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 | Mrwurm
Join Date: Feb 2002 Posts: 184 South East Michigan 
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2002-07-12 40316
Before I bought my tractor (NH TC30), I told one of the dealers that the John Deere and Kubota both had enough down-force on the loader to lift the front of the tractor without curling the bucket. He quickly took a tractor off the lot and sent it into the service bay. When it came back out it had enough downforce to lift the front end without curling the bucket. OK, heres the question. I assume he adjusted a relief valve. Where is it ?
(a TC30 has the old style NH selective control valve like on a 1720, 1920)
Jerry
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 | Art White
Join Date: Jan 2000 Posts: 6898 Waterville New York 
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2002-07-15 40379
I wasn't aware that when set top factory specs they would do that. ....
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| Mrwurm
Join Date: Feb 2002 Posts: 184 South East Michigan
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2002-07-15 40382
Art, some class II TC owners have told me that there machine will easily lift the front end without curling the bucket. As I understand it, the hydraulic pump puts out 2150 psi and the loader valve goes into relief at 1800 psi. I am certain there are good reasons for this, but it does seem that there is room for a 'little' adjustment.
Jerry ....
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| JerryGoucher
Join Date: Feb 2002 Posts: 100 NW AR
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2002-07-15 40399
If you will let the brakes off and or have it out of gear it should lift the front wheels. That way it can roll as it lifts and not try to lift the whole tractor.
Good Luck
JerryG ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-07-17 40443
Here are a couple of distinctions that helped me gain a bit of an understanding of hydraulics. These distinctions aren't necessarily directly related to the subject of pressure adjustment.
A pump is rated for the pressures it can withstand rather than the pressures it can produce. A pump with a load produces little pressure. It's the load that creates pressure. Most modern gear pumps are rated for continuous pressures over 3,000 lbs. and intermittent pressures over 4,000 lbs. It's both heat and volumetric efficiency that limit a pump's pressure rating.
The 2150 lbs. pump rating probably refers to the adjustment on the tractor's system relief valve. The pump should be capable of withstanding greater pressures. Most auxiliary valve assemblies have their own pressure relief valves. If somebody knows a reason for one to be set below the tractor's relief valve, I'd be happy to hear it. If the tractor on the lot disappeared into the shop for a very short time, it's likely that the pressure relief on the loader valve was adjusted. The relief setting on many valve assemblies is a screw adjustment. Many tractors relief pressure are adjusted by disassembling the valve and changing shims under a spring. Such an adjustment would take more time.
My Ford 1710 with an Allied 195 loader won't lift the front wheels when the bucket is flat either. That's because the bucket won't go low enough. If I angle the bucket down a bit before lowering it, the loader lift raises the front wheels off the ground easily.
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| Mrwurm
Join Date: Feb 2002 Posts: 184 South East Michigan
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2002-07-17 40447
Good post as always, Tom. I have heard that sometimes loader cylinder packings are not capable of surviving the 'full' system pressure. Or maybe the loader frame or tractor would be overloaded by the forces generated by the greater power output. This is in response to your ponderings as to why a selective control valve would have a different relief setting then the main system relief.
Your comment about angling the bucket down and then lowering it is exactly the point I'm getting at. My tractor can almost accomplish this as well. I can feel it want to raise but it just can't do it. I know that only a 'little' more pressure would make it work better. Say 50 or 100 psi more.
Jerry ....
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 | DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2002-07-17 40452
So are we saying that there is more leverage or more power in the curl function of the loader than there is in the lifting function? ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-07-17 40454
At least in my case power and pressure isn’t the problem. The loader lift has plenty of power to lift the wheels. There's just not enough downward travel to do more than take a bit of weight off the front.
If I angle the bucket down then the blade edge is closer to the ground and it doesn't take as much downward travel to lift the wheels. I think angling the bucket down would reduce the leverage and increase the pressure required to lift the front because the point of ground contact would be closer to the rear axles. However, I believe that the curl does exert more force than the lift due to frame geometry and a curl may well be able to lift the front while the lift can't on some tractors. Mine isn't like that, although I can recall trying to lift the edge of a 6" concrete slab once. the lift wouldn't tough it but the curl did.
Good point about the possibility that loader cylinders are rated lower than a tractor's system pressure. There's probably a max pressure spec somewhere in the loader's manuals. Another possibility is that the geometry of the loader's frame would allow too much stress on the tractor frame if full system pressure were allowed.
Gee that's a bunch of posts from me today. I must have been saving up while we were at our camp. I do have a lesson to pass along I learned while there. Bug dope that contains DEET tears up mono-filament fishing line. You get it on your hands and then onto the fishing line. I lost a decent pike that hit a brand new Mepps spinner several feet from shore. I could see it all happen. The water was shallow enough that the pike couldn't do much more than turn for deeper water. It barely bent the light rod before the 8-lbs line let go. I was using a steel leader so that wasn't the problem. Dang! Well, live and learn. I now have new spinners and new line.
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| Mrwurm
Join Date: Feb 2002 Posts: 184 South East Michigan
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2002-07-17 40455
Mark and Tom, this is how I understand the downforce verses curl thing. The force exerted by a hydraulic cylinder is related to how much surface area is exposed to the fluid pressure. (that's surface area 90 degrees to direction of travel) On the lift cylinders, the up stroke uses the surface area of the entire piston. On the down stroke the surface area is the area of the piston minus the area used up by the rod. On the curl cylinders, the entire piston area is exposed in the 'curl-down' direction making this the stronger direction for this cylinder. So, the it makes sense that the curl-down function of the bucket can lift the tractor easier the down-stroke function of the lift cylinders. (surface area in inches multiplied by psi)
I'll bet Tom knows how to do the math.
I apologize if you already knew this.
DISCLAIMER: I am no hydraulic mechanic, but this is how it was explained to me. ....
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2002-07-17 40461
Tom, I kept some bug dope in my tackle box one year and forgot to remove in over the winter. It not only ate the line, it disolved parts of the reel! ....
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2002-07-17 40469
I am going to have to digest the info on hydraulic pressures for a day or two, and try to wrap my brain around the concepts. I will be back with questions. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-07-18 40477
Jerry: That's exactly right. The strong sides of most tractor loaders are on the dump and lift functions. I was thinking of frame geometry--the lengths of arms, distances from pivot points etc. I believe that the curl has a leverage advantage compared to the lift for both up and down pressures. I could be wrong here but that's my impression.
In my concrete slab example, I would have been using the bucket roll up and the lift functions and both are on strong cylinder sides. The roll up lifted the slab edge and the lift didn't, and that might support the idea the bucket has a leverage advantage compared to the lift. It might, but I guess it's not a very good example because the roll up may have gained leverage by using the ground as a pivot point.
There was a discussion here several years ago about this seemingly backward design of bucket cylinders. The strong side of a cylinder also is slow compared to the weak side. You'd think most people would want power for the roll back and speed for the dump, but it works the other way. Manufacturers have tended to keep the backward design and make happy owners by providing fast-dump functions on their loader valves. While there are operations, such as compaction that need power on the roll-down, the answer to the backward design question seems to be expense. If the bucket cylinders were reversed, then the cylinders would move and the shafts would be stationary. That would require a more complex design--flexible lines must be used; more things protected from damage etc. However reversing the cylinders is feasible and such a design isn't uncommon on heavy equipment.
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2002-07-18 40490
Ok. Are we saying that as the cylinder and rod assembly gets longer (extends) it can exert more force than if it is contracting? ....
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| Mrwurm
Join Date: Feb 2002 Posts: 184 South East Michigan
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2002-07-18 40491
Yes Mark, that's the way I understand it. Though I'm no expert.
Jerry ....
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2002-07-18 40492
Well at least you can say you understand it. I don't, but I believe I have seen proof of it while using the loader. ....
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 | treeman
Join Date: Feb 2002 Posts: 251 Wisconsin
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2002-07-18 40493
So... If we have a 3" cyl. with a 2" rod dia, the piston surface area is 7.065 sq in., and the rod area is 3.14 sq in. If we are running 2000 psi on our hyd. pressure, that would give our cylinder 14,130 lbs. of push and 7,850 lbs. of pull. Of course this doesn,t take in account any friction losses. ....
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 | Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2002-07-18 40494
Mark;
If the oil pressure at our control valve for the pistons is 2000 PSI and the surface area of the piston is 3 square inches than the force of the piston is 6000 lbs. The return stroke piston is 3 square inches minus the area of the hydraulic cylinder rod. The cylinder rod for examples sake is 1.25" or 1.23 square inches, there for the piston size for the return stroke is ~ 1.78" and the force available is 3,560 lbs.
Therefore is you are lifing the bucket there would be 6000 lbs of force on the cylinders and lowering the bucket there will be only 3560 lb.
Hope this is a little clearer. ....
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| DRankin
Join Date: Jan 2000 Posts: 5116 Northern Nevada
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2002-07-18 40496
Yes, very clear now. The rod is actually blocking some portion of the piston and reducing the surface area. ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-07-19 40505
Another peculiarity of this same idea is a loader fast dump. Fast dumps usually use what are called regenerative hydraulic circuits. A regenerative circuit connects both side of a cylinder together and feeds pressure to them. Because the piston side of the cylinder has more area, the cylinder moves toward the shaft end. Essentially, a regenerative circuit just pushes oil from one side of the cylinder to the other. It is faster than a normal dump because virtually all the oil needed to move the cylinder is already there and doesn't have to be pumped. The load itself also does a lot of the work. The down side is that a fast dump doesn't have a lot of power. One is unlikely to lift any tractor's front wheels. ....
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| Peters
Join Date: Feb 2002 Posts: 3034 Northern AL
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2002-07-19 40508
Some plastic injection molding machines us an accumilator tank, simular to a pressure tank on the well. Basicly you open the valve and it has all the oil it needs at pressure.
It would make a quick dump. Not sure I want a 3000 psi tank full of warm oil on a tractor though. I believe some excavators have them, but have not looked at all the hydralics.
Peters ....
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| TomG
Join Date: Feb 2002 Posts: 5406 Upper Ottawa Valley
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2002-07-20 40524
Some old Ford farm tractors and probably others also had accumulators. Mysterious gadgets and I've never seen one to my knowledge, but I’ve heard it's a bad idea to put a wrench to the fittings of a mystery tank on an old tractor.
The accumulators probably were needed due to the very small hydraulic pumps then used on tractors. Sort of reminds me of the original PC and DOS. Who'd ever imagine that mere users would ever want more than 640K memory?
I noticed that I twisted at least one detail in my concrete slab example. When levering the edge of the slab up with the curl, the roll back would have been used, which is the weak rather than strong side of the cylinder. The example makes me fairly certain that the curl has a lot of leverage advantage compared to the lift. The idea that max bucket lift is maybe 10' compared to maybe 2' of curl from about the same cylinder movement also illustrates the leverage.
A practical note related to wheel lifting by the loader is that it's a good idea to periodically lift the wheels and inspect the welded loader frame joints. The idea is that weight on the frame will spread the joints and reveal cracks that otherwise might be missed. I did that a couple of week ago along with checking the torque on the frame bolts--also a good idea.
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