This is an older thread but I thought I would comment.
Most RV LP systems are "low pressure" all of the appliances work at and require 11" water column pressure about (6.35 oz). The automatic change over regulator takes tank pressure (anywhere from 28 psi to 220 depending on temp) and first reduces it to 10psi in the changeover head (first stage) then the main regulator (second stage) reduces it to appliance pressure. By there function autochange overs ONLY allow gas from one tank at a time then the the "supply" tanks pressure drops below 10psi it will switch to the other full tank. The tank connection pigtails are usally supplied with a "excess flow check" in the tank end and as posted earlier if you open the valve too quickly it might close, if this happens close the valve and reopen it slowly. Some of the older POL connections had a restricted flow orifice in them and this was not an issue.
All new tanks of 40# capacity or less now have an OPD valve (overfill protection device) which is a float inside the tank that will not allow the tank to be filled past 80% capacity (legal limit) they also include a check valve that will not allow gas to flow unless there is something connected. All of the newer ACME style pigtails have a thermal fuse built into them that will melt in a fire and hopefully shut off gas flow.
If I can help on any other Propane questions let me know.
Jim & Debbie England
Do you have Gas? 2015 F350 6.2L CCLB DRW 4.30 axle. 2012 Yellowstone Ridgeline 34RLT Fifth Wheel