Environmental Engineering Reference
In-Depth Information
devices. Physical phenomena discovered centuries ago have been the
starting point for many of the viable flow meter designs used today.
Moreover, the recent technology explosion has enabled flow meters to
handle many more applications than could have been imagined centu-
ries ago. Before selecting a particular type of flow measurement device,
consider (Kawamura, 2000):
1. Is liquid or gas flow being measured?
2. Is the flow occurring in a pipe or in an open channel?
3. What is the magnitude of the flow rate?
4. What is the range of flow variation?
5. Is the liquid being measured clean, or does it contain suspended
solids or air bubbles?
6. What is the accuracy requirement?
7. What is the allowable head loss by the flow meter?
8. Is the flow corrosive?
9. What types of flow meters are available to the region?
10. What type of post-installation service is available to the area?
2.13.4 differential Pressure flow Meters
*
For many years
differential pressure
flow meters have been the most
widely applied flow measuring device for water flow in pipes that require
accurate measurement at reasonable cost. The differential pressure type
of flow meter makes up the largest segment of the total flow measurement
devices currently being used. Differential-pressure-producing meters
currently on the market include the Venturi, Dall type, Hershel Venturi,
universal Venturi, and Venturi inserts. The differential-pressure-produc-
ing device has a flow restriction in the line that causes a differential
pressure, or head, to develop between the two measurement locations.
Differential pressure flow meters are also known as
head
meters
, and,
of all the head meters, the orifice flow meter is the most widely applied
device. The advantages of differential pressure flow meters include:
•
Simple construction
•
Relatively inexpensive
•
No moving parts
•
External transmitting instruments
•
Low maintenance
•
Wide application of flowing fluid, suitable for measuring both gas
and liquid flow
*
This section is adapted from Husain, Z.D. and Sergesketter, M.J., in
flow measurement
,
Spitzer, D.W., Ed., Instrument Society of America, Research Triangle Park, NC, 1991, pp.
119 -160.
