Critical Nozzles

according to DIN EN ISO 9300

For the flow adjustment of air and pure gases in recurring calibration tasks of flow measurement devices, critical nozzles according to the standard DIN EN ISO 9300 are an ideal, long-term stable transfer standard. They are particularly efficient when used with nozzle galleries.

Our offerings range from precisely manufactured Venturi nozzles, also known as Laval nozzles, with throat diameters (d) larger than 0.17 mm, to complete nozzle measurement sections and nozzle galleries in nominal pipe sizes from DN 4 to DN 400. Smaller micro nozzles with throat diameters (d) less than 0.17 mm can be produced in accordance with the standard in a drilled, cylindrical throat geometry.

With critical nozzles, flow rates of air or gases can be set with very high stability. Therefore, they are excellent for calibrating all types of mass and volumetric flow measuring devices for air and gases, such as gas meters, LFEs, mass flow meters, and all other types of flow meters.

Practical Tip:

Nozzle galleries combine the critical flow of multiple individual nozzles and allow the adjustment of very precise volume and mass flows. Our standard nozzle gallery concepts are available in nominal diameters from 10 to 50 mm. For larger flows, we realize nozzle galleries with inlet/outlet sections, DIN flanges, and shut-off valves in combined nominal diameters between DN 50 and DN 400, according to customer requirements.

Main Features

Nozzle throat diameter d from 170 μm to 100 mm
Inlet radius 2 x d, outlet cone 8° full angle
Inlet nominal diameters from DN 15 to DN 400
Connection via adapters or flanges
Suction or positive pressure operation
Short response time and high accuracy
Very good long-term stability, no moving parts

Data Sheet

Critical Venturi Nozzles according to DIN EN ISO 9300

For supercritical operation

Venturi nozzles, also known as Laval nozzles, feature an optimized inlet radius and outlet cone. As a result, these nozzles exhibit low pressure loss and very good pressure recovery. Venturi nozzles with throat diameters greater than 1 mm can be operated critically with a differential pressure between inlet and outlet of 120 to 200 mbar.

Operating Note

Suction operation is the preferred mode for these nozzles, as the atmospheric density at the inlet is very stable. For pressure operation, a very stable pressure control should be used. Optimal, free, and undisturbed flow conditions exist in the inlet area of the nozzle with „large space characteristics“: No wall should be closer to the nozzle axis and the inlet plane than five times the nozzle diameter.

Calibration Options

Type: Calibration in pressure or suction operation
Medium: Air or pure gases
Certificate: Factory, DAkkS-DKD, or PTB calibration

Property	Functionality
Flow Range	0.6 L/h up to 6000 m³/h (equivalent to air)
Accuracy	Manufacturing accuracy Calibration accuracy (best possible)	±5 % of set value (standard) ±0.25 % of m.v. for Q < 10 Nm³/h ±0.12 % of m.v. for Q ≤ 10 Nm³/h
Calibration periods (best possible)	5 years for Q < 2 Nm³/h 10 years for Q ≤ 2 Nm³/h
Pressure Ranges	Input pressure 1 - 7 bar absolute
Operating Temperature	0 ... +50 °C
Media Compatibility	Air and gases compatible with stainless steel
Material	Standard: Stainless steel, other materials available upon request

Critical Venturi Nozzles according to DIN EN ISO 9300

For supercritical operation

Operating Note

Calibration Options

Type: Calibration in pressure or suction operation
Medium: Air or pure gases
Certificate: Factory, DAkkS-DKD, or PTB calibration

Main Features

Nozzle throat diameter d from 20 μm to 170 μm
Inlet nominal diameters from DN 4 to DN 18
Connection via adapters or clamp connectors
Suction or positive pressure operation
Short response time and high accuracy
Very good long-term stability, no moving parts

Data Sheet

Various Configurations

Configuration of Nozzle Adapter 10-A-300-a

Nozzle O-ring sealed, plug-in type for cylindrical pipe adapter 10-A-300-a or 10-A-301-a, threaded connections G1/8″ or G1/4″.

Configuration of CFO-SS-6MO-6 Adapter

Nozzle O-ring sealed, plug-in type for Swagelok SS-6MO-6 or SS-400-6 adapter, connections: compression fitting or external thread.

Configuration of CFO-4-VCR-7-4 Adapter

Nozzle integrated into sealing washer, metallic seal in Swagelok 4-VCR-7-4 adapter with union nut and internal or external thread.

Configuration of Nozzle Adapter FRO

Throttle or nozzle, for example, welded into SS-4-VCR fitting, with compression fitting and external thread.

Data Sheet

Single nozzle adapter for DN 4 to DN 10

Compact, handy, suitable for standard pipes

Small nozzles as individual measuring sections in flow ranges of up to approximately 6 m³/h can be connected to standard pipes with nominal diameters from DN 4 to DN 10 using commercially available clamp fittings or simple pipe adapters. For larger nozzles and flows, individual nozzle sections are usually constructed with flange connections.

Easy handling, quick response time, high measurement and adjustment accuracy of the flow, very high long-term stability, and correspondingly long recalibration intervals of the critical nozzles are unbeatable features for recurring calibration tasks in volumetric flow measuring devices for air and gases.

Calibration Options

Type: Calibration in pressure or suction operation
Medium: Air or pure gases
Certificate: Factory, DAkkS-DKD, or PTB calibration

SNG-30 and SNG-50: Galleries with Critical Nozzles according to DIN EN 9300

SNG Critical Nozzle Galleries DN 30/50
With more than 2^n-1 combinations

Multiple binary-staged critical nozzles can be connected in parallel and combined within a nozzle gallery. This allows for air or gas flows to be adjusted with the resolution of the smallest nozzle and approximately double the flow of the largest nozzle across a wide flow range.

A nozzle gallery of the SNG type (Sonic Nozzle Gallery) can generally be equipped with critical nozzles of various throat diameters to be used in any combination. However, a binary approach is usually pursued. The nominal flow rate of the n nozzles used is based on that of the smallest nozzle (Q1) and is, for the larger nozzles, 2, 3, etc., up to (2n-1) times Q1.

Short Description

A nozzle gallery enables the calibration of measuring devices for volumetric or mass flow over a wide measurement range with just one compact flow adjustment system. The galleries can be fully automated with pneumatically controlled valves. They consist of the inlet block, the nozzle string with a central block, and the outlet block. There are 4 connections for sensors (2 for pressure, temperature, and relative humidity) and up to 9 connections for nozzle adapters, with the connection on the (upstream) side of the inlet collection block potentially accommodating the nozzle with the maximum throat diameter. Each nozzle adapter can be equipped with a critical nozzle.

The throat diameters used should, according to DIN EN ISO 9300 standards, be at least 4 to 10 times smaller than the inlet nominal diameter (30 or 50 mm).

Operating, Valve, and Calibration Options

Type: Calibration in pressure or vacuum operation
Medium: Air or clean gases
Valves: Manually or pneumatically controlled
Bloc and Bleed Control: 2 valves per nozzle string
Certification: Factory, DAkkS-DKD, or PTB calibration

Property	Functionality
Flow Range	up to 5m³/h (equivalent to air)
Accuracy	Manufacturing accuracy Calibration accuracy (best possible)	±5 % of set value (standard) ±0.25 % of m.v. for Q < 10 Nm³/h ±0.12 % of m.v. for Q ≤ 10 Nm³/h
Calibration periods (best possible)	5 years for Q < 2 Nm³/h 10 years for Q ≤ 2 Nm³/h
Pressure Ranges	Input pressure 1 - 10 bar absolute
Operating Temperature	0 ... +50 °C
Media Compatibility	Air and gases compatible with stainless steel
Material	Standard: Stainless steel, other materials available upon request
Process Connections	Inlet block: 2x G 3/4"i, 3x G1/2"i and 1x G1/4"i Outlet block: 2x G 3/4"i, 2x G1/2"i and 1x G1/4"i Middle block: 1x G1/8"i