If the given operating conditions exceed a mechanical seal's maximum loadability, it is possible to reduce the pressure to be sealed in steps using two or more mechanical seals arranged in succession. The pressure reduction is usually spread evenly over all the mechanical seal, but different pressure reductions per step are possible.

If a chamber in or near the machine is under the same (or lower) pressure than that to be sealed in the final mechanical seal, there is often no need for a buffer fluid. Circuit: If the (buffer) fluid is close to boiling temperature, pressure reduction via a parallel circuit is preferred; given a large Dt or intermediate cooling, a series circuit is also possible.

Pressure reduction in a series circuit

Pressure reduction in a parallel circuit