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How to Size Grease Interceptors

General Procedures:

To Determine the Flow Rate of Each Sink:
Calculate the capacity of the sink in cubic inches....length x width x depth =___cu. in.
Convert the capacity from cubic inches to gallons per minute (GPM)....___cu. in./231 = ___GPM.
Adjust for displacement....___GPM x .75 = ___GPM.
Result is the flow rate required to drain the sink in one minute.*
*Note: If drain down time is not critical, an interceptor with a lesser flow rate up to 1/2 the calculated flow rate may be specified.


Three compartment pot sink, each compartment 12" x 12" x 15"
12" x 12" x 15" = 2160 cu. in. x 3 comp. = 6480 cu. in.
6480 cu. in. / 231 = 28 GPM.
28 GPM x .75 = 21 GPM.
A 20 GPM interceptor would permit the sink to drain in slightly more than one minute.
*Discharge from spray hoods is determined by the flow rate of the hood.

Sizing for Multiple Fixtures:

Determine the flow rate for each fixture to be serviced by the interceptor.
Add together 100% of the largest flow rate, 50% of the second largest, and 25% of all others.
Result is the recommended flow rate of the interceptor.

*It is not recommended to pass commercial dishwashers through an interceptor.