mutti_wilson
Well-Known Member
I am trying to size a motor to plan a brush hog build. I've attached an image from the spec sheet. Do I double the GPM or or is 20.9 GPM the max flow?
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Understanding Max Pump Flow
- Thread starter mutti_wilson
- Start date
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- Tags
- brush cutter mower
mg2361
Senior Member
What Brand/model machine?
funwithfuel
Senior Member
That spec sheet shows tandem pumps @79 lpm which is roughly 20 gpm. Most machines only run aux spool off 1 pump unless you have an option for 2 pump flow. Remember that the 20gpm shown is free flow, no load. As your work load increases, your pump displacement decreases. You don't want a motor that needs 100% of that 20 gpm unless your going through a gearbox for torque multiplication. It gets involved even for something this simple.
John C.
Senior Member
You are going to need the pressure your motor is going to run at along with the flow and pressure curve for the pump. The pump will put out max flow to about half of the pressure band and then destroke as it starts pulling more torque than the engine can provide. Remember that the flow may also be required to go other places as well. Excavators are problematic running motors sometimes because they have to swing and travel at the same time you are using the aux motor. All that flow requirement will slow everything on the machine down to keep from killing the engine.
mutti_wilson
Well-Known Member
Hitachi EX60-2
mutti_wilson
Well-Known Member
Yes, I understand that it'd be robbing from something else. I'd just have to keep that in mind while using it. From looking at the pump curve it appears I can ignore the "1" graph and only use "2" since I would not be tracking while using the mower. It'll only be activated when I hold the button down. I still don't understand how I size something based on this though. Haha. I was looking at some commercial flail heads and one model was rated for 8-22GPM. That's not very precise at all.
I found these 2 motors. Both have the same GPM Max of 15.8 GPM which seems like it would be ok.
https://www.northerntool.com/shop/tools/product_200737735_200737735
74 ft/lbs torque 770RPM
https://www.northerntool.com/shop/tools/product_200737736_200737736
272 ft/lbs torque 475RPM
I don't think I would need the torque of the second motor. I am looking at starting with a 48" deck and possibly even trimming it down if need be. I think the RPM is fine. Not 540RPM like a PTO, but they would both work.
I believe the answer is yes but would you recommend a case drain? It's easy to run one back to the tank return line so it's no big deal.
Thanks for the help guys. This forum is great.
funwithfuel
Senior Member
Max torque and flow are required for getting things going, after that it's just whatever is required to maintain speed, at that point the momentum of the flail itself should require very little.
terex herder
Senior Member
You are going to have to match your hydraulic motor to your machine pressure. Cheap motors are often 2,000 psi, Your graph shows your mini hoe is rated nearly twice that. You have very little power available. I suspect you will find the performance inadequate to mow grass, let alone brush.
mutti_wilson
Well-Known Member
I've got blackberries all over my property that need control. Nothing heavy duty but not really possible to mow with my tractor with hillsides and ditches etc. I believe he is using a cheaper 5.90 cu in motor. The motor would see the higher pressure for just a bit while it's starting right? I'm not turning a high torque load, it's basically free spinning as funwithfuel noted.
I have an adjustable cushion relief valve installed on my aux lines for my thumb that is set at 2,000PSI right now. I also have a needle valve that I've used to adjust the speed of the thumb. I'd run the valve wide open for flow/heat when using the mowere. The relief valve would bypass a bit on startup correct?
This was my inspiration for the idea.
This guy is running one on a 1.8ton unit and it does ok.
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funwithfuel
Senior Member
Do you have straight gear pumps or variable displacement. I'm guessing variable. I want to caution against using a needle valve with the variable pump, it looks at the needle valve as a load. Your pump is going to compensate all that it can to maintain that pressure and flow. Here's the ugly part. Its generating heat which degrades your oil , makes hoses and O-rings brittle and shortens the life of your pumps. I would suggest finding out how to adjust flow for your particular machine. Some can be adjusted by a potentiometer hidden somewhere, some can be physically limited in spool stroke, some have an adjustment built into the display panel. Much better to do it right and have it last longer
Good luck
Good luck
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mg2361
Senior Member
The EX60-2 uses a pressure reducing valve in the pilot circuit for controlling the flow to the attachment by regulating how far the auxiliary spool moves.
Midnightmoon
Senior Member
What's your budget? I would look at a blue diamond and buy a motor like they have on theres. They use motors you can find aftermarket like a parker ect.
If someone has a similar brush hog ask for the motor info off there unit. Takes the guess work out of what will work.
If someone has a similar brush hog ask for the motor info off there unit. Takes the guess work out of what will work.
mutti_wilson
Well-Known Member
How does that work since the spool is cable actuated? Mine is now solenoid actuated so pseudo pilot powered but I don't see any way of limiting the spool stroke the way the return spring is designed. I barely have the needle valve turned in and it's only operating a thumb so it's not used for long periods of time. If I were mowing I'd open it up completely. I just wanted to slow the thumb down a bit since it's not a proportional solenoid. I'd also like to get a tilt bucket in the future having one of those flinging back and forth is not ideal.
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mg2361
Senior Member
Oops
! My literature says an EX60-2 is the same as a Deere 190E which is where I got my information. Guess not. Sorry.
mutti_wilson
Well-Known Member
This is what I was planning on doing.
funwithfuel
Senior Member
You need anti-cavitation valve plumbed in at the motor. It just runs the oil in the motor back into itself through the opposite port. Your motor may actually be equipped with it . Check the schematic for your motor.