Air Compressors For Pneumatic Systems
Many of the larger office buildings and government buildings use pneumatic (air) operated controls. Thermostats, VAV Boxes and Motorized dampers are operated with air pressure instead of electricity. This means there is a maze of air lines running through the ceilings and walls. The main air line will predominantly be of copper and measure 3/8" OD. Branch lines to VAV Boxes and Thermostats can be in plastic tubing in sizes 1/8", 3/16" and ¼". The lines are supplied with compressed air from an air compressor usually tucked away in a mechanical room where the noise of operation will not disturb tenants. The compressed air for systems like this is low pressure in the range of 11 pounds per square inch. The air is directed through valves to regulate the pressure and turn on and off the compressor. One concern with compressed air is that condensation will occur in the storage tank and can also be carried through the lines to components of the system. This moisture can destroy the thermostats and damper actuators. It therefore makes sense that the air has to be dry when compressed. This is accomplished by piping the compressed air from the compressor directly to an "air dryer" before the air can contact any other parts of the system. The air dryer is a small refrigeration unit that condenses moisture out of the air and rejects the water to a drain. The compressor will also have a storage tank larger than a SCUBA tank that will collect condensate. This water can be drained manually or automatically with an optional accessory. The air compressor is not much different than ones used in any auto service garage and requires regular maintenance. Failure of the compressor for a pneumatic system can be disastrous in a large office building. The drive belt(s) should be changed on a regular basis and spares left on site. The oil in the compressor has to be changed on a regular basis with 10W30 or 5W30, non-detergent oil and the storage tank needs to be drained (when there is no auto drain kit). The tank will require more frequent draining when the weather is hot and humid. Pneumatic systems are very simple to operate and maintain and energy efficient.
Auto service garages will often have the refrigerated air dryers on their system also to protect the pneumatic tools they use in servicing vehicles, however garage compressors will operate at a minimum of 90 PSI, but more commonly 100 + PSI. These systems and the ones used in carpentry will often have lubricators installed on the main outlet of the compressor to move small amounts of oil throughout the system to prevent rusting of the tool mechanisms.