so better is a German Brand, either Presta or Schrader [Schwalbe calls 1 type AV auto valve] or continental ..
air pressure difference keeps the check valve closed in a PV,(The little knob-nut locks it shut) SV cores use a spring.
not all prestas are replaceable valves , the valve core in schrader are always replaceable.
Last edited by fietsbob; 10-06-14 at 07:38 AM.