A seal support system for a mechanical seal includes a system vessel for containing barrier fluid. Closed loop pipe work connects the vessel to a mechanical seal with a device provided for feeding barrier fluid to the system vessel. A further vessel is provided that is able to be in fluid communication with the system vessel. The further vessel may be provided with an elastomeric membrane, which may be filled with a gas under pressure to an extent required to allow for the effect of the highest anticipated temperature which might occur in a particular application.