Is there a train ticket I can get from Central to Bruges, then returning to the airport on a Sunday , or round single to Bruges then single to airport be the ticket ?
Doing a round trip like this on a Sunday (or a Saturday), you need to buy two tickets (at the same time, when you set out in the morning) - a Weekend Return Bruxelles to Brugge and a Single Bruxelles to Brussels-Airport-Zaventem. On the return journey you just show whichever ticket is relevant for the portion of the journey, although there is a through train every hour you may find it convenient to change in Bruxelles.
You will need the single ticket to the Airport to exit through the gates there.
Don't forget that if you are returning to the airport late-ish on a Sunday, the trains will have originated at the coast and may well be very full if it is a nice day.
Very kind. Tvm