Anyone try these (BX tractor upgrade)?

[Bri-Guy-GA]

Does the hydraulic flow rate of the tractor affect the ability to lift beyond what Kubota designed the loader for? Basically if you add new cylinders that can handle the additional weight can the tractor provide enough pressure to actually utilize it?

 

[torch]

Does the hydraulic flow rate of the tractor affect the ability to lift beyond what Kubota designed the loader for? Basically if you add new cylinders that can handle the additional weight can the tractor provide enough pressure to actually utilize it?

Don't confuse pressure with flow. Flow rate determines how fast a cylinder will move, pressure determines how much force a cylinder can exert. Volume of the pump determines flow rate, force of the engine determines maximum pressure (up to the relief valve setting of course).

Let us assume a cylinder volume of 1/2 gallon. A flow rate of 3 gallons per minute will cycle (in and out) that cylinder in approximately 20 seconds (3 times per minute) (not exactly, for "reasons", but close enough for this example).

A flow rate of 6 gallons per minute can theoretically cycle that same cylinder 6 times per minute, or every 10 seconds).

Now let us assume that the cylinder piston has a surface area of 3 square inches. A pressure of 1,500 psi will exert a force of 4,500 lbs at the end of the rod. Increase the pressure to 2,000 psi and the force increases to 6,000 lbs.

(note that the force at the cylinder rod end does not equal the lifting force due to leverages and angles)

Pressure and flow rate do interact somewhat due to friction loss, leakage rates and engine load. For example, at max pressure the force required to spin the pump increases and may slow down the engine (or even stall it at idle). Slowing down the engine (and therefore the pump) rpm reduces the flow rate because the pump can only displace a certain volume of fluid per revolution. High flow rates in small diameter hose causes turbulence, which "uses up" some of the available pressure.

Also, pressure cannot build without resistance to flow -- pushing the cylinder piston against the stop results in maximum pressure increase, but zero flow (not counting relief valve discharge) disconnecting the hose and pointing it at a pail results in zero pressure but maximum possible flow.

But despite the interaction at the opposite ends of the scale, under most operating conditions flow can be considered mostly independent of pressure.

 

[torch]

Does the hydraulic flow rate of the tractor affect the ability to lift beyond what Kubota designed the loader for? Basically if you add new cylinders that can handle the additional weight can the tractor provide enough pressure to actually utilize it?

Oh, so to actually answer your question: No. To lift more weight you need to increase the pressure or increase the cylinder diameter (ie: larger surface area for pressure to push against).

Increasing the cylinder diameter will also increase the volume required to fill that cylinder, so it will slow down the speed of motion. So the trade-off is speed vs power. Bigger = more force but less speed.

Increasing the pump volume will fill a given cylinder faster, speeding up the motion. But it won't increase pressure or lift capacity.

 

[Old Machinist]

Does the hydraulic flow rate of the tractor affect the ability to lift beyond what Kubota designed the loader for? Basically if you add new cylinders that can handle the additional weight can the tractor provide enough pressure to actually utilize it?

This cylinder force calculator does not take flow rate into account for calculating force.

I entered an example using the specs from my John Deere modification and according to that I increased the force of the lift cylinder by 56%. That would not equate to 56% increase in lifting force. The geometry of all the loader specs would have to be accounted for to figure that out.

My loader would have had a 1.5" bore cylinder with a 1" rod. Entering those specifications at 2000 lbs pressure came out to be 3,534 lbs outward stroke force and 1.963.5 return.

I upsized the cylinder to a 2 inch bore with a 1.25" rod which calculates to be 6,283 lbs outward force and 3,829 return.

 

[WI_Hedgehog]

Does the hydraulic flow rate of the tractor affect the ability to lift beyond what Kubota designed the loader for? Basically if you add new cylinders that can handle the additional weight can the tractor provide enough pressure to actually utilize it?

Building on what @TheOldHokie @torch said, the hydraulic pressure created by the tractor's hydraulic pump remains the same, assuming I don't use shims to change the relief valve pressure.

The hydraulic flow (volume of hydraulic fluid moved per unit of time) out of the tractor's hydraulic pump remains the same; in theory I could change out the pump, though that's something I'm not considering.

The Front End Loader lift cylinder diameter is changing,

OEM is about 1-1/2" (1.54"), and the cylinders from​

HydrosPlus are 1-3/4".​

So the surface area of the piston that the hydraulic fluid pushes against increases:

pi * radius ^2​

radius = 1/2 * diameter​

OEM: 3.1415 * 1.54"/2 * 1.54"/2

=> 3.1415 x 0.77 * 0.77 = 1.86 square inches​

HydrosPlus: 3.1415 * 1.75"/2 * 1.75"/2

=> 3.1415 x 0.875 * 0.875 = 2.41 square inches​

2.41 / 1.86 - 1 = 30% increase in surface area.​

So the tractor can lift about 30% more.

If the OEM cylinder is 1-1/2" instead of 1.54" then:

2.41 / 1.767 - 1 = 36% lifting ability increase.​

Tests show about a 32% increase in lifting ability, so that's in the ballpark.

Hydraulic pressure P1 driving the OEM piston remains unchanged, so the pressure P2 driving the aftermarket cylinder is the same as P1:

P2 = P1,​

P1 = P2​

BUT, the piston area of the OEM cylinder is smaller than the piston area of the aftermarket, so the OEM effective lifting force F1 is less than aftermarket F2.

To the other part of your question, you can see the amount of hydraulic fluid used to push P2 is more than the amount used to push P1, in this case let's say P2 is 32% larger than P1, so:

P2 has 32% more lifting strength than P1​

P2 uses 32% more fluid than P1​

P2 lifts 32% slower than P1​

Now, in real life P1 at maximum lifting force is stalling out and therefore lifting slower than if not lifting a load, and P2 being "32% stronger" is likely not stalling out and therefore lifting faster than P1 (maybe, in theory), but only near P1's maximum load capacity. If P1 (the OEM lift cylinders) are not near maximum load they should lift 32% faster than P2 (the aftermarket HydrosPlus cylinders).

Maths. There you have it in tech-nick-al terms, and stuff. Not saying it's right, but it looks all sciencey. And it has a color picture, can't beat that! (Well, maybe two color pictures would beat it. And a graph. I should have included a graph.)

 

[WI_Hedgehog]

Not to be outdone by a later poster (poser? posterior?), here's a graph:

Best of all it uses the word "Engineer" and is actually on-topic, as in "related." (But not like marrying your sister "related.")

You can see (whether or not you understand it is unrelated) that Hydraulic Force increases with a larger bore (they even used the correct terminolology) and Cylinder Pressure. BUT, our Cylinder Pressure remains constant because the hydraulic pump is still outputting the same pressure as before (we're not shimming the relief valve) (....yet), which is about 1840 P.S.I. Looking up around 1800 on the chart we see a larger bore leads to more Hydraulic Force (or forces since there are two cylinders).

Here's some more pictures, because we probably all like to see what we're talking about, and I'm no good at video:

I can confidently say some of what I said is likely correct, maybe even all of part of it. Maybe.