beer in CO2 lines..!?!?

I have a big problem, i just got a new 20lb CO2 tank that I am trying to use to dispense 3 kegs at the same time, I am only using one double gauge regulator and a 3 way manifold, I have the 3 kegs and CO2 tank inside a fridge at 38 F when I first connected the line to the kegs and i opened the co2 i was able to see the beer going back to the CO2 lines not only in one keg but all of them same thing.
I disconencted everything and made sure everything was assambled correctly, tried again but this time only dispensing co2 to one keg and same issue beer going to the co2 line, the preasure on the regulator is 13 psi

I checked for leaks and nothing not a single bubble

The beer gets half way to my beer line and then it stops and never gets to the regulator but i am concern about this issue, can anyway help me with this to find out what is it that i'm doing wrong

Any help is much appreciated

Do you have a check valve installed for each run off of your 3-way manifold? The scenario you are describing is definitely not good and a check valve should stop or at least minimize that from happening. Also, how full are you filling your kegs? I like to fill mine really full so I pulled my gas in dip tubes and cut them really short just to be sure the beer never touches it and avoid exactly what you are describing.

I do have a check valve on in each line, the kegs are FULL all the way to the top... so what you are saying is that my problem is becaus the gas in dip tubes are touching the beer??

Ditto on the check valves. Put one on each output of the three-way manifold, rather than one on the input. Either way will protect the regulator, but the three valves will also keep beer from one keg at a higher pressure from going into a keg at a lower pressure.

Do I need to set the pressure higher since I am dispensing 3 kegs at same time???

Yes, you are at risk if your gas line is in the beer that close to the top of you keg. No pressure will be the same whether feeding 1 keg or 4. ASre all of your kegs this full though!

ok so I am gonna try to take some beer out to see if that helps and from now on I wont be filling up the kegs all the way up. But i mean before i was using a 20oz tank with a regulator to dispense one keg which it was full all the way to the top as well and i didnt have this problem....

If you use corny kegs you need the check valves, I use Sanke kegs and the taps have check valves built in. If you don't use them you take a chance of beer making it's way to your expensive regulator, not worth the worry IMHO.