Simscape Pneumatic: Volume between resistive tube and constant area orifice

I'm modelling a basic gas flow system. The pipe the gas flows through feeds into a large vacuum chamber. I wanted to model this using my pressure source, a pneumatic resistive tube for the pipe, then a constant area orifice for the opening into the vacuum chamber (followed by a Constant Volume Pneumatic Chamber for the vacuum chamber). This wouldn't run, until I added a Constant Volume Pneumatic Chamber branching off between the resistive tube and the Constant Area Pneumatic Orifice. Why is this? I set it to a small volume so I don't think it will make much difference, but it seems odd that it is necessary. Could I add a different component? Is this the correct way to model a pipe abruptly ending inside a large chamber?