Depending on how elaborate your setup is you probably don't need a bleed valve at all. Open up all the valves before and after your pump and let the liquid drain in. Give it at least 10 or 20 seconds. If you are having problem with air in the lines, give it a little longer before you turn on the pump, up to 60 seconds. If you are having problems with cavitation (not necessarily the same thing as air in the lines), make sure there is little/no resistance before the pump. Note that boiling liquids are more likely to capitate than cold water.