Onsite Arithmetic: Pump Tank Math — Answers

Onsite Arithmetic: Pump Tank Math — Answers

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Here are the answers to today’s practice problem.    

1. If there is a rectangular pump tank with dimensions of 5 feet wide by 8 feet long, what are the gallons per inch in the tank?
Answer: Determine this by taking the area x 1 feet of depth x 7.5 gallons/cubic foot ÷ 12 inches/foot = gallons/inch.

5 feet x 8 feet x 1 foot = 40 cubic feet

40 cubic feet x 7.5 gallons/cubic foot = 300 gallons ÷ 12 inches/foot = 25 gallons/inch

2. What if the pump tank is circular and has a diameter of 5 feet? What are the gallons per inch in this circular tank?
Answer: Determine the area, and then determine the gallons per inch the same as for the rectangular tank.

Area of a circle = , so area is 3.14 x 2.5 feet x 2.5 feet = 19.6 square feet x 1 foot = 19.6 cubic feet

19.6 cubic feet x 7.5 gallons/cubic foot = 147 gallons ÷ 12 inches/foot = 12.25 gallons/inch

3. If in both tanks the pump height plus the blocks underneath the pump equals 18 inches, how many gallons does it take to cover the pump?
Answer: For the rectangular tank: 18 inches x 25 gallons/inch = 450 gallons

For the circular tank it takes: 18 inches x 12.25 gallons/inch = 220 gallons

4. If the pump needs to deliver a total of 150 gallons, (assuming there is a check valve) how many inches are between the on and off floats to deliver the dose?
Answer: For the rectangular tank: 150 gallons ÷ 25 gallons/inch = 6 inches between floats

For the circular tank: 150 gallons ÷ 12.25 gallons/inch = 12 inches between floats

5. What operating depth is needed in each tank to accommodate the necessary gallons to cover the pump and provide the required dose?
Answer:
For the rectangular tank: 450 gallons of depth to cover the pump + 150 gallons per dose = 600 gallons and 25 gallons/inch of depth; take 600 gallons ÷ 25 gallons/inch = 24 inches

For the circular tank: 220 gallons of depth to cover the pump + 150 gallons per dose = 370 gallons ÷ 12.25 gallons/inch = 30.2 inches

The easier way, of course, would be to add the 18 inches to cover the pump to the required depth to deliver the dose volume; the answer should be the same.

This article is part of a series of practice problems for installers:



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