Product Brochure
- 10 -
Sizing by Flow Rate
Table A - Procedure for Sizing Grease Interceptors
STEP FORMULA EXAMPLE
1 Determine cubic content of xture by multiplying length x
width x depth
A sink 24” long by 20” wide by 12” deep.
Cubic content: 24 x 20 x 12 = 5,760 cu in
(61.0 x 50.8 x 30.48 cm
3
)
2 Determine capacity in gallons.
1 gallon = 231 cu in
Contents in gallons:
5,760 / 231 = 24.9 gallons
(94,451.42 / 1,000 = 94.45 litres)
3 Determine actual drainage load.
The xture is normally lled to approximately 75% of capacity
with water as the items being washed displace about 25% of
the total xture content.
Actual drainage load = 75% of xture capacity
Actual drainage load:
.75 x 24.9 = 18.7 gallons
(0.75 x 94.45 = 70.84 litres)
4
Determine ow 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 dened as the actual
time required to completely drain the xture.
Flow rate = Actual Drainage Load
Drainage Period
Calculate ow rate for one minute drainage period:
18.7 / 1 = 18.7 g.p.m. ow rate
(70.84 / 1 min. = 70.84 l.p.m.)
Calculate ow rate for two minute drainage period:
18.7 / 2 = 9.4 g.p.m. ow rate
(70.84 / 2 min. = 35.42 l.p.m.)
5 Select Interceptor.
From Table B select the interceptor with a ow rating at least
equal to the calculated ow rate. When the calculated ow rate
falls between two sizes, select the larger of the two
interceptors.
For a one minute drainage period:
18.7 g.p.m. (70.84 l.p.m.) ow rate = 20 g.p.m. G.I.
For a two minute drainage period:
9.4 g.p.m. (35.42 l.p.m.) ow rate = 10 g.p.m. G.I.
Table B -Metric conversions based on PDI sizes
PDI Size 4 7 10 15 20 25 35 50 75 100
Flow Rate US Gallons per Minute (gpm) 4 7 10 15 20 25 35 50 75 100
Flow Rate Liters per Second (L/Sec) .25 .44 .63 .95 1.26 1.58 2.20 3.16 4.74 6.3
Grease Capacity Min. (lb) 8 14 20 30 40 50 70 100 150 200
Grease Capacity Min. (kg) 3.63 6.35 9.07 13.61 18.14 22.68 31.75 45.36 68 91
It is reccomended that HGI’s such as Endura® interceptors are sized by ow rate. The use of a ow control with a Hydromechanical Grease
Interceptor is considered mandatory. Without a properly sized ow control, the discharge rate through into the interceptor may exceed the
design rating of the unit, causing lower eciencies and increase the risk of grease, passing into the downstream system. Be careful not to confuse
liquid capacity and ow rate. Liquid capacity is stated in gallons (or liters) while ow rate is referenced in gallons per minute (GPM) or liters per
second (L/Sec).
Key Design Considerations
Fixture Capacity: Most commonly used and recommended method for Hydromechanical Grease Interceptors. This
method looks at the maximum capacity of xtures connected to the interceptor and the time taken to discharge that volume of
wastewater through the interceptor. Units are expressed in Gallons Per Minute (gpm).
Calculation takes 75% of maximum capacity of all xtures and based on a 1 or 2 minute period of time taken to discharge, results
in a gallons per minute ow rate. This number is rounded up to the next available size of interceptor, i.e. 16.7gpm become a
20gpm Grease Interceptor.
Pipe Size:
Pipe
Diameter
Maximum
Flow Rate
(gpm)
Size of interceptor
1-minute drain
period (gpm)
Size of interceptor
2-minute drain period
(gpm)
2-inch 20 20 10
3-inch 60 75 35
4-inch 125 150 75
Use our simple online sizing calculator
and DFU conversion at...
www.SizeMyGI.net