To work properly, double mechanical seals require a buffer system which fulfills the following basic conditions:

• The buffer compartment (between the product side and the atmosphere side of the mechanical seal) must be filled with clean buffer fluid.
• During operation the buffer fluid pressure in the buffer chamber must always be higher than the process pressure. Under normal circumstances it is aimed to achieve a buffer fluid pressure lying 10% or at least 2 bar above the highest occurring process pressure.
• Replacement of buffer fluid in the mechanical seal in order to prevent overheating. Given these basic conditions, the resultant duties to be performed by a buffer system are as follows:
• build-up of pressure in the buffer chamber
• compensation of leakage (leakage)
• circulation of buffer fluid
• cooling of the buffer fluid.

Buffer systems are categorized in four groups according to the type of circulation:

• thermosyphon circulation
• circulation device outside the seal
• circulation device integrated in the mechanical seal
• combined pressurization and circulation device.

The first three categories are closed-circuit systems, in which the buffer fluid circulates under a virtually constant level of pressure. This type requires additional pressurization by gas or by the buffer fluid itself. In the fourth category both the circulation and the pressurization are brought about by a single buffer unit. In this case the buffer fluid is relieved after each circulation and collected in a pressureless storage vessel.

Buffer systems with thermosyphon circuit

Buffer systems with circulating device outside the mechanical seal

Buffer systems with circulating device integrated in mechanical seal

Buffer systems with combined ressurization and circulation device