Why do CUT manufacturers not install larger hydraulic pumps?

[Piston]

The thing that gets me, is they offer larger pumps as an option with larger tractors in the 80hp range or so. I wish they would offer the option with CUT's. If you want it, pay for it, if not, don't... pretty simple

Realistically though, when will we really draw the line? CUT's have come so far over the last 10 years or so it's incredible. Who would have EVER thought that we could now get a compact utility tractor with over 60 hp engines? It really is incredible how much power we have in such a small package. I always wish for more FEL lift capacity on my tractor, but realistically, how much more could a CUT handle? There comes a time where the FEL can lift so much, but it's useless when you can't keep the rear end on the ground, or becomes so heavy that now beefier components are needed in the "compact" tractor, which take up more space, which make it bigger, which basically turns it into a "utility" sized machine.

I really think we are at the peak of what can be called a CUT.

What would solve every problem I've ever come across, would be if they just offered HST transmission in utility sized machines. If R&D teams just came to me to ask how to make their tractors better, that's all I'd tell them. Unfortunately, they don't even know who I am :laughing:

I really don't think it will be long before you start seeing HST transmissions in utility sized tractors. It would come with a price increase of course, just like CUT's do, but the utility market can afford a price increase. I compared a fully loaded JD 4720 HST and a Kubota L5740 fully loaded, with a Case 75C/NH T4.75 fully loaded, and the larger utility tractor came in at a couple hundred dollars LESS than the CUT's.
I know that's not exactly apples to apples, but add a few grand to the price, and HST, and I'm a customer tomorrow.

 

[newbury]

When you are running a backhoe it may be okay to use up your HP with the hydraulics, but when needing to go up hills and/or pull something at the same time, you should have a fair amount of HP reserved for that.

I don't know if there is any data for what a large pump takes to simply pump through your Power Beyond ports and back to the tank compared to a small pump. But since loader lift capacity is typically more focused on than loader speed, I would bet that is why pumps in new tractors have smaller GPM capacity. Also the HP it takes to drive the big pumps would be a concern.

Your typical industrial backhoe has way more pump capacity than a farm tractor but they are not typically pulling say a hydraulic flail mower up a hill in a field. A backhoe is stationary when in use.

And the OP wrote:

<snip>I don't want to run my tractor at 2500 rpms to use 20 Hp on my wood splitter or backhoe just to reduce the cycle times. <snip>

I believe that your typical wood splitter also would be stationary.

The OP wanted to run a wood splitter or backhoe.

 

[J_J]

The thing is that the manufactures will never put a pump solely matched to a hyd pump for this reason.

Sitting still and doing nothing but BH work would be fine, but any more load placed on the pump by other hyd use or just moving the tractor would stall the engine.

You know you can stall the engine using the drive train with the largest load possible, and that will also take away the HP required to run the pump which will add to the stalling.

There is a happy medium where you should be able to use max HP for tractor load and hyd load without stalling.

If you want a fast BH, you will need more GPM's.

 

[TomSeller]

And the OP wrote:
I believe that your typical wood splitter also would be stationary.
The OP wanted to run a wood splitter or backhoe.

Correct, and the OP also made this statement in his next post which led to additional discussion. There are trade offs to a larger pump.

I just can't see any advantage to the small pumps that are used other than everyone trying to save a buck on the cost so they can compete on price.

 

[tlm720]

Pto pump is not an option if saving fuel is the goal. Too much power loss in the pto. Plus all the other costs. Additional reservoir, etc. I'm not asking for a huge increase in flow. Maybe a way to get full flow at a lower rpm like a 2 speed drive on the pump. I don't need 40 Hp to run a wood splitter and don't need to have my engine running full speed. We need an epump. No need for bigger lines or valves since it is not more flow, just rated flow at a lower engine speed.

 

[GManBart]

What would solve every problem I've ever come across, would be if they just offered HST transmission in utility sized machines.

Amen!

 

[the old grind]

.... I'm not asking for a huge increase in flow. Maybe a way to get full flow at a lower rpm like a 2 speed drive on the pump. I don't need 40 Hp to run a wood splitter and don't need to have my engine running full speed. ... No need for bigger lines or valves since it is not more flow, just rated flow at a lower engine speed.

What I've often wondered is when do we know the pump's output at a given speed(?), ie do we need to be at PTO rpm to get full flow and/or pressure. Some of us have gauges rigged up for pressure testing, adjusting relief or just curiosity, if not flow meters. Can they be used in a similar situation, say pump flow within 1 or 2 gpm and a similar cyl diameter just to get some examples of flow proportion to engine speed by timing?

To get zippy retract does a 25% rpm drop sacrifice 25% of flow when only pumping out the roomier end of a cylinder? Not that I imagine a full scale proportional pressure/flow tradeoff with a positive displacement pump, but I can imagine there might be divergent curves in a rpm/flow comparison and hope for a sweet spot somewhere.

Too much YMMV to compare one tractor/pump to another? I'm too new to hydraulics to offer my lab-rat services, but maybe someone has already got their hands oiled up wondering such things....

 

[J_J]

Max pump flow is at max rpm, so if you run half speed, you should expect half GPM.

However on some tractors, with a flow divider, the attachments don't work so well until the rpm of the tractor is about half. The first part of the flow will go to steering which is what a priority flow divider is supposed to do.

The retract mode of a cyl will usually be faster

 

[the old grind]

Thanks, J_J! Makes sense that rpm & flow are proportional with a PD pump. It would seem that pressure demand (say light vs hvy load on FEL) affects hp required.

Next question, and to be gracious not for you alone: is much flow diverted to steering when parked & running a splitter, or is it all there for the tapping at the remotes?

My older Ford 1520 had PTO rpm of 2250 for 540/2000 (flag on tach face) and 'max' rpm at ~2800 IIRC.
TractorData.com Ford 1520 tractor information
A friend's similar-sized JD 955, has PTO speed of 3200 for 540/2100 on PTOs. If TD's data is reliable.
TractorData.com John Deere 955 tractor information

With apparently at least 400 rpm diff between our max's it looks like pump gear ratios are as random as PTO internal ratios from one make/model to another.

btw: Having toyed with the notion of adding a belt driven pump as an alternative to a PTO pump of similar cost & output what saved me from daring is that there's no room to put a chunk that big under a CUT's hood. What had attracted me was the possibility of tweaking pulley ratios seeking what the OP wants, more flow at less engine rpm. Could have been a nightmare if running/revving to max then went beyond what's good for the pump. :duh: So much for another crazy idea, but a racing mind comes up with worse & I'll leave out the examples.

 

[J_J]

If you are doing work that only requires little pressure, then it takes little HP to develop that pressure.

At idle, you will have slow hyd, and you could have low or high pressure.

A priority divider circuit for the steering, will always try and use the first fluid available. For instance, if you have a 10 GPM pump, and the flow divider is set or designed for 3 GPM, it will use the first 3 GPM pumped and there may not be any left for the other hyd functions.

Just recently those people with BX tractors say they have no FEL hyd until engine rpm is about 1500. The hyd transmission is probably using the main part of the flow. If the engine rpm increases over that limit, then the hyd start to work. That means that the FEL is only getting some of the total pumped fluid.

If you work out the formulas, you will see that GPM and pressure determines the amount of HP necessary to develop the pressure.

Did you look at the picture I posted of my hyd pump. That is a very small hyd pump in size and about 3 GPM. It is mounted on one side of the engine using a bracket like a generator or alternator. It is driven by a fan belt. If you work out the belt pulley ratios, you can get the engine to power the pump at it's max rpm.

If you are sitting still and not steering, then that priority steering fluid is routed through the steering valve and back to tank, essentially wasted.

Now a smart person might recover that lost fluid using check valves and recombine both outputs for a total flow for whatever. Log splitter maybe. It can use all the GPM's available but the load on the cyl will determine the pressure developed.