Hydraulic rush hog on Excavator- Return line

Teamfold · Oct 9, 2017

Hi,
I just put a CID hydraulic brush hog onto my Cat E-120 Excavator (28,000 Lbs) I Connected the lines to the thumb circuit (the Aux spool valve pilot lines are connected to an electric solinoid).
I wired a switch that keeps the fluid flowing.
The supply fluid is connected properly.
The hydraulic motor will not come up to speed.
I realize that the spool is made for cylinders.

Can I dump the return right into the hydro tank?

Mike

oldnslo · Oct 9, 2017

Does the thumb function restrict the amount of flow available? when running motors, flow is speed, pressure is torque. Type of spool doesn't matter until you try and stop the brush hog, then bad things could happen if you don't some form of "run down" protection in the motor circuit.

What amount of flow is required to drive the bush hog Vs what your excavator produces?

Dirthog · Oct 10, 2017

First thing you are going to need to do is find out how much flow the brush hog takes I don't think you are going to get enough out of the thumb circuit. We put them on excavators all they time and they are hogs when it comes to flow they need lots and need to be sized for the machine. Not only that the return should be dumped right back to tank as it will make massive amounts of heat running it back through the valve. And you need a valve so the motor does not run dry or stop suddenly when you let off the pedal or very bad things happen!!

Teamfold · Oct 10, 2017

Thanks for the reply,
The excavator has 2 pumps, each can produce 20 GPM @3500 psi.
The thumb circuit is piped w/ 3/4" hose to the boom, 1/2" to the cutter (25')
The brush hog needs 10-15 GPM @ 2500 psi.
I installed a relief crossover valve @ the brush hog. it is set for 2000 to act as a run down.

oldnslo · Oct 10, 2017

Are there any other functions using flow from the same pump as the thumb? 10 - 15 GPM sounds like a small bush hog since that is only around 20- 25 hydraulic HP.

15 GPM in 1/2 hose gives a velocity of around 25 feet per second and approx 4.5 PSI pressure loss

My two cents the system will over heat from all the line and fitting losses and perform poorly since pressure drop across the hydraulic is what does the work.

Dirthog · Oct 16, 2017

Just because the pumps will put out 20GPM doesn't mean it all goes to one attachment next can produce and does produce are two different things get a good flow meter and save your self a lot of problems. Not only that the thumb circuit would NOT have that kind of flow as it would be to fast to control. Each pump works one track then they both run boom up and on most machines I have seen arm the bucket is the only one that uses just one pump as a rule.