Instead we did all the other things needed required for a hanging test. I am going to pick up some replacement relays locally which should work (they are rated for a minimum 24v and I am using 12) . If not I will have to wait a while for new ones.
In order to retract the pressurisation tube and quick disconnect after pressurising we are going to use a simple pulley system which pulls the line and electrical cable off to one side of the stand.
For the pressurisation and venting I decided to go with simple hard wired electronics instead of a separate micro controller which would be triggered by the computer.
This is the quick disconnect sam made a while ago. It looks a bit crude but works every time.