LIT194-Handbook of TII.pdf - Diamond Head Sprinkler Supply

Dynamic Pressure DeterminationDynamic pressure is the pressure when water is flowing in the system. Dynamic pressure in asystem can be determined by flow tests, using pressure gauges or by calculation if information onpipe types and sizes, valves, meters or other appurtenances are known. The dynamic pressure canbe calculated at a given point in the system by starting with a known dynamic pressure at somepoint, adjusting for elevation change and subtracting friction losses in pipe, fittings, valves, meters,etc. as shown below:Dynamic Pressure = (PSI dynamic ± h e elevation ) - h f pipe - h f fittings - h f valvesWhere:PSI dynamic = the known dynamic pressure at a given point in psih e elevation = pressure change due to elevation in psih f pipe = the psi loss due to “friction” losses in the pipeh f fittings = the psi loss due to “friction” losses in fittingsh f valves = the psi loss due to “friction” losses in valves, meters or otherappurtenances between the source and the given point in the systemControlValvePoint “B”Point “A”WaterMeter100 ft.MElevation ViewExample:In the diagram above the dynamic pressure at point “A” is 90 psi. The pipe is 2 inch class 315PVC, 200 ft. from point “A” to point “B” with a flow rate of 50 gpm. According to themanufacturer, the control valve will lose 6.0 psi at 50 gpm.90.00 psi at point “A”- 43.30 psi loss due to elevation gain (100 ft. x 0.433 psi per ft.)46.70 psi at point “B”- 3.86 psi friction loss in pipe (1.93 psi loss per 100 ft. x 200 ft. / 100)42.84 Subtotal- 0.39 psi friction loss in fittings (estimate, 10% of friction loss in pipe)42.45 Subtotal- 6.00 psi loss in valve - from manufacturer data36.45 psi dynamic pressure at point “B”®Handbook of Technical Irrigation Information5