Mechanical Seal Systems
How to Select the Right Seal for Mixing Applications
Pressure Compensator Systems
1. Mode of operation of the pressure compensator
The pressure compensator is a hydraulic cylinder with a piston rod (Fig. 8). The entire circular area AB of the lower side of the piston is subjected to the vessel pressure PB. The seal liquid pressure PS applied to the upper side of the piston can only be generated with the smaller annular area AS because only the atmospheric pressure is exerted on the piston rod. The forces are balanced in the static state: PB x AB = PS x AS
The surface area ratio AB/AS is always greater than 1. This ensures that the pressure in the seal liquid is always higher than vessel pressure. Differential pressures of 2-10 % are typical.
2. Pressure compensator for a single agitator
As shown in Fig. 2 and Fig. 8, the lower chamber of the pressure compensator is connected to the head-space of the vessel via the seal flange (yellow). The upper chamber is connected to the seal liquid chamber (red). This arrangement ensures that the pressure in the sealed chamber (without auxiliary power!) automatically follows the vessel pressure. The seal chamber pressure is usually constant in continuous flow systems (Fig. 9).
The inboard pair of seal rings is directly exposed to corrosive products and/or high temperatures. They are therefore regarded as particularly critical. Especially in batch operations or under very fluctuating operating conditions during continuous operation, these rings are completely unloaded by the pressure compensator.