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?
What Brand/model machine?
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.
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.
Hitachi EX60-2
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.
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.
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.
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.
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
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.
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.
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.
Oops ! My literature says an EX60-2 is the same as a Deere 190E which is where I got my information. Guess not. Sorry.
Look at Surplus Center in Omaha NE. for motors. Yes run a case drain.
Notice the case drain line added and running down the side of the boom. The gerotor / geroller LSHT motors are not designed to free spin down while the blades spin down.
Does that mean an overrun clutch should be included?
You will need to plumb a check valve to act as a relief valve. this is normally in an H pattern.
This is what I was planning on doing.
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.
I haven't done much on this aside from buying an old parts mower. I was checking the other day to see how my swing function was when operating my thumb and it's almost non existent. There is more function when retracting the thumb than when extended it which makes sense to me. I would assume the swing would work better with a motor instead of a cylinder? In my untrained brain it would seem like a motor would have more back pressure than just filling a cylinder. Looking at the schematic they are on the same pump. The rest of the machine functions decently but the swing is almost useless which isn't ideal since sweeping when mowing seems reasonably important. If flow could be limited to the thumb or the mower motor would leave more flow available to the swing motor? The issue is how to limit that flow. It's an older EX60-2 and the aux circuit is a cable operated spool. I've converted it to be actuated via a solenoid but it's an all or nothing scenario. I don't see any effective way of limiting the spool travel and as funwithfuel mentioned that putting a needle valve between the spool and motor would cause the pump to try and compensate running a mower which would be a more continuous deal would be unwise. I can always just mow in and out with the boom I suppose.
So do you mean to say that a solenoid engages your option spool via cable? Something like a remote fuel shutoff solenoid?
I machined 2 caps that replace the dust cap on the topside of the control valve and encase the cable clevis on the bottom side. A 24v solenoid is tapped into the pilot circuit and actuated via a rocker switch on my joystick. Pressurized oil just pushes the spool back and forth.
So what you could do, to limit oil consumption for the option is limit spool travel. Since you've already made the nice spool cover, simply drill and tap end of cap for a "bump stop" and since that end doesn't receive oil any way you can make the spool stop wherever you'd like. You could adjust speed and flow with one adjustment.
Both sides are actually under oil pressure but I think a bump stop is a great idea. That is a pilot pressure line running into the top of that cap. I'll have to think of a way to seal off the adjuster. Maybe another cap over the bolt. I could tap the side of the bottom cap and run the pressure there. I'd mill off the top and build another o ring sealed cap to fit over a bolt and locknut that would be where the hose is currently. The only problem is that this will only restrict flow in one direction which would be fine for mowing but kind of a bummer with the thumb. Although it may be fine since I'm not going to be restricting it much.
You could use sealing nuts. https://www.boellhoff.com/us-en/products-and-services/special-fasteners/sealing-nuts-seal-lock.php
Again you could use an adjustable pressure reducing valve to limit pressure on one side of the cap.
As I thought about this more, bumpstops may not survive 450 psi hits. The proper thing to do, and it would be very time consuming, is to shim the spool centering spring. By shimming, you keep the spool centered, but when applied, the spring becomes solid sooner, limiting spool travel. I hope this makes sense.
That should be pretty easy. Thanks for the suggestions. It'll be a little trial and error to figure out how much to shim it, but doable.