Here are the answers to today’s practice problem.

1. Using the same rectangular (4 feet by 7 feet) and circular (5-foot diameter) pump tanks from last month, if the alarm float has a minimum 5-inch swing to set off the alarm, determine how many gallons will accumulate before the alarm is tripped.

Answer: For the rectangular tank, the gallons per inch was calculated as 17.5 gallons per inch. The gallons accumulated are 17.5 gallons per inch x 5 inches = 87.5 gallons or rounded off to 88 gallons.

For the circular tank, the gallons per inch is 12.5, so 12.5 gallons per inch x 5 inches = 62.5 gallons or rounded to 62 gallons.

2. If the average daily flow is estimated at 450 gpd for a three-bedroom house and the local regulations require the tank to hold one day's flow above the alarm float to give the homeowner the opportunity to get the pump fixed, how large a tank is needed to provide the required volume? How deep in inches does the tank need to be to provide the required volume?

Answer: For the rectangular tank the necessary volume is found by adding the required volumes to determine capacity:

Volume to cover the pump and block = 315 gallons

Dose volume = 150 gallons

Alarm volume = 88 gallons

Total = 553 gallons

Reserve capacity = 450 gallons

Total capacity = 1,003 gallons or at least a tank with 1,000 gallons of workable capacity

1,000 gallons ÷ 17.5 gallons/inch = 57.1 inches. I would say a tank that is 60 inches deep to provide 3 inches of air space.

For the circular tank, add the required volumes to determine capacity:

Pump and block = 220 gallons

Dose volume = 150 gallons

Alarm volume = 62 gallons

Total volume = 432 gallons

Reserve capacity = 450 gallons

Total capacity = 882 gallons

882 gallons ÷ 12.25 gallons/inch = 72 inches or 6 feet deep; adding 3 additional inches would make it 75 inches.