Graham condensers are easy to overload if used as reflux condenser due to the small diameter inner tube, and this causes excess condensate to splatter and pressure might build up.
Also see Post 281432 (https://www.thevespiary.org/talk/index.php?topic=9749.msg28143200#msg28143200)
(Rhodium: "What Graham condensers are good for", Methods Discourse)
Graham condenser are only used for for downwards distillation, see see Post 281432 (https://www.thevespiary.org/talk/index.php?topic=9749.msg28143200#msg28143200)
(Rhodium: "What Graham condensers are good for", Methods Discourse).
If you try to reflux using one of those they will flood directly, as the coil is so thin...