Rear hydrollics & PSI: New Holland Tractor Review  -- New Holland Tractors Discussion Forum and Review Rear hydrollics & PSI: New Holland Tractor Review -- New Holland Tractors Discussion Forum

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 10-12-2002, 22:31 Post: 43762
KWH



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 Rear hydrollics & PSI

I have two factory installed remotes on my new TC33D(r-side of fender).They're going to be used for top&tilt and for a down pressure kit on my posthole digger.In determining the correct rams for these three items I present the following questions.Q:#1-What PSI comes out of these hydrollics? Q:#2-Both remote handles are in the middle of the throw,does moving the handle in each direction indicate it would open and close a ram? Q:#3-If I were to put a ram on both sides of the lower link arms,wouldn't I get full down pressure? Thanks






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 10-13-2002, 06:21 Post: 43770
RickB.



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 Rear hydrollics

Pressure at the remote valves is approximately 2000psi.
Three point hitches do not have downpressure, and are not adaptable to having downpressure by modifying the linkage as you suggest. No downpressure will be transferred to the draft links until the rockshaft is rotated all the way to the maximum raise position, and then internal damage to the rockshaft housing will probably result. Proper use of a top-n-tilt will not cause damage. The downpressure option for PHD's uses different geometry and is OK when used properly.
Moving the remote lever one way will extend a cylinder, moving it in the opposite way will retract it. I don't believe TC33 remote valves have a provision for a float position






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 10-13-2002, 07:37 Post: 43772
TomG

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 Rear hydrollics

Rick's response is correct. I'll just expand it a bit.

An important concept in hydraulics is that loads develop pressure, not pumps. In an open centered system, which is what you have, the pump circulates oil continuously through the high-pressure line back to the sump. There always has to be an open return line to the sump. Operating a valve blocks the high-pressure line and diverts oil to a cylinder. Only enough pressure is developed to move to load. Maximum pressure is set by a relief valve so if a heavy load doesn’t move the relief valve opens and the hydraulics stall. Relief valve settings vary a bit but are usually around 2,000 lbs. When the pump isn't working against a load, there's about 100-lbs. pressure at the valves.

The valves on your remote are likely for double acting cylinders, which power a cylinder in both directions. When operated, the pump flow goes into one side of the cylinder and exhaust oil that is on the other side of the cylinder goes back to the sump usually through a separate line. Operating the valve in the other direction reverses the operation and the cylinder moves in the other direction. In many setups, operating the valve nearest to the inlet hose in either direction stops the other valve from working and the 3ph from lifting. The valves and 3ph are hooked in series and operating a valve block flow from the pump to valves and the 3ph that are down-stream.

A tip cylinder goes between a lower link and a lift arm. Extending the tip cylinder pushes up on the lift arm. No down pressure on the link occurs because virtually all 3ph's don't hold the lift arms down. Nor would you want the arms held down most times. Down-pressure on an implement would take weight off the rear wheels and reduce traction. If a ground-engaging implement couldn't rise over bumps etc, it could easily break the tractor. Down-pressure kits on PHA's exert pressure through a sort of off-centre trick. There is a discussion in the archives. I think that installing two tip cylinders extends the range of tilt that can be put on the hitch, but it won't apply down-pressure.






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 10-13-2002, 20:48 Post: 43783
KWH



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 Rear hydrollics

Thanks for the response. Now, I have been looking in magazines for a ram. most say they operate @ 2500psi max. Does this mean that my 2000psi system will push these rams. Also, I notice none of them state a power rating(i.e., like motors do).Is it to suggest that two rams that operate at the same pressure(one being 3' in diameter,one being 2' in diameter) have the same force? You'll have to forgive my laymaness on hydraulics. Thanks for the lesson






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 10-14-2002, 06:58 Post: 43793
TomG

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 Rear hydrollics

I think my term is cylinders for what you refer to as RAMS. A 2,500 lbs. rated cylinder should work for virtually all tractor applications, but it'd be a good idea to check the tractor's relief valve pressure rather than assume it's 2,000 lbs. My Ford 1710 is 2,130 lbs. The relief valve sets the maximum pressure a system can achieve.

Regarding basic hydraulics: It's a variation on the basic idea of mechanical advantage. The ratio of the distance traveled by input force to the output force gives the mechanical advantage. The output force is the input times the mechanical advantage. A hydraulic jack has a lever that operates a small diameter piston that feeds a larger output piston. A hand on the jack lever moves a great distance compared to the output cylinder. The small amount of oil displaced by a full stroke of the small piston does little in the larger diameter output cylinder. In hydraulics, the mechanical advantage is the ratio between the area of the input cylinder piston to the output piston.

It's a little tougher to see in a rotating engine and especially one with a gear type hydraulic pump, but it's the same principal. One engine revolution displaces a small amount of oil in the pump and produces a small movement in an output cylinder. The engine travels a great distance compared to a hydraulic cylinder.

The above protracted explanation is relevant to the difference between 2" and 3" cylinders. The same amount of oil put into a 3" cylinder moves it a shorter distance than if put into a 2" cylinder. A 3” cylinder gives the system greater mechanical advantage since the engine has to travel further to achieve the same cylinder movement.

You might recall a previous comment that loads rather than pumps develop pressure and only enough pressure to move a load is developed. Because a 3" cylinder has greater mechanical advantage, it will move a given load with less input pressure than a 2" cylinder requires. However, at a given engine rpm, the movement will be slower. Since a 3" cylinder will move a given load with less pressure, greater loads can be moved before the pressure relief cylinder opens. The simple explanation is that 3" cylinders can lift more than 2" ones but at slower speeds. However, the basic explanation is minus the hydraulic basics, which I hope are at least a little useful.






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Discussion Boards > Active Subjects > Messages as Posted > New Holland Tractor Review Forum

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