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projects:air-for-workshops [2011/08/05 21:09] – [The solution] spineryprojects:air-for-workshops [2011/08/08 08:24] – [Compressed air for small flexible workshops] spinery
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 ====== Compressed air for small flexible workshops ====== ====== Compressed air for small flexible workshops ======
 +
 +I'm still in the preocess of rewriting this, sorry for the mess if you're reading this right now.
 +
 +For a long time I was trying to develop a flexible, general purpose compressed air system for a small workshop. Instead of providing a continuous air supply for air for a single task, I decided it would be better to be able to perform a broader range of tasks for a limited amount of time.
 +
 +(list tasks here)
 +
 +This led me to consider a pneumatic installation working under 30 bar pressure, which is focused around air containment rather than air quantity generation. 
 +
 +I was considering using the following components:
 +
 +Compressor: 
 +Atlas Copco LT 5-30, circa 240 to 330 litres per hour, 30 bar, 12000 PLN
 +Kaeser K series, 35 bar, pricing unknown
 +Boge SHR series, 35 bar, pricing unknown
 +
 +(35 bar compressors provide 1500 litre more air per tank than 30 bar)
 +
 +
 + 
 +Tank: 300 litre 35 bar vertical tank, 60cmx1600cm, 140 kilograms
 +
 +The compressor is the most optimal in the LT range, because it doubles the amount of air it can generate over the cheapest LT5 with only 20% increasement in price. It can fill our tank in half an hour to maximum pressure, and has enough power to run the more demanding air tools all by itself – so we have continuous operation for all hand tools, and can operate two tools simultaneously for extender periods of time.
 +
 +30 bar pressure is not the tool operating pressure. Tools operate at a much lower pressure of 6 to 8 bar, and professional painting pistols operate at 2-4 bars (but have very large air consumption). The air pressure is reduced in the plumbing, therefore eliminating the need for a desiccating device, producing a good quality of air. Due to the height of the tank, I hope that oil drops will be eliminated gravitationally. It will not eliminate oil vapour if present.
 +
 +This system has an additional advantage. The 300 liter tank is relatively small (and easy in transport due to size and weight), yet has an impressive capacity of 9000 litres of 1 bar air. As far as I understand, the air consumption for tools and compressor FAD are calculated for 1 bar air. For the most demanding tasks, such as sand blasting and hi quality spray paint coating, where the air consumption can exceed 1000 litres per minute, this setup performs considerably well. Let us do some calculations.
 +
 +First, let us see how the tank capacity is reduced by the necessity to maintain pressure above certain operational limits:
 +4 bar air limit * 300 litre tank = 1200 litres, equals 7800 litres of working air in tank
 +6 bar air * 300 liter tank = 1800 litres, equals 7200 litres of working air in tank
 +8 bar air * 300 liter tank = 2400 litres, equals 6600 litres of working air in tank
 +
 +The tank capacity is still impressive, especially that air demanding tasks can be performed with the compressor operation starting at high pressures, countering the task air consumption.
 +
 +We severely limit the start-stop cycles of the compressor, favouring continuous operation. When the pressure in the tank reaches the tool operation pressure and starts to decline (or we keep buffer to prevent that), the compressor is turned on, and will work for circa half an hour continuously, filling up the tank. The amount of air that is used during that time, adds to the compressor's working time. While continuous air consumption tasks must be planned ahead to fit within the tank capacity and compressor FAD combined, all the non-continuous tasks that exceed the compressor's momentary FAD should have a median air use inside the comprassor's FAD. To put it more simply, the compressor's operation is contunuous, and tool use is not. So the tool median air consumption should not exceed the continuous pressure generation of the compressor at most times. 
 +
 +The benefits of this solution is it's relatively low cost, potential and expandability. The 300 litre tanks cost as much as a lower-medium class 8-15 bar compressors with 180-200 litre tanks, yet it contains three to two times the amount of air. Buying another tank reduces the start/stop sequences of the compressor, and increases the amount of air available for operation. 
 +
 +
 +
 +do a cost study, compare with screw compressor
 + 
 +Doing a setup that is focused around accumulation of air rather than enerating it in huge volumes has an additional benefit. Generating huge amounts of air demands large engines, and continuous power supply, which, in turn, demands a central power grid that allows for quick and abundant access to power of fossil fuels. For someone with limited resources, taking the power grid for granted is not a wise approach (I have witnessed this on several occasions). Moreover, creating a makeshift energy source of high power is impractical for a DIY user. The choice of air as a motive force for power tools used in the workshop is not without basis as well – an adequately equipped workshop houses many tools that can create replacement parts, both for themselves and other tools. Since they are purely mechanical parts, they are relatively simple to make, unlike electric and electronic devices, which often demand exotic or increasingly complex materials. In addition, such system can be adapted as an energy accumulator from renewable/ecological energy sources, such as wind, sun, burnt organic matter/gas, or wood gas engine, especially that the chosen compressor features a belt powered option, allowing for a wide range of power sources to be connected.  Multiple tanks provide necessary redundancy for such system (and are an investment that is less  likely to break than the compressor unit itself). 
 +
 +
  
 I have limited experience with pneumatics, so it would be pretty nice if someone could read this and provide some criticism. If the opinion is positive, I will build this system, and publish the results, performance and issues that arise with it. I have limited experience with pneumatics, so it would be pretty nice if someone could read this and provide some criticism. If the opinion is positive, I will build this system, and publish the results, performance and issues that arise with it.
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 I have a crazy idea regarding hi-volume sanding using this setup. Obviously, with large volumes of air running out of the sander's nozzle, we will be running out of air really quickly. The alternative here is to burn small amounts of heavily compressed (efficiency!) air/propane mixture (could also be oil or wood gas) in a chamber, and to use the generated pressure as a motive fluid to power an injector. Heat generated will allow for production of steam, that can be delivered to the motive fluid prior to its entrance into the injector, but after the fuel has burned. Such a device should also be an effective vacuum pump for gasses and liquids (a blessing if your basement ever gets flooded, ask me how I know). I've got no calculations on this one, though, as such calculations exceed my current abilities. I did however convert a Karcher pressure washer into a pretty efficient injector for expelling water out of a basement. It involved a PVC pipe, and could spew water out at rather impressive volumes, even though the injector nozzle was misaligned.  I have a crazy idea regarding hi-volume sanding using this setup. Obviously, with large volumes of air running out of the sander's nozzle, we will be running out of air really quickly. The alternative here is to burn small amounts of heavily compressed (efficiency!) air/propane mixture (could also be oil or wood gas) in a chamber, and to use the generated pressure as a motive fluid to power an injector. Heat generated will allow for production of steam, that can be delivered to the motive fluid prior to its entrance into the injector, but after the fuel has burned. Such a device should also be an effective vacuum pump for gasses and liquids (a blessing if your basement ever gets flooded, ask me how I know). I've got no calculations on this one, though, as such calculations exceed my current abilities. I did however convert a Karcher pressure washer into a pretty efficient injector for expelling water out of a basement. It involved a PVC pipe, and could spew water out at rather impressive volumes, even though the injector nozzle was misaligned. 
 https://secure.wikimedia.org/wikipedia/en/wiki/Injector https://secure.wikimedia.org/wikipedia/en/wiki/Injector
 +
 +____________
 +OK, it appears I've been miscalculating the air consumption. The litres are calculated for atmospheric pressure, that is 1013 millibars (right?), which is a bit over 1 bar.
 +The correct calculations look as follows:
 +
 +300 litres of tank capacity * 30 bar max pressure = 9000 litres of air
 +
 +300 litres of tank capacity * 8 bar tool operational pressure = 2400 litres of air
 +
 +So we have 9000-2400=6600 litres of air available before the pressure starts dropping below 8 bar tool operational pressure. If we assume that a tool uses 220 litres of air per minute, then
 +6600/220=30 minutes of undisturbed operation.
 +
 +It should be able to survive around 6 minutes on the bigest meanest sandblasters :P The kind you use for bridges. And then it would take half an hour for the compressor to rebuild the pressure.
 +
 +And this means that we can use higher pressures for smaller sandblasters, and still get good operational times. If we double the air consumption rate, we get 15 minutes of continuous operation, and that's a LOT.
projects/air-for-workshops.txt · Last modified: 2014/04/02 06:57 by 127.0.0.1

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