Sizing a gear pump for project

[davedj1]

As some of you know I am building a dump trailer that will have a crane mounted on the tongue. I need help picking out a pump to order. 6.5 hp gas motor.
Here is a list of what is going to be on the pump:
dump cylinder, 5" bore, 30" stroke
two- 2" bore, 41" stroke cylinders for telescopic boom, two sections
2 1/2" bore, 18" stroke for lifting boom
a small hydraulic motor for turning the boom

I will probably buy one from SC
I'm looking at something in the .24 cu in (looks to be about 3.1 gpm)
up to .48 cu in (looks to be 6.2 gpm)
I calculated these numbers based on gas motor turning at 3000 rpm
Sound reasonable?
Thanks

 

[Rich B1]

Pressure X Flow/1714=HP.

You have the engine power, work backwards. What is your relief going to be set at?

Don稚 rule out the idea of using a 2 stage log splitter pump sized to fit your engine power. You will have some decent flow under no load, but still be able to move your loads at reduced flow/ high pressure.

 

[Texasmark]

I have a 16 gpm pump, around 2200 PSI max, I bought from Northern Tool for my log splitter I built, reasonably priced. It requires 8 hp to run at full load. I have an old lawn mower 15 hp engine hooked to it and it works great. The two stage runs high flow at low pressure, just enough to overcome the losses of the system with a 1-1 V belt drive from the pulley on the engine...standard one that came on it when new and mowed grass. Engine is rated at 3000 + RPM at WOT which makes the pump run at a good cycle clip. Upon contacting the log, the velocity goes to zero as the pressure goes to redline, cracking the log, upon which time the resistance of the log decreases, the pressure decreases, the velocity of the fluid returns and the wedge finishes the cut all while the engine purrs right along.

The pump is connected to the V belt drive sheave mounting foot via Lovejoy connections to ensure no lateral stress ison the pump....NT had all the parts and were economically priced

 

[davedj1]

Pressure X Flow/1714=HP.

You have the engine power, work backwards. What is your relief going to be set at?

Don稚 rule out the idea of using a 2 stage log splitter pump sized to fit your engine power. You will have some decent flow under no load, but still be able to move your loads at reduced flow/ high pressure.

Using your formula I came up with 5.8 hp
based on 2000psi and 5 gpm
I wonder if a two stage pump would be predictable enough. At what point/weight would it kick in to high pressure? Say if I have a light load in the dump box vs a heavy load. Or if I pick up 50# vs 400#?

 

[Rich B1]

An unloader pump is going to have a preset unload pressure. Sort of variable flow hydraulics without a piston pump.

You want some power reserve, you don稚 want your pump to kill your engine.

The unloader pump will give you decent cycle times with a smaller engine under no load, but keep you within the engine痴 power band under heavy load.

 

[Texasmark]

The system I described, when going to high pressure, low volume mode will setup for the working load once it converts from low pressure to high pressure....as I recall the transition point is defined and may also be a flow curve vs pressure. The fact that the application is log splitting, there is an abrupt change in load when the ram contacts the log. If the log totally resists, the pressure will build to the relief pressure where it will sit till you let go of the handle or the engine stops...which it shouldn't if sized to the specified value.

On rotten logs, the pump doesn't have such a steep transition point, nor does the speed so the transition is smoother. You should be able to find a curve on the pump relating speed to resistance, and speed vs pressure. Those 2 curves will answer your question. Basically, the heavier the load, the pump will slow as required, need more HP to do it's work, but maintain a steady force against the resistance. Higher weights would just slow the flow and increase the pressure to the capacity of the overload valve....2500# type number.

I don't have exact numbers as a log splitter runs at low pressure and high speed until the ram contacts the log at which time the log stops the ram for a second as the pump builds pressure against the blockage. Once the pump has generated adequate pressure to continue moving the ram, the flow will pick back up somewhat, since continuing to split after the initial crack doesn't take as much pressure resulting in faster speed... again speed depending on how much pressure the pump has to maintain.

 

[davedj1]

I understand how the log splitter pump works as well as the relief settings.
So I guess my question is to you Texasmark, are you recommending I use a log splitter pump? I'm not opposed to the idea.
Thank you for your input.

 

[Texasmark]

I understand how the log splitter pump works as well as the relief settings.
So I guess my question is to you Texasmark, are you recommending I use a log splitter pump? I'm not opposed to the idea.
Thank you for your input.

Just a maybe this will work for you. Personally don't see why it wouldn't as I use mine to control other things with hydraulic cylinders.

 

[oldnslo]

Dave,
A possible point of concern for using a log splitter pump would be the crane operation. Would you want the potential for sudden speed changes when operating the crane? For the dump bed I do not foresee any problems with using a log splitter pump.

 

[davedj1]

Dave,
A possible point of concern for using a log splitter pump would be the crane operation. Would you want the potential for sudden speed changes when operating the crane? For the dump bed I do not foresee any problems with using a log splitter pump.

I don't think that would be a good thing but on the other hand, I'm not looking to lift that much that far out. I really don't know that's why I'm asking here...lol
I suppose I could start with a regular pump and see what happens. I'm trying to find the right size pump to get. I've been watching every video I can find and reading some online calculators trying to grasp it. Trial and error could get expensive.