We decided to put a needle valve to have 'finer' adjustment of the flow out. Our evaporator would not keep up with uninhibited flow.

Due to vertical space constraints, our 'helix' is not perfect and limits our options for adjusting the number of wraps.

After running out the sap - we've purged / rinsed the lines with water and have let that steam out. We didn't see any problems with doing it this way.

Now I'm going to have to dig out my old heat transfer book... If I still have it.