The following information on the Keyser pipe and photo are from an extensive blog post on Reborn Briar
I have three other Keyser Hygienic pipes and they are all very similar in terms of the system. They are briar bowls and shanks with an aluminum mortise with a tube in the centre running to the airway in the bowl. This is matched with a military mount stem with a tube with a down turn on it that fits into the airway in the mortise. The swirling smoke rolls around the inside of the mortise where the moisture in the smoke condenses on the sides of the aluminum mortise. The cooled air is drawn into the down turned tube in the stem and it delivers a cool, dry smoke. The system is fairly straightforward and simple. The genius of the design is that any stem fits any pipe of the same size. Replacement stems are easily purchased and all that is necessary is the size of the pipe and the replacement will be a ready fit.