Single-acting mechanical seals

Single-acting mechanical seals are not used as widely in the agitation field as they are in other engineering applications. They are used frequently in pumps and machines in which lubrication or cooling by the product itself can be counted on. Today most agitators employ double-acting mechanical seals. Areas in which single-acting solutions are used, as shown in Fig. 7, remain the exception.

One such exceptional area is that of scrubber agitators in flue-gas desulfurization units. Here the agitator's mounting position and the operating parameters have led to the use of single-acting seals almost exclusively. The product-lubricated seal ESD42 was developed specifically for this application and is widely used. Though double-acting mechanical seals are found occasionally in desulfurization units, they do not afford any particular advantages. Indeed, the simpler single-acting design is better suited to this extremely harsh environment.

The single-acting design is also used to advantage in dry-running mechanical seals. The lack of a lubricant eliminates the need for an additional sealing system.

Other applications of single-acting mechanical seals usually employ pressureless buffer fluids for relatively straightforward sealing duties, see Table 2. Sealing against the atmosphere is accomplished with relatively inexpensive radial sealing elements.