Every setup is different,.. the same numbers do not always mean the same flow rate. Put your brush head in a bowl, switch on the water and see how much you get in a minute. A lot of guys use only 1 litre per minute,.. I use more but find I can work faster because of it. On a trolley system you prob want to get used to a lower flow though, so start with 1 litre per minute and when you get the hang of things you might even drop a bit lower.