Frequently Asked Questions
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Sizing by Capacity
Capacity:
International Plumbing Code (IPC) also references/uses DFU’s
Note:
Capacity sizing is typically applied to gravity grease interceptors (GGI) resulting in a liquid capacity that is substantially greater
than an equivalent hydromechanical GI.
falls below 90%) results in actual grease capacity that is operationally equivalent to a GGI that is 5-6 times that of the HGI.
Example:
Commercial sink with food waste with 1-1/2” trap, plus mop sink and special purpose sink 2” trap.
3+3+3=9 (DFU)
Referencing table below 9 DFU will require 750 gallon min. interceptor volume.
Floor Drains & Floor Sinks:
Take the volume of water produced by the number of hose bibs (ie 1.5-2.0 gpm per 3/4” faucet)
Drainage Fixture
Units
Interceptor Volume
(min.)
8
500
21
750
35
1000
90
1250
172
1500
216
2000
Fixture
Fixture Units Public
Floor drain, non-emergency
2
Special purpose sink w/1-1/2” trap
3
Special purpose sink w/2” trap
4
Special purpose sink w/3” trap
6
Commercial sink w/food waste w/ 1-1/2” trap
3
Bar Sink
2
Mop Sink
3
Laundry Sink
2
The conversion of DFU (Discharge Fixture Units) to Flow Rate equivalent is not directly achievable by application of a standard
formula. As an experienced manufacturer in the Grease Management market, we have been able to identify and validate a
a
manufacturers recommended method of conversion
to determine Hydromechanical Grease Interceptor equivalency, to a
respective Gravity Grease Interceptor volume where initially determined by total calculated DFU discharge.
Step 1:
The total DFU is used to identify the respective Gravity Interceptor volume (US Gallons).
Step 2:
Multiply the selected volume by the respective factor, (
See HGI Conversion Factor column above
) dividing the result by
30 (min). 30 minutes is the typical retention time used as the basis of design for Gravity Grease Interceptor (GGI) volume.
Example:
Therefore, 1250 (USG) x 1.75 (Conversion Factor) = 2188USG. Now divide the 2188gallons by the 30 minute retention time and the
output is 72.9GPM. Using established practice, this number is rounded up to the next standard size of interceptor available and so
conversion of a 1250USG Gravity Grease Interceptor is considered to be a 75GPM Hydromechanical GI.
Total DFU
Int. Vol. USG
HGI GPM
HGI Conversion Factor
HGI size
8
500
17
1.00
20
21
750
31
1.25
35
35
1000
50
1.50
50
90
1250
73
1.75
75
172
1500
100
2.00
100
216
2000
167
2.50
2x 100
307
2500
250
3.00
*
3x 100
342
3000
350
3.00
*
3x 100
How can I convert DFU to GPM?
* NOTE: BEYOND VOLUME OF 2500 USG HGI CONVERSION FACTOR BECOMES CONSTANT AT 3:00
