A sealing system is disclosed for preventing liquid escape from the reservoir of an apparatus, such as an x-ray tube, that utilizes a diaphragm for maintaining constant liquid pressure in the reservoir. The sealing system of embodiments of the present invention contains liquid that leaks from the reservoir as a result of rupture or other failure of the diaphragm. In one embodiment, a diaphragm cooperates with an outer housing of an x-ray tube to define a reservoir for containing a cooling liquid. The diaphragm sealing system surrounds the diaphragm and includes a semi-permeable membrane that enables air to pass through to the diaphragm to expose it to atmospheric pressure for proper operation thereof. Upon diaphragm failure, the membrane has hydrophobic and oleophobic properties to prevent cooling liquid from escaping the diaphragm sealing system, and hence, the x-ray tube, thereby preventing the cooling liquid from presenting a health or safety hazard.