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The International Fluid Power Society
6/9/2007
ALL ABOUT AIR – WHITE PAPER #1, Recycle Exhaust Air and Save © by Thomas W. Kreher, Applied Pneumatic Controls
Does it seem illogical to compress, dehydrate, filter, regulate and add lubricant to prepare compressed air then expand it through a valve into a cylinder or air motor and dump it out through an exhaust muffler and start over? An exhaust manifold at 30 PSIG could be a ready source of clean, dry, "FREE" compressed air for many uses. Many systems currently have an exhaust manifold to contain the exhausted air and pipe it out of the immediate work area. The additional plumbing for most other applications and systems could easily be justified with the pay back of free air. By using special quick connect fittings blow guns normally regulated to 30 PSIG could be directly connected. By using the 30 PSIG as an air spring to return cylinders to the home position the saving is multiplied.* The exhausted air can be filtered, coalesced, further dehydrated if necessary and regulated down for Instrument air. Air for venturi vacuum generators, blow off, agitation, cooling, tension, mist bearing and chain lubrication is free. The compressor would have a lighter load, last longer and reduce the cost of electricity. Compressed air used as a spring has advantages over mechanical springs. The air has a flat rate that does not change with extension/compression as mechanical springs do. With 30 PSIG clean lubricated compressed air to return cylinders they would start faster. For example with a typical system using 80 PSIG for both the work stroke and return a slight delay occurs when the valve is shifted into the work stroke. The 80 PSIG return air must decay to provide a differential pressure adequate to break away and provide energy for thrust. After break away a cylinder is often moving at a rate of imbalance of only 20 PSID. The velocity and force are controlled by the rate of exhaust. By using an ‘air spring’ at 30 PSIG the differential would be approximately 50 PSID. The cylinder would start sooner, move faster with more thrust. The final force and return stroke speed would be slightly reduced. Air motors would have an ample supply of clean, lubricated air. A larger motor can be used to compensate for lower pressure. Pressure in the exhaust or low pressure manifold can be maintained with a regulator that would make up pressure as required and relieve over pressure. Reduced pressure lowers the dew point so the low pressure air is dryer. The expanded, lower pressure air is cooler until heat is adsorbed. Air spring cylinders only require 3 way valves rather than 4 way valves. Standard cylinders are less expensive than spring return cylinders. An air spring never wears out or breaks. Large diameter air bags could provide great force with the lower pressure for less cost than conventional cylinders.