Utility Requirements
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8.3.4.1 Air Compressors
When choosing an air compressor the following points should be considered:
• Ideally the compressor should be installed in a dust free, cool (use air conditioning as re-
quired) and dry place.
• The compressor must be oil-free. This can be achieved by using membrane or Teflon
coated piston and scroll compressors. The compressor should be fitted with a fine dust
inlet filter.
• The compressor must be capable of delivering the required flow rate and pressure suited
to your particular system (see Compressed Gas Requirements). Generally the compres-
sor should be large enough so it does not run continuously (e.g. > 50% of the time),
which will cause overheating.
• The extra cost of choosing an oversized system may often be justified. The reduction in
duty cycles will lower maintenance costs and extend the life of the system. A suitable
compressor coupled to an adequate buffer will ensure a more constant flow rate leading
to better performance. When spinning, the system uses a constant flow of air, but surges
will occur during sample lift.
• Take into account the pressure loss along the line between the compressor and the final
gate valve. The pressure drop depends on the pipe diameters. An internal diameter of 8
mm has been found to be suitable. The plastic tubing used to carry the supply from the fi-
nal gate valve to the console has an outside diameter of 8 mm and is supplied by Bruker.
• Some types of dryers, e.g., absorption dryers can use up to 25% of the air flow to regen-
erate the drying material. If this type of dryer is used then the output capacity of the com-
pressor must be sufficient to supply this requirement.
• Many compressors are fitted with dryer and a tray to collect excess water. Regular
checking of the dryer and emptying of the water collector will ensure trouble free opera-
tion. This arrangement is quite satisfactory in environments with normal humidity (< 80%).
However in areas of higher humidity (> 80%) a cooling coil with an automatic water drain
must be fitted to the compressor outlet. This will ensure that filters do not become over-
loaded.
• Although not directly concerned with air quality, compressors are a source of vibrations
which may interfere with NMR performance. You should consider using a compressor fit-
ted with a vibration damping housing if it is to be situated close to the spectrometer. The
output noise level should be < 75 dBA.
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