The magic numbers
7.48→ gallons in one cubic foot of water
8.34→ pounds in one gallon of water
0.785→ circle factor (area = 0.785 x D x D)
0.433→ psi added by one foot of water
2.31→ feet of head in one psi
1,440→ minutes in one day
Change inches to feet FIRST: inches / 12.
Area & volume
Rectangle area = length x width
Circle area = 0.785 x D x D
Box volume = L x W x depth
Round volume = 0.785 x D x D x depth
★Then gallons = cubic feet x 7.48
A pipe is a round tank on its side: circle end x length x 7.48.
Dosage - the pounds formula
lbs/day = flow (MGD) x dose (mg/L) x 8.34
Works for chlorine, alum, lime - any chemical.
★Flow must be in MGD, dose in mg/L.
A one-time batch (a main to disinfect)? Use its volume in MG in place of flow.
Flow & conversions
Flow = amount / time
GPM x 1,440 = GPD
GPD / 1,000,000 = MGD
Per minute -> per day is always x 1,440.
Detention time
Detention time = volume / flow
★Match units: gallons / GPM = minutes; gallons / GPH = hours.
Volume on top, flow on the bottom, every time.
Pressure & head, and percent
psi = feet x 0.433
feet = psi x 2.31
Feet is the bigger number, psi the smaller.
Percent removed = (in - out) / in x 100
★Always divide by the amount you started with (the in).