1. Water in a pipe travels 210 feet every three minutes. What is the velocity in feet per minute?
2. Convert the answer in #1 to feet per second.
3. A pipe has a diameter of 1 foot and the velocity in that pipe is 2.5 ft/sec. What is the flow rate in cubic feet per second?
4. Determine the chlorinator setting in pounds per day if you have a flow of 200 gpm and your target chlorine dose is 2.0 mg/L.
5. A 0.52 MGD system is feeding chlorine at a rate of 12 lbs/day. What will be the resulting mg/L chlorine dose?
1. The formula is set up in the answer required (ft/min) or feet divided by minutes.
(210 feet) / (3 minutes) = 70 ft per minute
2. There are 60 seconds per minute.
(70 ft/min) / (60 sec/min) = 1.17 ft/sec
3. The answer called for is in cuft or ft3 which means I need to multiply 3 numbers together. For a round pipe or tank it will be 3.14 X R, ft X R, ft X (Depth, ft or Length, ft) Remember R is Radius and Radius is 1/2 the Diameter = (1 ft) / (2) = 0.5 ft
3.14 X 0.5 ft X 0.5 ft X 2.5 ft/sec = 1.96 ft/sec
OR IF YOU USE DIAMETER:
0.785 X 1 ft X 1 ft X 2.5 ft = 1.96 ft/sec
4. The answer is going to be in Pounds Per Day which is a loading formula problem =
Flow, MGD X Concentration, mg/L X 8.34 lbs/gal, but the flow is given is gpd not MGD so we need to do a conversion to get from minutes to days – there are 60 minutes in one hour and 24 hours in one day or 1440 minutes per day.
200 GPM X 1440 min/day = 288,000 gal/day OR the long way
200 gpm X 60 min/hr X 24 hrs/day = 288,000 gal/day
Now we need to get from gallons to million gallons by dividing gallons by 1,000,000 or just shuffle 6 decimal places to the left = 0.288 MGD
Now fill out the formula and complete
0.288 MGD X 2.0 mg/L X 8.34 lbs/gal = 4.8 lbs/day
5. Whoa – they give you the lbs/day and ask for the dose in mg/L which is usually what you find when working a Loading formula. If you are used to using the Davidson pie chart you have this one. If not you will use the following formula:
Dose, mg/L = (Chemical feed, lbs/day) / (Flow, MGD X 8.34 lbs/gal)
= (12 lbs/day) / (0.52 MGD X 8.34 lbs/gal)
= 2.76 mg/L