Hydraulic top link issues

[MtnViewRanch]

Again, in my pea size brain, is my 17gpm flow rate contributing to this problem?

NO, I sell top & tilt sets to Kubota M8540-60 and 9540-9960 machines all the time. All have double .060 restrictors. I have yet to hear any complaints from them. Also JD 5000M series tractors with 18.4 GPM pumps, no problems that I am aware of. Personally installed a "T&T" set on a local 5085M last year and everything worked perfect. No squealing, units were perfect operating speed, ZERO problems.

Sometimes stuff just happens, a series of conditions that make things just right to have these things appear, simply a fact of life and we just need to deal with those situations as they come along.

The main reason that I even went to the double flow restrictors was because of a couple of JD machines, one smaller, one just under your size, more like an M7040. It took double restrictors to get these guys squared away so that things worked properly, Why, I have no idea,:confused3: just that's what ended up working.

I think that your restrictor on the rod end should do the trick for you. If it seems to slow, drill it out to .070.

 

[LD1]

The rate at which the fluid leaves the rod side is directly related to the weight/geometry of the implement. The harder it's pulling on the cylinder, the faster the fluid leaves.

The rate at which the base end isreplenished is directly related to pump flow/tractor rpm.

Gotta have a balance. Yours was clearly not. A heavy implement, and restricted inlet was clearly an issue
There are a lot of other variables too, like cylinder rod size. A larger rod for a given cylinder, will make the pressure under the weight of the implement higher, which means fluid leaves faster. AND there is less of it.

 

[ovrszd]

The rate at which the fluid leaves the rod side is directly related to the weight/geometry of the implement. The harder it's pulling on the cylinder, the faster the fluid leaves.

The rate at which the base end isreplenished is directly related to pump flow/tractor rpm.

Gotta have a balance. Yours was clearly not. A heavy implement, and restricted inlet was clearly an issue
There are a lot of other variables too, like cylinder rod size. A larger rod for a given cylinder, will make the pressure under the weight of the implement higher, which means fluid leaves faster. AND there is less of it.

I run a JDM1008 (10ft) mounted brush cutter on the Kubota. When you move the lever to extend the top link while the cutter is off the ground, it drops very fast. But I also like the fast speed because I use it to turn around on the ends. Rarely raise the 3t, just retract the top link and lift the cutter. Also if I hit an unseen object, my first grab is the top link. So I'll hafta work with that next Summer and see if I can deal with the slower response times. If not I'll drill it out a little as Brian suggested. At least now I know if I go too big and get the vacuum problem I can simply go back to a smaller size.

Thanks guys.

Again, hope some little bit of this info helps the OP.

 

[Gordon Gould]

This is really interesting and complicated to think about. So I could very well be all wet but the way I see it is that it must matter if the tank return is above or below the oil level in the tank. Because, If as you extend the ram and the heavy implement draws a vacuum on the dead end of the cylinder because it can't fill fast enough and then you close the valve you are left with a vacuum on the dead end of the cylinder and oil under pressure from the implement weight on the live end of the cylinder. Then, if you reverse the valve to retract the ram that opens the dead end with the vacuum to the tank. The vacuum will suck either oil or air back into the cylinder from the tank depending on the whether the port is below or above the oil level in the tank. ?????????????

gg

 

[ovrszd]

This is really interesting and complicated to think about. So I could very well be all wet but the way I see it is that it must matter if the tank return is above or below the oil level in the tank. Because, If as you extend the ram and the heavy implement draws a vacuum on the dead end of the cylinder because it can't fill fast enough and then you close the valve you are left with a vacuum on the dead end of the cylinder and oil under pressure from the implement weight on the live end of the cylinder. Then, if you reverse the valve to retract the ram that opens the dead end with the vacuum to the tank. The vacuum will suck either oil or air back into the cylinder from the tank depending on the whether the port is below or above the oil level in the tank. ?????????????

gg

Gordon, I can't confirm that as accurate. That is what my mechanic friend was explaining to me.

After my experiments today it looks like the "air" is collecting at the barrel side of the cylinder piston? When I removed the quick coupler from the rod end hose oil ran out......

I've been involved in several debates regarding hydraulic situations similar to this. More often than not a definitive answer isn't found. In this case I can only relay my findings. Sometimes the scientific solution isn't determined.

 

[Kodiak45]

Sounds like I probably need to get a restrictor, but just one right? I will admit that I do "slam" the lever instead of feather. I'll look into getting a restrictor from Grainger in the next day or two. Does it matter which end of the hose? Good thread, lots of learning on here.

 

[npalen]

The restrictor is typically placed at the cylinder end of the hose for safety if no other reason. A blown hose would let the implement down a little slower with the restrictor at the rod end of the cylinder.

 

[Leejohn]

The way I see it in his clip there is no weight on the top link. What I see is when the att. hits soft dirt it pushed the top link in and when it hard dirt it pushed the top link out. So I say it's air on the piston base end side, the air is picked way before the top link.

 

[boggen]

the spool valve leading to the top link cylinder in question, on the given tractor.

the only way that cylinder going to move. is if fluid on both ends of the cylinder can move in and out of the cylinder at the same time. if air is only on one side. and only oil on other side, from valve, hose, and into cylinder is pure oil. no air entertained in the oil. then there is oil leaking at the valve or air going through the spool valve. ((assumption valve is in neutral position and you are not operating the valve to extend / contract the cylinder))

if the spool valve is out of adjust, or rather partially moved to either expand or contract the cylinder. you no have to take the entire system into consideration. as soon as that valve, but as soon as that valve gets put in neutral position and at min only oil in one side. and cylinder still moving. then it would be a spool valve issue.

spool valves, have different ports on them, from power beyond, to tank, etc.... and there are different types of spools that can be inserted into the spool valve assembly to achieve different results. for example float. were hoses connected to the valve, connected to wrong ports? i do not remember the lettering codes P, T, a1, a2, b1, b2, X? to tell what ports are what on the valve body.

example for above... instead of a hydraulic cylinder with double ports on it. just a single port of hydraulic cylinder is actually getting oil from the valve. air in this single connection could cause a spring effect.

there could be issue with the internal check valve within the spool valve. allowing oil to bypass around the spool valve. and in that allowing the cylinder to move.

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i would agree with given statement. if hose between valve and cylinder holds more oil than the given end of cylinder. there might be an issue getting oil into the cylinder and getting air out. one would physically need to bleed the out of the line. much like bleeding car brake lines. and the piston of the cylinder would need to be pulled out or pushed in pending on which hose and connection point on cylinder you were wanting to bleed out.

granted the cylinder might fully fill up eventually. once slow little steady of stream of oil ran down the hose to cylinder. but if the hose and/or cylinder has a higher area were it is ran (upside down U) you may not get any oil to the hydraulic cylinder at all. and just wasting time fully extending / contracting the cylinder. and would need to bleed the hoses and cylinder manually like car brake lines.

there are some different thread types out there. for fittings, and some do and do not require pipe tape or pipe dope to be put on threads. if there is not a good seal, at the threads air suction and/or pressure could be happening. regardless of how much you tighten stuff up with wrenches.

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issue with tank return above fluid level. the only way an issue could come up. is if all the pipe from were it comes into the tank. to the cylinder. was measured up for volume. and the hydraulic cylinder (given side) had more volume. than what is in all the pipe/hose up to that point. there should be a check valve in place near or in tank that most likely stops the "back siphon effect" of drawing air in.

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if air is getting into the hydraulic oil. check the oil itself. before turning it on in morning (setting over night) look at oil in tank. then try messing around and running with tractor.... does the oil look different? ((there might be water contamination, but if air is getting into the oil. it will most likely cause tiny little bubbles within the oil. that may not float up and out of the oil during run time. and needs enough time for the air to float up and out.

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a restrictor is the equivalent. of a needle valve, or any other valve (spool valve), were you just barely open the valve. to let liquid flow through it. much like only opening up kitchen sink faucet, and you just want a dripple of a stream to come out. the larger the hole in the restrictor the more you open up the facet handle. the restrictor is just a permanently open valve that is opened up just a very little bit.

if you open the spool valve fully up to get as fast as possible reaction speed in either extending and/or contracting the hydraulic cylinder. and you hear a squealing sound. and you hear relief valve going off (squealing). then most like the "restrictor" has to small of a hole going through it. going with a bigger hole would be like opening a valve up. to allow more oil to move. this might also be indication the valve assembly for the TNT is to small. instead of gong with say a 3/4" valve setup you went with 1/2" setup or what not.

if the valve body and spool valve itself going to the top cylinder is physically sized to small. for GPM and pressure rating of the tractor. you might have issues and need a restrictor is were i am thinking. internal back pressure inside of valve is to much, and needing a restrictor in line to given cylinder, to help balance out pressure inside the valve assembly itself. if there is any defects with the spool itself. oil / air could be leaking pass the spool valve.

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suggestion would be ((i assume extra rear hydraulic ports were added to tractor, for TNT)) try moving the hoses connecting to the TNT to the original ports on the tractor and see if it makes a difference. if it does, it might state there is problem with the valve.

 

[boggen]

i would agree with given statement. if hose between valve and cylinder holds more oil than the given end of cylinder. there might be an issue getting oil into the cylinder and getting air out. one would physically need to bleed the out of the line. much like bleeding car brake lines. and the piston of the cylinder would need to be pulled out or pushed in pending on which hose and connection point on cylinder you were wanting to bleed out.

need to correct above. (doh doh) air is compressible. when fully extending and contracting to work out air. hold the spool valve fully open until you hear relief valve (squeal) sound kick in. that way the pressure actually builds up and compresses the air inside the cylinder. and allows the oil to get into the cylinder.