Ok so I have presta valves on my bike and I use the shrader adapter piece .

My question is this: after I open the presta valve , screw on the adapter and fill up my tire , do I need to take the adapter back off and close the presta valve , or can I just leave it open ? It holds air when its open obviously since the air inside is pushing it closed , but Im not sure and flat tires are NO good so I need to know .

Can anybody answer my stupid question for me ? Thank you