Bently Nevada 21000 and 24701 Proximity Probe Housing Assemblies: What to Check Before Ordering
The housing series is only the first choice. Probe family, lead length, standoff, penetration, fittings, mounting thread and approval status determine whether the assembly belongs on the machine.
A proximity probe housing looks like a mechanical accessory, yet an incorrect assembly can stop a vibration or position measurement before the electrical system is even considered. The housing has to reach the target, protect the probe and cable, accept the conduit arrangement and preserve access for adjustment. On a hazardous-area machine, the ordered approval and fittings also have to agree with the site design.
The 21000 and 24701 are related all-metal housing families for externally mounted proximity probes. They share the same purchasing problem: a short description such as “21000 housing” leaves most of the configuration undefined. The complete catalog number is the useful record.
0121000 or 24701: start with material and environment
Baker Hughes identifies the 21000 as an aluminum-body housing with a 304 stainless steel sleeve. The 24701 uses a 303 stainless steel body with the same sleeve material. Typical weight without fittings is approximately 1.1 kg for the 21000 and 1.8 kg for the 24701. Both families are designed around external probe mounting, but material, mass and the existing machine specification should guide the selection.
Aluminum housing body
Often selected where the installed drawing already calls for the 21000 arrangement and lower housing mass is useful. Do not change series solely because another housing is available.
Stainless steel housing body
Used where the installed specification requires the stainless body or its mechanical and environmental characteristics. Confirm the precise series on the machine record.
02Understand what the housing assembly contains
The manufacturer describes the assembly as more than a protective cover. The system can include a screw-on dome cover, housing body with threaded conduit ports, an optional-length probe sleeve, O-rings, reverse-mount proximity probe, thread seal, optional fittings and an optional standoff adapter. Each item has a different role in installation and service access.
Functional stack of the assembly
From external access to the target surfaceThe assembly protects access; it does not correct an incorrect probe system. Probe family, extension cable and Proximitor sensor must remain electrically compatible. The mechanical order should therefore be reviewed together with the installed transducer-system record.
03Read the complete catalog number from left to right
The standard format is 21000-AA-BB-CC-DDD-EE-FF or 24701-AA-BB-CC-DDD-EE-FF. The characters after the series define the installed probe and the geometry. Omitting one field invites a supplier to quote a mechanically different assembly.
The AA field is especially important. Manufacturer options cover 3300 XL 8 mm, 3300 XL NSv and 3300 XL 11 mm probes, with variations for connector protection and selectable approvals. BB identifies probe lead length. CC and DDD together define how far the housing and probe extend toward the target. EE and FF close the mechanical interface.
21000-28-10-00-094-04-02
The ordering string identifies a 3300 XL 8 mm approval-selectable probe, 1.0 m lead, no standoff, 9.4 in penetration, fitting option 04 and mounting-thread option 02. Verify the installed approval and drawing before release.
21000-00-00-00-087-03-02
Codes 00 in the probe, cable and standoff positions mean those items are not included. The remaining fields still define an 8.7 in penetration, fitting package and mounting thread. “No probe” does not mean “unconfigured housing.”
24701-28-05-20-024-03-02
This stainless-body example combines a 3300 XL 8 mm approval-selectable probe, 0.5 m lead, 2.0 in standoff and 2.4 in penetration. The fitting and mounting-thread codes must still match the conduit and machine opening.
24701-34-05-30-028-04-02
Option 34 calls for a 3300 XL 8 mm probe with connector protector and selectable approvals. The code continues with a 0.5 m lead, 3.0 in standoff, 2.8 in penetration, fitting option 04 and thread option 02.
04Geometry errors are discovered at the machine, not the warehouse
Penetration is not a convenient estimate. It is derived from the machine mounting surface, standoff, sleeve route, target location and required probe gap. A housing that is too short cannot reach the target. An assembly that is too long can interfere with internal parts, leave the probe outside its useful adjustment range or create unnecessary unsupported length.
Measure the installation stack
Record the mounting face, any adapter, wall thickness, internal clearance, sleeve support point, target surface and expected thermal movement. Compare these measurements with the installed drawing and complete catalog number.
- Housing mounting thread and available engagement
- Standoff length and probe penetration
- Probe lead length, routing and connector access
- Target location, surface condition and operating gap
05Hazardous-area approval belongs to the complete assembly
The official datasheet states that 21000 and 24701 housings are available with CSA approvals and that approved versions are rated for hazardous areas. It also describes both families as CSA Type 4 enclosures and compliant with API 670 for externally mounted proximity probe housings. Those statements do not make every catalog-number combination explosion-proof.
Record the complete label and approval marks. CA housings have ordering and end-user restrictions described by the manufacturer.
A plug, reducer or cable seal is part of the ordered mechanical arrangement. Fitting availability by itself does not create an approval.
Check the applicable installation drawing, country-specific approval and barrier or wiring requirements before purchase.
For North American explosion-proof applications, the manufacturer identifies CA21000 and CA24701 variants with specific conditions. It also notes that only qualifying CA versions ordered with designated fitting options carry that CSA explosion-proof rating. A standard 21000 or 24701 fitted with explosion-proof hardware should not be represented as a certified CA assembly without the correct product identity and documentation.
06Plan the installation around the measurement, not the enclosure
The housing supports external access to the probe and lead. The measurement still depends on correct probe-system compatibility, target material and geometry, mechanical mounting and electrical gap. A sound work package protects the existing configuration before the old assembly is disturbed.
- Capture the installed baseline. Record the full housing number, probe and Proximitor system, gap voltage, channel reading, machine state and photographs of the complete installation.
- Measure the mechanical stack. Confirm the mounting thread, standoff, penetration, sleeve support, target position, conduit entry and access needed to remove the dome.
- Verify the electrical system. Match probe family and lead length to the extension cable and Proximitor sensor. Do not mix components on the assumption that every 8 mm probe is identical.
- Inspect the offered assembly. Compare actual label photographs, ordered options, threads, sleeve condition, O-rings, probe, connector protection and fittings with the RFQ.
- Install under the approved procedure. Apply site isolation and hazardous-area controls, protect the probe lead and set the gap using the transducer-system instructions.
- Prove the channel. Confirm gap voltage, static position, dynamic response, cable security, conduit sealing and monitor status before returning the machine to normal operation.
07What a useful supplier record should contain
A stock photograph and a shortened model number are not enough for a configured housing. Ask for evidence tied to the exact assembly offered, particularly when the probe and fittings are included.
| Record field | What to request | Why it matters |
|---|---|---|
| Complete identity | Full catalog number, serial label and approval markings | Shows all six configuration fields and the actual housing designation. |
| Mechanical condition | Body, threads, sleeve, dome, ports, O-ring surfaces and fittings | Damage or corrosion can affect installation, sealing and future service access. |
| Probe content | Probe number, lead length, connector, protector and readable labels | Confirms that the supplied probe agrees with AA and BB options. |
| Dimensions | Standoff and penetration measured against the catalog code | Prevents a correctly labelled but wrongly interpreted geometry from reaching site. |
| Test evidence | Continuity or insulation checks where appropriate, probe-system response and date | Separates a visual inspection from functional evidence. |
| Commercial terms | Condition, lead time, packing, warranty and return route | Provides a recovery path if incoming inspection finds a mismatch. |
08Questions maintenance and purchasing teams ask
Can a 24701 replace a 21000 because both accept similar probes?
Not by assumption. The body material, mass, dimensions, approval identity and installed specification differ. A series change needs an engineering review of the machine drawing and environmental requirements.
Can the housing be ordered without a probe?
Yes, the ordering structure includes a “probe not required” option. Cable and geometry fields still need to be specified correctly, and the separately supplied probe must match the transducer system.
Does fitting option 03 or 04 prove that the assembly is explosion-proof?
No. Approval depends on the qualifying housing designation, ordered combination, marks and installation conditions. A fitting description alone is not certification evidence.
What information produces the fastest accurate quotation?
Send the full model, label photographs, quantity, installed machine, required condition, delivery destination and outage date. Add the probe system, measured geometry, approval requirement and whether fittings must be included.
When should the newer 31000/32000 family be considered?
Baker Hughes notes that the newer family provides more flexible mounting and improved environmental resistance for installations that do not require an explosion-proof housing. It is an engineering alternative, not an automatic like-for-like replacement.
Send the full housing code with the inquiry
Label photographs, measured geometry, probe-system details, approval requirements and the outage date allow a configuration-specific availability review.