LRDG Pattern condensers

[Charlie Down]

On the Chevrolet 1533X2 trucks there are 2 different types of condenser. The most common has a can with a pipe connected to the radiator and the cap on the can, that ended at the bottom of the can below the water level to condense the steam, and giving a closed pressurised system. As steam was piped to the can the pressure would increase in the can, and when the radiator cooled the positive pressure in the can would force the condensed steam back into the radiator, preventing lose of water by vented steam. Simple and straight forward to me, although I'm not sure how the pressure was controlled without a pressure relief system, or was it merely a case of keeping an eye on the temperature gauge?
However the other type has a second smaller diameter tube exiting the top of the condenser and then bending down the side of the can. I presume this was some sort of pressure relief tube. Would this pipe be below the water level in the can, in which case the pressure build up would force water out of it very quickly, or was it above the water level in which case the can wouldn't become pressurised. The third option would be for it to be above the water line but it would have a pressure relief valve on it. This pressure relief valve would have to be fitted to the smaller pipe before sealing the can up.
The first photo shows a can without the second tube, the second photo show the tube and the brackets that held it and the condenser can on the side of the truck. This doesn't appear to be a case of early and late condensers, they seem to have both been used early after the operational debut of the trucks.
So how does this system compare to later condensers on CMP trucks, and is my theory right or have I missed something?