Air over hydraulic expert needed

[heavy metal machine]

First a little back ground for you guys. I am a pour machinst working a full time day job trying to run my part time machine shop on a limited budget. I own a Auto Turn automatic turret lathe vintage 1978 machine made by EMI-EMC. I am told that this machine is made in the U.K. The machione is rather basic to run and the operating system of the machine is fairly straight forward. In a nut shell a bunch of cross slides and a turret moved by hydraulic cylinders powered by air over hydraulic slave pumps all of which is told what to do via a switch board and some relays, silenoid valves and limit switches.
Each cross slide has it's own slave pump and the turret has it's own slave pump. When each cylinder is actuated it is in rapid mode until it hits a limit switch which tells a selinoid valve to switch system over to needle valve to control the feed rate. When the lather is in automatic operation the cylinder hits a limit switch and returns to the home position and the machine moves on to the next command.

Now for the problem. I notice one day after doing a part change over that the vertical cross slide was moving way slower than it should and it wouldn't fully cut a part off. I tried opening the needle needle valve which should increase the feed rate and nothing happened even with it wide open. So I checked the fluid level and much to my surprise I have made the mistake of allowing the hydraulic fluid level get to with in 1 " of the bottom of resevoir.

I am not sure but I fear I have intorduced air into the hydraulic system over a period of time. The way it looks the vertical cross slide and rear cross slide are the only two systems affected at this time. The slides will rapid just fine but they cut at about 90% of what they should cut at when they switch over to the feed mode of the cylce. Infact when the travel of the slide nears the limit switch or dead stop, they move about .05 per minute. Like I said before it is real slow.

So does any one have any opinions on what other problems I could have? I contacted a person about this issue and he said I could have one of three problems or even possibly all of them.
1) air in the lines, which is all i am hoping it is.
2) the slave pumps could need repair kits put in them. But what are the chances of two of those going bad at the same time?
3)bad silenoid valve that switches the system over from rapid mode to feed mode. Again what would the chance be that two of those would go bad at the same time?

I have read the manual about bleading the system. But I am not really even sure if I am doing that right because it varried from what this guy told me to do over the phone. So yes, I am second guessing everything at this point. The book says in manual operation, set the slide to rapid within 1/2" of the end of stroke and let it feed the rest of the way to the dead stop and then let it dwell for a few second and then return the slide back to its home position. Repeat several time and keep an eye on the resevoir level through out function. This guy I talked to said in auotmatic mode run a short program to operate the slide and set the slide so that it will feed the entire stroke of the slide from home to dead stop. Who or what is right? Without knowing the answer to the question and niether solution really seming to work, I tried cracking the supply and return lines at the cylinder that operates the vertical cross slide (furthest cylinder from the pumps) to try and bleed the air out there. I did get some air bubles but nothing that i would have thought have affected things. But maybe any air is a bad thing all to gether.

My questions for any one that was willing to read this far are this; where would you try and bleed the system out next so I can totally rule out whether or not the problem is air? How do I rule out the next easiest thing to fix...whether or not I have a bad silenoid valve? Why aren't the front cross slide and the rear turret affected like the other two cross slides?

Even though I am under pressure to get some parts made for a customer I am trying to keep a good look on things and look at it as a learning experience. So the way it looks worst case scenereo is that I will end up putting repair kits in the slave pumps and a replacing a few silenoid valves. About the only problem I would have then is how do I get the air out of the system so I can get back to work? Back to square one.
thanks for any help I may get.
Jr

[Brian H.]

Do you, by any chance, have a schematic of the hydraulic circuit? That would help in the troubleshooting. For now, I think that your problem is primarily air in the lines/cylinders. Having air bubbles at your connections is a pretty good sign that there is a lot of air in the system. Concerning the valves, I don't think that the solenoid valves would have gone out, especially since the cylinders will indeed change from rapid to slow feed. To me, that indicates that the valves are doing their job of rerouting the fluid just fine. The pumps, depending on their construction, may have been damaged due to a lack of fluid. Still, I would leave those alone unless nothing else works to fix the problem.

I suggest that you go into automatic mode, and write a program to rapid to within 1/2" of the dead stop, then feed until the cylinder is completely extended or retracted (make sure to make it do this in both directions, if you can), and hold the cylinder there under pressure for a few seconds, then have it return. What will happen is that when the cylinder is bottomed out and under system pressure, some of the air will be absorbed by the oil. When you return the cylinder, the oil with the air in it will hopefully be extracted. I can't say how well this will work, since I don't know the specifics of your system, but it will take a lot of strokes to get all the air out.

Although this doesn't really relate to your problem, remember to filter your new oil before you put it into the reservoir, and check your filters regularly.

I hope that this helps somewhat, I will talk to some people tomorrow and see if I can come up with something more for you.

[heavy metal machine]

Here is a schematic of the system. Let me know if ther is anything else that some one might need to trouble shut the problem i am having.

[heavy metal machine]

i have been trying to bleed the rear cross slide system for over 2 hours now. the cross slide gets about 1" of the dead stop and moves at about the rate of .001 per every 2 minutes. the needle valves are wide open and nothing happens. i am noticing alot more than usual, oil puddling up in the cabinet where the resevoir is located. but it seems like there has always been a certain amount of that. could the leaky line be the problem? will the system just eventually cycle faster and faster as the air is removed? what are the chances that the oil filter is plugged or perhaps the two supply lines for the rear and vertical slides? i have never seen a filter on the machine for the hydraulic fluid but perhaps it is in the oil resevoir. not sure but i guess there is only one way to find out.

[Brian H.]

Okay, let's see...

I didn't get to talk to my professor today (I am a student in Mechanical Engineering Technology, specializing in fluid power), but I printed off the schematic you posted, as well as the rest of this thread. I will definitely try to talk to him tomorrow to see if he can come up with anything.

I do have a couple of questions in the meantime, though: Does the rear cross slide cylinder basically stop moving at that same 1" from the dead stop regardless of whether it is in rapid or slow feed mode, or does it only happen in one specific mode? Does this happen only in one direction, or in both? Have you refilled the reservoir to its proper level?

You said that the feed rate is slower than it should be throughout (I assume) the entire range of travel. If the reservoir is full, then I would tend to suspect a blockage in the return line from the rear cross slide cylinder. I can see in the schematic that there should be a small filter somewhere between the cylinder and the needle valve, I would check it to see if anything is clogging it. Could be something in the supply line, too, but I'm not sure - that seems less likely.

Also, the main filter is very likely inside the reservoir. In that case, it is likely connected to the intake. Given that it has presumably not been replaced since you have had the lathe, I would suggest putting a new one in, even if for no other reason than that it's probably old, and therefore, dirty. Dirty filters can cause a surprising amount of flow resistance.

In my opinion, the leakage around the reservoir is probably just an overly leaky line. I am not really sure now what the deal is with air in the lines, it seems like that isn't the only problem. Air in the lines alone wouldn't seem to cause the cylinders to slow way down like they do.

I'll try to see if I can come up with some answers for you, but it may take a while to sort through this. Hope we can get this thing working for you.

-Brian

[heavy metal machine]

damn i am proud to know that i am actually getting some expert help on my problem. thanks a bunch for everything thus far. the problem only happens in the feed mode for both the vertical and rear cross slides but they will rapid back and forth with no problem at all. both are slow moving from the start of the feed into work mode but once they get to with in 1"-2" of the dead stop position they just about come to a complete stop. so yes it only happens in the one direction. the rear cross slide i can make do a dwell at the end of stroke and also do a back feed operation but on the vertical slide i can only feed it in the down direction. yes i have kept the resevoir full ever since i started working with the problem. last night i had a thought to removing the resevoir lid so the air in the resevoir can escape at that point over night. the blockage of the filter/lines is a good point. tonight i will take the top of the resevoir off and take a look at the filter. inside of it is the only place i can find where it could possibly be. i will take a few pictures of the inside of the cabinet and scan some pics from the book so you can see what is what and get a better idea of what the issue might be.

last night i tried to force the verticcal slide down using a c-clamp. the thought was maybe i can force the air into the resevoir. i did that for about an hour. it didnt seem to help much if at all. but i did notice something weird...while doing that it seemed to have moved the front cross slide slightly forward. so then i put a block infront of that cross slide to prevent that from happening.

would the leaky line be allowing air to get into the system or would they just be a place for the air to espace?

[ronm]

I'm not familiar at all w/the specific system on your lathe, but I've worked on hydraulics on farm & industrial equipment for many years. I have to say, look at the filter before you go any farther w/the problem. You would not believe the number of times I've seen a problem cured by changing filters, when the system appeared to be totally messed up...most filters are on the suction side of the system, where a restriction will cause air to be drawn into the system.
Just 2c worth as usual, but HTH-Ron.

[heavy metal machine]

i am gonna give the filter idea a try. it seems logical that a dirty filter could restrict the flow to the point of nothing being able to move. besides i have no idea when the last time any of them had been changed because i have only owned the machine for about a year and half now. i ordered the parts today and hopefully everything will be here by wednesday. i'll keep you posted to see if it works. thanks for the input.

[Brian H.]

I have marked all of the filter locations on the schematic with circles. The big green circle is, of course, your main filter in the reservoir, which you are replacing. I'm not sure if you are replacing the others, too, but the three small filters with red circles around them REALLY need to be checked. The one blue one at the far left is just for future reference. Feel free to PM me if you need anything.

-Brian

(Edited to improve picture)

[DR]

I can't be much help here....but, a question, have you let the machine cycle for hours to warm things up and clear the cobwebs?

I've never owned an Auto Turn (they were popular in their day), in years past I did have a Hardinge and an Eguro that had similar hydraulic systems. Those machines were notorius for doing strange things if they were idle for an extended period. Cycling the machines for hours would clear things up.

There's another less pleasant thought, the Hardinge and Eguro machines were only designed to run straight cutting oils. Many times users would run water soluble oils in their machines to be compatible with their other cutting fluids. The soluble oils have chlorine additives which can destroy contacts in the various control/limit switches. Does the machine have any warning labels about using only straight oils? The 1978 vintage implies to me the machine may only use straight oil. Does it currently have soluble oil?

You should also ask this question over on the Practical Machinist site. Auto Turns were popular enough that some of the machine service techs frequenting the site may be familiar with them. I remember hearing that the these machines got quirky as they aged.

[Mark McGrath]

Send an email to these guys.

http://www.emi-mec.ltd.uk/

Thats a common problem with these machines once they age a bit.We threw our last one out years ago.
Check for air in the system,muck in the flow control valves,muck under the piston in the air side of the intensifier which restricts full stroke.
I would send the slide forward and when it stops moving loosen the out connection of the cylinder.Whether it moves or not will help deciding where the problem is.
Clean lubricated air is critical for these machines.They will run on dirty wet air but not for long.
There used to be a guy called Jim Harris who posted on the PM board who run a few of these things.
Mark.

[heavy metal machine]

i'll try forwarding a link about this post to the practical machinist site to see if any more help can come from those guys. thanks for the idea. like i said earlier it seems logical that the problem could in fact be dirty filters. so i am going to try that. if i knew any one that was looking for a machine like this i would sell it to them for a fair price. i am in the market for something newer. truth be told i cat complain to much about this machine. as slow as it may be it has made a lot parts with out to much of a hassle.

[heavy metal machine]

today i removed just one of the inline filters on one of the slow moving slides and reassembling it with out a filter in the line. i did not have a filter to replace the "one in doubt" with so the intention was only to trouble shoot the issue at hand. much to my surprise the cross slide moved as it did before. i only cycled it about 4 times so i could find out whether or not bad filters were the problem. it sure seems like it might be.

i wont have my replacement parts for a few more days so i wont know for sure if this will solve the problem. but after this evening things sure seem promising. who would have thought that as serious as i thought my problem was that it would could have been a dirty filter of all things!

i will let you all know in a few days if changing a few filters solves my problem all together. thanks to all that were willing to participate in helping me solve my problem.

i truley do appreciate the help
jr