Help with PTO pump selection

[dgarrett]

Hello, I have a Kabota B2320 which only has a < 8GPM capability with a 3.7 gallon reservoir. This will not work for what I need which is a in-row cultivator for a small vineyard ( 4.6 acres ) because I need to run two cultivators, one each side of the row and at 8GPM capacity for two hydraulic motors there will not be enough for the torque that I may need, not to mention the undersized reservoir. My question is will a PTO driven pump driven off the 17hp @ PTO be able to supply enough PSI and GPM to drive two motors in parallel? I was targeting 1000psi and two 8GPM motors, but I worry that I do not have enough HP at the PTO or that the hydraulic motors will not have enough torque at lower PSI to cultivate the 2-4 inches of dirt depth that I want with a cultivator diameter of 12 inches.

I Was going to use a 20 gallon reservoir.

Any help would be great!

 

[J_J]

The 17 HP has the capability to run a 25 GPM at 1000 psi.

3.6 CU IN PRINCE HC-PTO-7A PTO PUMP 540 RPM

5.7 CU IN PRINCE HC-PTO-2A PTO PUMP 540 RPM

Do you have 1000 PTO speed ?

You could also run a gear pump with a stepped gear ratio.

You are still limited to 17 HP.

Will you run those hyd motors in series or parrallel?

If you run them is series, you can drop the pressure across two motors.

If you run the motors in parrallel,each motor will get half the total GPM.

Pressure determines for ce, and GPM determines the speed.

 

[dgarrett]

Thanks JJ
For the PTO speed I have 540 or 960 RPM.
I was thinking to run the motors in parallel but it sounds like keeping them in series will allow for higher torgue because the pressure will be higher than if running in parallel, is this correct?
How do I know what the PSI will end up being? It seems it depends on the size of the motor displacement, so I don't know how to tell if it will end up being 500PSI or 1500PSI.

 

[dgarrett]

Thanks JJ
For the PTO speed I have 540 or 960 RPM.
I was thinking to run the motors in parallel but it sounds like keeping them in series will allow for higher torgue because the pressure will be higher than if running in parallel, is this correct?
How do I know what the PSI will end up being? It seems it depends on the size of the motor displacement, so I don't know how to tell if it will end up being 500PSI or 1500PSI.

 

[bigdeano]

If you just hook the motors in parallel they won't both run the same speed. One could even stop and the speed of the other one would double. You would need a 50-50 flow divider valve to make it work right. Hooked in series they will run equal speed. Check the back pressure rating of the first motor so the seal doesn't blow.

 

[J_J]

You could use two 1500 psi motors in series and a 3000 psi pump.

 

[dgarrett]

I only have 17hp at the PTO so I think I would need more HP to spin up to 3000psi, but I guess it depends on the pump.

A question about series vs parallel: If they are in series then half the PSI is dropped across each pump but they receive all the flow available? if so then in parallel they would be full PSI but half the flow. Which is these combinations would work best with a 17hp input if I wanted low RPM and the highest torque?

Thanks in advance

 

[J_J]

You get the highest torque with the highest psi, and large cu in.

Psi is developed by the hyd component.

GPM dictate the speed.

A hyd pump is designed to withstand the pressure developed.

If you look at hyd pumps, they are rated to a certain pressure.

Hyd components are rated for a certain pressure.

Read the specs on this motor and you will see all the parameters.

11.6 cu in DYNAMIC BMRS200H2KS HYD MOTOR

 

[dgarrett]

that helps a lot.
So just to make sure I understand you correctly the hyd component that you gave a link for has a psi rating of 1914psi. and say I was to use a Prince PTO pump that could with stand 2000psi then the circuit at 15.8GPM would have 1914 psi?

 

[J_J]

Technically, the hyd motor can develop the rated pressure at any GPM from 1 to 15 GPM

You want to match the psi for all components, and certainly a relief valve in each circuit.

Also, you need the HP to power the hyd pump without stalling.

 

[buickanddeere]

JJ if a pair of 1500psi motors are placed in series in a 3000psi system. The first motor in particular will fail when it hits 3000psi as it stalls against something .

 

[J_J]

I would think you would have a crossover relief on each motor set at 1450 psi to protect the motor which has a continuous pressure of 1500 psi.

Excerpt:

Series circuit.

Connecting two fluid motors in series minimizes pump size and eliminates the need for a flow divider. Line sizes are also smaller than in a comparable parallel circuit, and piping is usually simpler, with only one pressure line and one return line required. Maximum torque at each motor is adjustable with the relief valves. The speed of motor A is controlled by the bleed-off flow control valve. Direction of motor B is controlled by the 4-way valve, which has an integral 2-way valve, which vents the relief valve when the motor is stopped. Total system pressure is then available at motor A.

Parallel connection (right)

Pump pressure can be lower in a parallel circuit because in a series circuit the pressure at the pump must be the sum of the pressure drops across the motors. However, where motor pressures vary widely, there is a loss of efficiency in supplying the motors requiring lower pressures. This circuit is most efficient where the load on each motor is the same. Raising the pressure on one motor renders the others less efficient and may disrupt the speed relationship. In parallel circuits, the only way to increase torque of the highest-pressure motor is to increase system pressure.

On our Power-Tacs, we use a series parallel combination to drive the wheel motors.

 

[dgarrett]

Would the tractor motor stall if it was only commanded to output half it's HP? The pump spec says you need close to the max PTO HP to support the psi of the hyd motor. The reason I ask is you mentioned the hyd device will always operate at it's designed psi.

 

[J_J]

That is not what I said.

A hyd cyl or motor will develop the pressure based on the load.

For instance, a hyd motor with light load might develop only 1200 psi, and under full load might be around 2500 psi.

You can half the HP by using half GPM's or limiting the pressure to half.

If you reduce both pressure and GPM by half you reduce the HP to 1/4