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The SI unit is cubic metres per second (m 3 /s). Another unit used is standard cubic centimetres per minute (SCCM). In US customary units and imperial units, volumetric flow rate is often expressed as cubic feet per second (ft 3 /s) or gallons per minute (either US or imperial definitions).
ΔP is the pressure drop across the valve (expressed in psi). In more practical terms, the flow coefficient C v is the volume (in US gallons) of water at 60 °F (16 °C) that will flow per minute through a valve with a pressure drop of 1 psi (6.9 kPa) across the valve.
where: [2] Q f = total residual flow during the test (gallons per minute); c = discharge coefficient (unitless). This is usually 1.0 if using a diffuser. If using a wand to measure the stagnation pressure, the coefficient value depends on the shape of the flow hydrant orifice.
The equation for head loss in pipes, also referred to as slope, S, expressed in "feet per foot of length" vs. in 'psi per foot of length' as described above, with the inside pipe diameter, d, being entered in feet vs. inches, and the flow rate, Q, being entered in cubic feet per second, cfs, vs. gallons per minute, gpm, appears very similar.
K-Factors have also previously been calculated and published using the United States customary units of pound per square inch (psi) and gallon per minute (gpm). Within the United States, US measurements are still often used instead of metric. [3] [4]
Standard cubic centimeters per minute (SCCM) is a unit used to quantify the flow rate of a fluid. 1 SCCM is identical to 1 cm³ STP /min. Another expression of it would be Nml/min. Another expression of it would be Nml/min.
In Imperial units it is defined as the speed in revolutions per minute at which a geometrically similar impeller would operate if it were of such a size as to deliver one gallon per minute against one foot of hydraulic head. In metric units flow may be in l/s or m 3 /s and head in m, and care must be taken to state the units used.
Actual cubic feet per minute (ACFM) is a unit of volumetric flow. It is commonly used by manufacturers of blowers and compressors. [1] This is the actual gas delivery with reference to inlet conditions, whereas cubic foot per minute (CFM) is an unqualified term and should only be used in general and never accepted as a specific definition without explanation.