Venturi nozzles and nozzles

The basic equation of flow (2.3) is also valid for nozzles. The flow nozzle (Figure 2.3) is a device with a circular hole having a smoothly tapered part at the inlet and a cylindrical part at the outlet.

The accuracy of the nozzle flow measurement is slightly higher than the accuracy of the diaphragm measurement due to the absence of an additional error in the insufficient sharpness of the input edge. Nozzles as narrowing devices for flowmeters have not received the spread, since the head loss in them is little less than in the diaphragms, and making them is much more complicated.

A narrowing device with a high accuracy of flow measurement and not creating large head losses is the Venturi nozzle.

A venturi nozzle is a tapering device whose inlet part is made in the shape of a standard nozzle, and there is a cone in the mouth that serves to reduce head losses.

Depending on the length and the central angle of the cone, long and shortened Venturi nozzles are distinguished. In water supply and sewage systems, short venturi nozzles are more often used. Venturi nozzles are made of two types (Figure 2.4).

The first type is designed for pipes with a conditional pass from 50 to 200 mm, performed with a nozzle made of non-ferrous metals and cast-iron housing. The second type is designed for pipes with a conditional pass from 250 to 1400 mm, performed with a cast iron nozzle, coated with an anticorrosive body without flanges.

When installing the Venturi nozzle, the alignment of the pipe and the nozzle must be observed. There should be no sources near the Venturi nozzle, leading to distortion of the flow.

 

Venturi tubes

 

Venturi tubes were proposed earlier than other narrowing devices. Depending on the size of the diffuser, the Venturi tubes are short and long. There are three design versions of Venturi pipes: A - steel welded from sheet material at Du = 200... 1400 mm, Roux up to 16 MPa; B - with cast unprocessed input parts, processed with a neck at Du = 100... 800 mm Rouge up to 25 MPa; B - with treated inlet nozzle, cone and neck at Du = 50... 250 mm, Rouge up to 4 MPa.

 

The most simple and convenient to manufacture are welded Venturi pipes.

 

 

The standard Venturi tubes (Figure 2.5) consist of the following main parts: the inlet cylinder, the tapering cone, the neck, the expanding cone and the output cylinder. All parts are assembled by welding. The pressure is taken from the averaging annular chambers. In the lower part of the annular chambers, cork valves are installed for draining the liquid.

Venturi pipes are connected to steel pipelines by welding. In some cases, flanges can be connected.

A feature of standard Venturi pipes is their small metal capacity. The necessary lengths of straight sections in front of Venturi tubes are substantially

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