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Old 01-23-2013, 07:36 PM
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Default Hydraulic cylinder help needed

I got an older Central Machinery metal cutting bandsaw for free. I cleaned it up good, added oil to the gearbox, replaced the blade guide bearings and installed a new blade. It seems to cut really good.

The only problem is the cylinder that controls how fast the blade lowers. Initially it did nothing and there was no resistance up or down. I removed it, put it in the vise vertically and removed the top fitting with the ram all the way in. I added several ounces of hydraulic oil until it was full. I figured this was the best way to top it off and get the air out of it. I reinstalled it and it was working correctly other than it didnt begin to resist until it was about halfway down. I figured it was probably still not 100% full of oil and may still have some air in it. But, it was still very useable.

About an hour later I raised it up to check something else and when I went to lower it, once again there was zero resistance. No matter what position the on/off valve is in or how tightly the fine control valve is screwed in, no resistance up or down.

Has anyone worked on one of these things before and know how to get it full of oil and all of the air bled out of it? It may be bad seals but when I try to pull the cylinder out, I can only get it to come about 1" and then the pressure is strong enough I cant get it any further. I cant see how the cylinder disassembles anyways. Any recommendations?
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Old 01-23-2013, 08:02 PM
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So if I'm looking at that right, the ball valve with the red handle should be a on/off, or engage/disengage... and the little twist valve that looks like your ice maker water hookup is the control for how fast the fluid can move. So all that thing is doing is moving the fluid from one side of a plunger to the other, as the cylinder goes through its stroke? Can you take it completely off to R&R? And is that hose on the left completely crimped, or is there still pretty free flow in there?

If its behavior changes mid stroke, then yeah I'd speculate you still have some air in there. Is there a way to crack the whole thing apart, and see if there's an o-ring inside that could be replaced? Even though that wouldn't really solve your problem, as you should be able to compensate for a bad internal seal with just more dampening at the valve, so it sounds like it's leaking somewhere and sucking in air. You could try the soapy water thing, or just T-tape up all the joints really well and see if that solves it.

Another way to test for leaks is dump the oil then fill it with water- water is less viscous and would reveal your leak sooner. Or go the other direction and try putting some super thick fluid in it, just to mask whatever isn't working right.

How long is it compressed, and how much stroke does it have? You may be able to just pick up a spare and not even mess with it..

http://www.ebay.com/itm/Clippard-and...item3a7da0a415

And if I were to totally re-engineer the thing, what if you replaced it with an air cylinder you could activate with a foot pedal, hooked to your shop air. Give it dampening on the way down, but hands free on the way back up! ok, hth!
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Old 01-23-2013, 08:15 PM
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worn seals in the piston?
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Old 01-23-2013, 08:22 PM
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This needs to be a low buck fix, because it isn't worth putting a lot of money in to it. So for now we'll stay away from engineering power air lift cylinders and laser guided cutting systems Cool idea though. The cylinder is 12.5 inches long with a 1 3/4" diameter and the throw is only about 2.5" the way it is setup on this saw. You are correct with the functions of the 2 valves. That is just a flat spot on one side of that tube, it really isnt close to being pinched off. What you see sticking out of the cylinder in the picture is the maximum extension of the ram required.

I'm mostly wondering if there is someone out there who is experienced with these types of cylinders that would take it apart, put it back together again and fill it with oil and bleed the air? If it needs an O ring and we can find one, so much the better.

This is a 6 1/2" x 10" 3/4 HP saw. Its vintage 1998 so I can't find any exact replacement cylinders for it. I can buy a new cylinder for a 7" x12" 1HP saw that may require some mods but I think it would work. But, its $160 with shipping so I'm hoping there is a way to repair the current one inexpensively.
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Old 01-24-2013, 05:09 AM
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I think it has an internal check valve - when its working it has no resistance to lifting the saw but has resistance to lowering it. I'll bet the valve is sticking open allowing flow both ways. Taking the cyl apart for an r&r is the best bet.
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Old 01-24-2013, 06:54 AM
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I think you need to do a fill at both ends. Set it vertically and compress the ram then fill the end closest to the ram shaft. Then pull the ram out and reverse the process with the other end (fill the end opposite the ram).

It sounds like you have it half full now. Let me know how this works. Terry
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Old 01-24-2013, 08:21 AM
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Quote:
Originally Posted by ttubb View Post
I think you need to do a fill at both ends. Set it vertically and compress the ram then fill the end closest to the ram shaft. Then pull the ram out and reverse the process with the other end (fill the end opposite the ram).

It sounds like you have it half full now. Let me know how this works. Terry
I believe Terry is correct. The oil just moves from piston end to the rod end and vise versa. The piston end has more capacity however, so you can overfill because of the different displacements. Keep adding small amounts of oil and use it until you get it corrected. If you can take it apart to check the "o" ring on the piston that would be a good idea as that could also be contributing to the problem. O ring could just be hard and dried out.
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Old 01-24-2013, 08:48 AM
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I've got a box of metric o rings of various sizes. If it does not have the size you need, Rocket Seals will likely have it in stock.
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Old 01-24-2013, 11:31 AM
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I took it off again and chucked it up in the vise. I removed all the control piping and rigged up a come-a-long to the workbench. I used that to pull the shaft about 5" out of the cylinder. That cable was as tight as a banjo string, there must be a big spring inside the cylinder to help offset the weight of the saw arm, sort of like a counter weight.

I then filled the cylinder with hydraulic fluid using the hole furthest away from the shaft. I then slowly released the comealong and let the shaft retract back into the cylinder. I stood the cylinder vertically in the vise and then filled it with more oil using the top hole. This should have gotten it as full of oil as possible on both sides of the internal cylinder piston.

I put it back together and tightened all of the plumbing to ensure no air or oil leaks. I put it back on the saw and it works like before i.e. the saw arm goes from vertical to about a 45 degree angle before the cylinder catches it. With the valve closed it holds it without let it leak down. When you open the on/off valve and just barely open the speed valve, it slowly lowers the saw.

So, its back to working like before. I cycled it 20-30 times over a 20 minute period and it kept working. I'll let it sit for half a day like yesterday then check to see if it has stopped working again or if its really fixed this time.
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Old 01-24-2013, 01:57 PM
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Quote:
Originally Posted by Air Randy View Post
I stood the cylinder vertically in the vise and then filled it with more oil using the top hole. This should have gotten it as full of oil as possible on both sides of the internal cylinder piston..
When you did the above, was the shaft fully compressed?
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