790 - Raising Hydraulic Pressure

[tpike35]

No Tom it's not your system ..It's me I not very good with this computer stuff /forums/images/graemlins/blush.gif So I'll try again /forums/images/graemlins/confused.gif attached is the page on raising the pressure ...Sorry it took so long /forums/images/graemlins/crazy.gif

 

[keeney]

OK, I never was good with percentages.

The force will go up in the ratio of about 3 / 4. A 30% increase.

The speed will go down in the inverse ratio, or a 25% decrease in speed.

 

[tomrscott]

Here are the actual numbers for increasing the bore from 1.75" to 2", with and without increasing the pressure to 2500psi. As you can see, a quarter inch of bore increase does more than the pressure increase, and both increases together would be quite impressive, much more competitive with a number of imports. JD's lawyers are really stiffing us.

Bore ____ Rod _____ PSI ____ Push ____ Pull
1.75" ___ 1.10" ____ 2050 ___ 4931 ___ 2983
1.75" ___ 1.10" ____ 2500 ___ 6013 ___ 3637
2.00" ___ 1.125" ___ 2050 ___ 6440 ___ 4403
2.00" ___ 1.125" ___ 2500 ___ 7854 ___ 5369

Hydraulic calculator site:
http://www.baumhydraulics.com/cyl_calc.htm

 

[tomrscott]

Here are the real numbers for your comparison, the difference caused by increasing the cylinders just a quarter inch, both with and without the pressure increase we've discussed. With both increases, the lift system really gets into respectable range, much more competitive with some of the import competition. The JD lawyers have really stiffed us. That said, I really like my 790, but I do wish it was all the tractor it could have been.

Bore ...... Rod ....... PSI ...... Push ..... Pull
1.75" .... 1.100" .... 2050 .... 4931 .... 2983
1.75" .... 1.100" .... 2500 .... 6013 .... 3637
2.00" .... 1.125" .... 2050 .... 6440 .... 4403
2.00" .... 1.125" .... 2500 .... 7854 .... 5369

Hydraulic calculator site:
http://www.baumhydraulics.com/cyl_calc.htm

You can see that while pressure makes a difference, cylinder bore and rod diameter have a real large effect also. A larger rod size makes no difference to pushing, but reduces the pulling force because its cross sectional area subtracts from the surface area on the back side of the piston. I increased the rod size to a typical size on a 2" cylinder.

 

[tomrscott]

Okay, that time it wasn't blocked up, but it was pretty low resolution. I did manage to enhance it a bit and -- squinting my eyes with just the right "calibration" -- was able to read the text, or at least pretend I was reading it, in a thoroughly convincing manner. What I thought it would have said, if I could have read it for real, made sense! /forums/images/graemlins/grin.gif

Seriously, it did help. Confirmed what the other posts indicated. I think I've got a good handle on it now. I just have to get a couple more hydraulic fittings so I can hook up my pressure gauge and then test it pre and post shims.

I'll post here exactly what I get, along with pictures of a cool pressure gauge set up that I'll bet you're going to like.

Thanks all!

 

[JerryG]

The size of the machine and the weight is not always the only criteria that a manufacture looks at in setting hydraulic limits. We have at least one example (NH) that has limited the lift of a loader, because on front axle design. I hope that this is not the limiting factor in the case.

 

[tomrscott]

What I do know is that tip-over risk was what the dealer blamed for the low hydraulic strength, and a lot of folks seem to have done the mod to increase psi to 2500 with no problems.

I've not heard of any axle or frame problems on the 790, other than the issue of tweaking the FEL if you lift too much on just one side, but that doesn't seem like a big limitation.

 

[glalonde]

Read this thread that I posted a while back
http://www.tractorbynet.com/forums/showflat.php?Cat=0&Board=jdown&Number=447914&Forum=All_Forums&Words=8594&Match=Username&Searchpage=0&Limit=25&Old=allposts&Main=447054&Search=true#Post447914

 

[G Winton]

Used the shims in my 790, the loader works much better and I can lift a 5x5 round hay bale with the rear lift. Could not do that before. I do not have a spear for the front but two bales might be too much load for the tractor anyway.

 

[kennyd]

Used the shims in my 790, the loader works much better and I can lift a 5x5 round hay bale with the rear lift. Could not do that before. I do not have a spear for the front but two bales might be too much load for the tractor anyway.

Welcome to TBN

Talk about reviving a thread from the dead

Did you a gauge to set the new pressure?

 

[EV59]

Just remember.....Sure the 790 is strong enough to pick up more weight, however using the tractor in most conditions that we all use tractors....it could become UNSTABLE therefore UNSAFE...the 790 is a narrow tractor and could easily tip over when working on uneven terrain or when making sharp turns.

To properly and safely handle heavier loads....use a larger framed tractor.

ev59
SC

 

[sd624]

Heres how to do it if you choose to do so. I bumped mine to 2500.

http://www.angelfire.com/mi2/fpp/boost790.pdf