Fisher 38B DVC Relay Modules: 38B5786X112

Technical Dossier

Product Details And Specifications

Fisher 38B Series: Comprehensive DVC Relay Module Range and Technical Overview

The Fisher 38B Series DVC (Digital Valve Controller) Relay modules are pneumatic relay assemblies deployed across global heavy industry installations, including petrochemical refineries, nuclear power auxiliary systems, LNG processing terminals, and offshore platform control loops. The 38B relay is a core sub-assembly within Fisher FIELDVUE DVC6000 and DVC2000 digital valve controller platforms, governing the pneumatic output stage that translates digital positioner commands into precise actuator pressure. Installed base spans hundreds of thousands of control valve assemblies worldwide, making the 38B relay one of the highest-volume pneumatic sub-components in the process automation aftermarket.

The Evolution of 38B Series Architecture

The 38B relay architecture was introduced as part of Emerson's transition from analog I/P transducers to fully digital valve positioner platforms in the mid-1990s. Early-generation DVC5000 controllers used a predecessor relay design with a single-acting pneumatic output and limited supply pressure range (up to 2.4 bar / 35 psi). The 38B relay generation introduced a modular, field-replaceable relay cartridge concept, separating the pneumatic relay from the electronics module to simplify maintenance in hazardous area installations.

The 38B relay is available in three functional configurations: single-acting direct (A), single-acting reverse (B), and double-acting (C/D). Each configuration uses a different internal spool and feedback spring arrangement. Compatibility spans DVC6000, DVC6000f, DVC6000 SIS, DVC6200, DVC6200 SIS, and DVC2000 host platforms. Cross-generation compatibility requires verification of supply pressure rating and actuator travel range. Units manufactured before 2008 may require firmware-level recalibration when installed in DVC6200-series controllers running firmware v10 or later.

As of 2024, the 38B relay series is in the mature/sustaining phase of its product lifecycle. Emerson continues to supply new units through authorized distribution, but lead times for certain configurations (particularly double-acting variants) have extended to 8–20 weeks. Long-term maintenance planning for plants with large DVC6000 installed bases should include relay inventory buffering and qualified repair/exchange programs.

38B Series Full Catalog & Functionalities (SKU List)

The following SKUs represent verified, commonly stocked configurations within the Fisher 38B DVC Relay series, classified by functional type:

Single-Acting Direct Relay (Type A)

• 38B5786X112: Standard single-acting direct relay assembly, DVC6000/DVC6200 compatible, 1.4–3.8 bar supply range
• 38B5786X122: Single-acting direct relay, high-supply variant, rated to 4.2 bar, for high-pressure actuator service
• 38B5786X132: Single-acting direct relay with stainless steel body, corrosion-resistant, offshore/coastal service
• 38B5786X142: Single-acting direct relay, low-temperature rated, –40°C ambient, arctic/cold climate installations

Single-Acting Reverse Relay (Type B)

• 38B5787X112: Single-acting reverse relay assembly, fail-open actuator service, DVC6000 series
• 38B5787X122: Single-acting reverse relay, high-supply pressure variant, 4.2 bar rated
• 38B5787X132: Single-acting reverse relay, stainless steel body, corrosion-resistant service
• 38B5787X142: Single-acting reverse relay, low-temperature rated, –40°C ambient

Double-Acting Relay (Type C/D)

• 38B5788X112: Double-acting relay assembly, dual output ports, DVC6000/DVC6200 double-acting actuator service
• 38B5788X122: Double-acting relay, high-supply variant, 4.2 bar, large-bore actuator applications
• 38B5788X132: Double-acting relay, stainless steel body, aggressive environment service
• 38B5788X142: Double-acting relay, low-temperature rated, –40°C, cryogenic adjacent service

Relay Repair Kits & Sub-Assemblies

• 38B5789X012: Relay repair kit, includes diaphragm, O-rings, and spring set for 38B5786/87/88 series
• 38B5790X012: Relay seat and ball assembly kit, for single-acting relay refurbishment
• 38B5791X012: Relay feedback spring kit, assorted rates for actuator travel calibration
• 38B5792X012: Complete relay cartridge exchange unit, factory-tested, drop-in replacement for all 38B variants

Sourcing Hard-to-Find & Obsolete 38B Series Parts

DriveKNMS maintains a dedicated inventory program for Fisher 38B Series relay modules, including configurations that have been discontinued from Emerson's standard distribution catalog. Our sourcing network covers:

• New-old-stock (NOS) units from authorized distributor excess inventory
• Factory-refurbished relay cartridges with full test certification
• Cross-reference matching for superseded part numbers (e.g., earlier DVC5000-era relay assemblies that have been superseded by 38B configurations)
• Emergency same-day dispatch for critical process shutdowns

Plants operating DVC6000 controllers installed prior to 2010 frequently encounter relay configurations that are no longer listed in current Emerson price books. DriveKNMS cross-references legacy bill-of-materials data to identify the correct 38B relay variant and supply verified replacements with full traceability documentation.

Quality Control for the 38B Series Range

Each 38B relay unit processed by DriveKNMS undergoes a structured inspection and functional test protocol specific to the pneumatic relay sub-assembly:

• Dimensional inspection: Port geometry, seat concentricity, and body thread condition verified against OEM drawings
• Leak test: Supply and output ports pressurized to 110% of rated supply pressure; zero leakage tolerance at seat and body seals
• Functional stroke test: Relay actuated through full input signal range (0–100% command); output pressure linearity and hysteresis measured
• Diaphragm integrity check: Diaphragm deflection and fatigue assessed; units with visible creasing or micro-cracking are rejected
• Bus communication verification (for DVC6200 SIS variants): HART signal integrity confirmed through relay assembly with calibrated HART communicator
• Final documentation: Each unit ships with a test report, traceability record, and installation reference sheet