# Onsite Arithmetic: Pump Math Part 4 – Answers

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Here are the answers for today's practice problem.

1. Determine the gallons per inch.
Convert the width and length to feet and then calculate gallons per inch the same as in previous problems: Area x 1 foot x 7.5 gallons per cubic foot ÷ 12 inches/foot

So, 49 inches ÷ 12 inches/foot = 4.1 feet and 68 inches ÷ 12 inches/foot = 5.67 feet

4.1 feet x 5.67 feet x 1 foot x 7.5 gallons/cubic foot ÷ 12 inches/foot = 14.5 gallons/inch

2. If the pump runs for three minutes and the effluent levels measured from the surface change from 66 inches to 73.5 inches, determine the pumping rate.
The difference between 66 inches and 73.5 inches is 7.5 inches. Multiply the gallons per inch by 7.5 inches to get the volume pumped, then divide by three minutes to get the rate in gallons per minute:

14.5 inches x 7.5 gallons/inch = 108.75 gallons ÷ 3 minutes = 36.25 gallons per minute

3. If the system has a check valve and the required dose is 75 gallons, how long should the timer be set for the “on” setting in a timed dose system?
The pump needs to deliver 75 gallons, so 75 divided by the pump rate will determine the minutes the pump needs to run to deliver the necessary volume.

75 gallons ÷ 36.25 gallons/minute = 2.06 minutes

4. If the number of cycles required for the system is six times per day, how long should the “off” timer be set for?
The runtime during a day is 6 x 2.06 minutes or 12.36 minutes out of a day, which is 1,440 minutes long (60 minutes/hour x 24 hours = 1,440 minutes). So the off time is 1,440 – 12.36 = 1,427.64 minutes of off time divided by 6 = 237.94 minutes or roughly 238 minutes.

5. If the timer was set to pump six times a day and the cycle counter read 3,442 today and 2,899 on the previous visit 120 days ago, is the system operating properly?
If the system is operating properly, the pump should have run 720 times between visits (6 x 120 days = 720); the difference between cycle counts is 543. That is 177 fewer times (720-543) than should have been counted, so something is not right and the problem needs to be determined.

6. The elapsed time meter reads 215.8 hours today. On the last visit 120 days ago it read 192.6 hours. What is the total time recorded in minutes? What are the total flow and the average flow for 120 days? Is this system operating properly?
The difference in elapsed time is 215.8 hours - 192.6 hours = 23.2 hours.

23.2 hours x 60 minutes/hour = 1,392 minutes

1,392 minutes x 36.25 gallons/minute when the pump is running = 50,460 gallons pumped ÷ 120 days = 420.5 gallons per day, which is less than the daily flow of 6 x 75 gallons which equals 450 gallons per day. So this time the system is probably working the way it should.

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