The Venturi Meter

The venturi meter used in the apparatus pictured is made by Technovate who is now out of business. The meter is made of clear plastic to make the apparatus more "visual" even if there is really nothing to see. The range of this meter varies according to the needs of the user. The upstream section is 1 nominal schedule 80 pipe, while at the throat, the diameter is 5/8 in (approximately). The meter is mounted using union fittings for illustrative purposes.

It is not known at this time where clear plastic venturi meters can be obtained. When Technovate was marketing them, Tecquipment was making a selling one that was quite similar in dimensions.

The meter has 4 static pressure taps which are connected with plastic tubing to two air-over-water manometers (part of a manometer board). The inside pair are used to determine a pressure drop (i.e., head loss) which is calibrated as a function of flow rate measured at the volumetric measuring tank.

The pressure taps attached before and after the union fittings are connected with plasting tubing also to an air-over-water manometer (part of the manometer board). While water flows through the meter, this manometer gives a reading of overall pressure drop experienced by the water after passing through the meter. These data are used to determine a pressure coefficient.

Typical data obtained with the venturi meter is presented here in the graph, and two curves are presented. The vertical axis is of flow rate, and the horizontal axis is the head loss. The line labeled theoretical flow rate is obtained by using the Bernoulli equation with the continuity equation. The line labeled actual flow rate is that measured at the volumetric measuring tank at discreet points.

At any head loss, there will correspond two flow rates: one actual and one theoretical. The ratio of these flow rates is the meter discharge coefficient. Also at any head loss, a Reynolds number can be calculated. A graph of discharge coefficient as a function of Reynolds number is also provided here.

Due to the nature of this experiment and to the volume of data obtained, students are required to submit only the performance graphs, without commenting on accuracy.


Actual and theoretical flow rate through the venturi meter versus reading obtained from the manometer (horizontal axis).


Semilog graph of venturi discharge coefficient as a function of throat Reynolds number, based on actual flow rate.

 

Meter and Manometer Details

Read about the turbine meter, the orifice meter, the venturi meter, the rotameter, or the manometer board.

Read about the relative performance of these meters, compared using dimensionless ratios.

Go back to the Fluids Lab list of experiments.