Very little, depending on valve type, construction, area and spring characteristic and orientation in piping system (plus of course pressure behind (downstream) the valve and any local resistance/sticking9.
Any reliable valve constructions/brands will have datasheets published giving general information on minimum pressure to overcome spring pressure. For low pressure systems, for instance biogas collected from different waste products, opening resistance and pressure loss could be significantthis.
If you have a particular problem: please give us all details, as there usually is a 'common practise' for optimum choice of valvetypes and 'sensible brands' depending on application.