Understanding flow measurement principles ing technologies to see which might be the most desirable.
Techniques available to deter mine continuous open channel flow rates include;
• Empirical equations in conjunc tion with level measurements(Man ning's Equation), • Flume/weir primary elements used in conjunction with secondary level measuring devices, • Velocity level meters using veloci ty/area method. The first method is a slope/area method where the conduit itself acts
as a primary element. While the empirically derived equations can be correct, the actual slope of the
v-'l—
surface of the flowing water may differ significantly from that of the invert of the pipe and therefore be very difficult to measure. Rough
By George Pastoric*
pen channel flowmeter ing has become an area of increasing concern in light of new legislations
aimed at reducing pollution of our
All of this detracts from their
main concern, simply to measure
ness of the conduit lining is also a factor which, since it is not con stant, can be at best an estimate. Weirs and flumes offer tradi
flow.
tional solutions shaping a flow so
Once we define the application, we see before us a limited range of
that the level of the surface is in a
technologies available to meet the application. The user can then begin to evaluate various flowmeter
flow.
known relationship to flowrate. Measured level is worked back to Continued overleaf
water systems.
Authorities are imposing string ent demands on dischargers,asking them to report both the quality and quantity of materials being dis charged. Both sides are caught in a struggle to develop and work within
achievable terms of compliance. Flow measurement can be diffi
cult in that the original designs of discharge lines do not lend them selves very well to the installation requirements of most flowmetering technologies. Add the fact that these lines are never full, and that the level in these pipes is constantly changing - conditions which some flowmeters cannot cope with. Finally, flow monitoring may only be required for a limited time in some applications. This means that
Leak detection for
underground storage tanks. Proven
technology intrinsically safe @
the expense and trouble associated with accessing a suitable flowmeter
ing site, let alone that of installing any primary device can keep com pliance officers busy with construc tion projects when they should be looking at other concerns. Implementing a flowmetering technology that will fulfill the required accuracies can leave indus tries with large and costly construc tion projects which could involve fabrication of flowmetering sites and primary elements worth much more than the cost of any selected flowmeter(s).
The new Series DMS from Warrick Controls is the solution for
underground storage tank monitor ing. Utilizing intrinsically safe com ponents, the Series DfylS actively monitors up to fourtank systems for over-fill protection, leak detection
Environmental Science & Engineering, April 1989
and can distinguish between hydro carbons and water.
The Series DMS is available for
double wall fibreglass and steel tanks, fuel tanks, chemical tanks
and monitoring wells. For more detailed information, write or call...
Dqvis Controls LIMITED
4251 Dundas St. West, Toronto, Ontario M8X 1Y3
(416) 233-3211 Telex 06-967684 Fax (416) 239-2386
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