Is there a limit how many times you can do this?

Hi we have travel plans to fly from London to shanghai. We then have a flight to the phillippines booked from shanghai within the three days. We plan to spend a few days in the phillippines then return to shanghai for a second transit visa free period before the final connecting flight to London? Is this possible as both times we arrive in shanghai we have connecting flights, but it means we spend 4days in shanghai in two occasions within a two week period! Thanks