|Flow rate||Nominal size|
residual oil (mg/l)
In class II tanks the separation of oil and water is effected by gravity; therefore no filters are needed. The remaining oil residue is allowed to reach a maximum of 100 mg/l; the lower the flow rate, the less oil left in the water.
Class I tanks include a coalescence filter. This type of filter ensures that the exiting water will contain no more than 5 mg/l of oil.
The nominal size (NS) 3 type oil separator carries in its oil separation compartment 2 filter blocks; the NS6 type has 4 filter blocks and the NS10 6 filter blocks. The integrated partitions force the water to flow though these filters. The robust design of these filters allows them to be cleaned with high pressure washers
When choosing the right system it’s best to refer to the EN 858-2 standard. The proper nominal size according to this standard can be calculated according to the following formula:
NS = (Qr + fx * Qs) * fd
NS = nominal Size in l/s
Qr = maximum flow rate of the rainwater in l/s
Qs = maximum flow rate of wastewater in l/s
fx = impediment factor depending on the nature of the discharge
fd = density factor for the relevant light liquid (Table I)
|kind of use|| fx
| Industrial wastewater: car washes, petrol stations, cleaning of
oil covered parts, etc.
| Oil contaminated rain water from impervious areas: car parks,
roads, factory yards, etc.
| Retain any spillage of light liquids and protect surrounding
|Density (g/cm3)||Up to 0.85|| From 0.85
up to 0.90
up to 0.95
|Density factor fd|
| Class I and II combination
The oily water flowing from a car wash site cannot be left untreated. Assume that the wastewater produced by each cleaning unit is 2 l/s. In this case the operating car wash consists of 2 high-pressure washing units. According to EN858-2 an amount of 1 l/s must be included for each extra unit. In effect, the total amount of water (Qr) collected by the area is 3 l/s. There is no other wastewater available besides the water from the car cleaning (Qs = 0). In the case a class I separator is used, fd can be found in table II. It follows that the density of engine oil is 0.89, so that fd = 1.5. In table I we find fx = 2.
NS = (Qr + fx * Qs) * fd
Qs = 3 l/s
Qr = 0
fx = 2
fd = 1,5
NS = 9 l/s
Pipelife solution: NS = 10
By filling in the formula, NS = (Qr + fx * Qs) * fd, it follows that NS = 9. The most suitable Pipelife Class I Oil Separator is the NS10. Now in combination with a sludge separator the wastewater can be cleaned from the light fluids according to the EN858 standard with the NS10 Pipelife Oil Separator.
If you’re not certain which system best suits your needs, please contact us. Our experts will help you with further information, explanations and professional advice.