# Onsite Arithmetic: Flow - Answers

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Here are the answers to practice problem No. 4

1. If the pump tank is 49 inches by 60 inches by 70 inches deep, calculate the gallons per inch.

Convert length and width to feet.

49 inches ÷ 12 inches/foot = 4.1 feet

60 inches ÷ 12 inches/foot = 5 feet

Calculate volume (cubic feet) in 1 foot of depth

4.1 feet x 5 feet x 1.0 foot = 20.5 cubic feet

Convert to volume in gallons.

20.5 feet  x 7.5 gallons/cubic foot  = 153.75 gallons/foot

Calculate gallons per inch.

153.75 gallons/foot ÷ 12 inches/foot = 12.8 gallons/inch

2. The OFF float is at 62 inches and the ON float activation is at 57 inches. What is the dose volume?

Subtract OFF minus ON

62 inches – 57 inches = 5 inches

Multiply total inches by gallons per inch

5 inches x 12.8 gallons/inch = 64 gallons

3. If the supply line is 80 feet of 2-inch SCH 40 PVC, what is the drainback volume in gallons?

Calculate drainback. To do this requires knowledge of the gallons per foot in a 2-inch pipe. This can be obtained from tables available through pipe supply companies or calculating the volume of a cylinder by taking the area of a circle times the length of the pipe. It’s much easier to look it up on a table!

0.17 gallon/foot x 80 feet = 13.6 gallons

4. If the cycle counter reads 46,490 today and read 45,850 the last visit 120 days ago, what is the number of cycles recorded?

PCR – LCR = Number of cycles

46,490 – 45,850 = 640 cycles

5. What is the total flow and average flow for the 120 days?

Calculate total flow.

640 cycles x 64 gallons/cycle = 40,960 gallons

Calculate average daily flow.

40,960 gallons ÷ 120 days = 341 gallons/day

6. If the design flow was 300 gpd for the system, what does this tell you?