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Water Master™

Fire service tanker GPM calculator

Please e-mail your questions or comments to: drridgway@aol.com

This GPM calculator is based on the ISO™ formula that determines how many gallons per minute a tanker will deliver for grading purposes.

The numbers you see are from an actual test on a 3500 gallon Water Master™.
Follow the instructions below and see how your tanker compares.
Tank Size Fill Time Dump Time Distance Total Time GPM

Automatic recalculation 

ISO™ Shuttle Test Form by Tank Size
Note: This form is a longer version of the one above and gives the GPM for one mile through 10 mile round trips. The default fill and dump time data in this form is the same as below. The different GPM figures are a result of how the tank capacity is determined. (Actual weight vs calculated capacity - 10%) You may use your own tanker data and print this form for your records.

ISO™ Shuttle Test form by Weight
Note: This form contains actual data from an ISO™ shuttle test on a 3500 gallon Water Master™. The actual weight of the vehicle is used vs the tank size in the form above. You may "play" with the data to see the effects of different fill/dump times. You may also use your own tanker data and print this form for your records.

Water Master™ Shuttle Form
Note: This form will allow you to enter data for up to 10 tankers to calculate and record your overall water shuttle performance. Fire departments have our permission to print and use this form.

Instructions for water shuttle calculations:

  1. Tank Size: Enter the tank capacity in US gallons.

  2. Fill Time: Enter the fill time in minutes and tenths (tenths = seconds divided by 6). The actual time for filling shall be the time required for the tanker to travel 200 feet to the fill site, maneuver into position, fill and travel 200 feet from the fill site.

  3. Dump Time: Enter the dump time in minutes and tenths (tenths = seconds divided by 6). The actual time for dumping shall be the time required for the tanker to travel 200 feet to the dump site, maneuver into position, dump and travel 200 feet from the dump site.

  4. Distance: Enter the distance (miles) of the round trip from the dump site to the fill site.

  5. Total Time: The total time is calculated by the script and is sum of the travel time + the fill time+ the dump time.

  6. GPM: The GPM is calculated by the script.

ISO™ Formula: Gallons Per Minute= The tank size less 10%, divided by: Fill time + Dump time + Travel time. (Travel time= .65 + 1.7 x Distance.)

For an in-depth study of the ISO™ grading procedure read: Your Next ISO™ RATING--Simple Solutions, By Larry H. Stevens
(This is the complete book, so be prepared for several minutes download time.)
Visit Larry H. Stevens Web site: www.isoslayer.com


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