Hydraulic gear pump vs axial piston pump.

[Mobiltech]

You will need some pretty large lines to run 500 lpm

 

[Davidov]

It's not problem lines ofc,but it was only as example.

 

[56wrench]

The hydrostatic pumps i am thinking of would be found on NH TX66(mid 1990’s) combines or the bigger JD combines or other similar size machines. They were designed to handle 250 engine hp and the bigger ones off newer combines should handle more than that

 

[Tones]

There's another thing that comes into play when running any hydraulic driven mowers and that is pressure spiking which track drives don't suffer from so much. On closed loop systems with a hydraulic transmission pump set at 6000psi spike pressures can top 20,000psi but only last millie seconds. These spikes hammer the guts of the pump and motors. I found all this out when I was running a forestry mulcher and the pump went to lunch at 1700hrs from new. The replacement pump I had the pressure set at 4800psi which was still working properly when I sold the machine at 6500hrs.
Davidov; how are you going to plumb the hydraulic motors?

 

[Welder Dave]

You need the right combination of pressure and flow to get the motor at the proper RPM. Higher pressure and less flow may be better than higher flow and lower pressure. Flow gives the speed but pressure gives the torque. If it spins fast but powers out easily it won't be very efficient. Commercial mulchers have done a lot of R&D to figure out the right speed and torque requirements. It's best to have some kind of safety/overload protection built in.

 

[Tones]

You need the right combination of pressure and flow to get the motor at the proper RPM. Higher pressure and less flow may be better than higher flow and lower pressure. Flow gives the speed but pressure gives the torque. If it spins fast but powers out easily it won't be very efficient. Commercial mulchers have done a lot of R&D to figure out the right speed and torque requirements.

On the contrary Dave, pressure creates heat which then turns into a loss of power. Running a higher flow can be turned into inertia and using enough pressure to keep the production up. Most commercial manufactures IMHO wouldn't know their ass from their elbow and run on 100% BS, a fact I have proved many times.

 

[Welder Dave]

I was thinking in general terms, that's why I said you need the right combination. If you use a smaller size gear pump to get the speed but it doesn't have enough pressure the mulcher will power out too easily. Too much pressure does create more heat and may cause damage to other components. There are some good mulchers that have it figured out. I've said all along it's not a simple thing he's trying to design and talking to a hyd. shop would be a good idea. Another thing to consider is how balanced the cutter shaft needs to be. I know on higher speed flail mowers for grass and heavy weeds if they aren't balanced can vibrate themselves to death. Something like a rototiller not so much but I don't know at what RPM balancing becomes important. He mentioned 2000 RPM.

 

[Davidov]

@56wrench I checked on internet,and all the results i am getting for NH tx66 are tandem gear pumps.
Some other pump i found that looks like piston pumps,were from TX68 models,but their splines on shaft don't match what i need.I have friend of mine who is also farmer and owns tx66,will ask him what pump he have on his machine.
@Tones I didn't do much about hydraulic plumbing my self,but i had help of 2 mechanics,1 of them works on hydraulics on excavators and loaders.If u mean how are motors connected on loader,well they have just 3 lines in total,1 is pressure line,1 is return line,1 is case drain.
Hydraulic pump that is powering flail mower have it's own oil tank,oil cooler,oil filtration.Oil under pressure goes directly towards motors,no hydraulic distributor in its path,nothing.There is some pressure relief valves only and i think that's all.Return line goes trough oil cooler,oil filtration and back into reservoir,i think its in that order.

So high flow,low pressure is not bad idea ?,gear pump low pressures or piston ?..As i have 260hp diesel engine,i could use some 170-180hp(130-140kw) for powering main hydraulic pump for flail mower.That would be some hydraulic pump gear type with flow of 450-500lit/min(120-130 gal) at 170-180bar (2500-2600psi) ,or piston pump 250 lit/min (65-70 gal) at 350bar (5000psi).
And vane pumps ,i was checking them earlier today on internet,they are something between gear and piston,which was mentioned here also.Some loaders have those pumps factory instaled.Little more max working pressure,slightly less flow,but same smaller casing, unlike piston pumps.I could use them also,it's not out of option ofc.

 

[Tones]

Yeah that magical 2000RPM number, more bs. I dialed the rotor speed back to 1600 RPM which added more torque in turn added more production and a whole lot less bearing problems.
To summarize, changed from a 100cc motor to 2 63cc motors which then gave a total size of 126cc all fixed displacement, driven by a 100cc pump equaling 250lpm at 2500 engine RPM, reduced pressure from 6200psi to 4800 psi, rotor speed reduced from 2000RPM to 1600RPM. Production went up,costs went down.

 

[Davidov]

Ur mulcher head rotor is driven on both sides also ?.

 

[Tones]

Davidvo ,there's 2 ways of plumbing multiple hydraulic motors on one circuit. One is to run the feed line from the carrier to the first motor the return then goes to the 2nd motor with the return going to the carrier. This then sets the motor RPM as if there's only 1 motor.
2nd way is to T the feed and return lines to each motor thus doubling the size of 1 motor which is what I did as per previous post.

 

[Tones]

Ur mulcher head rotor is driven on both sides also ?.

Yes. Also helped to get enough belts on to coup with the extra power without making the overall width bigger which was important for the select clearing is was doing.

 

[Davidov]

Yes sorry..my english is not best.If u mean't on that about plumbing motors,then yes,currently they are now T connected.
I will look into some piston or vane pumps,just to see what i could find,with what specs ,etc ...main problem would be ofc pump shaft diameter and number of splines,bolt holes orientation,those needs to match.Will talk to some hydraulic shop to see what are their opinion.If they try to sell me new parts,they are useless to me.
Also forgot to mention about Screw type wood chipper,hydraulic drive would be bad idea for sure.I talked with some mechanic in my area,he say cheapest and easiest solution would be to try using semi truck rear axle differentia...i think that would be overkill for what i am planing to make.Well,anyway will yet see about that,need to look more into it.

 

[Tones]

IMO Danfoss make some of the best hydraulic transmission pumps being the 90 series. They come in different sizes and spline shaft arrangements to suit. The on/off can be controlled by cable or electric. Pumps come with a SAE standard fit (bolt pattern and spicket).

 

[56wrench]

Just a thought on vane pumps. They don’t handle shock loads very well. A shock load may break vanes

 

[Welder Dave]

Slower RPM for more torque makes sense with the added bonus of longer bearing and component life. I don't know if there are cushion valves that work for hyd. motor applications that would reduce shock loads on the pump and rest of the system.

 

[Tones]

Slower RPM for more torque makes sense with the added bonus of longer bearing and component life. I don't know if there are cushion valves that work for hyd. motor applications that would reduce shock loads on the pump and rest of the system.

Yeah, I fitted an Stauff accumulator to overcome that problem. It lasted 5 hours then blew the bladder. Oh well. Still have it here if you want it. postage only

 

[Welder Dave]

Now that you mention accumulators that's what graders can use to cushion shock loads. Maybe there's something better for hyd. motor applications??

 

[Mobiltech]

Do the track motors you’re using have built in brakes. If so you will have to remove those.
Are they 2 speed motors or single speed.

 

[cfherrman]

I've seen high pressure accumulators, just have to buy the right specs