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Bull 125 cylinder seal replacement

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I have a Bull 125 air hammer.  I am replacing the seals, again, in the main cylinder. If anyone has specific expertise in doing this I'd be very grateful for any tips or advice.  Specifically, Tom Trozak drills a small hole in one of the seals to avoid an air block.  Some people think this is crazy, others, including the cylinder makers tech specialist, think it makes sense.  So I'd like a third opinion--as well as any other insight.  My phone number is number removed.  Talking always seems better than typing to me.  

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  • 1 month later...

Daniel,  Just cut a notch in the upper (rod end) seal, just through the outer flap. The cup seals face away from each other, to seal against working pressure from opposite directions. In normal operation, the piston speed causes the seals and the air trapped between them to warm up. When the hammer slows down or stops cycling, the air trapped between the seals cools down, and the atmospheric pressure from both ends presses hard on the seal because of the vacuum between them. This can cause intermittent sluggish operation, and premature wear of the seals. It can even lock the piston so tight in the bore you had to remove the cylinder tube from the hammer, clamp it in a vice, and tap the piston rod with a mallet to break it loose. I used to drill a little hole, but found they got plugged up with goop over time. Now I just cut a notch (upper lip only) and they work well.  125.CYL.ASSEM.edit.2017.04.07.pdf

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