venting single pipe system

todd1471

Went on a call today,  Problem: first floor rads pissing and pressure going up and down.  I used street pressure to clean mud leg.  In the process noticed no vent on return piping.  2/1tee horizontal 1" looking down  6" nipple, 90,  nipple another 90 looking down piped into Hartford loop.  this is done on feed and return.  Can I replace  the ladder 90 with a 1/34/1 90 vent both drops.

thank you,Todd