I have never heard it expressed as gradient but I assume you are referring to changes in elevation. When performing hydraulic calculations for sprinkler systems, you account for changes in elevation between two points using the following formula:
P = 0.433 H
P = pressure in psi
H = elevation change in feet
Does that help?
Hydraulic Low Gradient (HLG) adjustments refer to modifying the available Water Supply at point of connection to reflect changes due to the lowest level of the resevoir (or tank) provided by the Water Purveyor.
Here is an example (from a previous project):
Q vs HL Test: P(s) = 47 psi; P(r) = 39 psi @ Q = 704 gpm
HLG = 442 ft (provided by Water Purveyor)
Finish Floor Elevation (FF) = 343 ft
(Point of Connection was set at FF or Base of Riser less a ft in this case)
(HLG) - (FF) = 99 ft
P(s)[Adjusted] = (99)x(.434) = 43 psi
P(r) [Adjusted] = 35 psi @ Q = 704 gpm
The shape of the flow curve does not change; however, all points will be adjusted down.
I hope this helps!
Hydraulic Gradient is being used by Insurance Companies to evaluate existing systems. The evaluation is usually related to performance issues based on years of service of the systems and current conditions. Hydraulic Gradient is also used when modifying or additions to systems is taking place. Most Insurance Companies want a more accurate reading of the system performance at current time then as installed new.
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