What determines hydraulics capability?

jim_wilson · Jul 28, 2004

This is just sort of a general question - what determines the lift capability of say an FEL? How does the pressure and flow of the pump affect it vs. how does the sizing of the hydraulic cylinders affect it? Will more flow and or pressure on the same size cylinder give more lift or do you have to go to a bigger cylinder for more lift? Is there a limit to how big of a cylinder can be supported on a certain size pump? Again just general questions - I don't know much about hydraulics and am looking for a little education.

MMM · Jul 28, 2004

Pressure and cyl size determine lift capacity- flow is speed. It takes more hp to raise a heavier load with bigger cyls. Might consider structural limits of loader and tractor also.

JerryG · Jul 28, 2004

what determines the lift capability of say an FEL? 
Many things, cylinder diameter, pressure, loader geometry
How does the pressure and flow of the pump affect it vs. how does the sizing of the hydraulic cylinders affect it? 
Pressure gives you more lift, flow gives you speed. The larger the cylinder diameter, the more it will lift but the slower it will go.
Will more flow and or pressure on the same size cylinder give more lift or do you have to go to a bigger cylinder for more lift? 
Larger cylinders and more pressure both give more lift. The more flow the faster the lift takes place.
 Is there a limit to how big of a cylinder can be supported on a certain size pump? 
I would say no, but there would be a limit as far as practicality. At some point a person would get tired of waiting for the cylinder to extend and a larger flow pump would be needed.

SPIKER · Jul 29, 2004

JerryG said it very well. good answer /forums/images/graemlins/smile.gif

Mark M

AndyMA · Jul 29, 2004

( It takes more hp to raise a heavier load with bigger cyls. )

This is only true if you want to go as the same speed as a smaller cylinder with a lighter load. If you have the pressure you can lift the same load with almost any hp motor and pump as long as you have time for the volumn (flow) to fill the cylinder.

Andy

OkieG · Jul 29, 2004

I don't know much about hydraulics and am looking for a little education. 

I don't know much either. Besides what's already been mentioned, one thing comes to mnd, though. There is more diaphram (not sure if that's the right word) surface for the hydraulic fluid to push against when extending the cylinder rod, as opposed to retracting it. The end of the rod itself (the end that's in the cylinder) takes up space on the diaphram and so less surface is available for fluid to push on when retracting.

The practical consequence of that, is that the cyllinder generates more power wnen extending, but may extend more slowly than it will retract with the same flow. Does that make sense?

OkieG

timb · Jul 29, 2004

OkieG's correct on the difference pulling/pushing in a 2-way cylinder. One other thing to keep in mind - there will be a fluid 'tide' effect. More fluid is required to fill the piston side than is recovered from the rod side as you push on the piston end - and vice-versa coming back. The thicker the rod relative to the piston the greater the difference. That will cause the level of fluid in the sump/tank to change. There will be some limit eventually to how much 'tide' the system can deal with. (Why you usually have to check your fluid level with the FEL all the way down and all the cylinders retracted. You'll get a different (lower) reading if any/all cylinders are extended.)

_RaT_ · Jul 29, 2004

The shear size of the fluid reservoir pretty much eliminates this concern in most tractors if not all. With almost 15 gallons resting there in my little tractor, the fluid required to either hold or make up for the hydraulic ram is more then sufficient. Whether my loader is up or down, the reading is the same to the naked eye.

timb · Jul 29, 2004

For sure - for the most part I think a legitimate CUT or bigger tractor is unlikely to have any problem, although it's not going to be just fluid volume but sump shape (surface area) that impacts this. (Think of a tall column of fluid versus a flat pan - the same amount of fluid volume change in the cylinders will make for a different amount of height change).

I ran into this more when trying to brainstorm some attachments for a GT with a useful, but limited hydraulic system that didn't leave room for much 'tide'.

qqq · Jul 29, 2004

( How does the pressure and flow of the pump affect it vs. how does the sizing of the hydraulic cylinders affect it? Will more flow and or pressure on the same size cylinder give more lift or do you have to go to a bigger cylinder for more lift? )

You might want to check out hydraulics 101 . In a nutshell, there's something called Pascal's law that says pressure applied to an incompressible fluid (like hydraulic fluid) is transmitted with no loss in pressure to all the surfaces in the container (like the cylinder walls, and the end of the piston, etc). So, if you have hydraulic fluid at 1000 PSI (pounds per square inch), its going to exert 1000 pounds to every square inch inside the cylinder. The end of the piston has some amount of surface area, for example a 2 inch piston has about 3 sqaure inches of surface area, so its going to have 3000 pounds of pressure on it (at 1000 PSI).

As others have noted, flow will affect your speed, but the force boils down to two things, the amount of pressure and the size of the piston (really the surface area of the end that the fluid is pushing against). So, all other things being equal, if you want more lift you need more pressure, and/or a bigger cylinder.

For example, if you had 2000 PSI, that 1 inch cylinder would now have 6000 pounds of pressure. If you went to a 4 inch piston, the surface area is now about 12 square inches, and you'd get 12,000 pounds of pressure at 1000 PSI.

Hope this helps. By the way, I'm looking at getting a BX23, how do you like yours, where did you end up getting it, and how was the price? (Feel free to PM me the info if you'd like. Thanks.)