OT-homemade air compressors - Page 4
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  1. #61
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    Metl,
    Thanks for the detailed reply. None of our reefers have heaters in the compressors, and they may sit unplugged for months waiting for a load at ambient temps anywhere from -10 to +90f. Our older units which we are trying to phase out were R12 and we didn't have much problems with picking up oil until we swithed over to 409a. I have no experience with HVAC or R22 but I can see if these compressors are adapted from that use it may explain some of these problems.

    As we are phasing out our older carrier 69NU units in favor of Carrier Thinlines we are saving what good compressors we have for stock, not buying replacements. I've handled some of the new generation hermetics and they are noisier but have reduced condenser fan noise and run a lot less with the newer better insulated boxes so overall I think they're quieter.

    Way back when we had some ThermoKing red nose and blue nose units with Copeland compressors, they were a huge PITA but not because of the compressor. 90's vintage TKs I've come across had non hermetics, lots of seal leaks at the motor coupling. They seem to smoke motors at the same rate as the Carriers but a lot easier to change, particularly at the top of a 30' ladder.

    None of which has to do with compressing air, sorry folks...

  2. #62
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    metl: Thanks for the info ...that's really helpful.

    Another question to everyone: I picked up a couple of hermetically-sealed refrigeration units from a scrap pile behind an A/C shop. They look like small beer kegs with tubes sticking out, and they are pretty heavy ... about 200 lbs or more.

    If I cut these open, would there be a compressor inside worth using? If not, I'll take them down to the recycling yard. Thanks!!

  3. #63
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    "There's inadequate heat absorbing capacity in the gas passing thru the motor windings, so they run just hot enough for just long enough for the varnish, or whatever insulation is used, to break down and finally cause a burnout"

    That explains so much $ spent and hours of unpleasant labor, thanks again metl.

  4. #64
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    Ok, I might as well add this idea. I've been thinking about building my own compressed air system and one idea that I thought of goes like this: take a long tube, arrange flap valves and a head at the top. Air exits to driers and on to the tank from the top. Tank is any normal rated air tank. The long tube would be maybe 3 inches diameter, and could be say 6 ft long.

    At the bottom, a reservoir sits adjacent to the vertical tube. The reservoir has a capacity at least equal to the volume of the tube. Between the two is a pump, probably directly mounted to a motor. This pump is for oil, and the working fluid is oil. In use the motor drives the pump until the oil has nearly filled the tube, at which point a valve operates and the oil falls under gravity back into the reservoir. At a suitably low level of oil in the tube, the valve operates again, and the pump again transfers the reservoir oil to the tube. Air is sucked in at the head as the fluid level falls, and is compressed as the fluid refills the tube. Air is bled off through a valve, goes through the drier, sees a pressure gauge, and goes on to the tank. All normal plumbing for air systems.

    Obviously the tube must be rated for pressure use, and I would think probably burst pressure rating would be upwards of 1000 psi. I don't know, but maybe sched 40 would be ok, at least it would up to a certain tube diameter. The valve I speak of would be operated either by pressure or by fluid level. This valve might bypass the pump and open the tube to the reservoir, then operate to close off the reservoir and the bypass. The motor would run constantly during the 'on' time of this air system.

    Because the piston in this case is the oil itself, internal heatsink fins would extend downwards from the head at the top of the tube. Heat from the compressed air would be absorbed by these fins, which would transfer the heat to the oil as it rises up around the fins and is in intimate contact with the fins. These fins might only need to extend say a foot or so down inside the tube, as the most heat generated is when the air is quite well compressed, and the oil level at this point is near to the top of the tube. Having taken much of the heat of compression away, the action is more efficient. Water coming out of the air sinks through the oil and collects in the lowest part of the tube, where it can be removed through a drain valve in somewhat normal fashion. If some oil is drained as well, that cam just be poured back into the reservoir, which is never under pressure. It does need to breathe, so a filter would be added to it at the top. This is where any oil would be added back in as well.

    There's obviously some issues I haven't delved into too far, such as how fast can this cycle repeat, but this is the gist of the idea.

    I hope nobody's head exploded reading this. [img]smile.gif[/img]

    This is beyond buying off the shelf parts and putting them together, but I think it's workable and should be fairly quiet and long lived.

  5. #65
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    Actually a twin vertical tube arrangement would eliminate the reservoir and speed up the action. The oil would just be pumped back and forth between the two tubes. Rigging a motor with a fluid pump would be easy- the valving would be the thing to figure out.

  6. #66
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    Does anyone know if u can make a air compressor using portable window air conditioner

  7. #67
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    Quote Originally Posted by brookedad2020 View Post
    Does anyone know if u can make a air compressor using portable window air conditioner
    Most of us can, but someone that uses "U" for "You" probably can't...

    Get a HF 20% off coupon in the sunday paper and BUY one....


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