Engine speed and 3PH lifting capacity...

[fredhargis]

I haven't asked a really stupid question for a while, so though I'd bring up this one: is the lifting capacity of the 3 PH related to the speed the engine is running? I ask because I have one attachment that is one the edge of my tractor not being able to lift it (Kubota B2920). This thing (an aerator) with blocks weighs about 850#, and is within 24" of the ends of the arms. Adding one block (33#) makes it too heavy to pick up, at least at about 1600 rpm. So if I ran it at 2200 RPM, and opened the 3 PH speed valve will it then lift the heavier weight? I'd try this out, but it's a lot easier to ask here and make a fool out of myself. BTW, I'm not interested in adding more weight to the aerator...more of a curiosity question.

 

[suprnova]

According to the new (not sure what year yours is) B2920 spec sheet, the pump capacity is 8.3GPM, providing a lift of 1356lb @ lift point/1058lb at 24" from lift point. If you're certain your aerator only weighs 850, it may be safe to assume that 1600rpm doesn't provide the maximum pump capacity. I don't know the information for that particular pump though to figure out where maximum capacity is achieved.

 

[corey9212]

I haven't asked a really stupid question for a while, so though I'd bring up this one: is the lifting capacity of the 3 PH related to the speed the engine is running? I ask because I have one attachment that is one the edge of my tractor not being able to lift it (Kubota B2920). This thing (an aerator) with blocks weighs about 850#, and is within 24" of the ends of the arms. Adding one block (33#) makes it too heavy to pick up, at least at about 1600 rpm. So if I ran it at 2200 RPM, and opened the 3 PH speed valve will it then lift the heavier weight? I'd try this out, but it's a lot easier to ask here and make a fool out of myself. BTW, I'm not interested in adding more weight to the aerator...more of a curiosity question.

It should be able to lift that with no problems if the weight is only 850# when I had my BX2660 it lifted 1200# square bales with a 50# bale spear and moved them off of the 3 point hitch easily.

I do know the rpm's increase speed and response so I would imagine it will increase lift capacity as well.

 

[k0ua]

In my "opinion" it should not matter if you are at idle or if you are at full throttle, the pressure should be able to be built to maximum pressure up to the relief valve pressure. Hydraulic pumps don't make pressure anyway they make fluid flow. the pressure is a function of restriction. In other words if you put a pressure gauge on the output of the hydraulic pump you will see very little pressure, just the small restriction of the hoses to the flow of the fluid. now when you move a control valve to push the flowing stream of fluid to look into a cylinder like the one in your 3pt. you will now build up a head of pressure and the cylinder piston will start to move and lift the load. The load will lift slower at a lower RPM because the flow rate of the pump will likely but much less at a lower RPM than a higher RPM. but the pressure that can be achieved will likely be the same. Now if the pump is worn, and has internal leakage, I "suppose" it may not be able to deliver maximum pressure as set by the relief valve until the RPM is increased enough to increase the flow rate to overcome any leakage. Keep in mind my knowledge is theoretical, not practical in this field, and I hold no qualifications in this field whatsoever. But now you have heard my "opinion"..

James K0UA

 

[Don87]

I didn't see anything stupid about the question. But I would like to know the answer.

Try it and let us know.

 

[SPYDERLK]

In my "opinion" it should not matter if you are at idle or if you are at full throttle, the pressure should be able to be built to maximum pressure up to the relief valve pressure. Hydraulic pumps don't make pressure anyway they make fluid flow. the pressure is a function of restriction. In other words if you put a pressure gauge on the output of the hydraulic pump you will see very little pressure, just the small restriction of the hoses to the flow of the fluid. now when you move a control valve to push the flowing stream of fluid to look into a cylinder like the one in your 3pt. you will now build up a head of pressure and the cylinder piston will start to move and lift the load. The load will lift slower at a lower RPM because the flow rate of the pump will likely but much less at a lower RPM than a higher RPM. but the pressure that can be achieved will likely be the same. Now if the pump is worn, and has internal leakage, I "suppose" it may not be able to deliver maximum pressure as set by the relief valve until the RPM is increased enough to increase the flow rate to overcome any leakage. Keep in mind my knowledge is theoretical, not practical in this field, and I hold no qualifications in this field whatsoever. But now you have heard my "opinion"..

James K0UA

Nothing wrong with theory.
All pumps will have internal leakage. Worn will be worse. Hot, thin hyd oil will leak faster too. ... When cool the system will probably develop full relief set pressure at lo idle. When hot the increased internal leakage will likely prevent reaching full pressure at idle even on a new system. Now at 1500 rpm you should be able to get full pressure even hot. Things might be very slow because the hi press leakage flow will use a lot of the pumps potential and there wont be a lot of net/output flow. More engine speed will get you the hyd speed back. I would only start getting concerned if I couldnt get full relief pressure until at least 1500RPM. Even at that there should still be a lot of life left in the pump.
larry

 

[k0ua]

All pumps will have internal leakage. Worn will be worse. Hot, thin hyd oil will leak faster too. ... When cool the system will probably develop full relief set pressure at lo idle. When hot the increased internal leakage will likely prevent reaching full pressure at idle even on a new system. Now at 1500 rpm you should be able to get full pressure even hot. Things might be very slow because the hi press leakage flow will use a lot of the pumps potential and there wont be a lot of net/output flow. More engine speed will get you the hyd speed back. I would only start getting concerned if I couldnt get full relief pressure until at least 1500RPM. Even at that there should still be a lot of life left in the pump.
larry

Thanks for providing some more dimension to the explanation of pump leakage, and considering the temperature of the fluid. Something I didn't even think about. I know much more about electronics than hydraulics, but thanks to TBN, I have learned a little!

James K0UA

 

[fredhargis]

Thanks guys. I may try it out just to see ...the tractor is 2010, and now has 140 hours. It's hard to imagine any internal problems with the pump; but I guess stranger things have happened.

 

[SPYDERLK]

It could be the relief valve is set low.
larry

 

[daugen]

I'm not sure there is a direct relationship here but since both the FEL and three point hitch run by hydraulic
power, then I would expect some commonality of response. I've never had a problem picking up my new very heavy LP
84 inch mower with my Kubota at fairly low rpm. Personally my experience with the FEL grapple picking up heavy trees was that
I needed between 1800-2000 rpm to pick up the heaviest logs. Maybe it would have picked them up but just more slowly at lower rpm, but several times I went nowhere at a lower rpm and when I goosed it up to 2000 rpm, I clearly picked up more capacity.
But maybe my tractor's sweet spot is 1800 rpm, I don't know.

Add the hydraulic demands of an HST trans to the mix while using the FEL or 3PH and it's interesting to see how my tractor reacts, slows down usually, if I increase the demand on the system. Might make an interesting "science project" to test it, both with light and full capacity loads.
There are a lot of electro/hydraulic nannies operating on the Kubota, though I have managed to stall it several times. Always when the rpm was fairly low. And yes I thought I had stall guard on. I'm sure op error, new tractor, still learning its personality.