Help with loader problem

[rockquarry]

Hi all, been lurking here at TBN for awhile now and need some help that a search hasnt proven usefull. I disconnected one of my loader lines to run a cylinder on bush hog and have done this a few times but I have noticed that since doing this when I use my loader (yes I hooked the line back up) when I go to dump the bucket, it dumps about halfway then stops and i have to wait for a few seconds for it to continue dumping. I do keep the joystick in the dump position but the bucket just stops for some reason. It doesnt seem to bind anywhere and it curles the bucket up just fine. all other hydraulic funtions seem fine. I thought it might have gottn air in the line but I've tried to bleed it by moving the joystick through all the functions completely, raise the loader all the way, lower it dump the bucket and curl the bucket all seems fine except on the dump. its been doing this for a year now and i cant seem to figure it out. please any help would be most appreciated

 

[john_bud]

Run the tractor to warm the fluid. Then dump the bucket fully and hold the control against the stops for 5 seconds. It will make some buzzing or vibrating sound as the relief valve opens --> that's normal. Then curl the bucket up and hold the control for 5 seconds against the stop. Repeat that cycle 3-4 times and it will bleed out all of the air in the cylinder.

If you still have the issue after doing that, give us an update!

jb

 

[JackIL]

Rock,

The problem may be "cavitation." This can happen if you are: (1) dumping a heavy load or (2) back-dragging with the bucket. Cavitation can occur when the pump is "small" as is usually the case on CUT loaders. High "back loading" causes the return oil out of the curl cylinders faster than the pump can supply the needed make-up oil on the other side of the cylinder heads. This sucks in air through the system vent which must be purged by cycling the cylinders as explained in another post.

There are 2 things to do to minimize or prevent this problem. One, operate the engine at full throttle to get the maximium pump output flow. Two, when dumping heavy loads, dump as fast as possible--do not "feather" the curl control valve, but instead push the handle all the way into the float position so the regenerative action occurs.

JackIL

 

[rockquarry]

I tried bleeding the system like John said and that didnt solve the problem and I'm pretty sure it's cavitation like Jack stated. I use my tractor to move alot of rock (usually much bigger and heavier pieces than i should be) and I do dump the bucket when at almost idle and do feather it, I found out if I just dump the bucket with some big rocks in it they can shift and upset the tractor, not to mention having to pull the seat out of my backside when it settles down. I just feel more comfotable dumping slow with a bigger load.

is this cavitation bad on hydraulics? It doesnt bother me I just wanted to know if something was wrong with the loader or not

 

[JackIL]

Rock,

You can still keep the engine speed up so that the pump is at full capacity even if you need to feather the dumping. You will just have to develop a more sensitive touch on the control lever. If the bucket curl hangs up on you as you are trying to feather the dump of a big load of rocks, you have lost control anyway. You might want to consider backing off a bit on how much you try to get in each bucketful.

I'm not sure if cavitation will damage your pump, but, cavitation can cause damage, especially to cylinder liners and pistons in engines. I would try to keep the system purged as much as practical.

 

[RonMar]

I disconnected one of my loader lines to run a cylinder on bush hog

RockQuarry can you describe a little better exactly what line or lines from the loader you are removing/replacing? Are you running a single acting cylinder with it back on the brushhog?

I do not think this is cavitation. Cavitation is usually caused by restricting the supply to the pump(clogged strainer, crimped supply line). Cavitation is when the fluid that just passed thru the gear trys to get back to the supply side due to the difference in pressure caused by a lack of supply fluid. In extreme cases, it is possible to draw the fluid away faster than the pump can supply it, but this dosn't cause cavitation as there is no reversal of flow in the pump. In fact, you are completely unloading the pump. Cavitation on the other hand is hard on the pump. the reversal of flow and the eddies this causes can erode the gears and pump body.

I also don't think you are drawing more fluid than the pump can supply. The hydraulics are a Open Center circuit. In neutral, the fluid flows thru the loader valve core relatively unobstructed. As you move a lever, the fluid flow is slowly diverted from this normal path to the cylinder based on the ammount you move the lever. At the same time the return from the cylinder is slowly opened to the valve return side to give that fluid somewhere to go. The key here is that you are doing this slowly. If you are doing this slowly, you are only taking a small portion of that main flow into the valve so I think it unlikley that you are drawing more fluid than the pump can supply even when letting down a large rock. To draw more fluid than the pump can supply, you would have to have the control valve FULLY opened then physically move the bucket/cylinders faster than they would when just being fed with the pump(dumping that big heavy rock quickly

Is the line you disconnect the one that goes to the push side of the bucket rollback cylinders? If so this could be as simple as a loose connection on that line where it connects to the loader valve.

If you are letting down a heavy load, the push side of the dump/rollback cylinders draws more fluid in for a given ammount of rod extension than the rod end returns. This can place the push side of the cylinder and it's associated lines under a vacume. If the fitting where the push lines are attached to the working ports(the one you removed?) is leaking a bit, this would cause air to be drawn into the system at that fitting, then you will have to purge the air from the system to restore normal function untill the next time air is drawn in under vacume. Here is a test. Place the bucket flat on the ground. Using the bucket dump, try and lift the front of the tractor off the ground. This will place the push side of the dump cylinders under pressure. Check all the fittings for any sign of leakage. Unfortunatly because of the densities, it is way easier to draw air into a vacume than to leak fluid out under pressure so you may not find anything. If you have only messed with one fitting, I would look there first.

The best way I have found to purge the air out of the dump/rollback cylinders is to fully cycle the bucket 2-3 times with the loader as low as possible, then do it again with the loader at it's highest position.

Let us know what you find out.

 

[whitetiger]

Do you mean that you unplugged one of your loader hoses from a coupler and plugged in another hose to raise your mower? If so, switch your raise and dump hoses at your couplers and see if you still have the same problem or if the problem is now with your raise-lowwer circuit. It sounds like you have a problem with one of your quick couplers.

Hi all, been lurking here at TBN for awhile now and need some help that a search hasnt proven usefull. I disconnected one of my loader lines to run a cylinder on bush hog and have done this a few times but I have noticed that since doing this when I use my loader (yes I hooked the line back up) when I go to dump the bucket, it dumps about halfway then stops and i have to wait for a few seconds for it to continue dumping. I do keep the joystick in the dump position but the bucket just stops for some reason. It doesnt seem to bind anywhere and it curles the bucket up just fine. all other hydraulic funtions seem fine. I thought it might have gottn air in the line but I've tried to bleed it by moving the joystick through all the functions completely, raise the loader all the way, lower it dump the bucket and curl the bucket all seems fine except on the dump. its been doing this for a year now and i cant seem to figure it out. please any help would be most appreciated

 

[rockquarry]

I unhooked the line that is connected to the push side of the cylinder to dump and curl the bucket. I didnt unhook it at the quik coupler I unhooked it where the rubber hose from the quik coupler block connects to the hard line on the loader arm. I was using it to run a single acting cylinder on a brush hog. I did check to see that the connection was tight this morning and I still have the same problem but I did notice that when I was dumping one load I kept the tractor at about 2000 rpm and it did not act up like before. I do think it has to do with dumping while at idle

 

[rockquarry]

well I need to correct what I last said. I was using it somemore this afternoon and had the throttle up to about 2000 rpm and a full bucket and it still seem to just stop alittle more than halfway dumped. it does seem to be and intermintant problem (doesnt do it every time) and it will do it when im just moving the bucket to the dumped position with an empty bucket. I'm stumped.

 

[RonMar]

I bet you are sucking air at the fitting you removed to hook up the single acting cylinder. Air is only about 1/300th as dense as hydraulic fluid and can easilly be sucked in and not have any fluid leak out, particularly on the push side of the dump cylinders as they don't get that much pressure put to them(gravity does most of the work dumping the bucket). Is it a SAE/JIC fitting or a NPT fitting. If it is NPT, did you put new teflon tape on the threads when you re-installed it? If it is a SAE/JIC fitting, any dust or debris could cause it not to seat correctly and admit air when the system goes into a vacume there.

 

[rockquarry]

I dont know what type of fitting it is. I do know that when we (my father-in-law, It was his brush hog) we just went to the local farm supply store got a 6-8' length of hydraulic hose and some NPT fittings. so I can only guess its NPT. I didnt use teflon tape. I seem to remember reading somewhere about not to use teflon tape on hydraulic stuff. dont remember where i read it of if it was in reference to just to not use in on a certain type of fittings. either way I'll take it apart tomorrow and put some tape on it then go through the whole pushing it against the stops to get the relief valve to open and get all the air out and see if that helps.

Thanks for all your help and info guys even if i dont get this thing to work right.

Jeff (rockquarry) Ill post some pics sometime so you can see how I came up with my user name

 

[RonMar]

Getting the relief to open dosn't really make any difference other than letting you know you cycled the ram as far as it is going to go. What does make a difference is cycling the rams when they are pointed up(lift arms at full height) and when pointed down(lift arms as low as possible but will still allow full bucket travel). It is like a doctor/nurse getting air out of a cyringe. they point the port on the cyringe(needle) toward the ceiling so the fluid forces the air out first when they push the plunger.

Air and fluid don't separate well in the confines of the small lines. The air and fluid will separate guite easilly in the larger space of the cylinder with the air of course going to the top. You need the port to be at the highest point so the air exits first and the fluid last, forcing that air all the way back to the valve where it will continue on into the resovoir and separate from the oil completely. With the lift arms down low, the port on the push side of the bucket cylinders is at it's highest point. With the lift arms at their highest, the port on the ram end of the bucket cylinders is on the top. If there is a lot of air, this may take a few cycles in each position to get it all out.

 

[john_bud]

Ron,

My understanding is that holding the control until the relief opens does do some good. For one it gives the air time to get past the packings and out of the cylinder. It also is a positive indication that the ram is moving to it's full extents. Could be wrong, but that's how heavy equipment mechanics trained me to do it. It has worked for me every time I have rebuilt a cylinder and installed it dry.

jb

 

[RonMar]

Holding the lever with the safety relieving does keep the system at full pressure and does indicate that the ram has reached it's full travel. It can force air out of the rod packing, it can also force air past the piston seals, but that is just relocating the air to the other side of the piston. That air can't go anywhere on the other side unless fluid is pushing it. I do trip the safties, but that is just to let me know it has gone as far as it can go. I don't as a rule hold them there. I have always relied more on piston position and cycling to remove the air from hydraulic systems.

 

[rback33]

You are definitely experiencing cavitation. The fact that it is intermitent really proves that. The weight of the bucket and rocks pulls the cylinder rods out faster than the pump can cylce it through to the base end of the cylinder. AS mentioned before, using regen and/or operating at higher rpms are the only ways to help/solve the issue. Regen makes it go away, higher RPM's helps reduce it. BTW, it does not hurt anything. It is just annoying sometimes.

 

[schmism]

a few quick points on cavitation

Cavitation - Wikipedia, the free encyclopedia

I most of the descriptions for it i didnt feel properly describe whats happening.

In the simplest terms it occurs then the fulid flow around a surface seperates from surface because it can no longer maintain lamanar flow.

generally cavation is considered a VOID in the liquid. (not air) as the "bubble" colapses a tremendious amount of energy is releaseed. (there is some debeate weather this colapsing energy (under the right conditions) can be considered cold fusion) anyway with the release of the eneargy is assocated with sound and sometimes light (or other electromagnetic radiation). The energy release is sufficent to vaporize the material makeing up the surface of that the fluid seperated from on a microscopic level, however if left to continue long enough it can cause physical degigration of the surface. IE if you look at the wikipedia link it shows a turbine that was worn down due to cavatation.

although this wear is usualy only a significant issue in extremly high speed applicatications such as steam turbines.

 

[rockquarry]

Well I tightend all the fittings and checked for leaks and found no change in the problem. I do believe it is pulling the cylinders out faster than the pump can handle. no big deal I just wanted to know why. Thanks all

Jeff