Modeling closed circuits with pipe flow module (linking inlet and outlet)

Hi Comsol experts,

I an trying to model a closed pipe circuit consisting of a network of pipes, bends, valves, junctions and heat transfer areas. A pump is inserted to create the force (dP) to move the water inside the pipes.
Is it possible to model this with a closed pipe circuit or do I need to have an inlet and an outlet?
If inlet and outlet is necessary, how do I link the boundary conditions of the inlet and inlet (mainly velocity and pressure and temp) to model my closed circuit?

Any help is very much appreciated :-)

Regards
"A novice cfd/pipe flow dude" / Morten