Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Pressure Measurement
category: Instrumentation & Controls / Field Instrumentation
toc_depth: 3
description: >
− When to use: selecting, specifying, and installing pressure measurement instruments on construction and process-facility projects -- local-indicating gauges, electronic transmitters (gauge, absolute, differential, multivariable), pressure switches, diaphragm seals, snubbers, and associated isolation and test valves -- across industrial process, water and wastewater, HVAC/mechanical, fire protection, and commercial work, from high vacuum through 10,000 psi gauge.
+ When to use: selecting, specifying, and installing pressure measurement instruments on construction and process-facility projects — local-indicating gauges, electronic transmitters (gauge, absolute, differential, multivariable), pressure switches, diaphragm seals, snubbers, and associated isolation and test valves — across industrial process, water and wastewater, HVAC/mechanical, fire protection, and commercial work, from high vacuum through 10,000 psi gauge.
Not intended for: differential-pressure flow elements that infer flow (use sync/flow-measurement); hydrostatic/DP level transmitters that infer tank level (use sync/level-sensors); RTDs, thermocouples, and temperature transmitters (use sync/temperature-instrumentation); pressure-regulating and pressure-relief valves with actuators (use sync/control-valves-and-actuators); fieldbus segment and network design (use sync/process-control-networks); display, alarming, and historian configuration (use sync/scada-and-hmi-systems); general loop documentation and P&ID conventions beyond the instrument itself (use sync/process-instrumentation); and BAS-native pressure points such as duct static and HVAC differential pressure (use sync/building-automation-system).
---
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## The pressure-measurement instrument family appears in nearly every facility type, and this standard applies across all of them. {note}
−## Industrial process plants, water and wastewater treatment works, HVAC and mechanical systems, fire-protection systems, and general commercial construction all rely on pressure indication and transmission. The selection logic -- range, accuracy, wetted material, connection, and signal -- is common across these settings even though the service pressures and chemistries differ widely. {note}
+## Industrial process plants, water and wastewater treatment works, HVAC and mechanical systems, fire-protection systems, and general commercial construction all rely on pressure indication and transmission. The selection logic — range, accuracy, wetted material, connection, and signal — is common across these settings even though the service pressures and chemistries differ widely. {note}
## Instruments shall be selected, supplied, calibrated, and installed in accordance with this standard and the project instrument index.
…5 unchanged lines
## Hydrostatic or differential-pressure level measurement that infers liquid level in a vessel is covered by [[sync/level-sensors]]. {note}
−## Temperature measurement -- RTDs, thermocouples, and temperature transmitters -- is covered by [[sync/temperature-instrumentation]]; coordinate with that standard where a single multivariable transmitter reports both pressure and temperature. {note}
+## Temperature measurement — RTDs, thermocouples, and temperature transmitters — is covered by [[sync/temperature-instrumentation]]; coordinate with that standard where a single multivariable transmitter reports both pressure and temperature. {note}
## Pressure-regulating and pressure-relief valves with actuators are covered by [[sync/control-valves-and-actuators]]; this standard covers only the measuring instrument, not the final control element. {note}
…3 unchanged lines
## General instrument loop documentation, P&ID symbology beyond the pressure instrument, and control-panel wiring practice are covered by [[sync/process-instrumentation]]. {note}
−## Building-automation pressure points that are BAS-native sensors -- duct static pressure and chilled-water differential pressure for HVAC pump control -- are covered by [[sync/building-automation-system]]. {note}
+## Building-automation pressure points that are BAS-native sensors — duct static pressure and chilled-water differential pressure for HVAC pump control — are covered by [[sync/building-automation-system]]. {note}
## Where a pressure instrument is installed on a process covered by OSHA Process Safety Management (29 CFR 1910.119) because it handles a highly hazardous chemical above its threshold quantity, the instrument's mechanical-integrity, calibration, and documentation records are PSM process-safety information; this standard sets the instrument requirements, and the project PSM program governs the records retention. {note}
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| ASME B1.20.1-2013 (R2018) | Pipe Threads, General Purpose (Inch) |
| ANSI/NEMA 250-2020 | Enclosures for Electrical Equipment (1000 Volts Maximum) |
−| NFPA 70 (NEC) Article 501 | National Electrical Code -- Class I Hazardous Locations |
+| NFPA 70 (NEC) Article 501 | National Electrical Code — Class I Hazardous Locations |
| ISA TR84.00.04-2015 | Guidance for Application of IEC 61511 / ISA-84 |
−| AWWA M20 | Water Meters -- Selection, Installation, Testing, and Maintenance |
−| NSF/ANSI 61 | Drinking Water System Components -- Health Effects |
+| AWWA M20 | Water Meters — Selection, Installation, Testing, and Maintenance |
+| NSF/ANSI 61 | Drinking Water System Components — Health Effects |
## ANSI/ISA-51.1 remains the primary terminology authority for pressure instrument performance terms even though it predates current transmitter technology and is presently under revision; where its 1979 definitions of accuracy, span, range, hysteresis, and repeatability are cited on a datasheet, the cited terms carry the ISA-51.1 meaning. {note}
…68 unchanged lines
## Pressure gauges shall conform to ASME B40.100 for accuracy grade, dial size, scale range, and overpressure rating.
−## ASME B40.100-2022 consolidates the former B40.1, B40.2, B40.5, B40.6, and B40.7 documents and is the governing standard for analog dial-type gauges. Its accuracy grades -- Grade A at ± 1 % of span, Grade 2A at ± 0.5 %, and Grade B at ± 2 % -- are the values cited on gauge datasheets in this standard. {note}
+## ASME B40.100-2022 consolidates the former B40.1, B40.2, B40.5, B40.6, and B40.7 documents and is the governing standard for analog dial-type gauges. Its accuracy grades — Grade A at ± 1 % of span, Grade 2A at ± 0.5 %, and Grade B at ± 2 % — are the values cited on gauge datasheets in this standard. {note}
## Each instrument shall be calibrated against a reference standard traceable to NIST per ASME PTC 19.2 before it is placed in service.
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## A safety requirements specification (SRS) shall exist and be referenced before any instrument is specified as SIL-rated.
−## IEC 61511 requires a documented SRS that defines the safety function, its safe state, and its target SIL before instrument selection. Calling out a "SIL 2 transmitter" with no SRS behind it is a contractual and safety risk -- the rating is meaningless without the function definition that sizes it. {note}
+## IEC 61511 requires a documented SRS that defines the safety function, its safe state, and its target SIL before instrument selection. Calling out a "SIL 2 transmitter" with no SRS behind it is a contractual and safety risk — the rating is meaningless without the function definition that sizes it. {note}
# Environmental and Service Conditions {toc}
…9 unchanged lines
type: select
options:
− - NEMA 4X (316 SS) -- outdoor / wash-down
+ - NEMA 4X (316 SS) — outdoor / wash-down
- NEMA 4X (fiberglass / polyester)
− - NEMA 7 explosion-proof -- Class I Div 1
− - NEMA 4 general weatherproof -- sheltered
− - NEMA 12 -- indoor industrial
−default: NEMA 4X (316 SS) -- outdoor / wash-down
+ - NEMA 7 explosion-proof — Class I Div 1
+ - NEMA 4 general weatherproof — sheltered
+ - NEMA 12 — indoor industrial
+default: NEMA 4X (316 SS) — outdoor / wash-down
```
…11 unchanged lines
options:
- General purpose (unclassified)
− - Class I Div 2 -- intrinsically safe / nonincendive
− - Class I Div 1 / Zone 0 -- explosion-proof
− - Class I Div 1 / Zone 0 -- intrinsically safe + barrier
+ - Class I Div 2 — intrinsically safe / nonincendive
+ - Class I Div 1 / Zone 0 — explosion-proof
+ - Class I Div 1 / Zone 0 — intrinsically safe + barrier
default: General purpose (unclassified)
```
## Transmitters shall be rated for the ambient temperature at the installed location.
−## Standard transmitters operate from -40 °F to +185 °F (-40 °C to +85 °C); extended-range units reach -67 °F to +221 °F. Cold-climate outdoor installations and hot process-adjacent mountings both push past the standard band, and the wrong rating produces drift or a dead display in the field. {note}
−
```datasheet
label: Ambient Temperature Rating
…4 unchanged lines
step: 1
setpoints:
+ - -67
- -40
- 185
+ - 221
```
+## Standard transmitters operate from -40 °F to +185 °F (-40 °C to +85 °C); extended-range units reach -67 °F to +221 °F. Cold-climate outdoor installations and hot process-adjacent mountings both push past the standard band, and the wrong rating produces drift or a dead display in the field. {note}
+
## Transmitters mounted on hot process lines shall be installed with capillary standoffs or impulse-line isolation so process heat does not conduct into the sensor and shift the zero.
## All wetted parts of instruments in potable-water service shall be certified to NSF/ANSI 61.
−## Every material in contact with drinking water must be NSF 61 certified, including the gauge socket, the transmitter diaphragm, and any seal fill fluid. AWWA M20 carries the same requirement for water-system instruments, and the certification must be stated explicitly -- it is not implied by a 316 stainless-steel call-out. {note}
+## Every material in contact with drinking water must be NSF 61 certified, including the gauge socket, the transmitter diaphragm, and any seal fill fluid. AWWA M20 carries the same requirement for water-system instruments, and the certification must be stated explicitly — it is not implied by a 316 stainless-steel call-out. {note}
# Instrument Selection and Measurement Type {toc}
## The instrument type shall be selected from local gauge, electronic transmitter, pressure switch, or a combined gauge-plus-transmitter (duplex) arrangement based on the loop function.
−## A local gauge gives standalone visual indication with no power and no signal. A transmitter delivers a remote analog or digital signal to the control system. A pressure switch provides a discrete contact at a setpoint. The duplex arrangement pairs a transmitter for control with a local gauge for backup indication, which is the common pattern at field instruments where an operator needs to confirm the reading at the equipment. {note}
−
```datasheet
label: Instrument Type
…7 unchanged lines
```
+## A local gauge gives standalone visual indication with no power and no signal. A transmitter delivers a remote analog or digital signal to the control system. A pressure switch provides a discrete contact at a setpoint. The duplex arrangement pairs a transmitter for control with a local gauge for backup indication, which is the common pattern at field instruments where an operator needs to confirm the reading at the equipment. {note}
+
## The 80 % case on US industrial and commercial projects is a two-wire 4-20 mA HART transmitter in a NEMA 4X enclosure, with a local gauge specified alongside for backup indication. {note}
## Local gauges remain near-universal as backup even where a transmitter carries the signal, because an operator at the equipment must be able to read pressure with no power and no DCS. Treat the transmitter and the local gauge as a pair on most field instruments rather than an either/or choice. {note}
−## The measurement reference -- gauge, absolute, differential, or sealed-gauge -- shall be specified explicitly for every instrument.
+## The measurement reference — gauge, absolute, differential, or sealed-gauge — shall be specified explicitly for every instrument.
−## A gauge instrument reads relative to atmosphere; an absolute instrument reads relative to a vacuum reference; a differential instrument reads the pressure difference across two ports; a sealed-gauge instrument reads against a fixed sealed reference for cryogenic or high-vacuum service. Confusing gauge and absolute reference in vacuum or low-pressure service produces readings that are wrong by one atmosphere, so the reference is never left to be inferred. {note}
−
```datasheet
label: Measurement Reference Type
…7 unchanged lines
```
+## A gauge instrument reads relative to atmosphere; an absolute instrument reads relative to a vacuum reference; a differential instrument reads the pressure difference across two ports; a sealed-gauge instrument reads against a fixed sealed reference for cryogenic or high-vacuum service. Confusing gauge and absolute reference in vacuum or low-pressure service produces readings that are wrong by one atmosphere, so the reference is never left to be inferred. {note}
+
# Range and Span {toc}
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## Overpressure capability shall meet or exceed the service.
−## ASME B40.100 Grade A gauges are rated to withstand 130 % of full-scale without permanent error. Transmitters typically tolerate 2x to 3x their range without damage. For differential-pressure cells the static line pressure that the cell sees is a separate and often larger limit than the DP overpressure, and it must be specified alongside the DP range. {note}
−
```datasheet
label: Overpressure Rating
…7 unchanged lines
```
+## ASME B40.100 Grade A gauges are rated to withstand 130 % of full-scale without permanent error. Transmitters typically tolerate 2x to 3x their range without damage. For differential-pressure cells the static line pressure that the cell sees is a separate and often larger limit than the DP overpressure, and it must be specified alongside the DP range. {note}
+
## Differential-pressure transmitters shall have a static line-pressure rating equal to or greater than the maximum line pressure the high side will see.
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## Gauge accuracy grade shall be specified per ASME B40.100.
−## Grade A delivers ± 1 % of span and is the field default; Grade 2A delivers ± 0.5 % for readings used in adjustment or acceptance; Grade B at ± 2 % is acceptable only for coarse utility indication. The grade is matched to how the reading is used, not chosen for its own sake. {note}
−
```datasheet
label: Gauge Accuracy Grade
…6 unchanged lines
```
+## Grade A delivers ± 1 % of span and is the field default; Grade 2A delivers ± 0.5 % for readings used in adjustment or acceptance; Grade B at ± 2 % is acceptable only for coarse utility indication. The grade is matched to how the reading is used, not chosen for its own sake. {note}
+
## Transmitter reference accuracy shall be specified as a percentage of calibrated span.
−## Mid-tier process transmitters specify a reference accuracy from ± 0.065 % to ± 0.25 % of calibrated span. Tighter accuracy carries cost and is justified by custody-transfer, performance-test, or safety-loop service rather than applied universally. {note}
−
```datasheet
label: Transmitter Reference Accuracy
…7 unchanged lines
```
+## Mid-tier process transmitters specify a reference accuracy from ± 0.065 % to ± 0.25 % of calibrated span. Tighter accuracy carries cost and is justified by custody-transfer, performance-test, or safety-loop service rather than applied universally. {note}
+
# Process Connection {toc}
## The default process connection for gauges and most transmitters shall be 1/2 in NPT conforming to ASME B1.20.1.
−## The 1/2 in NPT connection is the workhorse for both gauges and transmitters; 1/4 in NPT appears on small or high-pressure instruments. NPT threads are the most common pressure-instrument connection and are governed by ASME B1.20.1. Flanged connections per ASME B16.5 are reserved for elevated temperature or high pressure. {note}
−
```datasheet
label: Process Connection
…9 unchanged lines
```
+## The 1/2 in NPT connection is the workhorse for both gauges and transmitters; 1/4 in NPT appears on small or high-pressure instruments. NPT threads are the most common pressure-instrument connection and are governed by ASME B1.20.1. Flanged connections per ASME B16.5 are reserved for elevated temperature or high pressure. {note}
+
## Steam service above 400 °F or pressure above 600 psi shall use an ASME B16.5 flanged connection of Class 300 or higher, rated for the service temperature and pressure.
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## Wetted materials shall be selected for compatibility with the process chemistry; 316 stainless steel is the default but is not universally suitable.
−## 316 SS covers most water, air, steam, and benign-process service. It is not suitable for high-chloride, strong-acid, or strong-caustic chemistry, where chloride stress-corrosion cracking and pitting attack the wetted parts. Hastelloy C-276, Monel, or PTFE-lined wetted parts must be specified explicitly for aggressive chemistry such as chlorine, acids, and caustics -- they are never assumed from a generic stainless call-out. {note}
−
```datasheet
label: Wetted Material
…9 unchanged lines
```
+## 316 SS covers most water, air, steam, and benign-process service. It is not suitable for high-chloride, strong-acid, or strong-caustic chemistry, where chloride stress-corrosion cracking and pitting attack the wetted parts. Hastelloy C-276, Monel, or PTFE-lined wetted parts must be specified explicitly for aggressive chemistry such as chlorine, acids, and caustics — they are never assumed from a generic stainless call-out. {note}
+
## Carbon-steel wetted parts shall be used only for dry, non-corrosive gas-utility indication and shall not be used in any wet or corrosive service.
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## A flush-diaphragm remote or direct seal shall be specified for viscous, slurry, crystallizing, or sanitary service.
−## A direct-connected gauge or transmitter on a viscous, slurry, or crystallizing process plugs at the connection and stops reading. A flush-diaphragm seal isolates the instrument behind a process-wetted diaphragm and a captive fill fluid, keeping the process out of the sensing element. Sanitary and hygienic processes require a flush seal with a tri-clamp connection and a 3-A certified or NSF-listed assembly. {note}
−
```datasheet
label: Diaphragm Seal
…7 unchanged lines
```
+## A direct-connected gauge or transmitter on a viscous, slurry, or crystallizing process plugs at the connection and stops reading. A flush-diaphragm seal isolates the instrument behind a process-wetted diaphragm and a captive fill fluid, keeping the process out of the sensing element. Sanitary and hygienic processes require a flush seal with a tri-clamp connection and a 3-A certified or NSF-listed assembly. {note}
+
## The seal fill fluid shall be selected for the service temperature and any food or potable-water contact requirement.
−## Glycerin is the standard fill for general and vibrating service; silicone oil suits high-temperature ambients above 140 °F; food-grade white mineral oil or food-grade silicone is required for sanitary and NSF service. The fill fluid is a process-contact material through the diaphragm, so its food or potable rating matters as much as the diaphragm metal. {note}
−
```datasheet
label: Fill Fluid
…8 unchanged lines
```
+## Glycerin is the standard fill for general and vibrating service; silicone oil suits high-temperature ambients above 140 °F; food-grade white mineral oil or food-grade silicone is required for sanitary and NSF service. The fill fluid is a process-contact material through the diaphragm, so its food or potable rating matters as much as the diaphragm metal. {note}
+
# Local Gauges {toc}
## Local-indicating gauges shall be Bourdon-tube dial gauges with a stainless-steel case unless the datasheet specifies a digital or differential type.
−## The Bourdon-tube dial gauge is the standard local indicator for most pressure service. A digital gauge with an LCD display suits readings taken close-up where resolution matters, and a differential-pressure dial gauge (diaphragm or piston type) suits filter-monitoring and other low-DP applications where a Bourdon tube cannot resolve the small difference. {note}
−
```datasheet
label: Local Gauge Type
…6 unchanged lines
```
+## The Bourdon-tube dial gauge is the standard local indicator for most pressure service. A digital gauge with an LCD display suits readings taken close-up where resolution matters, and a differential-pressure dial gauge (diaphragm or piston type) suits filter-monitoring and other low-DP applications where a Bourdon tube cannot resolve the small difference. {note}
+
## Gauge dial size shall be 4 in for standard field mounting, 6 in for eye-level panel boards, and 2.5 in for manifold-mounted or space-constrained locations.
−## Dial size is driven by viewing distance and available space. A 4 in dial reads cleanly at the equipment, a 6 in dial reads across a control room or panel front, and a 2.5 in dial fits a crowded manifold. Oversizing wastes space and undersizing hurts readability. {note}
−
```datasheet
label: Gauge Dial Size
…6 unchanged lines
```
+## Dial size is driven by viewing distance and available space. A 4 in dial reads cleanly at the equipment, a 6 in dial reads across a control room or panel front, and a 2.5 in dial fits a crowded manifold. Oversizing wastes space and undersizing hurts readability. {note}
+
## Gauges in vibrating service shall be liquid-filled with glycerin (or silicone for high-temperature ambients) to damp pointer flutter and protect the movement.
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## Transmitters shall provide a 4-20 mA two-wire output with HART revision 7 unless a digital fieldbus is specified.
−## The two-wire 4-20 mA loop with HART revision 7 is the 80 % default for US industrial projects: it powers and signals on one pair, and HART carries digital configuration and diagnostics over the analog loop. Foundation Fieldbus H1, PROFIBUS PA, and WirelessHART (ISA100/IEC 62591) are specified where the project network architecture in [[sync/process-control-networks]] calls for them. {note}
−
```datasheet
label: Signal Output
…8 unchanged lines
```
+## The two-wire 4-20 mA loop with HART revision 7 is the 80 % default for US industrial projects: it powers and signals on one pair, and HART carries digital configuration and diagnostics over the analog loop. Foundation Fieldbus H1, PROFIBUS PA, and WirelessHART (ISA100/IEC 62591) are specified where the project network architecture in [[sync/process-control-networks]] calls for them. {note}
+
## HART revision shall be specified as revision 7 minimum.
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## Pressure switches shall be snap-action with an adjustable setpoint and a deadband suited to the control function.
−## A pressure switch closes or opens a discrete contact at a setpoint to start a pump, trip an alarm, or interlock equipment. The single-pole double-throw snap-action switch is the common form. Where the switch performs a safety function, a transmitter with a programmable trip in the logic solver is generally preferred over a mechanical switch because it is testable and diagnosable per [[sync/process-instrumentation]]. {note}
−
```datasheet
label: Pressure Switch Configuration
…6 unchanged lines
```
+## A pressure switch closes or opens a discrete contact at a setpoint to start a pump, trip an alarm, or interlock equipment. The single-pole double-throw snap-action switch is the common form. Where the switch performs a safety function, a transmitter with a programmable trip in the logic solver is generally preferred over a mechanical switch because it is testable and diagnosable per [[sync/process-instrumentation]]. {note}
+
## The pressure-switch setpoint shall be specified in service engineering units.
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## A snubber shall be specified for gauges and transmitters in pulsating service from reciprocating pumps, compressors, or pulsating flow.
−## Pressure pulses from reciprocating equipment fatigue a Bourdon tube or sensor in weeks. A snubber -- sintered-metal or adjustable piston type -- damps the pulses before they reach the sensing element. On a pulsating-service gauge the snubber and a glycerin case fill are specified together, because each addresses a different part of the same problem. {note}
−
```datasheet
label: Snubber
…6 unchanged lines
```
+## Pressure pulses from reciprocating equipment fatigue a Bourdon tube or sensor in weeks. A snubber — sintered-metal or adjustable piston type — damps the pulses before they reach the sensing element. On a pulsating-service gauge the snubber and a glycerin case fill are specified together, because each addresses a different part of the same problem. {note}
+
## An isolation valve shall be provided at every gauge and transmitter so the instrument can be isolated for calibration or removal without shutting down the process.
−## A 1/2 in NPT needle valve (gauge saver) isolates a single-port instrument. A two-valve block-and-bleed manifold serves a single-port transmitter, and a five-valve manifold serves a differential-pressure transmitter. Without isolation, calibration and replacement require a line shutdown, which is rarely acceptable in service. {note}
−
```datasheet
label: Isolation Valve / Manifold
…7 unchanged lines
```
+## A 1/2 in NPT needle valve (gauge saver) isolates a single-port instrument. A two-valve block-and-bleed manifold serves a single-port transmitter, and a five-valve manifold serves a differential-pressure transmitter. Without isolation, calibration and replacement require a line shutdown, which is rarely acceptable in service. {note}
+
# Functional Safety {toc}
## Instruments serving a safety instrumented function shall be SIL-rated and certified per IEC 61508, and applied within a safety instrumented system per IEC 61511.
−## Overpressure-protection and loss-of-containment safety loops require a SIL 2 or SIL 3 transmitter certified per IEC 61508 for hardware fault tolerance and average probability of failure on demand. The instrument's certified SIL is a property of the device; the SIL of the safety function is established by the SRS and verified for the whole loop, including the logic solver and final element in [[sync/control-valves-and-actuators]]. {note}
−
```datasheet
label: Safety Rating
…6 unchanged lines
```
+## Overpressure-protection and loss-of-containment safety loops require a SIL 2 or SIL 3 transmitter certified per IEC 61508 for hardware fault tolerance and average probability of failure on demand. The instrument's certified SIL is a property of the device; the SIL of the safety function is established by the SRS and verified for the whole loop, including the logic solver and final element in [[sync/control-valves-and-actuators]]. {note}
+
## Human-factors requirements for safety-loop pressure displays and alarms shall be evaluated per ISA TR84.00.04 guidance where the loop relies on operator response.
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## The recalibration interval shall be set by service criticality.
−## Safety-instrumented-function and critical instruments are recalibrated annually; general process transmitters carry a maximum interval of five years under typical plant standards. The interval belongs in the operation and maintenance manual and feeds the facility's mechanical-integrity program. {note}
−
```datasheet
label: Recalibration Interval
…6 unchanged lines
```
+## Safety-instrumented-function and critical instruments are recalibrated annually; general process transmitters carry a maximum interval of five years under typical plant standards. The interval belongs in the operation and maintenance manual and feeds the facility's mechanical-integrity program. {note}
+
# Installation {toc}
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## The Contractor shall furnish recommended spare parts for the installed pressure instruments.
−## A practical spares package covers the wear and consumable items: gauge isolation/needle valves, snubbers, transmitter LCD modules, manifold seal kits, and at least one complete spare of each critical transmitter range used in the project. Stocking a spare of each critical range avoids a long lead time when a safety or production loop loses its instrument. {note}
−
```datasheet
label: Recommended Spares
…9 unchanged lines
- One spare transmitter per critical range
```
+
+## A practical spares package covers the wear and consumable items: gauge isolation/needle valves, snubbers, transmitter LCD modules, manifold seal kits, and at least one complete spare of each critical transmitter range used in the project. Stocking a spare of each critical range avoids a long lead time when a safety or production loop loses its instrument. {note}