7745 loader slowing down - after replacing 4 cylinders with larger ones

[mp_montreal]

Guess it does take more oil to get the new cylinders working but the loader sure takes its sweet time to go up and down.

Went from 3.5 inch outside diameter to 3.5 inside diameter bore.

Sure is strong though.

New oil, hydraulic screen is clear. Put on a gauge and gets up to 2800 pounds press or so under load.

Wondering if there is any way to get faster movement out of the
joystick operated loader.

MP

 

[treaney]

Hi Mike,

LOADER GOING UP:
Based on the cylinder sizes you give, I estimate that your loader will take over 3 times as long to raise with the new 3.5" inside diameter cylinders than with the old ones!

Why? The pump is unchanged so you still have the same volumetric oil flow rate from the hydraulic pump. This is the limiting factor. If you assume a 2" inside diameter for the old cylinders, the area ratio of the new to old cylinders = 3.5 squared divided by 2 squared = 3.0625 = 3 for our purposes. So if your loader used to lift in 10 sec, it will now take 30 sec.

On the positive side, your lifting capacity has also increased by a similar factor i.e. if you could lift 1 tonne, you can now lift 3 tonne. Force = Pressure x Area. However, be careful as your loader is not designed to cope with this loading.

Q. Why did you change the cylinders?

LOADER GOING DOWN:
The only constraint here is how fast the oil can return to the sump. Diggers have fast return hydraulics but I don't think that this is an option for you as your are constrained by the tractors system. On my Crystal, there is a throttle valve that controls the rate of drop of the lift arms. I don't know if this is in the same hydraulic circuit as the spool valve but if there is one of these fitted on your tractor, open it fully and see if this has any effect.

Hope this helps.

TomZ
Tom

 

[Renze]

Cylinders from Baas Hydraulics, of this size, (between 80 and 90 mm), according to my datasheets, have a wall thickness of about 6,5 mm. That's roughly a quarter of an inch, so the 3.5 inch outer diameter might be 3" inside diameter.

Of a 3" piston the surface would be 45.60 mm2 and for a 3.5 inch piston, about 62.07 mm2. Roughly, i guess your force would have been increased by about 32%.

As you can see, my calculations differ quite a bit from Tom's.. The only way to make sure what you're doing to your front axle and loader frame, is to get to know the piston diameter of your old cylinders, as wall thicknesses may vary a lot...


If you ask your dealer for the optional 60 liter p/m pump, you would increase the speed by 3 to 5 %, compared to the old front loader cylinders with the standard 40 liter p/m.... So you would have incresed both force and speed..
I would go for a crankshaft driven pump like the 7340 have, I thought it was an option on the 7745..



Loader duty is quite a task, for any tractor, with the increased force, i advise to be even more carefull...

 

[mp_montreal]

Many thanks Tom/Renze for the expert analyses and advice

Since you both took the time to do the precise math, the least I can do is provide accurate details.

Cylinders: New OLD
---- ----
(inches)

Rod diameter (piston rod size) 1 3/4 1 9/16
Bore (inside diameter) 3 1/2 2 1/2


The concensus is definately that the larger size requires longer
transfer times for the oil thus I should definately expect a slower
reaction time.

Reason for changing cylinders in the first place was:

a) large snow bucket that would not lift when even half full
b) 3 of the cylinder started leaking
c) cost to repair old ones with new seals and labor more
than cost of newer larger cylinders

Taking all this into account, I went with the newer stronger cylinders.

Looks like any modifications I make to increase speed will be somewhat costly and not yield a significant speed increase.

Based on Tom's formula and the precise inside diameter measurements:

3.5 squared divided by 2.5 squared equates to 1.96 say 2.

Thus it should take twice as long to move but be twice as strong.
This has been my observation as well.

Guess patience is a virtue as they say so I'm willing to give up speed for strength.


PS: Renze - you are absolutely right about taking added care with the loadings. It will be struggle to keep the loadings down with the increased strength. This may sound corny but we should all remember: PLAY SAFE!

Many thanks guys! Keep up the good work. Judging by all the hits, I believe many people are becoming better educated with all the wisdom and responses. Great team effort Renze + Tom!

Mike

 

[Renze]

The actual max. force increase, is closer to the 300% Tom estimated, than the 32% i estimated, calculating with the 2.5" piston diameter.... If it was mine, i wouldn't borrow it to a friend anymore...