1 For surface waters, between 20 and 40 mm (upstream the strainer)  For municipal wastewater: for raw water, from 15 to 30 mm (but upstream from a straining and/ or lamellae settling process, fine screening is necessary); for sludge (if necessary), 10 mm or less.
Other studies. According to some studies, 18-year-old males have a refractory period of about 15 minutes, while those in their 70s take about 20 hours, with the average for all men being about a half-hour. Although rarer, some males exhibit no refractory period or a refractory period lasting less than 10 seconds.
They came regularly, but they were too far apart to be what we have called normal. The average menstrual cycle length (cycle length being from the start of one period until the day before the next flow) in many studies, and from many countries, is about 28 days, or a lunar month. However, regular has two possible meanings: