Transit visa

Hi on March 16th I fly out of London Heathrow on Air China at 2025 hours i land in Beijing at 14.45 hours on 17th March, I have about a 10 hour stopover and fly out of Beijong at 0105 on the 18th also by Air China on route to Auckland. I come back from Auckland via Beijing also by Air China on 7th April but only have about a 3 hour stopover before my flight back to Heathrow. I don't think I need a visa for this but could you confirm if this is the case? thank you Graham