As the last variant of this type, installation Fig. 10.4.7.1 is shown. Two compressors (item 1 and item 1.1) and two dryers (item 4 and item 4.1) upstream of a receiver (item 2) are cross linked to each other and should be suitable for automatic operation as, if one unit fails, whether compressor or dryer, the parallel unit takes on the total supply of the compressed air. The system operates automatically without manual switching, both dryers are fitted with a load governed control system. Here, too, compressor 1 takes on the base load, compressor 1.1 is meant for stand-by operation. The compressors operate as selected via a base load change-over switch.
Figure 10.4.7.1
Layout and sequence can be understood from the examples 10.4.3 and 10.4.6. For an installation of this type, i.e. cross-over connection of compressor and adsorption dryer, fitting a load depending control to each adsorption dryer is the correct and optimum solution. With dewpoint sensing at the outlet of each adsorption dryer, the output signal ensures quality remains constant for all load situations. Adaptation to varying load levels takes place automatically. From the multitude of possibilities, three fundamental rules emerge and these must always be followed.
Rule 1:
With a Dewpoint Dependent control system, automatic operation for each dryer can be achieved, as the dewpoint is utilised as the control signal.
Rule 2:
If a load governed control system is used ie. compressor and adsorption dryers are linked up for simultaneous running, free passage of the pressure to the pressure monitor must be ensured, irrespective of how the dryers are installed.
Rule 3:
If the adsorption dryer is mounted upstream of the receiver, a return feed of compressed air for pressure equalisation has always to be considered.
