I have an older 325L that the stick will free fall and swing back a forth some when it gets near vertical while booming up and pulling the stick in. Then it catches and damn near puts the bucket in the cab with you if you arent careful. Actually its not that bad but is aweful agrravating. Had the CAT tech out for two days to figure it out. His parting words were Bad news is I can't figure it out. Good news is that your excavator is in good shape, everything checks out well (pressures, flows, etc). Just had a new control panel in it 5 months ago. Any helpful thoughts?
If you are boomed up and only work the stick does it operate normally? When you operate the boom and stick together does the boom slow down?
does'nt matter. either way it does it. Does'nt appear to affect any other of the hydraulics either. Boom, bucket, swing, etc. all appear to work as normal. It is as if the stick cylinder is dumping fluid quicker than the pumps can keep up. i.e. when the cylinder gets to near vertical, it dumps all fluid and it takes the pumps a little bit catch up. However, the CAt Tech checked all pressures, flow, etc. and everything is to spec. even backpressure valves. I asked him if he thought it could be air in the cylinder, he did not think so.
It sounds to me like a regen circuit is not working. A lot of MFG's will divert the return oil back into the base end of the cylinder to help supply oil. I am sure one of the Cat guy's will be around soon to help out.
My First thoughts would be ram seals!!! Anyone check this on your machine?
I don't think it is the seals. The cylinders hold their own weight and don't drift or bleed off any. However, i am not a hydraulics man. I am interested in the regen circuit theory which would make sense I guess. As I understand it it diverts some of the fluid back into the cylinder on the extend cycle. If for some reason that circuit was closed would it then go back to the tank which would, I assume, leave a deficit for the cylinder until it "caught" up? If so, I would have also assumed it would show up somewhere in a pressure test? I am somehow finding it hard to believe that all the tests come back on spec while still having this problem. I ordered a service manual in hopes of gaining a better understanding.
If you think theres any chance it's in the seals shoot the Cylinder Barrel with a Infared Thermometer. If Fluid is bypassing the seals it will make some heat. BTW this is one of those things that's more of an art than a science.
It is usually done in the control valve. If we had a schematic it would be easy to identify how your system controls flow. The brand I am most familiar with regen is done through compensators. If you have a fax number send it to me in a Private message and I can fax you what a regen circuit looks like.
Have you checked track tension?. When was the last tiem you changed the cab-air filter
Yep - my 225 (excellent shape, low hours) does the same thing. I believe this is a dampening mechanical feature to prevent us from putting the stump through the cab. Let me guess - its only when you get close to full crowd, right?
Say what?
I'll second that?? Sarcasm maybe?
Just another young dumb kid here that uses the "we" phrase alot.......i was just trying to fit in haha. Actually i had a idea all typed up and realized the flaw in my theory, so i decided to make my post count jump with another worth while post........sorry it wont happen again,..'ERR? Pj
Sounds like you need a Cat tech whoe is an excavator expert. They have some special training to find the problems like that that do not make sense to most of us. I tend to agree with the regen circuit being at least part of the problem.
You got that right...
spoke with the field service guys at the CAT dealer yesterday and asked about the regen circuit on the cylinder. They claimed they checked it and it was o.k. They are reviewing field and inspection notes and speaking with CAT to come up with something. I think I will just have to take some uninterupted time and methodically go thru it starting with the seals and the regen circuit. My lovely wife keeps reminding me how expensive and time consuming my farming hobby is! She's right, as always. Crops look good though.
Good deal on the crops. You can always fix a broke machine, but you can't fix broke crops. When they are bad they are bad.
fftopic Thanks for taking us off topic there Squizzy lol enviroset: around here it's the best crop year we've had for many year's, 67" tall beans in unfertilized fields Pj
Great crops here too, almost too much rain this summer. I once had an old Hy-Hoe(made in Brantford, Ontario) with a very simple hydraulic system. Anyway the dipper would do the same thing. Apparently there was a small valve within one of the valve bodies that was supposed to maintain back pressure, so the dipper would continue to move at a controlled rate, in that near vertical position. Most certainly the Cat system is far more complicated than in the old Hy-Hoe, but maybe the need for that valve is still there. Phil
Just now read this thread, and was beginning to suggest a possiblity, then I ran across your post, your thinking much like I am Phil (that's scary!) Phil's describing an anti-cavitation valve. It does keep backpressure on the return side of a hyd circuit. That's my best guess of where your problem is.
Free Falling Stick on CAT 325: OCR... :lmao
Amen, OCR. If Phil starts thinkin' like me...he'll never be the same Phil anymore!
Free Falling Stick on CAT 325: Could be much worse... what if he started to think like me... Or should I even use the words "think" and "me" in the same sentence??? Or post???? OCR...
try to switch place of the line reliefs for the stick..
I have just skimmed through quickly so some of the points that I'm going to mention may have already been covered, so bare with me. The CAT mechanic probably would of checked these too, but it wont harm to re-check. As mentioned previously, work the machine for a generous amount of time to get the hydraulic oil up to operating temperature (simulate digging operations, or just simply stalling the cylinders, in particular the stick) then take the temps of the cylinders, if the stick cylinder sticks out like a sore thumb (higher temperature) then the cylinder is bypassing (could be either that the cylinder has expanded due to a large shock load which I have seen several times, but I would assume you would of mentioned if this was the case, or, more likely to be worn piston seals) If a raised stick lowers self-acting (drifting) you should check the SRV's (secondary/service line relief valve) for the stick circuit first. Firstly, check to see if the maximum permissible pressure peak in the service line can be built it, if it can’t adjust it to the required spec, if it can then remove the valve and inspect the o-ring’s, when you re-fit the relief make sure you use the correct tension to properly seat it in the valve to ensure correct sealing and operation. Check the function of the anti-cav valve, could well be that it’s worn excessively and as a result made a complete path from the rod end of the cylinder to tank. Make sure the control lever is actually neutralising for the stick function, if it’s not them eliminate the cause! Also check to make sure the spool is neutralising. If all of the above check out to be serviceable then I’m afraid it’s possible that the problem may be caused by too much internal wear within the control valve i.e. damage, cracks etc.
I think what your trying to describe is a flow restrictor Phil (sometimes called throttle valves, or on larger excavators restrictor blocks). On the smaller excavators it is found inside the control valve, more so, inside the spool itself and acts to control the maximum (pressure or pressureless) acting of the cylinders from their respective stroke i.e. boom cylinder retract, stick cylinder extend (on excavators) and stick cylinder retract (on face shovels) You’re sort of on the right track there ATCOEQUIP, but I think you got a little confused with the valve Phil was trying to describe. To put it simply, an anti-cav (anti-cavitation valve) serves to avoid cavitation and prevent damage to cylinders and corresponding components by supplying additional oil to the side of the cylinder where the oil is entering. The service pressure holds the valve closed during normal operation, the back pressure acts on the valve cone, trying to open it. Whenever the pressure at the service line is lower than the spring tension and oil pressure at the cone, the valve opens, supplying additional oil to the cylinder. Again, putting it simply, for example, when you lower the boom, the oil returns from the piston side and enters the rod side. Due to the weight of the attachment and/or load, the forces predominate the output flow of the pumps or to put it simply the speed of the oil exiting the piston side of the cylinder "overtakes" the volume of flow to the rod side, causing suction cavitation which due to the low-pressure/high-vacuum boils the oil causing vacuum voids which implode violently causing a lot of damage.
What is being described was common on most all hydraulic excavators in the seventies. The problem is that the stick can come down faster than the pump can supply oil to it. Once it is sitting vertical it stops moving until oil catches up and refills the cylinder. It generally slams hard making the stick jump very suddenly. Various fixes were devised over the years. The Japanese excavators ran two pumps from a common power source which supply specific circuits from each pump. This meant there was extra oil from each pump not being used so the designers made provision to use two pumps to a single circuit under the right circumstances. From my experience boom up and stick out were the first applications but later I saw machines that used two pump function for stick in as well. The problem with single pump function on stick in is exactly the problem described here. There were many designs to fix this, the most common in the seventies and eighties being a flow restrictor being installed on the stick in return line. Later on I saw two pump flow going out to the piston side of the cylinder and only single pump flow being allowed out of the rod side. Nowdays the manufacturers that have load sensing hydraulic systems use a regeneration valve in the stick circuit. It generally works like an anticavitation valve in that when piston side pressure has a specified amount less pressure than the rod side the valve is forced open running a percentage of return oil back into the piston side of the cylinder. Unlike an anticav valve the regen valve does not require a vacuum before it opens. That model of Cat excavator I generally considered at least a generation behind the Hitachi and Komatsu brands in technology. They were not load sensing and I don't recall them ever having a regen valve in that time frame. I will have to go back to the books and look it up but I suspect there are other functions in the main control valve that control or limit the limp stick problem. It could also be that the pumps do not supply enough oil when booming up at the same time as pulling the stick in to keep the stick cylinder full of oil. It might be an issue with old pumps no longer putting out enough oil. Unfortunately I have seen the problem many times in old machines with thousands of hours of operation. I generally takes someone who has worked through the problems before and knows something from experience. If you have to figure it out cold, you are going to spend a lot of hours, make a huge mess and loose plenty of oil checking components. More than once I've had to tell owner's that the cost of the repair might be more than what the machine is worth. Good Luck!
Hello If the machine where OK to begin with and has suddenly or over some time started behaving like this its well worth troubleshooting the symptoms. Is there an antidrift-valve on the stick circuit of this machine? Did the Field technician try to disconnect the pilot hoses to the "stick2" valve (Secondary valve for the stick cylinder) (two pump flow as mentioned earlier) and try to operate the machine with only one pump flow for the stick circuit?? If the machine got worse or the symptoms where the same this test would determine if it was, fore some reason, running the stick on only one pump. missing NFC pressure to that pump or something..
I ran a Komatsu that didn't respond well to controls... Felt like the machine was running on about halfthe cylinders.... They called the REAL mechanic out.... It was orings or or valves....don't remember... a bunch of packages of small parts he did a test that made the bucket uncurl while doing something else...which the bucket wasn't suppose to do It took him all of 5 minutes... Then the seeya when the parts come in... Then probably 2 hour to replace the whatever
I believe the valve you are referring to is known as a quick drop valve. The quick drop valve has a sleeve carried by a valve member for establishing an orifice through which the fluid expelled from the hydraulic cylinder passes. When the flow rate of the expelled fluid exceeds a predetermined flow rate, a differential pressure generated by the orifice causes the valve member to start moving toward a quick drop position. In so doing, the sleeve quickly establishes a more restrictive orifice to immediately generate a higher differential pressure to cause the valve member to quickly move to the quick drop position. The more restrictive orifice also causes a greater amount of the expelled fluid to be returned by the valve member to the expanding ends of the hydraulic cylinders, yet still allows sufficient flow therethrough so that the quick drop action can be stopped if so desired. The sleeve also functions similar to a check valve and moves to a position permitting substantially unrestricted fluid flow through the quick drop valve when the fluid is being directed to the hydraulic cylinder to raise the load. Just re-read through some of the posts in this thread and found a few discrepancies which I would like to clear up, dont take it the wrong way, just trying to get some accurate info to help in assisting you Couple of questions here, bare with me. 1. Are you sure you dont mean when its near horizontal in relation to the ground? 2. Does it ONLY happen under these circumstances? i.e. while using the boom up function AND using the stick-in function? 3. Does it "free fall" if the boom is fully raised, and the stick is fully extended (stick cylinder retracted) or would under similar conditions but using the stick-in function? 4. Did the mechanic that looked at it perform a cylinder bypass test? You would be suprised at some of the technical faults that can happen whilst still being able to maintain full system pressure and other specs.
A regen valve is kind of like a quick drop in that both allow rod side oil to go to the piston side of the cylinder along with supply oil from the pump. The difference is that what we call a quick drop valve allows free fall of the implement. Where we see them is in older bull dozer cylinders and they allow the blade to free fall to the ground. The regen valves in excavators don't have enough capacity to allow free fall of the stick. Regen valves are part of the main control valve while what we call the quick drop valves are mounted directly to the cylinder. I have seen a few machines with problems in the regen valves. Dash 6 Komatsu 200 machines had the problem of the regen valve not reseating properly and causing oil bleed off when the stick came into a pull in the trench. When enough flow and pressure built up the valve would reset with a huge bang and the stick would just blast through what ever material it was in. I know of about four updated valve sets in the time I was working on those machines. It may be possible this Cat has the same problem but the dealer wrench said it was tested and there wasn't a problem. I'm also thinking of another issue with this repair. Since the dealer wrench did not repair the problem, should they be paid for not fixing it?