Loader down force: Loaders  -- Tractor Attachments Implements 3ph Discussion Forum and Review Loader down force: Loaders -- Tractor Attachments Implements 3ph Discussion Forum

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 06-04-2000, 22:36 Post: 16893
MikeC



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 Loader down force

I'm not sure if my loader is working correctly. I have a JD855 with a 70A loader. When I put the bucket flat on the ground, then try to lower the boom more, I expect the loader to lift the front tires off the ground 2-3 inches, since the loader is supposed to have 5 inches of digging depth. Instead, it just sits there straining. If I then roll the bucket down, it will easily lift the front tires. From this position, if I raise the boom to sit the tires back down, then try to retract the boom cylinders again to get the tires back off the ground, it can't do it. I had a 755 which would easily lift the front end with the boom cylinders. Is there an adjustment for the hydraulic retract force on the boom cylinders, or is there something wrong with the loader, or is this the way it was designed? Thanks - Mike C.






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 00-00-0000, 00:00 Post: 16897
Eric Edwards



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 Loader down force

Well Mike, I don't have any answers but have similar questions. I have a JD750 w/ a 67 loader. I thought that it too would have down pressure from the boom cylinders when I purchased it, since a smaller ford I had looked at did. I was wrong. Only way to make the front airborn was with the bucket cyl.. Now I have a 430 loader on order for a recent used JD1070 purchase and I'm wondering if it is the same as my 67 loader or does it have true down pressure. Actually, I hate to be a pessimist but I doubt it does, since it has a float feature like my last loader but I'm just guessing. As far as digging depth is concerned, the way I understand it, is this. If you have a 4" depth capability then the loader, with a level bucket, can only physically be lowered this amount because of design characteristics limited by the length of the booms, where the loader attaches to your tractor and tire size. If this is correct, and I think it is, you could increase or decrease your depth ability by changing your tire size. Depth quoted by Mfrs include stock tire sizes for your tractor. I don't know if my ramblings helped but I'm sure someone here has command of these questions.






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 06-05-2000, 07:56 Post: 16902
TomG

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 Loader down force

What you describe is the way my loader works. I believe it's designed like that. There is enough down pressure on the boom with the bucket flat to lighten the front so there's little steering, but not enough to lift the wheels.

However, I can dig 4 to 5 inches with the bucket if it is angled slightly down. I imagine that manufactures of loaders with this design would reason that they could advertise a digging depth, since you can't dig much with a flat bucket anyway.

I'm guessing that there may be a reason for such a design. A loader could be digging with a flat bucket below ground level. If it hit a rock, all the force would be straight back. Something might break. Hit something with the bucket angled slightly down, and the front wheels rise off the ground. There's less force, and also a chance to stop the tractor.

Anyway, it happens to me from time to time. If I'm trying to pick up the last of a pile of gravel off the ground, I flatten the bucket and float the boom. If there's a dip right before the pile, the bucket angles down, the blade bites in adn digs,or the front wheels rise. Of course, if I have the bucket curled up too much, then the bucket just floats on top and doesn't pick up anything. Either way, I don't break anything--even if I do take an occasional gouge out of the ground. I do remind myself that a loader isn't designed to be an excavator, so maybe a design that limits the use of a loader to mild excavations is a good idea.






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 06-05-2000, 12:07 Post: 16909
Darryl Gesner



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 Loader down force

Mike - I also have an 855 with 70A loader. I can raise the front tires just barely off the ground with my loader lift cylinders while the bucket is level. No straining. If I first curl the bucket and try it, I can raise up higher. Note that I always have either a backhoe or a 5 foot rotary mower on the rear and the tires are filled, so that would undoubtely change the physics a bit. I love my 855! You?






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 06-05-2000, 21:35 Post: 16922
MikeC



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 Loader down force

I love my 855 as well. It's a very capable machine (for a homeowner) considering how gentle it is on the turf. I'm also impressed with how quickly I can mow my 2 acres with the 60" mid-mower, given all the obstacles and 180 degree turns. It competes with my Gravely walk-behind for mowing speed. Which hoe do you have? I'm shopping for one myself.






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 06-05-2000, 23:18 Post: 16931
Eric Edwards



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 Loader down force

Tom, although you have addressed the practical, ie techniques when actually digging, no one has yet touched upon the two real questions. You are correct, when digging, a level bucket makes no sense on level ground. But we were talking about Mfr's. specs. If the Mfr's could include a down angle in there calculation I'm sure that they could achieve a much greater digging depth then stated in most catalogs. I still maintain that the figure(3 or 4 inches)comes from the number of inches a level bucket can be lowered past the plane that the four tires are setting on (someone w/ knowledge please correct me if I'm wrong). The second question, which to me is more important, is: Do some tractors have different types of cylinders on the booms as opposed to the bucket or is the tractor weight simply to heavy for most loader lift capabilities. Bucket breakout force seems always to be more because of mechanical advantage, but, why doesn't a relief valve for the lift cylinders give way, lowering the tractor when you lift the front end by rolling the bucket? Any takers?






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 06-06-2000, 06:13 Post: 16937
TomG

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 Loader down force

Wish I knew enough about hydraulics to be a taker. Maybe next year.

My tractor is at our camp so I can't look, but I think the lift and bucket cylinders are the same diameter. I'd have to look to even have an impression about length. If they're the same diameter, they will produce the same force.

I also don't know how manufacturer specs are defined. My speculation is that if a manufacturer wanted to beef up the specs, an optimum digging angle for the bucket could be defined. The spec then would be greater than for a level bucket.

Regarding the relief valve: I think that the relief valve only sees pressure in a cylinder when a spooling valve is open. If true, no amount of pressure in the lift cylinders will open the relief valve as long as the spooling valve is centered.

Anyway, maybe there'll be some takers.






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 06-06-2000, 08:03 Post: 16941
MJB



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 Loader down force

Tom is probably right about the diameter of the cylinders being the same for the boom lift and the bucket roll, however these cylinders will not exert the same force. Any hydraulic cylinder will exert more force in extension than in retraction due the surface area available on the face of the piston in the cylinder. On the rod end of the cylinder the surface area of the piston is reduced by the area that the rod takes up, and given the same hydraulic pressure, less area equals less force. Therefore the loader will have more force lifting the boom than lowering and more force dumping the bucket than rolling back. If you look at some older loader designs made many years ago you will see that some reversed the position of the bucket attachment points such that the loader arms attached to the upper pins and the bucket cylinders attached to the lower pins. This would give greater force when rolling the bucket back than with dumping, which of course is probably more usefull design. Why did they change? Don't know. Maybe it costs more, or makes the buckets weaker, or probably because having the cylinders above the lift arms keeps them more out of harms way. Anyway my father has a little MF 1020 with an Allied loader on it that exibits the same lack of downforce on the loader boom but I have never found it to be a significant problem when digging. In order to increase the downforce with the boom you would have to adjust the relief to a higher setting, which of course might cause the bucket or lift arms to get bent under heavy use instead of just stalling the hydraulics. MJB






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 06-06-2000, 08:54 Post: 16943
Darryl Gesner



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 Loader down force

Mike - I have the JD #7 hoe on my machine. It works well and is a sub-frame mount. My tractor is also for homeowner use and it takes me no time at all to mow my 1/2 acre of lawn with a 5 foot rotary cutter. I bought the JD 513 cutter for mowing along paths and access roads on my rear 30 acres and was surprised to find that it does a fair job on the lawn as well. Sure beats pushing the 20 inch mower.






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 06-06-2000, 09:16 Post: 16944
Murf

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 Loader down force

It is not a matter of design, per se, it is a function of the design. Let me explain, when you lift the boom the pump fills one side of the cylinders and the boom goes up, however when you put the boom back down, gravity 'pulls out & passes' the pump. If any of you have ever watched what happens to a boats propeller when you gun the engine you will know what 'cavitation' is, the rapid entrainment of air into a liquid. This is what is happening in the loader circuit. Try this, put the loader all the way up, slowly, and empty, when it reaches the top leave your hand on the valve for a minute, then very, very slowly lower the bucket to the ground and try to lift the front-end again. If the front lifts this time then cavitation is the culprit, this problem is easily (& cheaply) fixed with a restrictor in the lowering side of the boom circuit, you will probably also want one in the bucket dump side of that circuit also. Best of luck.






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Discussion Boards > Active Subjects > Messages as Posted > Loaders Forum

Thread 16893 Filter by Poster:
Big Eddy 1 | Darryl Gesner 2 | Eric Edwards 3 | MikeC 3 | MJB 1 | Murf 2 | Roger L. 1 | TomG 2 |




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