Annubar vs compact orifice vs integral orifice selection is a differential-pressure flow problem: all three infer flow from a measured pressure difference, but their primary-element geometry, line-size fit, pressure-loss profile and installation method differ. The right design depends on fluid phase, line size, Reynolds number, required turndown, allowable permanent pressure loss, piping access and the quality of the upstream flow profile.
Quick DP flowmeter comparison
| Primary element | Best preliminary fit | Pressure-loss profile | Installation focus |
|---|---|---|---|
| Annubar averaging pitot tube | Medium and large pipes where insertion construction and lower permanent pressure loss are priorities | Lower permanent loss than an orifice because the probe occupies only part of the pipe area | Correct insertion depth and orientation, representative velocity profile, impulse-line arrangement and adequate straight run |
| Compact or conditioning orifice | Gas, liquid or steam service where an integrated flange-mounted assembly and compact installation are valuable | Higher than an averaging pitot design; calculate recovery and permanent loss for the selected beta ratio and duty | Plate centering, bore/beta selection, flange rating, straight run, condensate or gas management in impulse lines |
| Integral orifice | Small-bore lines and low-flow duties needing a factory-integrated meter run and self-centering orifice | Application dependent; verify available line pressure and maximum-flow loss | Small-line cleanliness, exact bore, density compensation, orientation and plugging risk |
| Traditional separate orifice plate | Standardized DP flow measurement where existing flanges, maintenance practice and project standards favour a separate primary element | Application dependent and normally material to the energy balance | Plate condition/direction, tap geometry, bore, centering, pipe ID, straight run and transmitter manifold |
These are technology-level differences. Accuracy and turndown cannot be assigned safely without the selected primary element, transmitter range, fluid properties, beta ratio, Reynolds number, installation and compensation method.
How the three assemblies differ
An Annubar is an averaging pitot sensor. Multiple upstream pressure ports sample the velocity profile, while a downstream port provides the low-pressure reference. The probe’s limited blockage reduces permanent pressure loss and can simplify adding a measurement point to an existing line. However, a disturbed velocity profile, incorrect probe orientation or plugged pressure ports can degrade performance.
A compact orifice assembly places an orifice or conditioning plate between flanges and couples it closely to the DP transmitter. Its defined restriction produces a strong differential-pressure signal and supports familiar orifice-based engineering practice. The tradeoff is a meaningful permanent pressure loss and the need to confirm beta ratio, straight run and maximum differential pressure.
An integral orifice combines a precision small bore with a meter run and DP transmitter. This reduces assembly and centering uncertainty in small lines where fabricating taps and straight pipe accurately is difficult. Small bores are more vulnerable to contamination or plugging, so process cleanliness and maintenance access are critical.
Verified Rosemount family limits for preliminary selection
| Rosemount assembly | Current official scope used in this guide | Do not assume |
|---|---|---|
| 3051CFA Annubar | The October 2025 Rosemount 3051 product data sheet lists 2–96 in. (50–2,400 mm) line availability and describes a fully assembled, leak-tested averaging-pitot solution. | One accuracy or straight-run value does not apply to every sensor size, mounting style or flow condition. |
| 3051CFC Compact Orifice | The current Emerson product page lists gas, liquid and steam service with line sizes up to 12 in. (300 mm), using compact or conditioning-plate options. | The same beta ratio, bore, pressure class or uncertainty across all line sizes. |
| 3051CFP Integral Orifice | The October 2025 product data sheet identifies 0.5–1.5 in. (15–40 mm) as its small-line range and supplies the calibrated orifice within a meter run. | Suitability for dirty, wet or polymerizing service without a plugging and maintenance review. |
Selection by application constraint
When permanent pressure loss is tightly limited
Evaluate an Annubar first, especially on larger pipes or utility lines. Calculate the actual permanent loss and confirm that the available differential pressure remains high enough for the required uncertainty at minimum flow. Low permanent loss does not remove the need for adequate signal strength.
When piping space and assembly simplicity dominate
A compact or conditioning orifice can reduce separate components and leak paths. It may also address short straight-run constraints when the exact conditioning design is selected and installed under its documented limits. Do not apply a generic straight-run rule: use the current sizing report for the selected plate, beta ratio and upstream disturbance.
When the line is very small
An integral orifice is purpose-built for small-bore measurement. Provide the true pipe size, schedule, fluid properties and minimum flow. Check whether suspended solids, wax, condensate, crystallization or freezing could block the bore or impulse passages.
When steam or gas density changes significantly
DP flow is proportional to the square root of differential pressure divided by density. If pressure and temperature change enough to alter density, uncompensated flow can be wrong even when the DP transmitter is working correctly. Define whether actual volume, standard volume or mass flow is required and whether pressure/temperature compensation or a multivariable transmitter is needed. For steam system context, see our steam pipeline instrumentation guide.
Engineering data required before sizing
- Fluid phase and composition, including moisture, solids and contamination
- Minimum, normal and maximum flow with required engineering units
- Operating and design pressure and temperature ranges
- Density, viscosity, compressibility and molecular weight where applicable
- Pipe nominal size, schedule, measured internal diameter, material and flange rating
- Available straight run and the type/location of elbows, valves, reducers and tees
- Allowable permanent pressure loss and pump/compressor margin
- Required output, protocol, hazardous-area approval and functional-safety requirement
- Ambient conditions, impulse-line routing, manifold and winterization or heat tracing
Our instrument inquiry and tag-list guide provides a practical structure for collecting this information. Pressure-drop consequences should also be reviewed with the pipeline pressure-drop optimization guide.
Product paths for detailed evaluation
Review the Rosemount 3051CFA Annubar, Rosemount 3051CFC Compact Orifice dan Rosemount 3051CFP Integral Orifice. The Rosemount 3051 pressure transmitter page provides related DP platform context. Browse the full flow measurement range when another principle may better satisfy the duty.
Official technical references
- Rosemount 3051 Product Data Sheet, October 2025
- Rosemount 3051CFA Annubar official product page
- Rosemount 3051CFC Compact Orifice official product page
- Rosemount 3051CFP Integral Orifice official product page
Request a quotation
Send the fluid, flow units, minimum/normal/maximum flow, pressure, temperature, density/viscosity data, pipe size and schedule, flange rating, available straight run, allowable pressure loss, impulse-line arrangement, output protocol and hazardous-area requirements to sales@santanfluid.com. For primary-element sizing review and quotation, contact SANTAN on WhatsApp China +86 136 9022 3185 or WhatsApp Indonesia +62 823 1767 3750.