Hydraulic gear pump vs axial piston pump.

[Davidov]

Hello everyone.
Is it true that piston pumps requre less power to run than gear pumps ?.And if they do ,is that allot less power or ?.
I mean lets take example as one gear pump with power output same as piston pump,would they both be able to run with same kw engines or not ?.
I don't know how to phrase this question better,i am not really good at english ....
Also if hydraulic pump maksimum power output is 100kw,what would be required diesel engine kw to be able to run that pump ?.Are we talking about 110-130kw diesel engine,or much more ?.

 

[cfherrman]

Hydraulics are typically 80% efficient

 

[funwithfuel]

In regards to HP/KW I get lost in the math. In regards to pumps, variable displacement typically run through closed center valves whereas gear pumps are associated with open center. The pumping losses are negated by the style of valve employed.
That said, the gear pump is delivering 100% of capacity per revolution. It's designed to run at rated rpm. The variable displacement by comparison delivers lesser amounts at lower rpm to reduce load on engine but maintain delivery per demand and accomplish work. The VDP is a winner

 

[Welder Dave]

Variable displacement pumps usually have load sensing (a design trait) that makes them respond to the load put on them to get max. efficiency and performance while keeping the engine in the optimal RPM range. A gear pump you usually need to manually lower the output at the valve to avoid stalling the engine with too much load where a VDP will automatically lower the output to keep from stalling the engine. You can still stall an engine with a VDP though. VDP's are more fussy about the cleanliness of the oil.
The basic formula is 1HP for each GPM at 1500 PSI for electric motors. I'm not sure the formula to convert to internal combustion engines but there are several HP calculators and formulas online. VDP's are more efficient and there are ratings of the different pumps online as well.

 

[Davidov]

@Welder Dave
Can i use those calculators online to calculate my pump power output ?.I don't need them to be 100% accurate ofc.
And can those calculators be used both for gear and piston pumps ?.
Could you maybe share link for one of those online calculators ?.

 

[Welder Dave]

Your best bet if you need 100% accuracy is to go to an established hydraulic shop where they can calculate everything from the exact pump you will use. The manufacturer will have all the design and engineering data for their pumps as well.

 

[Davidov]

I don't need anything 100% ,not even close.
I don't understand why is this so complicated ,all i ask is if there is difference in power requirement to run piston vs gear hydraulic pump.
These online calculators can show hydraulic pumps power kw output ,based on pressure,flow and efficiency.
So lets take example,using this calculator,its in bars and liters/min,i couldn't find one with psi and gallons.

Hydraulics calculator – calculate hydraulics

Hydraulikrechner - einfach Werte eingeben und sofort berechnen - Volumenstrom, Verdrängungsvolumen, Drehzahl, Drehmoment, Differenzdruck, Leistung und Fördervolumen einer Zahnradpumpe

www.hk-hydraulik.com

So anyway option 1: Gear hydraulic pump at 2000rpm 450 liter/min (119 gallons) at 170 bar (2500psi) ,equals 150kw.Doesn't matter if its 130-160kw,i don't need anything accurate 100%.

Option 2: Piston hydraulic pump at 2000rpm(variable or not ,don't matter to me) 300 liter/min (80 gallons) at 250 bar (3600psi) equals 149kw.Again don't care if maybe its 130-160kw ,no problem.

So we have 2 different pumps,that at full power equals +-150kw ,right ?.

Will one of those pumps require smaller diesel engine to run ?.Or they both require same powerfull diesel engine to run them,at max power output.
And if they do require different sized diesel engine,is that difference idk +- 50 kw ,or 100kw ?.
If piston pump needs 200kw diesel engine to run it,then gear pump will need 250kw ?.If there is difference ,and if its only +-50kw diesel engine,then to me it's all the same either i use gear or piston pump.

 

[Vetech63]

A piston or gear pump is going to operate anything hydraulically. The difference is going to be performance of what you are running. Some implements are going to need GPM and others will need PSI, or both. It may help if we knew what you are trying to build?

You also have to consider the peak HP/torque curves of your engine.

 

[Mobiltech]

Another difference is that a large displacement gear pump won’t last long at anything over 3000 psi. A piston pump will work fine at 6000 psi.
I would say for lower output low pressure a gear pump would be cheaper and work well. Anything over 2500 psi and over 30 gpm I would go with a piston pump.
Would you consider a vane pump just to confuse things more?

 

[BSAA65LB]

An engine for a gear pump system has to be sized for maximum flow and pressure. Flow X Pressure/1714 X Efficiency% = HP.

An engine for a variable displacement piston pump can be sized a bit smaller since the pump provides high flow at low pressures and low flow at high pressures. Add in HP limiting controls to the pump and engine size can be further reduced.

IME, (43 years with excavators), 170 HP with gear pumps gave considerably less performance than 170 HP with variable displacement piston pumps with HP limiting.

 

[Delmer]

A piston pump is more efficient. Basically the same comparison as a conventional internal combustion engine compared to a wankel, the wankel seems like a great idea, but it's hard to seal, just a like a gear pump is hard to seal the ends, whereas cylinders are easy to machine precisely and seal. I can't find figures, but I'll guess gear pumps are around 80% and piston pumps are 90-95% efficient. But there are other factors as well, especially when the pump size approaches the max the power unit can produce, gear pump can be set with torque limiting controls etc. that produce the pressure needed and drop the flow if HP/torque is limited.

 

[56wrench]

The only downside to an axial piston pump is - more moving parts and may require the reservoir to be mounted somewhat higher than the pump or it may require a charge pump to supply the main pump

 

[56wrench]

And axial piston pumps are more expensive than gear pumps

 

[Davidov]

@BSAA65LB Thanks that's some good information there.
@Vetech63 Hi,well i need these information for 2 projects to say...1st is screw type wood chipper for my farm,and 2nd project is wheel loader with flail mower.
1st project i didn't yet started so can't say much about it,only collecting informations for now,i might use hydraulics or mechanic drive of screw ,idk yet...have no idea which way to go xd.
2nd project wheel loader,i already made it to work to say ,mulched almost 2 hectares of some wild bush , with no malfunctions some 2 months ago.But i am not happy with hydraulic pump,it's weak and i have plenty of engine power left,or to say,not used ....

Diesel engine for screw type wood chipper i plan to use from combine,i have 1 in my garage,75kw at 2200rpm,no turbo.Will yet to find on internet what size of screw will be enough for that engine...

Diesel engine on wheel loader is 260hp ...so its starting point that can't be changed.I use 210cm wide (+-7 feet) flail mower from my farm that i used with my tractors,and it is powered by 2 hydraulic piston motors from track drive from 50ton excavator.(drum of flail mower is driven on both sides).
These are hydraulic motors i used on flail mower,size A2FE107.RPM of drum on flail mower is not in question,i target 2000rpm,with larger pump it will spin faster,i will reduce it on pulleys easy and cheap.

http://www.hydpump.com/pdf/A2FE.pdf

 

[Delmer]

There's a reason engineers have to take a lot of math classes...

Basically hydraulics is going to be limiting, mechanical drive is going to be easier and better for most raw power uses. For instance, I've never seen a wood chipper that is not powered hydraulically because there is no reason to use hydraulics, the drum wants to turn full power, full speed all the time. Now the feed rollers can be run hydraulically because it allows governor control and reversing, so there's reason to use hydraulics, plus it's not a large power requirement.

Even looking at large hydraulic components off an excavator final drive, or a combine hydrostat, those are not designed to handle large HP for long periods. Both are more incidental loads on the engine than main loads.

 

[Davidov]

Yes one option it is to be mechanical drive,i would probably use semi truck differential instead of hydraulic pump and motor,plenty of power,but will see yet...
What about wheel loader ?,can't go mechanical there .I need larger hydraulic pump.And based on those hydraulic motors i have and diesel engine,idk how large can i go with pump ...

 

[Welder Dave]

I miss read about your needing 100% accuracy. I think you need to figure out what flow and what pressure will work the best for your intended use. Then you figure out how much HP the engine needs to turn the pump without taxing it too much. It sounds like you have an abundance of HP though. You need to talk with a good hyd. shop and they can help with the calculations you need as well as the most suitable pump. There isn't a simple answer. I wouldn't think a wheel loader has the best transmission for a flail mower. I'm also not sure what type of flail mower you're referring to? Some flails are good for thick grass and weeds and light brush while others are designed for heavier brush and mulching.

 

[cfherrman]

Some of your applications might need some inertia and hydraulic powered systems don't have unless you put a flywheel with

 

[Truck Shop]

When it comes to just fluid pump-there are some interesting concepts-Roper-gear, Blackmer Vain,
And then there is a rather odd one that I have only seen two of, built in Stockton California some-
time back in the 40's-50's named Richmond Pump. It is a sphere on roughly 35* from each-shafts.
it required 25 hp to drive it. Were mounted originally under a farm delivery fuel truck. I used them
to build self contained slip tanks for bulk 10x40 and 15x40. These pumps would move a mass amount
of oil-I don't remember the volume compared to other pumps of size but considerably more.
Richmond Pump went out of business in the 60's IIRC--trivia. Anyone ever see one of these?

 

[Davidov]

@Welder Dave No abudance,i wan't to use as much as i can of the engine power,if i can use last breathe of that engine ,all on pump power,i will use it,even if engine will die in 2 years ,not care,engines are here sold on price of scrap iron.So i want to use all 260hp of that engine,but i guess some of that hp need to go for moving the loader,so lets say 200hp all for the pump.Questions is how big of a pump i can put there ?.As i say ,this existing pump on loader is too small ....
Btw mine flail mower is for heavier brush and mulching type,i used it with my tractors for few years,it can handle 2-3 inches thick wood no problem.
@cfherrman What inertia u mean ?,for screw type wood chipper ?.