Wastewater Calculations

Formulas, Conversion, etc. from Spellman Book

Velocity, V

V = distance traveled (ft) / duration of test (min)

V=\frac{d}{t}

Flow in a Channel, Q

Q = width (ft) x depth (ft) x Velocity (ft/min)
Q=\frac{w\cdot d}{V}

Flow through full pipe, Q

Q = AV

Q = (pi x D²/4) x V

Q = [ 0.785 x (Diameter-ft)² ] x Velocity (ft/s)

Q=0.785\cdot D\left(\operatorname{ft}\right)^2\cdot V

psi

pounds per square inch

1 day = _ min

1440 min

1 ft³ = _ gal

7.48 gal

Density of Water (pcf)

<explain>

62.4 pcf (lbs/ft³)

at T = 68F

1 ft Water (Head) = _ psi

<explain>

0.433 psi

1 psi = _ ft. Head

<explain>

2.31 ft

at T = 64F

theoretical atmospheric pressure (at sea level)

14.7 psi

Pressure of water at rest

P=\gamma h

density of water (pcf) x vertical distance (ft)

Gauge Pressure, P_G

P_{G}=P_{W}-P_{A}

water pressure - atmospheric pressure

Discharge (Flow), Q

Q = AV

Pump Rates

volume pumped over time

Gravity (ft/sec²)

32.17 ft/sec²

Law of continuity

Q1 = Q2

(AV)1 = (AV)2

Head Loss

Hf = K * V²/2g

K - coeff. of frictiom

g - ft/sec²

Centrifugal Pump (conversion)

Head (ft) = P (psig) * 2.31 / SG

Positive-Displacement Pump (conversion)

Head (ft) = P (psig) * 144 / γ

hydraulic horsepower (whp)

550 ft-lb/sec

0.746 kW

2545 Btu/hr

1.014 metric hp