Tractors rated hydraulic flows

[Stomper]

My tractor's (Kubota L2501) hydraulic system puts out 5 gpm at 2200 psi. I have been researching and found a hydraulic motor for a project I am building. The performance data for the motor says that 5 pgm flow will give me the 60 rpm that I am wanting. My question is, at what engine rpm are tractor hydraulics rated. In other words, to get the 5gpm flow what rpm would the engine be rinning. I want the motor to run at 60 rpm when the tractor engine is at or just above idle not at or near max rpm. How do I figure this into the selection of the motor.
The motor that I found is 15.4 cu.in. motor. How do I know if this motor is sized right or if I need a smaller or bigger flow motor to get the rpm I want at or near idle.

 

[IceStationZebra]

the stated flow will be at either rated rpm or max rpm, in your case the only speed they give is 2200rpm. At idle your engine is approx 1100rpm. The system flow will be less than 50% due to lower pump efficiency at the lower speed, but the exact amount will depend on several things including pump wear, system pressure and oil temp (ie actual viscosity). I'd figure on approx 45% of rated flow. So 5.5gpm x 45% = 2.48gpm

On the motor side you also need to factor in some inefficiency if you are trying to get 60rpm on the nose. You didn't say what kind of a motor so I'll use 93% for a gear motor. 2.48gpm x 93% = 2.30gpm flow available.

motor size = (2.3 gal/min x 231 cubic in/gal) / 60rpm = 8.86 cu in/rev. Depending how tight you need to regulate the speed you may need a flow control. and obviously if you rev the engine it will roughly double the speed. Also, at idle this motor would put out approx 2.9hp.

ISZ

 

[Sawyer Rob]

Rated flow in a brochure or manual is at the pump, you won't get that out of the remotes, and "sometimes" some of that flow is used for the power steering too...

Some tractors do have two pumps, with one for the power steering and the other for the rest of the tractor.

So you have to be carful about what you will REALLY get out of a tractors hydraulic system.

BTW, the GPM rating, is at max RPM...

SR

 

[RNeumann]

How about a bigger, PTO driven pump that can make the flow at the engine RPM you need?

Everyone seems to be saying the same thing- it either won’t work or is marginal at best.

 

[Sawyer Rob]

pto pumps are great, but then you have to have the hydraulic tank ect. to go with it...

SR

 

[RNeumann]

pto pumps are great, but then you have to have the hydraulic tank ect. to go with it...

SR

Yep, depending on what OP is doing he could tie into the existing case. But the PTO option is definitely more involved.

If it’s for a auger or something it would be easier to get a motor. But if he must use that size the PTO could work.

 

[Xfaxman]

The only way to know what your tractor is putting out is to measure it with a flow meter.

 

[Stomper]

The motor is for a capstan winch that I have been researching. Someone on another forum gave me this link which will definitely help for motor selection

Hydraulic Motor Calculations - Womack Machine Supply Company

 

[IceStationZebra]

Rated flow in a brochure or manual is at the pump, you won't get that out of the remotes, and "sometimes" some of that flow is used for the power steering too...

Some tractors do have two pumps, with one for the power steering and the other for the rest of the tractor.

SR

According to the info I found there is a separate power steering pump, so no flow sharing. Brian

 

[ericm979]

Most manufacturers use two pumps now. I haven't seen one that doesn't though it's possible someone still uses a single pump. I think that's simpler and possibly safer than diverting flow to the steering.
Some manufacturers add the power steering flow to the main flow and use that number in their litterature even though there's no way to combine the two other than on paper.