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Thread: Air Compressor............ Again......

  1. #1
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    Air Compressor............ Again......

    OK, I bought a compressor on January 1st 2005, it has done OK service, but this was before I really understood what a good compressor is, this one is NOT a "Good" compressor.

    In >> THIS << thread I outlined a problem I was having with this compressor. I thought the problem was fixed, but is is not.

    I thought I had fixed the problem, but it did not work, stuff gets between the valve seat and the rubber valve that is supposed to seal it, so it leaks, just a bit , but enough that the compressor does not really work right.

    You can see the part in question below.
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    The rubber valve has become hard, I did sand it smooth, but the rubber is still hard, so I came up with the idea to glue on a softer new piece of rubber, I did this, the rubber is about 1/16" thick, it should have worked but the problem is still this junk that gets all over the valve, it looks like rust or something from the tank

    I really want to buy a new compressor, the last one I'll buy for a very long time, the budget is tight, as we are getting ready to send our eldest daughter to Canada for high school. Right now, I'd just like to fix the compressor I have, and then start looking for a good used unit, they are out there now, as a lot of places here are going bankrupt, and a lot of these larger compressors run 3-phase motors, so they are out of reach of a lot of guys. I have three phase power in the building, because of the elevator and I have it wired into the Dungeon

    Back to fixing the compressor I have.

    The valve works like this, the compressed air comes from the pump to the valve, passes through and goes into the tank, the valve is a one way type, held down by a spring, when the pump is not pumping, the valve keeps the compressed air in the tank. There is also a bleed for the pump, this is the black nylon tube you see in the pics. When the pump shuts down, the pump stops pumping, the valve closes, but there is still pressure line from the pump to the valve. You don't want any pressure on the pump, because when it goes to start again, the pressure could be too high and the motor could not be able to turn the pump from a stop. The control unit triggers the valve on the bleed line, this lets any pressure in the line between the pump and the valve out, you know, that "pssssssssss" you hear when the compressor reaches it's preset pressure and shuts down.

    What happen now is compressor shuts down and the control unit triggers the bleed line, and the "psssssss" goes on and on and on, until the preset point is reached and the compressor comes on again......

    The problem is the junk from inside the tank(?) or the pump(?) gets between the valve seat and the rubber valve, and it leaks.

    I've taken it apart and cleaned it way too many times so now I'm looking for a solution.

    A new valve, something more mechanical would seem to be answer......

    I just had a thought while writing this..... where is the junk coming from that is fouling the valve?

    The pump takes in air through the air cleaners, and compresses it...... right?

    The air the is going into the tank, must be full of this junk, I'm now thinking it can't be from the tank, the air flow is going into the tank......

    Maybe I'm looking at this in the wrong way, maybe the air cleaners are falling apart, or.... But where is all the junk coming from?

    Maybe I'll have to tear down the pumps, maybe the rings are gone and the junk is oil, or......?

    Huh...... strange what happens when you try to coherently put your thought down.....

    Oh well, what do you think of that hypothesis?

    The junk that is fouling the valve cannot becoming from the tank (can it?) it must becoming from the intake side, the pump etc....

    More to look into
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  2. #2
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    The 'gunk' may be the compressed and overheated crankcase oil from your compressor.

    The oil is getting pumped past the piston rings on the piston's downstroke. This can happen if the crankcase vent is plugged, or if the rings are badly worn - or if the wrong oil was used.
    Jim D.
    Adapt, Improvise, Overcome!

  3. #3
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    Quote Originally Posted by Jim DeLaney View Post
    The 'gunk' may be the compressed and overheated crankcase oil from your compressor.

    The oil is getting pumped past the piston rings on the piston's downstroke. This can happen if the crankcase vent is plugged, or if the rings are badly worn - or if the wrong oil was used.
    Thanks Jim.

    The oil is the right stuff, I changed it about a year ago, and bought the right stuff, but I did notice that the compressor takes a LOT longer to reach it's preset pressure shut off point, so maybe the rings are bad.

    They are simple pumps, I guess I'll be taking mine apart and see what I can see....... Oh well, there goes my Sunday
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  4. #4
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    I forgot to ask in the first post, what Cubic Feet per Minute (CFM) do you guys consider a minimum for a compressor?

    I think I read somewhere here that a sander would take 8 CFM.

    I recently passed up on a decent Hitachi Bebicon compressor (a gold standard over here) that was 2.2Kw (about 3 Hp) and 265 liters per minute or about 9.35 CFM. It was three phase, not a problem, with a 21 UDS Gallon tank. One thing that I thought was good was the pump was fairly slow speed, designed to turn at only 730 rpm (I think that is slow) it sold for about $400.

    If I go used, that is the kind of deal I want to catch.

    So, what kind of CFM do you think I need to run air tools?

    Cheers
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  5. #5
    Stuart it's always something isn't it , hope you get it going for the compressor is an important part of my woodworking too ........
    Usually Busier than a Cat In A sand Box : Arkansas Red Wolf & Razorbacks Fan

  6. #6
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    stu,
    for a one man shop who actually uses air, like a vacuum pump (venturi type)
    sanders, diegrinders etc... look for either a two lung single stage pump with 3-1/2" bores or a four lung two-stage pump...either should displace 11+ cfm at 90psi.
    talk to a local compressor dealer and ask what they stock parts for so you`ll know brands to look for.
    in the last few years rotary-vane pumps have come unto their own and are becomming more affordable for small shops...the good thing about these units is that you can produce 20+cfm from a pump not much bigger than a portable compressor.....but they do whine.
    [SIZE="1"] associated with several importers and manufacturers.[/SIZE]

  7. #7
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    Quote Originally Posted by Stuart Ablett View Post
    Thanks Jim.
    The oil is the right stuff, I changed it about a year ago, and bought the right stuff, but I did notice that the compressor takes a LOT longer to reach it's preset pressure shut off point, so maybe the rings are bad...
    Stu,
    before you start tearing it down, check the crankcase vent. If it's plugged, then every downstroke of the piston will pressurize the crankcase, potentially forcing oil past the rings.

    If the vent is open, then, yeah, it might be worn rings.
    Jim D.
    Adapt, Improvise, Overcome!

  8. #8
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    Quote Originally Posted by tod evans View Post
    stu,
    for a one man shop who actually uses air, like a vacuum pump (venturi type)
    sanders, diegrinders etc... look for either a two lung single stage pump with 3-1/2" bores or a four lung two-stage pump...either should displace 11+ cfm at 90psi.
    talk to a local compressor dealer and ask what they stock parts for so you`ll know brands to look for.
    in the last few years rotary-vane pumps have come unto their own and are becomming more affordable for small shops...the good thing about these units is that you can produce 20+cfm from a pump not much bigger than a portable compressor.....but they do whine.
    Tod, thanks for the info.

    The compressor I have now is 4.3 cfm, I've found some good used units that have a LOT more CFM than that.

    Here is one, 7.3 Hp, and 21.2 CFM
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    It is about $700 right now, no bids and one day left, I won't be buying it, but that is the kind of unit I'm seeing for sale here. If I clear out a spot on the Dungeon Annex, and then set it up there, and run the pipes back into the Dungeon, I would be golden, an auto drain thing added and all I've have to do is change the oil now and then.

    The other road I could go is this type of unit.....
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    This type of unit has a couple of neat features, one is the box it is built into is sound proofed, so it is quiet, and keeping the unit in the box keeps everything nice and clean too.
    it is a 5 Hp unit, and does 15.5 CFM, it too is about $700 right now.

    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  9. #9
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    Quote Originally Posted by Jim DeLaney View Post
    Stu,
    before you start tearing it down, check the crankcase vent. If it's plugged, then every downstroke of the piston will pressurize the crankcase, potentially forcing oil past the rings.

    If the vent is open, then, yeah, it might be worn rings.
    Thanks Jim, I did check that, it was fine, and the oil level was also spot on the site glass too.

    Funny, the air vent is really simple on this compressor.........
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    ...... they are just using a marble in a plastic part, seems to work

    And here is the oil......
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    ..... the floaties are from the workshop, the sludge in the bottom is minimal, and the oil is still fairly clean. I also cleaned out the crankcase of the pump, it has only a bit of sludge in the bottom.

    I do have some good news and some bad news. The good news is, I know what the problem is, the bad news is......... I know what the problem is....

    I tore the pump off the tank and took it apart.........
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    The right and left heads...... gee, wonder where all the rusty junk was coming from

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    The valves, or reeds are really in rough shape.

    The pistons......
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    They have some junk on top, this one, the right one is the worst, but this just mostly wiped off, as the aluminum did not rust.

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    A close look at the rings show they are in OK shape, there is no "blowby" and the wear on the rings looks fine to my eye, the piston skirts are also fine.

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    Looking at the bores of the cylinders also show they are good shape.

    I think the air filters are not working well enough, I guess I'll have to improve them.

    cont...........
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

  10. #10
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    Once I cleaned off the junk, the heads and the cylinders needed some work, so I got out my glass plate that I use to lap my hand planes, and I set to work.........

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    The heads and the cylinder tops all ended up looking similar to this, I think this will be an improvement.

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    The valves, or reeds on the right cylinder were the worst this is the best I could get them, I think this will be an improvement over how they were, but is it good enough? I don't know. The left cylinder ones cleaned up nicely.

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    I got it mostly back together, I have to fit the cross over pipe, and go buy some new oil, but I'll do that tomorrow, time for bed now.

    I hope this fixes it for now, I will have to improve on the air filters, but that should not be hard, the holes are threaded with 1/2" pipe thread, so I can make something up if I have to, find a filter from something else and make a housing, or maybe just buy a good filter from Hitachi or something.

    Cheers!
    The pessimist complains about the wind; the optimist expects it to change; the realist adjusts the sails.
    William Arthur Ward

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