# Measuring flow rate

Using the Manning equation for flow from a depth measurement is not applicable under gradually varying flow conditions such as backwater conditions upstream of a dam or weir.

Rotary vane meters consists of equally divided, rotating impellers, two or more compartments, inside the meter's housings.

Variable Area - Rotameters Orifice Plate With an orifice plate, the fluid flow is measured through the difference in pressure from the upstream side to the downstream side of a partially obstructed pipe.

Variable Area Flowmeter or Rotameter The rotameter consists of a vertically oriented glass or plastic tube with a larger end at the top, and a metering float which is free to move within the tube.

## How to measure flow rate of water in a pipe

The detecting optics collects scattered light on a photodetector, which then generates a pulse signal. These alternating low pressure zones cause the obstruction to move towards the low pressure zone. In the Venturi Tube the fluid flowrate is measured by reducing the cross sectional flow area in the flow path, generating a pressure difference. The float rises until the annular area between the float and tube increases sufficiently to allow a state of dynamic equilibrium between the upward differential pressure and buoyancy factors, and downward gravity factors. They are the meter of choice for large commercial users, fire protection, and as master meters for the water distribution system. Area-Velocity Meter An area-velocity meter is an open channel flow meter that measures flow by making two separate measurements of depth and velocity. In most operations it is important to know that the right fluid is at the right place at the right time. A ruler or tape measure can be used to improve the accuracy of the cross sectional area measurement, and a stopwatch can be used to improve the velocity measurement by timing a floating piece of debris traveling a set distance. Transit time meters also use ultrasonic waves like a Doppler meter, but instead of bouncing the sound waves off particles in the water like a Doppler meter, transmit time meters send the ultrasonic wave between two sensors located some distance apart from each other along the length of the pipe, and use the transmit time of the sound waves to compute the water velocity. A fixed quantity of liquid passes through the meter for each revolution. Three holes arranged in a line allow the pressure probes to measure the velocity vector in two dimensions. The displacement can be related to the flow rate. The teeth on side B will now close off the fluid from entering side B. Furthermore, in parallel with the phase shift in frequency between inlet and outlet it is also possible to measure the actual change in natural frequency.

These openings divide up the fluid stream and as the gears rotate away from the inlet port, the meter's inner wall closes off the chamber to hold the fixed amount of fluid.

This is why hydrometry is a 4-step process: the continuous measurement of heights upstream of a hydraulic control see Figure 3or at another location where a unique height-flow relationship can be established, the realization of periodic gauges to build this relationship calibration curveallowing to convert the heights into flows, the layout of this calibration curve and the detection of its evolutions, then, after conversion of heights into flow, critical analysis of spatial and temporal fluctuations, then their archiving.

Note that the manometry for a venturi tube or orifice should be installed below the hydraulic grade line or pipe.

### Ultrasonic flow meter

Wear will reduce the accuracy. Flow Nozzles Flow nozzles are often used as measuring elements for air and gas flow in industrial applications. Other factors that affect liquid flow rate include the liquid's viscosity and density, and the friction of the liquid in contact with the pipe. The meters are normally made of aluminum to be lightweight, and are usually 7. Transit time meters also use ultrasonic waves like a Doppler meter, but instead of bouncing the sound waves off particles in the water like a Doppler meter, transmit time meters send the ultrasonic wave between two sensors located some distance apart from each other along the length of the pipe, and use the transmit time of the sound waves to compute the water velocity. Strainers are generally required to be installed in front of the meter to protect the measuring element from gravel or other debris that could enter the water distribution system. Some are designed to spin visibly in the fluid stream to aid the user in determining whether the float is stuck or not.

The speed map is plotted by 30 to 40 seconds of stationing at several depths and on several verticals.

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