Hydraulic pump suggestions?

[EdK]

I'd like to come up with a hydraulic pump configuration that would allow me (1) two-stage log-splitter type operation as well as the ability to (2) run a 8-10 gpm 2000psi accessory motor (not all at the same time - through valving). Of course, one could just keep it simple and run the splitter with a single flow rate at 2000 psi but that would seem a shame.

I'd appreciate anyone with a better understanding of hydraulics who might have a suggestion. I'd be willing to (and understand how to) juggle the engine hp and the splitter cylinder diameter to arrive at a reasonable splitter performance.

It seems as though one could force a two stage pump to shift to the smaller displacement stage to accomplish this. Perhaps it is better to build a two-stage pump out out discrete components to optimize for the application? I'm not sure. I'd prefer not to have to go to hydraulics classes to figure this one out

Thanks in advance for any ideas - Ed

 

[J_J]

ED,

A standard log splitter pump runs the splitter at two speeds, and two pressures. It switches automatically. It starts out at low pressure and high volume. As the force increase beyond the internal setting, it then switches to high pressure, and lower volume, and a slower time is realized.

EdK ---Of course, one could just keep it simple and run the splitter with a single flow rate at 2000 psi but that would seem a shame.

Not really. With no work being done, valve in neutral, nothing to block the fluid, the pump is just pushing hyd fluid from pump through valve back to tank, with no, or very little pressure. When you put some kind of load on the pump, then it builds pressure and as the load increases, the pump will try and pump at the max, and a relief valve should be in the circuit to protect the pump.

Changing engine speed will also change pump volume.

You might even be able to piggy back one pump behind another, using the first one to give you a steady pressure , and the rear pump as the log splitter pump, It would depend on the mating shaft on the first pump, whether it will take, say a 1/2 in round shaft, with key-way.

Here is a double pump, but I have never seen the combination you describe.

https://www.surpluscenter.com/item.asp?UID=2009080113572867&item=9-7028&catname=hydraulic

A 10 GPM at 2000 psi pump will require a 14 HP engine, where as the smaller log splitter pump can run off 5 HP.

You will have to make some logical decisions here.

 

[kennyd]

^^^^^^^^^^
What he said, you are designing two totally different systems.

Either forget about the two-stage pump or possibly use a belt to drive only one of the two different pumps at a time.

 

[dynasim]

A 2 stage regenerative valve is available, but they work on low flow rate systems.

chris

 

[EdK]

Thanks for the input... again admitting I don't really know what I'm doing but was thinking something like the following knowing a log splitter pump is a single pump but works at two different displacements:

1. turn a double pump at a constant RPM
2. Size such that the small displacement portion satisfies the high pressure(2000psi) log splitter needs and the 2000PSI/8GPM accessory motor while the larger displacement portion moves the splitter ram at high speed under light load (i.e. 350-700PSI).
3. Design valving such that the pump is automatically shifted between the two displacement circuits similar to a log splitter pump in condition #1 while condition #2 included the ability to force the small displacement circuit to run the accessory motor. Only one of these functions need run at a time (splitter ram or motor).

My thinking includes the assumption that a double pump can run with a load on only one side while recirculating fluid under no load from the other. I do not know if this is correct.

 

[fluidpower1]

Take a look at this Gear ump manufacturer to see pump configurations of up to four pumps in one envelope. They can all be different flow rates and I often se them to supply four different valves that operate four different functions at four different flow rates idependently and/or at the same time.

(1 to 161 cc) Multiple Pump Capabilities - Haldex

I've also used double shafted electric motors with two of these pumps for extra operations.

That way the pumps can be operated at minimal pessure and heat generation until flow is diverted to the actuators. Even then, pressure will only be whatever it takes to do the operation when no FLOW CONTROLS are used.

You can see some simple multi-pump circuits in a training book I use to teach basics and another one for circuit design here.
http://www.hydraulicspneumatics.com/200/eBooks/

Look in Chapter 8 for hydraulic pumps.

The Circuit Design book I use for an advanced class shows more pump circuits in Chapter 18 when it is posted later on.

 

[J_J]

My thinking includes the assumption that a double pump can run with a load on only one side while recirculating fluid under no load from the other. I do not know if this is correct.

You can turn one , two , or three pumps at the whatever rpm. They will only develop pressure when something like a cyl, or a motor is activated by a valve. You can activate all three or one or none. If you use manual valves, you have to shift them. If you use electric valves, you can develop a sensor wheel or program them in someway.

Are these pumps being driven by a gas motor, or electric motor. At any rate, you will have to figure how much HP is required to drive all pumps at max load.

Can you tell us your overall purpose for this configuration. Maybe there is a better way.

I have a PTO pump piggy backed on the back of my Variable Speed Pump. The shaft is turning both of them at the same rpm. Most of the time, the PTO pump is just recirculating fluid. If you used clutch type pumps, you could activate each pump whenever.

 

[EdK]

Not trying to keep the objective a mystery - just trying to avoid clouding with too much info. In terms of function think one internal combustion engine supporting hydraulic flow for (1) log splitter and (2) log cutoff saw. A simple firewood processor running from a single engine. Not trying to build or copy a sophisticated commercial offering but rather something small enough to be practical for a woodlot owner who heats with wood and perhaps generate a little supplemental income on the side.

 

[J_J]

EdK,

If that new automatic log-splitter valve had a PB on it, you could then run the output of the PB port to a motor spool valve to run the hyd motor, but not at the same time.

How much of this so you want to automate? I count about five functions on a wood processor. Loader, push log to cut position, spin motor, push saw down to cut, push ram for splitting. Maybe raising and lowering the cutting wedge.

Then there is the semi-automatic way. Cut and split using hydraulics, and all other functions done manually. Load, push log to cut position, push the motorized saw to cut.

 

[EdK]

EdK,
How much of this so you want to automate?

A manual log deck: tractor forks spread wide + timbers/manually roll logs into trough
(1-optional) Log advance to cut: could use rollers and push/optionally chain driven with motor
(2) cutoff operation: hydraulic chainsaw on pivot mount
(3) splitter: two-stage pump functionality
Wedge height: not needed (log diameter quite consistent)

So I'm planning two functions with the 3rd being an optional log advance. I intended this to be a step up from a completely manual operation without becoming so mired in detail/functionality(and cost!) so the project becomes unwieldy and never gets finished or even off the ground. I already own a splitter(no PB valve) and a hydraulic chainsaw. I could always let the splitter continue to run on a separate gas engine/pump power source if I had to but would greatly prefer to use the small diesel I have that will power the chainsaw and whatever else.