Venturi Nozzle
An ISA-1932 nozzle inlet followed by a divergent cone. It keeps the nozzle’s tolerance for hard service and recovers most of the pressure loss downstream: 5 – 20 % of the differential with a divergent of 15° or less (ISO 5167-3).
The ISA-1932 inlet, followed by a divergent cone
The upstream face is the ISA-1932 inlet: a flat face and two arcs. What follows the throat is different: a divergent outlet cone, and the element has its own discharge coefficient in ISO 5167-3.
The cone recovers part of the pressure drop before the flow returns to the pipe, which is why the permanent loss is lower than on a plain nozzle of the same ratio. The downstream tapping position moves with it, and is fixed by ISO 5167-3.
Advantages
Four ways to take the throat pressure
The upstream side is always corner tappings. At the throat the pressure can be collected four ways; the standard the meter is built to, the fluid, the line size and the number of transmitters decide which.
Annular chamber
Four or more tappings into a chamber machined in the nozzle body or carrier ring; one outlet. The ISO 5167-3 arrangement: the chamber averages the throat pressure around the bore.
Piezometer ring
Four tappings piped to a ring outside the pipe (with four tappings, a triple-T); one outlet. ISO 5167-3 arrangement, used on large welded spools where a machined chamber is not practical.
Single tapping
One tapping in the horizontal plane. The simplest build; it falls outside the ISO 5167-3 four-tapping rule, so the element is flow-calibrated.
Two horizontal tappings
One tapping on each side in the horizontal plane, each with its own line: steam legs with condensate pots at one level, or two independent transmitters. Calibrated, like the single tapping.
What decides it
| Standard and uncertainty | The ISO 5167-3 discharge coefficient, and its 1.2 – 1.7 % uncertainty, holds only with four or more throat tappings into a chamber, ring or triple-T. Single or paired tappings mean a flow calibration, and the calibration sets the uncertainty. |
| Fluid | Gas carrying liquid, or liquid carrying gas or solids: tappings stay off the top and bottom of the pipe (ISO 5167-3, 5.4.3.1). Steam and condensing vapours: horizontal tappings, each leg with a condensate pot at the same level. |
| Cleanliness | A chamber or ring joins small passages; on fouling service, separate tappings that can be cleared one by one are preferred. |
| Size and construction | Small and medium sizes, flanged or wafer: chamber machined in the body or carrier ring. Large welded spools: external piezometer ring. |
| Transmitters | One transmitter: one outlet. Two transmitters or redundancy: two horizontal tappings, or a ring with two outlets. |
Technical data
| Size range | DN 80 – DN 500 (3″ – 20″) |
| Pressure class | ASME Class 150 – 2500 / EN 1092-1 PN 6 – PN 400; other flange standards to the project |
| Standards | ISO 5167-3, ASME MFC-3M |
| Profiles | ISA-1932 inlet with a divergent outlet cone (ISO 5167-3) |
| Beta ratio | 0.316 – 0.775 (ISO 5167-3) |
| Construction | Welded into spool, flanged, or wafer between line flanges |
| Tappings | Corner tappings upstream; throat: four or more into an annular chamber, piezometer ring or triple-T (ISO 5167-3), or single / two horizontal tappings on calibrated elements |
| Measuring uncertainty | Stated on the calculation sheet for the duty; discharge coefficient uncertainty to ISO 5167-3 (1.2 – 1.7 %, set by β) |
| Permanent pressure loss | Lower than a nozzle without the divergent cone; 5 – 20 % of the differential with a divergent of 15° or less, for guidance (ISO 5167-3) |
| Installation thickness | Set by the tapping arrangement and the weld preparation, so it is fixed per design and given on the drawing |
| Marking | Tag number, size, rating, throat diameter, material and flow direction; marking method to the project |
| Quality control | ISO 9001 system; PED where it applies; profile and throat measured and recorded; EN 10204 3.1 certificates, 3.2 on request |
| Documentation | Sizing calculation, profile inspection report, material certificate (EN 10204 3.1) |
Material selection
Two rules set the specification. The nozzle is chosen for wear and corrosion resistance; the spool is matched to the line pipe so the weld and the thermal expansion behave as one.
Where it runs
Sectors this family is specified into most often.
What to send for sizing
The throat diameter comes out of the sizing calculation and the divergent cone is drawn from it. ISO 5167-3 fixes the profile; the installation drawing is issued as part of the project scope once the calculation is agreed.
The face-to-face length available matters here more than on a plain nozzle — the divergent cone needs length, and it is often what decides whether the element fits the spool.
Sizing enquiry sheet →| Process data | What it decides |
|---|---|
| Line size and schedule | Sets the body and the throat diameter d |
| Flange standard, rating and facing | Or butt weld ends where the nozzle is welded into the line |
| Medium, phase and density | Steam, gas and liquid are sized differently |
| Flow range — min, normal, max | Sets β and the differential at each point |
| Pressure and temperature | Operating and design, both |
| Tapping interface required | Plain, butt weld, threaded, flanged, compact per IEC 61518 or compression fitting |
| Face-to-face length available | The divergent cone needs length — it decides whether the nozzle fits the spool |
Documents
- Primary element: Venturi nozzle — ISA-1932 inlet with a divergent outlet cone — line size [DN 80 – DN 500], rating [Class … / PN …], β 0.316 – 0.775.
- Design: ISO 5167-3 / ASME MFC-3M.
- Construction: [welded into a spool / flanged / wafer between line flanges]; installation length fixed by the design and given on the drawing.
- Tappings: corner tappings upstream; throat: four or more tappings into an [annular chamber / piezometer ring / triple-T], or [single / two horizontal] tappings on a calibrated element.
- Materials: [ … ], to suit the process and the line piping class.
- Marking: tag number, size, rating, throat diameter, material and flow direction.
- Inspection and documents: profile and throat measured and recorded; sizing calculation, profile inspection report, material certificate EN 10204 3.1 (3.2 where stated).
Venturi Nozzle
Send the profile your specification calls for, the line size and the process data. If the specification is open, we will tell you which profile the duty actually wants.