A device that ensures automatically the correct pressurization for a closed buffer system circuit and which compensates leakage losses. An electrically or pneumatically driven piston pump is used to pressurize an accumulator with a pressure higher than the necessary buffer pressure. This "system pressure" remains available to pressurize the buffer system circuit for a limited period in the event of all the refill unit's pumps failing. The period of availability depends on the accumulator's useful capacity and on the magnitude of leakage losses needing to be compensated. The buffer pressure is set using the accumulator valve at the buffer fluid outlet from the refill unit. This valve closes absolutely tight when no additional buffer fluid is required in the sealing circuit.

Buffer circuit of a standard refill unit with pneumatic drive