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  1. #1
    BobL is offline Member: Blue and white apron brigade
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    Default Repair of hydraulic piston/cylinder

    The hydraulic piston/cylinder is the blade tensioner on a wood milling bandsaw but I'm posting it in this forum since it may have some similarity to an automotive brake master cylinder.

    Th situation is the master cylinder is adjusted manually with a screw ram just prior to milling to establish a hydraulic pressure of about 2000 psi on a master and in turn a slave cylinder which moves one of the wheels to tension the blade.

    The master piston is the shiny slug in the pic below and it fits inside the master cylinder as per long red arrow.
    The piece on the right caps the master cylinder and has an internal fine thread into which screw ram is located which also makes contact with the slug which pushes on hydro fluid etc.
    A hydro line then goes out the back of the master to the slave ram (R) which tensions the blade

    Tensioning.JPG

    Lately the pressure has not been holding dropping about 100 PSI every minute or so which is consistent with a very slow oil leak from the screws ram.

    I thought it might have a damaged O-Ring but when (after a great effort) I pulled it apart, it has no O-ring and am wondering what one does at this point in this sort of repair?

    To get the two halves of the master cylinder apart was no fun as I had to heat it up and use a pipe wrench with a cheater bar - turned out it was also Loctited on! HARD!
    First thing was I had to take the gauge at G off and let the oil dribble out
    Then to make sure I wasn't going to melt any O-ring with the heat I had to drive the internal piston up to the top of the cylinder which I did with a 6mm diam length of steel bar.
    At first piston didn't move so I leaned over the cylinder and pushed harder and when it did move all of sudden a jet of residual oil shot out of G and hit me between the eyes.
    I had glasses on but hydro still got into my right eye, hair etc.

    Any idea much appreciated.
    Thanks

  2. #2
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    Mmm! no o ring, no cup, are there no remnants of anything that could have dissolved, could it just rely on very close tolerance between the bore and piston

  3. #3
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    Another thought I have seen hydraulic cylinders with a groove in the bore to take a o ring, I am guessing you have already checked

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by China View Post
    Another thought I have seen hydraulic cylinders with a groove in the bore to take a o ring, I am guessing you have already checked
    AH HA! - I found it - even before I read your post.

    Any idea how to extract it?
    Not sure I want to go picking at it with one of my pickaroons.

    O-ring.jpg

  5. #5
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    I would go for something soft like a brass or plastic pick, the o ring is going to be replaced so it does not really matter if you nick it.

  6. #6
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by China View Post
    I would go for something soft like a brass or plastic pick, the o ring is going to be replaced so it does not really matter if you nick it.
    Thanks, it look more like a flap seal than a ring, any idea where to get a replacement?

    [EDIT] Did a bit of a web search - looks like its called a "rod (wiper) seal"

    Cross section looks something like this.
    Screen Shot 2021-05-27 at 7.41.49 pm.png

  7. #7
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    In south Australia my first port of call would be CBC Or BSC as they seem to be called these days, Don't if you have a branch in WA

  8. #8
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by China View Post
    In south Australia my first port of call would be CBC Or BSC as they seem to be called these days, Don't if you have a branch in WA
    Great thanks for that - there's one just 13 minutes away in Welshpool.

    Last night I cleaned everything up, and removed the threaded cylinder exit port and replace it with a threaded plug, added Loctite to threads, and filled it with new hydro fluid through the gauge port. While doing this I lost the little cap used to cover the hole in the top of the gauge used to fill it with gauge oil - DANG! Have fashioned a temporary cover but I hope I can find it in daylight or I will make something. The gauge also lost a bit of oil, I think they use Glycerol which I have somewhere?

    Let the Loctite cure ON and this morning I have set it on 2000 psi (normal operating pressure) and its dropped <5% in 30 minutes. This is way slower than before when it was dropping that much about every second and not that different from when I was successfully using the bandsaw mill in the past. I'm now wondering if there was something caught on the seal or there is a problem further down the line

  9. #9
    BobL is offline Member: Blue and white apron brigade
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    After the quick and dirty 30 minute press test that I performed at around 4:30am this morning and reported n in my previous post I then reset the pressure to 2200 psi and got the following graph over today.
    Similar pressure loss at first but then it seemed to start to even out.
    At A" I cranked the pressure to 2500 psi and it held (even went up a bit??)
    At "B" I dropped the pressure to about 2100 PSI and it seems to be holding?
    It looks like there is nothing wrong with this master cylinder - maybe it just needed to be "run up to a higher pressure to reseat the seal"?
    I think the pressure problems are elsewhere on the mill.

    prevTime.jpg

  10. #10
    BobL is offline Member: Blue and white apron brigade
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    Set the pressure to 2500psi about this time last Friday (3days ago) arrive and it has has not dropped below 2450.
    I think we're good to go.

  11. #11
    BobL is offline Member: Blue and white apron brigade
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    Mounted the Master cylinder on the saw mill this morning and 2500 PSI pressure held for more than an hour - seems like the problem has disappeared.
    Just wait - it will reappear again when I start cutting.

  12. #12
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    Probably just had some crud blocking some thing some where and dropping the pressure and cleaning has shifted it, hopefully for good.

  13. #13
    BobL is offline Member: Blue and white apron brigade
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    I hope so.

  14. #14
    BobL is offline Member: Blue and white apron brigade
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    Hydraulics no longer a problem on the mill but there are other probs I wont go on about here..

    Meanwhile my old 10 ton press with Blackhawk pump is dripping hydraulic fluid and after opening it up found the Master cylinder O-ring was worn and had gone hard. As well as an O-ring there is a white plastic wiper/seal of some kind and it has a crack in it..
    Any ideas where to get replacements?
    IMG_4989p.JPG

    Sorry no model numbers on the pump.

    I have contacted the people at CBC but no response yet.

  15. #15
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    Other than CBC, I can offer only Local companies I don't know if they do online sales, https://speediehydraulics.com.au/about/ Hydraulic & Pneumatic Solutions Since 1953 | B.L. Shipway
    The first one speedy have been around for ages, they have never not been able to help me, combination a of old school knowledge and state of the art technology.

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