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Grease Interceptor Sizing

Grease Interceptor Sizing

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 0.75 = ___ 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.

Example:

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

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.

Example:

1.	Fixture A:	35 GPM Flow Rate
	Fixture B:	26 GPM Flow Rate
	Fixture C:	18 GPM Flow Rate
	Fixture D:	12 GPM Flow Rate

2.	35 GPM (A) x 100%	=	35 GPM
	26 GPM (B) x 50%	=	13 GPM
	30 GPM (C + D) x 25%	=	7.5 GPM
	Total Flow Rate	=	55.5 GPM

A 50 GPM interceptor is recommended for this installation.

Typical Interceptor Installations:

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Drainage Products
Need help selecting the correct drain, interceptor, cleanout, fixture carrier or other specialty product? Visit the Watts Drainage Products Learn About page to download product recommendations, selection factors, typical installation diagrams and more.

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