Hydraulic flow explanation

[Timbgf]

Looking for some help understanding the flow (GPM) of the hydraulic systems. One of the tractors I am looking at (T494) has a total flow of 11.91gpm but it uses a dual gear pump. The other tractors (LS and Kioti) have higher total flow rates (15, and 16.5 respectively). I am not able to locate what the system psi is for each tractor but I am trying to understand which is better? The TYM has higher lift capacities so I am assuming there is a benefit to the dual gear pump but the lower flow has me confused.

 

[alexpops]

Not sure about the kioti, but the ls is split between steering and the rest, so you're only getting about 10gpm to loader and remotes. The ls is set up with about 2430 psi on the relief valve for the loader.

 

[Tx Jim]

Tractordata lists total hyd flow for a Tym T494 @ 14.5 GPM. 45 HP Kioti hyd is very similar to the Tym. Normally all other things equal system higher system pressure will lift more weight & higher flow gives faster cylinder piston movement

 

[old and tired]

This will be marginal information... Lift is partially, the amount of pressure but also the size of the lift cylinders. (but also to the geometry of loader).

The GPM is more of how fast something is done... the Lower GPM, the slower things move (but if the lift cylinder is smaller, no problem with the speed).

And the total GPM is normally split between what the power steering uses and what the rest of the hydraulic system uses.

TractorData.com TYM T494 tractor information

www.tractordata.com

Shows 9.5 gpm for the hydraulic system to use... What are the other tractors that you are looking?

 

[Timbgf]

Tractordata lists total hyd flow for a Tym T494 @ 14.5 GPM. 45 HP Kioti hyd is very similar to the Tym. Normally all other things equal system higher system pressure will lift more weight & higher flow gives faster cylinder piston movement

Thats weird, the TYM site says total flow is 11.91. 7.6 to implements and 4.25 for steering. It's much lower than the competition. All of the lift capacities are higher so I am wondering how the dual drive pump plays into it. I can't find the psi on any of the brands.

 

[Timbgf]

This will be marginal information... Lift is partially, the amount of pressure but also the size of the lift cylinders. (but also to the geometry of loader).

The GPM is more of how fast something is done... the Lower GPM, the slower things move (but if the lift cylinder is smaller, no problem with the speed).

And the total GPM is normally split between what the power steering uses and what the rest of the hydraulic system uses.

TractorData.com TYM T494 tractor information

www.tractordata.com

Shows 9.5 gpm for the hydraulic system to use... What are the other tractors that you are looking?

Thank you. I am also looking at an LS MT352c and either NS or NX Kioti. All cab models.

 

[ptsg]

The dual or tandem pumps that is used on most of sub compact and compact tractors these days makes for two separate hydraulic systems, although they will still share the same fluid.

One pump, the smaller displacement one, will handle the steering and the PTO valve. The big displacement pump, often called the main pump, will handle the loader, remotes and 3 pt hitch.

 

[WranglerX]

Also keep in mind, cylinder diameter + pressure also has effect on lift capacity....

Hydraulic Cylinder Calculator

 

[rScotty]

Also keep in mind, cylinder diameter + pressure also has effect on lift capacity....

Hydraulic Cylinder Calculator

That's right. Cylinder pushing force is just psi times the area of the piston in the cylinder.
Running at higher RPM gets you more flow rate - gallons per minute - but not necessarily more pressure.
New pumps make the same pressure regardless of RPM. Old worn out pumps do make more pressure at higher RPM.

ALL tractor pumps put out theoretically infinite pressure.
The actual pressure in the system is limited by the relief valve in the circuit. Say that twce....

It does't make a bit of difference in most operations whether the manufacturer decides to use two pumps (often in a tandem config) or to use a flow divider to split the flow from one pump.

For a 30 to 50 hp tractor running power steering, a loader, and a 3pt hitch 10 to 12 gallons/minuter flow is sufficent. A little more is nicer for 50 hp and up. They all have so close to the same pressure that pressure doesn't count.

If you want to run something with a hydraulic motor then more flow - up to 18 or 20 gallons/min. flow is handy and a hydraulic fluid cooling radiator is required. Easiest way to do that is with a PTO pump and separate reservoir.

Older farm tractors often ran their loaders and all their accessories with larger diameter cylinders and kept the hydraulic pressure down to about 1200 psi. They were looking for economy and long life. That is no longer the case, so pressures are higher now. To the accessory or to the job being done there was no difference between running more pressure or larger cylinders.

Today's compact tractors are limited to under 3000 psi partly because of "best practice" and partly because the pressure rating of tthe most commonly used - least expensive - hydraulic components mandates that max pressure.

It is common to set steering relief valves so that system runs at 1500 to 2000 psi, and set the FEL and 3pt relief valves so that those systems run closer to 3000 psi.

It costs the manufacturer (or the owner) nothing to adjust the relief valve for more pressure. Takes ten minutes max. And it costs the manufactrer very little if anything to upsize to slightly larger cylinders in the FEL. So lift capacity is not a good criteria for comparing tractors. Especially FEL capacity. Tractors are designed to pull, lifting is optional.

Hope this helps,
rScotty