Shell and tube heat exchangers
I believe they are the same thing as you can see from the link below.
Just the holding style for the head of the pressure vessel. The split ring uses a circular spring with a notch in it that you compress down the diameter a little and then the ring is sprung out into the notch to lock it in place. Very similar to how semi truck tires use a split ring to lock the rim over top of the bead of the tire. The split ring is very fast and with use of a basic tool you can take the head off the heat exchanger rapidly to clean it or whatever and then place cap back on and lock it in place with the split ring. The clamp ring fits on a flange on the exchanger end and locks together with a flange on the end cap. Very similar to a 55 gallon barrel with the top on and a ring that encloses the barrel end and is wrenched down for tightness.
