When you look into SPEL tanks you can see the difference
SPEL Stormceptors are the most widely used separators where it is acceptable to treat the ‘first flush’ ie. flows according to the nominal size (NSB) generated by rainfall rates of up to 6.5mm/hour. This covers most rainfall events in the UK. Any excess rainfall is by-passed without treatment.
The SPEL Stormceptor® by-pass separator is a well proven high quality factory made unit, designed and tested in accordance with the European Standard BS EN 858-1 and meets the requirements of the Environment Agency’s Pollution Prevention Guidelines PPG3 and the Construction Products Regulations.
SPEL Stormceptor by-pass separators are manufactured in class 1 and class 2 models and with or without silt capacity in accordance with BS EN 858-1.