Choose Valve Size

Step 1: Calculate Rainfall

1. Use rainfall intensity chart to find rainfall amount in inches per hour (in./hr.) for the site, then calculate to determine feet per hour (ft./hr.)
   
   Rainfall ___ in./hr. divided by 12 in. = ___ ft./hr.
   
   
2. Measure stormwater drainage area to be protected by oil stop valve , then determine square footage as follows:
   
   Length ___ ft. x Width ___ ft. = ___ sq. ft.
   
   
3. Multiply the rainfall (ft./hr.) in step 1. by the area (sq.ft.) in step 2 determine the oil stop valve flow rate in cubic feet per hour (cu.ft./hr.):
   
   ___ ft./hr x ___ sq.ft. = ___ cu.ft./hr.
   
   
4. Multiply flow rate (cu.ft./hr.) from step 3 by 0.1247 to convert flow rate to U.S. gallon per minute (gpm):
   
   ___ cu.ft./hr. x 0.1247 = __ gpm.

Step 2: Choose Valve Size

WARNING: EXCEEDING THESE FLOW RATES MAY CAUSE PREMATURE CLOSING.