Orifice plate-type hydraulic flowmeter

Another method by which flow rate can be determined involves the use of an orifice plate-type flowmeter in which an orifice is installed in the pipeline as shown in Figure 2.14.

orifice-flow-meter

The figure also shows the presence of two pressure gages, one each on either side of the orifice. This arrangement enables us to determine the pressure drop (AP) across the orifice when the fluid flows through the pipe and given by AP = Pi- P2- The higher the flow rate, greater will be the pressure drop.

The actual flow rate can be determined by the following equation:

equ-2

Where
Q is the flow rate in m3/s
C is the flow coefficient (C = 0.80 for a sharp-edged orifice and 0.60 for a square-edged orifice)
A is the area of the orifice opening in m^
S is the specific gravity of the flowing fluid and
AP = P1-P2 is the pressure drop across the orifice in psi or kPa.

Turbine-type hydraulic flowmeter

Figure 2.13 is a simple illustration of a turbine-type flowmeter.

This flowmeter has a turbine rotor in the housing, which is connected to the pipeline whose flow rate is to be measured. When the fluid flows, it causes the turbine to rotate. Higher the flow rate, greater is the speed of the turbine. The magnetic end of a sensor, which is positioned near the turbine blades, produces a magnetic field whose magnetic lines of force are interrupted by the rotation of the turbine blades, thereby generating an electrical impulse. An electrical device connected to the sensor converts the pulses to flow rate information.

turbine-flow-meter