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Sizing
For Basic Grease Interceptor sizing, please reference the Sizing Guide or the Plumbing &
Drainage Institute Standard PDI-G 101. Without a properly sized flow control, the flow
through the interceptor may exceed the rating of the unit, causing lower efficiencies
and allowing grease to pass through the interceptor into the downstream piping. Be
careful that you do not confuse liquid capacity and flow capacity. Liquid capacity is
rated in litres or gallons while flow capacity is rated in gpm (gallons per minute) or L/
sec (litres per second).
If sizing indicates that a larger Grease Interceptor is required, you maybe able to
compromise to a smaller unit by adopting to a 2 minute drain down time in your
sizing calculation. Although the smaller unit will be less expensive, the grease
capacity of a smaller unit will dictate the cleaning frequency required.
Sizing Calculator
STEP
1
Determine cubic content of fixture by multiplying length x
2
Determine capacity in gallons.
3
Determine actual drainage load.
The fixture is normally filled to approximately 75% of capacity
with water as the items being washed displace about 25% of
Actual drainage load = 75% of fixture capacity
4
Determine flow rate and drainage period.
In general, good practice dictates a one minute drainage pe-
riod; however, where conditions permit, a two minute drainage
period is acceptable. Drainage period is defined as the actual
time required to completely drain the fixture.
Flow rate = Actual Drainage Load
5
From Table B select the interceptor with a flow rating at least
equal to the calculated flow rate. When the calculated flow rate
falls between two sizes, select the larger of the two
PDI Size Symbol
Flow Rate US Gallons per Minute (GPM)
Flow Rate Liters per Second (LPS)
Grease Capacity Pounds (Lbs)
Grease Capacity Kilograms (Kgs)
Sampling Access
Some municipalities require a sampling port to monitor effluent quality. If
the unit is on the floor, or semi-recessed into the floor, a cleanout tee can
be installed downstream of the Grease Interceptor. If the unit is installed
in the floor, a backwater with its flapper removed, makes an effective
collection port. Like the FCD the backwater valve can be extended to
finish floor level using a sleeve kit.
For additional Sizing Tools and Maintenance Interval
Optimization, use our Endura® Calculator online
or email: tech-support@endurainterceptor.com
Table A - Procedure for Sizing Grease Interceptors
FORMULA
width x depth
1 gallon = 231 cubic inches
the total fixture content.
Drainage Period
Select Interceptor.
interceptors.
Table B - Procedure for Sizing Grease Interceptors
Mop Sink Sizing Guide
Size
2"
3"
4"
Floor Drains & Floor Sinks
Take the volume of water produced by the
number of hose bibbs (ie 1.5-2.0 gpm per 3/4"
faucet). ASPE also recommends using 4gpm
floor drain if you cannot use the BIBB method.
A sink 24" long by 20" wide by 12" deep.
Cubic content: 24 x 20 x 12 = 5,760 cubic inches
Calculate flow rate for one minute drainage period:
Calculate flow rate for two minute drainage period:
18.7 g.p.m. (70.84 l.p.m.) flow rate = 20 g.p.m. G.I.
9.4 g.p.m. (35.42 l.p.m.) flow rate = 10 g.p.m. G.I.
4
7
10
4
7
10
.25
.44
.63
8
14
20
3.63
6.35
9.07
Venting
Grease Interceptors must have a vented waste, sized in accordance
with local code requirements for venting interceptors to retain a
water seal and prevent siphoning. Most codes dictate that two
vents be installed, one upstream and one downstream of the
grease interceptor. The upstream vent must not be placed between
the air intake and the grease interceptor.
- 2 -
LPS
US/GPM
84
22
142
37.5
170
45
EXAMPLE
(61.0 x 50.8 x 30.48 cm
Contents in gallons:
5,760 / 231 = 24.9 gallons
(94,451.42 / 1,000 = 94.45 litres)
Actual drainage load:
.75 x 24.9 = 18.7 gallons
(0.75 x 94.45 = 70.84 litres)
18.7 / 1 = 18.7 g.p.m. flow rate
(70.84 / 1 min. = 70.84 l.p.m.)
18.7 / 2 = 9.4 g.p.m. flow rate
(70.84 / 2 min. = 35.42 l.p.m.)
For a one minute drainage period:
For a two minute drainage period:
15
20
25
15
20
25
.95
1.26
1.58
30
40
50
13.61
18.14 22.68
)
3
35
50
35
50
2.20
3.16
70
100
31.75
45.36
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