Hydraulic gear pump vs axial piston pump.

[cfherrman]

You have something spinning and you put a load to it, some applications the hydraulic motor isn't enough to keep it going, sometimes you need a flywheel to keep going. I have no idea if you need one or not.

 

[Davidov]

Hmm i think i understand what you mean ...well drum of flail mower is pretty heavy,it's like flywheel.

 

[Welder Dave]

If you want to basically have 200 HP driving as big of hyd. pump as possible on a mulcher type flail mower you're going to need a much bigger hyd. tank and a really good hyd. oil cooler if you want it to last. There isn't simple answers to what you're looking to do. You need to design a complete system from the tank to the flail mower. Maybe a single drive motor could provide the needed power and require less flow than 2 drive motors?

 

[Davidov]

I have hydraulic tank specially for pump that is driving hydraulic motors,and large oil cooler from 50t excavator.That's a must in hydraulics where some hydraulic motors are used.
About 2 motors,well i bought them because price was affordable,and i use 2,because my flail mower have drive belts on both side,left and right.I thought why 1 when 2 is better ,also 2 of those motors can produce more than enough power ,my only problem is hydraulic pump ....
I was looking on internet for more information with my problem,i found that piston variable pumps operate in closed loop hydraulic system.Is that necesarily ?,can i use that pump type with my open loop system ?.

 

[cfherrman]

If you are going open loop you should go with a regular pump, price can't compare

 

[56wrench]

If you use an open loop(open centre) then your variable piston pump will run at full stroke all the time which will wear it out prematurely

 

[Tones]

Davidov, ok, you have a 260hp engine but the engine has multiple functions to drive which all requires engine power, loader arms and power to the wheels. The power use for these needs to calculated. Let's say for arguments sake it's 100hp then the hydraulic system for the mower is 160hp. Pump size, the pump displacement should be the same as the hydraulic motor/ motors, ie, a 100cc pump drives one 100cc motor or two 50cc motors. Using smaller motors /motor diminishes the torque and creates a lot more heat, just like driving a vehicle up a steep hill in top gear. Next thing is rotor speed and how fast you want it to spin. In my experience 1600rpm is sufficient but others may differ so once you gather this info you can make a decision.
My preference for calculating motor and pump sizes is to use the metric system, the size in cc's is the oil required for 1 rotation and times engine RPMs give you the flow rate.
Cc's times psi divided by 600 gives you the required hp IIRC

 

[Welder Dave]

This is where a good hyd. shop would be a tremendous asset to help you design a system. Using random components off of other equipment may just complicate things, especially if you don't have all the critical specs. of the components you plan to use. I don't know if things like track motors are designed for continuous duty at their max. pressure and flow limits, etc.? These are all things you need to know.

 

[Davidov]

@56wrench So what is determining that pump stroke in closed loop system ?.So for my open loop i should use non variable piston pump ?,or gear pump.But i checked on internet,there is piston variable pumps designed for open loop systems.Idk how that works ....

@Tones Yes,my current pump i used is 133cc at 150bar pressure only,and motors are 2x 107cc ...i had to set rpm (i think they are +-2000) over belt pulleys.That pump is very weak for that mulcher head,no doubt about that.Also i don't use loader arms,they have large hyd. pistons that from small flow will take forever to operate.So i installed separate hydraulic distributor on loader,40liter/min flow,and i lift and lower flail mower head using small seperate hydraulic cylinders.But honestly i don't use that often,when i set height i rarely change it much.I mulch wild bushes and shrubs like type,not huge trees .Flail mower head is not in front of loader,but on side,right side.So i can mulch in 2,3 or more levels(by lifting and lowering),not directly from the ground level ,or to say,all at once.That's why this way is much easier on machine,and i don't need crawler,hydraulic drive.1st speed from loader transmission is perfect.

@Welder Dave I will go to hyd. shop too,but most of them won't make me design unless i buy from them parts ...and they sell new motors,new pumps ...those cost thousands of euros.I am trying to make something cheap,to work.And i almost made it,all i see as problem now is weak pump,and i try to figure out what is maxed out pump i can install on machine.Ofc i also need to consider transmission auxulary drive limits.But this exact same transmission from my loader is used on many others,larger ones,with engines 300-340hp and they have larger hydraulics pumps and operate on higher pressures,actually some of them have i think piston pump as main pump.

@Tones Also i forgot to mention,my loader factory engine was 150-155hp.So yes ..his main hydraulic pump(this i am using now) if i use some online calculator was taking at peak 70-90kw from it.Or u can check also,maybe i made mistake somewhere .133cc,150 bar,1500rpm.
And plus loader have 2 more hydraulic pumps,one for powering hydraulic distributor,ok that one take tiny amount of power,but other one is for steering,that one is not small pump,not at all.
I am sure,100%,that loader in first gear when it is mowing freely over ground,is not taking more than 20-40 engine hp for that operation.Otherwise factory would add larger engine from start.And this engine i added on it ,260hp.Is from larger loader ,that uses same exact transmission,but ofc ,larger pumps,larger machine,more tonnage,larger bucket ....

 

[Mobiltech]

So you are saying that your loader at full throttle or to the floor in first gear is the speed you cut at ? The reason I ask is because if you throttle back the engine no longer has 260 hp and your mower will slow down depending on rpm.
A wheel loader with fixed gear speed and torque converter is probably one of the hardest machines to run a mower on because the engine rpm changes constantly.

 

[Delmer]

Closed loop is different than closed center. Open loop and open center, and closed/closed are typical, but not the same thing. Closed center vs open center refers to the valves and pump design, loop refers to whether the oil goes back to the reservoir, or circulates between the pump and motor without going through the tank.

Closed center hydraulics have to turn the pump flow on and off somehow, so are better for something like an excavator that has various functions that need to be precisely controlled. Your mulcher is a more specific function, and one that will take a large and relatively fixed part of the engine HP, so open center valves is not such a big problem, you'll turn the valves on once and run for minutes or hours even. You do not have to use closed center valves on this if you already have closed center piston pumps and motors, you would control the pump directly on and off and the output would have no feedback to the control system. Possible/practical/advisable? only because it's a dedicated pump to a dedicated load. That's assuming the other hydraulics are run off the original loader hydraulic system. Or a smaller auxilary system. If you're trying to run all of this off one new big pump, you're in way over your head, and most of our heads also.

 

[4x4ford]

The way I understand this is he is looking for a dedicated pump to run the flail mower only the loader has separate systems for steering and arms and he is asking what size hydraulic pump he would be able to run with about 160-180 hp available for that just to error on caution to not stall the machine and he is using track drive motors from a large excavator to run the motor. First I’d want to make sure the size of piping and hoses are large enough to provide adequate flow not just pressure and that your pressure relief is set properly as far as what size pump you would have to get some one on here who works on that regularly I’m more of using what I have available and modifying from there

 

[56wrench]

I’m not sure what the current technology is, but years ago, variable displacement pumps were usually pressure and flow compensated. There was a compensator valve that controlled the angle of the swash plate inside the pump thereby adjusting the pump output as the system demand continuously changed. One method you could consider would be to use the hydrostatic drive pump and motor off a combine harvester or similar equipment and control the speed/on-off with an electric actuator or small hydraulic cylinder. Are there any used equipment dismantlers nearby?

 

[Davidov]

@Mobiltech Yes,well not really full throtle ,more like 80-90% of engine rpm i was using all the time,it works fine like that.As i say i mulch in 2 passes,no need to do everything at once.
@56wrench It's not bad idea,i was thinking about it.But yes,not many parts for sale from those combines,and when i did find some pump or motor ,they were ussualy smaller than what would i need.Combine harvesters are much lighter machines than 45-55t excavators.

 

[Delmer]

you're mistaking the weight of the machine for the HP rating and duty cycle. I'd guess an excavator final drive is nowhere near the HP of a combine transmission (that can climb hills at some speed). An excavator final drive is an excellent use of a hydrostat, it can run a acceptable speed at lower displacement through the motor, and at full displacement can produce adequate torque. You're not going to use that function though, you just want raw HP.

56wrench, that's exactly what I was thinking. You don't have to engineer the whole variable output control system to make bigger piston pumps work for this use. If the engine has 150hp available, then the hydraulic system just needs on and off, and a way to ramp up the motor speed slow enough to not break anything, appropriate relief valves. The transmission is not as ideal as if it was a hydrostat, but if your lowest gear at full speed is acceptable, then a hydrostat is not needed.

 

[Davidov]

@Delmer It's not really final drive,i think.It's 2x hydraulic motors that mount on final drive,Rexroth a2fe107 model.It's exact model on picture.And on second picture it's what i mean by final drive motor.I don't think these motors have any problem runing all the time,or to say to power flail mower all day long.Good hydraulic oil temperature,viscosity,quality oil fitering...don't see why would they not last long.On excavator its even worse,how many times in 1 day are they being powered,forward,backward ...i think that put more stress on motors.

https://www.interempresas.net/FeriaVirtual/Catalogos_y_documentos/3145/A2FE.pdf

Well anyway,i think i will get good results with just larger pump,and yet piston norma,piston variable,or gear ,still don't know which type to search for.Ofc hydraulic hoses i will replace for larger diameter,as to not affect the flow of oil.

 

[Welder Dave]

You need to know the max. flow the motors are designed for and the pressure in order to size a pump. If they typically need 3500 PSI or more a gear pump might get ruled out right off the bat. The motors may be high torque low speed so getting the RPM required might not be very efficient because you'd need a higher GPM pump to get the speed you required. A higher GPM pump would need more HP, more cooling and larger lines. You also lose efficiency (and power) using drive belts off the motors. A big advantage with hyd. drive is there's a built in relief compared to mechanical drive. It would be worth your while to pay a few hundred bucks to have a hyd's. specialist help you design a system. It would really suck to build something only to have it not perform as intended or have major issues that weren't considered. You need a pump and all the other associated hyd. parts. A shop would be glad to help you design it if you were going to be buying a pump and all the other components you need. It's not a simple thing you're trying to do.

 

[Davidov]

I posted on link above specs of those motors. 107cc,4000rpm(4400max),350bar/5000psi and some 420liter/110 gal/min.In my opinion it doesn't matter specs of the motors as long as they are higher than those of the pump.I run those motors just fine with small gear pump,and my power limit was my pump,not motors.
Every mulcher head,or flail mower have belt drive from motors,i didn't see one yet that have directly attached motors to the rotor.

 

[Welder Dave]

Like was previously mentioned if you want to run 3500 or more PSI you'll likely have to use a piston pump. Maybe a vane pump but I don't know what pressures they run. There is a good video on you tube explaining the difference between open and closed loop systems. You're going to need high capacity filters with high flow hyd's. I've seen flail mowers and such with direct hyd. drive. With a belt drive you'll also need to know how much side loading the motors are designed for. In the past I've seen motors not recommended for side loading. May not be an issue with the motors you have.

 

[Davidov]

1.4 tons can be maximum side load on drive shaft about 1 inch from housing.I think that is more than enough for me.
I have 2 large filters on return line before reservoir ,they are in total 500 liter/min capacity,both of them.Also i added safety by pass valve in case they can't handle the flow ,so nothing goes boom.

About pressure,i look at it from different way,idk if i am correct.Piston pump can produce high pressures ,but flow not really ,well ofc they can but pump would be really large,and expensive.
On other side gear pumps produce high flow and low pressure ,but smaller dimensions of pump.

Now using calculators for hydraulics online,just as example,it's same to me if i use gear pump 500 liter/min at 170-180bar or piston pump 250 liter/min at 350 bar ...their peak output power is more or less same.
Am i right ?.