Triple-acting mechanical seals

Triple-acting seals were developed to meet ultra-stringent safety requirements. They provide optimal back-up, because even the failure of one seal ring pair leaves a fully operable double-acting seal to handle the sealing function. Thus the process can be carried safely to its conclusion without having to switch off the agitator.

The seal is based on a double-acting mechanical seal with the buffer chamber shown in green in Fig. 9, plus an additional seal pair that is usually identical with those of the double-acting seal. This third pair is installed in tandem with what is now the middle pair. The resulting additional buffer chamber, shown in red in Fig. 9, can take over the function of the first buffer chamber in an emergency. This seal configuration is seldom used to expand the effective pressurization zone by reducing the incremental pressure; instead, the incremental pressure in the second chamber is utilized to monitor proper operation of the third seal pair. Consequently, the operation parameters are identical to those of the double-acting mechanical seal of the same type.

It makes sense to operate this seal with two pressure boosters on the two buffer chambers, because the safety level can then be enhanced yet again with additional monitoring employing the necessary automation.