Hydraulic flow rate loss for 3rd function

slingha · Mar 17, 2021

My tractor is rated at 11.34gpm at the pump. Im sure there is some loss through friction and whatnot. Does anyone have any idea if there's a rule of thumb as to how many gpm is available at the 3rd function valve? I do have a HST. The attachment I am looking at requires 7gpm and it is loader mounted. Thank you

Zebrafive · Mar 17, 2021

Usually HST is a different pump than the implement pump. Also some tractors have dual (two pumps stacked, or end to end) pumps, one for implements and one for Power Steering. If your steering is not included in the 11.34gpm, I think you will be fine.

ericm979 · Mar 17, 2021

Is that 11 gpm the implement/3pt system alone or is it "combined" flow where they add the steering circuit even though there's no way to use them together?

The rule of thumb for minimal pressure drop would have your 3rd function valve sized for 125% of system flow or more. If your implement system is 11 gpm and you size the valve etc properly you will have more than 7 at the implement. If it's a motor make sure the valve is rated for continuous operation and also consider a "motor spool" valve where the work ports are open when in neutral. With the usual style valve they are closed so cylinders remain in place, but that means that when you put the valve to the off position the motor comes to a sudden stop which could be hard on it or the stuff it's turning.

rademamj1 · Mar 17, 2021

My Kioti CK4010 has 11.7 GPM hydraulic pump flow, and 2.3 GPM is shared to the power steering. That leaves 9.4 GPM for attachment and implement hydraulics. The HST and 3pt hydraulics is run as a different system, and has its own dedicated hydraulic filter.

Bavarian · Mar 17, 2021

ericm979 said:
Is that 11 gpm the implement/3pt system alone or is it "combined" flow where they add the steering circuit even though there's no way to use them together?

The rule of thumb for minimal pressure drop would have your 3rd function valve sized for 125% of system flow or more. If your implement system is 11 gpm and you size the valve etc properly you will have more than 7 at the implement. If it's a motor make sure the valve is rated for continuous operation and also consider a "motor spool" valve where the work ports are open when in neutral. With the usual style valve they are closed so cylinders remain in place, but that means that when you put the valve to the off position the motor comes to a sudden stop which could be hard on it or the stuff it's turning.

You're right with that free flow for motors.

If there is an existing system already, there is an easy fix to that problem. Put a T in every line of the attachment. Connect the open ends with a check valve. We've manipulated the springs just enough to hold the internal ball against it's seat. If the implement gets started and pressure builds up in the line, the ball will be even pressed harder against the seat and stays closed.
If the circuit is abruptly closed, the momentum of the spinning implement (and the motor) can suck that weak check valve open and stop the rotation more gently.

Torvy · Dec 27, 2021

rademamj1 said:
My Kioti CK4010 has 11.7 GPM hydraulic pump flow, and 2.3 GPM is shared to the power steering. That leaves 9.4 GPM for attachment and implement hydraulics. The HST and 3pt hydraulics is run as a different system, and has its own dedicated hydraulic filter.

Rademamj1, how did you find the info on the amount of flow shared to the power steering? I am trying to compare various makes and models, but Kioti just lists the total pump capacity.

IndyJay · Dec 27, 2021

Torvy said:
Rademamj1, how did you find the info on the amount of flow shared to the power steering? I am trying to compare various makes and models, but Kioti just lists the total pump capacity.

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