 425°C (800°F) but lower than that of the base metals joined.

calibration: refers to either calibration adjustment or cali-brationverification,butnot specifically tooneor theother.

calibration adjustment: the adjustments made on a gauge so it indicates within the specified accuracy limits.

calibrationverification: thecheckingof agaugebycompar-ison with a given standard to determine the indication error at specified points of the scale.

capsule: see diaphragm capsule.

case: the housing or container that supports, protects, and surrounds the internal pressure system and other compo-nents.

case, liquid filled: a case that is filled with a liquid such as glycerin or silicone fluid to at least 75%of its total internal volume. Liquid-filled cases may be either open front or solid front types. The purpose of this construction is to exclude ambient corrosives orprotect the internal compo-nents from damage caused by severe vibration or pulsa-tion.

case, open frontwith case pressure relief: a casewith apres-sure relief device or openings and no partition between the pressure element and the window [see Figure 1-3-2, illustration (a)]. An alternate construction is a plastic window especially designed to relieve internal case pres-sure.

case, open front without case pressure relief: a case having no partition between the pressure element and the window, and no pressure relief devices or openings [see Figure 1-3-2, illustration (a)].

case, pressure tight: a case capable of maintaining a pres-sure differential between the inside and the outside of the case.

case, sealed: a case that is sealed to exclude ambient corro-sives.

case, solid front with pressure relief back: a case having a partitionwithminimumopening(s) between the pressure element and the window, and a pressure-relieving back.

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Figure 1-3-1 Elastic Elements

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Figure 1-3-2 Cases

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The partition may be an integral part of the case [see Figure 1-3-2, illustration (b)].

coefficient of thermal expansion: volumetric change per unit of temperature change.

cold flow: a physical change in the shape of a part at room temperature due to applied forces.

compressibility: the property of a substance capable of being reduced in volume by application of pressure.

connection: see mounting.

correction: the quantity that is algebraically added to an indicated value to obtain the true value. The algebraic sign of the correction is opposite to the sign of the error.

dial: the gauge component that contains the scale artwork and nomenclature.

diaphragm: an elastic element in the formof a single flat or convoluted plate that deforms to provide displacement in response to a change in pressure differential across the plate (see Figure 1-3-1).

diaphragm capsule: an elastic element comprised of two convoluted diaphragm plates jointed to form a capsule or pressure container that expands and contracts in response to a change in pressure differential across the plates. Diaphragm capsule elements may have one or more capsules to provide appropriate displacement (see Figure 1-3-1).

diaphragm seal: a diaphragm seal is a mechanical separator using a diaphragm or bladder together with a fill fluid to transmit pressure from the medium to the pressure element assembly. Other terms used are chemical seal and gauge isolator. This device is intended to keep themediumout of the pressure element assembly.

The purpose of this device is to prevent damage from corrosion or clogging, to maintain sanitary requirements of the medium, or to reduce the process temperature to which the pressure element assembly is exposed.

elastic element: the elastic component of the pressure element assembly that moves in response to pressure changes. It may be a Bourdon tube, bellows, diaphragm, or other type of member (see Figure 1-3-1).

end piece: see tip.

environment: see environmental conditions.

environmental conditions: the conditions external to the gauge, including weather, temperature, humidity, salt spray, vibration, corrosive atmosphere, and other similar conditions that could affect the performance of the gauge.

error: the difference between the indicated value and the true value of the variable beingmeasured. A positive error denotes that the indicated value is greater than the true value (see also correction).

error, fatigue: the change of pressure indication that results from repeated applications of stress (pressure cycles). It is expressed as a percentage of span, number of cycles, and minimum and maximum values of pressure cycles.

explosive failure: elastic element failure caused by the release of explosive energy generated by a chemical reac-tion inside the element.

fatigue failure: elastic element failure resulting from repeated applications of stress.

fiber: any nonmetallic, flexible, threadlike contaminant with a length-to-diameter ratio of at least 10:1.

fill fluid:

(a) in a liquid-filled gauge, the case fill liquid used in a sealed pressure gauge

(b) in a diaphragm seal assembly, the liquid used to fill that portion of the pressure-sensing system between the diaphragm and the pressure-sensing element flow through seal: see in-line seal.

fluctuation: a nonperiodic surge of pressure.

freeze point: the temperature at which a liquid and a solid may be in equilibrium.

friction error: applicable to mechanical gauges only, it represents the contribution to the accuracy error of the gauge resulting from the mechanical friction of the internal components of the gauge.

full scale pressure: see pressure, full scale.

gasket: a means used to seal joints exposed to the process medium or fill fluid.

gauge, absolute pressure: a gauge that indicates absolute pressure.

gauge, compound: a gauge that indicates both positive and negative gauge pressure.

gauge, differential: a gauge having two pressure connec-tions and a pointer, which indicates the difference between two applied pressures.

gauge, duplex: a gauge having two pressure connections and two pointers, which indicate two applied pressures simultaneously.

head effect: a change of an instrument’s indication or output when the elevation of the instrument is above or below the seal.

Hg: mercury.

in. H2O: inches of water (ISA RP2.1); a unit of pressure measurement. 1 in. H2O (20°C) is equal to 1 in. of water at 20°C (68°F) and 980.665 cm/sec2 gravity (0.036063 psi).

hysteresis: a retardation of an effectwhen the forces acting upon a body are changed (as if from viscosity or internal friction).

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in. Hg: inches of mercury. 1 in. Hg is equal to 1 in. of mercury at 32°F (0°C) (0.4911 psi).

in-line seal: a diaphragm seal installed directly in the process flow line.

internal stop: see stop, internal.

kg/cm2: kilograms per square centimeter. 1 kg/cm2 is equal to kilogram force per square centimeter.

kPa: kilopascal. 1 kPa is equal to 1,000 Pa.

lens: see window.

life, fatigue: the number of pressure cycles beyond which leakage of the pressure element assembly may occur.

Accuracy may be degraded even if leakage has not occurred (see error, fatigue).

link: the component that connects the elastic element to the movement.

liquid column: a pressure-measuring device employing a column and reservoir of liquid (oil, water, mercury, or other liquid). Pressure is indicated by the height of the liquid column, measured at the meniscus.

liquid-filled case: a case that is filled with a liquid such as glycerin or silicone fluid to at least 75%of its total internal volume. Liquid-filled cases may be either open-front or solid-front types. The purpose of this construction is to exclude ambient corrosives or protect the internals from damage caused by severe vibration or pulsation.

liquid-filled gauge: a gauge inwhich the case is filledwith a liquid.

liquid-level gauge: a gaugewith a dial graduated in units of head heights, such as feet (meters) of water.

long-term stability (closed system): for diaphragm seals, the resistance to decomposition, physical disintegration, or other chemical change over a long period of time.

lower housing: the diaphragm seal component connected to the process line and wetted by the process fluid.

manometer: see ASME PTC 19.2.

medium: the process fluid (gas or liquid), also known as media.

NOTE: the terms “media” and “medium”areused in this Standard in place of the term “fluid” insofar as the process fluid may be a nonhomogeneous fluid (e.g., one that contains solid particulate) in certain applications and, therefore, isn’t strictly a fluid. There-fore, the terms “media” and “medium” indicate a gas, liquid, or non-homogeneous process fluid.

mid-housing (cleanout ring): the diaphragm seal compo-nent located between the upper and lower housing.

mirror, dial: a dial with a reflector band adjacent to the scale for the purpose of reducing reading-parallax errors.

mounting: the means by which the gauge or diaphragm seal is installed or supported.

mounting, flush: a gauge provided with supporting means on the case so that it may be set through a hole in a panel.

When installed, the dial is approximately flush with the panel (see Figure 1-3-3).

mounting, gauge: see mounting.

mounting, stemsocket:agauge supportedbyattachment at the stem (socket) pressure connection (see Figure 1-3-3).

mounting, surface (wall): a gauge whose case can be mounted to a wall or flat surface (see Figure 1-3-3).

NIST: National Institute of Standards and Technology nomenclature, dial: may include, but is not restricted to, the following:

(a) materials of wetted parts

(b) restricted application notices such as USE NO OIL

(c) presence of special features such as an internal stop normal operating conditions: the environmental condi-tions in which the stated accuracy applies.

NPT: American Standard taper pipe threads. Defined by

ASME B1.20.1.

operating pressure: see pressure, operating.

overpressure: the applicationof apressurebeyond the full-scale pressure.

overpressure failure: elastic element failure caused by the application of internal pressure (positive or negative) in excess of the rated pressure of the element.

Pa: see Pascal.

particle: any solid contaminant other than fiber.

partition: see baffle wall.

Pascal: unit of pressure measurement. 1 Pa is equal to 1 N/m2.

piston gauge: a device that indicates the presence of a predetermined pressure by means of weights loaded on an effective area such as a floating piston or a ball.

plug, pressure relief: a plug inserted in the gauge case wall that, in theeventof anelement leak, vents,minimizingcase pressure buildup.

pointer: the component that, in conjunction with the dial, indicates pressure.

pointer adjustment: ameans of causing a change in indica-tion. The change is approximately equal over the entire scale. Some examples of this type of adjustment are adjus-table pointers, rotatable dials, rotatable movements, and other similar items. This adjustment, if provided, is gener-ally accessible to the gauge user.

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Figure 1-3-3 Cases/Mounting

GENERAL NOTES:

(a) These diagrams are schematic and not intended to show design details.

(b) Surface and flush-mounted cases may also be stem mounted.

ASME B40.100-2022

Copyright ASME International Provided by Accuris under license with ASME Licensee=Puget Sound Naval Shipyard/5960068009, User=Monaco, Nicholas

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positive pressure: see pressure, positive.

pressure, absolute:apressureusing zeroabsolutepressure as datum (see Figure 2-1-1).

pressure, ambient: the pressure surrounding the gauge, usually atmospheric (barometric) pressure (see Figure 2-1-1).

pressure, burst: see pressure, rupture.

pressure, closing: in a pressure limiter valve, the system pressure at which the sealing mechanism closes, isolating the pressure-sensing instrument from rising system pres-sure.

pressure, differential: the difference between two pres-sures (see Figure 2-1-1).

pressure, full scale: the highest numerically defined graduation on the unretarded portion of the scale.

pressure, gauge: a positive pressure (greater than ambient) or negative pressure (less than ambient) using ambient pressure as datum (see Figure 2-1-1).

pressure, maximum inlet: the maximum pressure that can be applied to the inlet port of a pressure limiter valve continually or repeatedly without degradation in the performance of the valve.

pressure, maximumworking:maximum inlet pressure; see pressure, maximum inlet.

pressure, negative (vacuum): gauge pressure less than ambient pressure using ambient pressure as datum (see Figure 2-1-1).

pressure, operating: the pressure at which a gauge is normally operated.

pressure, over-range: for pressure limiter valves, the maximum pressure differential between inlet and outlet ports for a given closing pressure. This pressure maybe continuously or repeatedly appliedwithout degra-dation in performance. It may be expressed as a pressure orasapercentageof theclosingpressureabove the closing pressure.

pressure, positive: gauge pressure greater than ambient pressure (see Figure 2-1-1).

pressure, process: the pressure of the process medium at the pressure connection of the sockets.

pressure, proof: the maximum pressure a gauge can with-stand without plastic deformation of the pressure element. Proof pressure may be a semidestructive test and should not be conducted repeatedly on the same gauge. Itmaybeexpressedasapressureorasapercentage of full scale.

pressure, rated: full scale pressure unless otherwise speci-fied.

pressure, reopening: forpressure limitervalves, the system pressure at which a closed sealing mechanism reopens, generally expressed as a percentage of closing pressure.

pressure, rupture: for pressure gauges and diaphragm seals, the maximum pressure above which the pressure element assembly may no longer hold pressure.

pressure, set: for pressure limiter valves, closing pressure;

see pressure, closing.

pressure, system: the pressure of the process medium at the inlet pressure connection.

pressure, variable:pressure that increases or decreases, or both, at a rate greater than that allowed for steady pres-sure; may include high pressure, short duration impulses (pressure spikes).

pressure element: the assembly, including the elastic element, that converts a pressure change into motion.

Itmayalso includea stem, tip, restrictor, andother compo-nents (see Figure 2-1-2).

pressure gauge: a device that senses and indicates pres-sure using ambient pressure as datum.

pressure rating: the maximum operating pressure.

pressure relief plug: a plug inserted in the gauge case wall that, in theeventof anelement leak, vents,minimizingcase pressure buildup.

pressure-sensing instrument: in a system with a pressure-limiting valve, the instrument being protected by the pres-sure limiter valve.

process connection: a method for attaching or installing a diaphragm seal to a process line, tank, vessel, etc.

psi: pounds per square inch; a unit of pressure measure-ment. 1 psi = 1 pound force per square inch gauge pres-sure.

psia: 1 psia = 1 pound force per square inch absolute pres-sure; see psi.

psid: 1 psid = 1 pound force per square inch differential pressure; see psi.

pulsation: a periodic surge of the pressure source.

range: the high and low limits of the scale (including retarded portions) expressed in the sequences and units in which they occur. For example: 0/100 kPa, 200/500 psi, 30 in. Hg vac/30 psi.

range spring: in a pressure-limiting valve, the spring against which the pressure-sensing element works. Chan-ging the load on the range spring changes the closing pres-sure.

rate of pressure change:pressure change per time interval.

readability: the uncertainty inherent in the observer’s ability to determine the indicated pressure value.

Factors that may affect readability include distance between observer and scale, and illumination. For

ASME B40.100-2022

Copyright ASME International Provided by Accuris under license with ASME Licensee=Puget Sound Naval Shipyard/5960068009, User=Monaco, Nicholas

Not for Resale, 02/26/2026 16:32:16 UTCNo reproduction or networking permitted without license from Accuris mechanical gauges, additional factors include length of scale, graduation configuration and spacing, pointer design and width, parallax, stability of pointer, pointer and scale colors, and the liquid level line in liquid-filled gauges.

receiver gauge: a gauge designed to indicate the output signal from a pneumatic transmitter. It is calibrated in termsof the transmitteroutput.Thedialmaybegraduated in units of pressure, temperature, flow, or other measure-ments corresponding to the transmitter input.

refrigerant gauge: a gaugewith a dial graduated in units of pressure and equivalent saturation temperature for refrigerants other than ammonia.

reinforcing rings: in a diaphragm seal: rings that support clamping forces on nonmetallic lower housings.

repeatability: the maximum difference between any two ormoreconsecutive indications for the sameappliedpres-sure under the same operating conditions, approaching from the same direction, after lightly tapping the gauge. It is usually expressed as a percentage of span.

repeatability of closing pressure: for pressure-limiter valves, the maximum difference between several consec-utive closing pressures for the same applied rate of pres-sure change under the same operating conditions. It is usually expressed as a percentage of closing pressure.

resonance: the condition in which an object or system is subjected to an oscillating force with a frequency near its own natural frequency. For purposes of this Standard, the frequency with the highest amplitude, as discovered through a frequency scan, is considered the primary reso-nant frequency; however, additional (lesser) resonant frequencies may also exist and should be considered by the manufacturer.

response time: the time required for a change in system pressure to be indicated by the instrument.

restrictor: the device that restricts fluid flow between the pressure source and the pressure element. It is used to reduce the effect of pressure fluctuations or to control flow from a pressure element that has failed in service, or both. It may be integrally mounted or separate from the gauge.

retard gauge: a gauge having a scale that is compressed at one or both ends. One example of themany different types in common use is shown in Figure 1-3-4.

ring: the component that secures the window to the case.

Ring configurations will vary for design and aesthetic reasons.

ring, bayonet: see ring, cam.

ring, cam: a ring similar to a threaded ring except that the threads are replaced by a cam arrangement.

ring, friction:a ring retainedbymeansof an interferenceor friction fit between it and the case.

ring, hinged: a ring retained by a hinge-type device and a single retaining screw.

ring, slip: a ring similar to the friction ring except that it has a clearance fit with the case and is secured by screws.

ring, snap: a ring that snaps into a groove on the case.

ring, threaded: a ringhaving threads thatmatch threadson the case.

sanitary seal: a quick disconnect type of diaphragm seal, where theupperand lowerhousingsareheld togetherbya unique clamp, permitting ease of dismantling and cleaning.

scale: markings on the dial, consisting of graduations, related numerals, and units of measure.

sealed case: a case that is sealed to exclude ambient corro-sives.

service temperature range: the high and low temperatures between which the fill fluid will remain serviceable.

set point: for pressure limiter valves, closing pressure; see pressure, closing.

shock (impact) resistance: the maximum deceleration a gauge can withstand without damage or evidence of a change in accuracy of more than a specified value. It is expressed in g’s (acceleration of gravity), time duration (10% to 90% of the leading edge of the shock pulse), and number of impacts.

significant surface: see surface, wetted.

silver brazing: brazing using a nonferrous filler metal containing silver.

single gauge: a gauge having one pressure connection and one pointer, which indicates one applied pressure.

siphon:anattachmentdevice intended toprovide, ineffect, a heat exchanger where vapors can condense. Siphons are most often used when measuring steam pressure.

size, gauge: the nominal diameter of the gauge, which can be expressed as the approximate inside or outside of diameter of the case size depending on the type of gauge (see Figure 2-2.3.1.5-1).

Figure 1-3-4 Example of a Retard Gauge

GENERAL NOTE: Scale shown is retarded from 10 to 30.

ASME B40.100-2022

Copyright ASME International Provided by Accuris under license with ASME Licensee=Puget Sound Naval Shipyard/5960068009, User=Monaco, Nicholas

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snap ring: see ring, snap.

snubber: a surge-dampening device that is designed to minimize the effect of pressure spikes and surges on instruments while allowing changes in system pressure and low frequency pulsations to be transmitted to the instrument.

socket: the main supporting component of the pressure element assembly towhich the elastic element is attached.

It may include the pressure connection and mounting for the movement and case.

soft soldering: see soldering.

soldering (soft soldering): ametal-joining processwherein coalescence is produced by heating to a suitable tempera-ture and by using a nonferrous alloy fusible at tempera-tures below 425°C (800°F) and having a melting point below that of the base metals being joined.

solid front: in a pressure gauge, the partition between the pressure element and the window (see baffle wall).

span: the algebraic difference between the limits of the unretarded portion of the scale.

span adjustment: a means of causing a change in the angle of pointer rotation for a given change in pressure. This adjustment is not generally accessible to the gauge user.

span, compound gauge: see span.

span, suppressed scale: see span.

specific gravity: the ratio of a fluid’s density to the density of water at 4°C (39.2°F).

specific service gauge: gauge designed for a specific service, suchas indicating thepressureof explosive, corro-sive, or viscous media.

spike: a short duration, highamplitude sudden riseordrop in system pressure.

spontaneous explosive failure: see explosive failure.

spontaneous ignition temperature: the temperature at which ignition can occur resulting from the generation of heat that cannot be readily dissipated.

standard: see standard, calibration.

standard, calibration:apressure instrumentused todeter-mine the accuracy of a gauge (see ASME PTC 19.2).

standard, transfer: see ASME PTC 19.2.

standard, working: see ASME PTC 19.2.

steady pressure: pressure that increases or decreases, or both, at a rate less than or equal to that allowed for steady pressure.

stem (socket): see socket.

stop: the component that limits the motion of the pointer (see stop, internal, and stop pin).

stop, internal: a stop designed to restrain the pressure element motion by acting directly on it or on the move-ment mechanism.

stop pin: the component on the dial that limits the angular rotation of the pointer.

suppressed scale gauge: agaugehavinga scale that starts at some value appreciably above zero. One example of the many different types in common use is shown in Figure 1-3-5.

surface (wall) mounted: a gauge whose case can be mounted to a wall or flat surface (see Figure 1-3-3).

surface,wetted: any surface that directly contacts thepres-sure media.

surge: a sudden rise or drop in system pressure.

take-up: the portion of the scale between the position where the pointer is stopped and its true zero pressure position.

temperature, ambient: the temperature of the atmosphere surrounding the gauge.

temperature, process: the temperature of the medium at the pressure connection of the gauge or gauge accessory.

temperature, storage: the extremes of temperature (high and low) that the instrument or accessorywill be exposed to when not pressurized.

temperature error: the change of pressure indication that results when the gauge components are at a temperature different from the temperature at which they were cali-brated.

test gauge: a gauge used to check the accuracy of other gauges or pressure-actuated devices. The test gauge has an accuracy significantly better than the device being tested.

thermal decomposition point: the temperature at which changes in the chemical or physical characteristics of a material are initiated.

threaded ring: see ring, threaded.

threaded window: see window, threaded.

Figure 1-3-5 Example of a Suppressed Scale Gauge

70 80

GENERAL NOTE: Scale shown is suppressed from 0 to 50.

ASME B40.100-2022

Copyright ASME International Provided by Accuris under license with ASME Licensee=Puget Sound Naval Shipyard/5960068009, User=Monaco, Nicholas

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Torr: a unit of pressure measurement, typically used in situations where vacuum will be measured. 1 Torr is equal to 1.0 mm Hg absolute pressure.

traceability: documentation of the existence of a calibra-tion chain between an instrument andaprimary standard.

transfer standard: see standard, transfer.

vacuum: see pressure, negative.

upper housing: the diaphragm seal component that includes a connection for the pressure instrument.

upper housing, continuous duty: an upper housing that prevents damage to the diaphragm or leaking of the process fluid should the pressure instrument leak or be removed.

upper housing, continuous seal: an upper housing that prevents leaking of the process medium should the pres-sure instrument leak or be removed; however, the diaphragm may be damaged.

upper housing, non-continuous duty: anupper housing that does not prevent damage to the diaphragm or leaking of the process fluid should the pressure instrument leak or be removed.

upper housing, non-removable: an upper housing that if removed from the bottom housing with the instrument installed will result in the loss of fill fluid.

upper housing, removable: an upper housing that may be removed from the bottom housing with the instrument installed without loss of fill fluid.

vacuumgauge: a gauge that indicates negative gauge pres-sure (vacuum).

variable pressure: see pressure, variable.

vapor pressure: the pressure of the vapor in equilibrium with the liquid.

vibration resistance: themaximumsinusoidal acceleration a gauge can withstand without damage or evidence of a change in accuracy of more than a specified value. It is expressed in g’s, or amplitude over a frequency range and time period.

viscosity: the resistance that a gaseous or liquid system offers to flow when it is subjected to a shear stress.

Also, known as flow resistance.

volumetric displacement: the volume of fill fluid displaced by the movement of a diaphragm.

volumetric spring rate: the flexibility of a diaphragm.

welding: a metal-joining process wherein coalescence is produced by heating to suitable temperatures to melt the basemetals together, with orwithout the addition of filler metal. If filler metal is used, it shall have a melting point and composition approximately the same as the base metal.

wetted parts: components of the device that directly contact the process medium.

wetted surface: the portions of the wetted…