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Log Splitter 2 Stage Gear Pump - no high gear!

werminghausen

werminghausen

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Hi,
my log splitter pump gave up and I need it back. The piston is moving super slow at all times since yesterday. It builds up high pressure and splits as before in low low gear when I have big piece of wood on the splitter. But the pump does not shift back into high gear to move fast at low pressures.
Pump is a fairly new: Bucher 16gpm 2 stage at my 35ton splitter with a B&S 10hp engine. Does anyone know what is wrong with this pump and can it be fixed?
Best, Martin
 

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werminghausen

werminghausen

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Interesting, you think the pump itself might be fine? And the problem is caused by low flow on the suction side.

Suction hose is fine, fluid level is fine too, at the lower end of the dip stick but still okay.
I don't know if there is a screen in the suction port. I think the screen/filter is at the return.
Splitter is a Yardmax YU3566

One thing I noticed: When the piston is moving very slowly the piston speed will not decrease from full engine speed to idle.
2020-07-16 10.16.53.jpg 2020-07-16 10.16.35.jpg
 
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homemade

homemade

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I belive most two stage splitters are adjustable for what pressure it shifts from high to low flow. If it doesn’t want to shift back, then it could be a stuck shifting check ball or something.


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werminghausen

werminghausen

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Yes I guess you are correct. If the control valve is stuck in ' low gear position'
Or the control valve seat leaking.... then the pump would still produce pressure in the low gear but would be 4 times slower than in high gear.
However if the control valve is functioning then there could the possibility that the key of the high gear that locks it to the drive shaft could be broken/ sheared off and the set of high gear is not turning?

Also of concerns: In snail mode right now...there is some vibration in the hydraulics and a stuttering piston movement when the piston moves freely. When pressure is built up by splitting a log then the movement is smooth.

Here is diagram of that pump. It is a Chinese product (grrrrrr) and I tried to understand a bit of it. See my mark ups.
Best, Martin
ps. I am very familiar with hydraulics (lines, pistons and switches) but never had a gear pump open. These pumps in general might be very robust...except for mine.
 

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kevin j

kevin j

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I can’t open your file on my phone, but if you’re somewhat familiar with hydraulics it should be straightforward for you to figure out. A two stage pump is essentially two gear pump sections or pumps in one large housing. the small gear set goes out to the load all the time. The large gear set goes through a check valve and out to the load. It also has an unloading valve that goes from the gear set back to the inlet port so that when the load pressure gets above some psi it pilots that unloading valve open and just re-circulates the oil on the large gear back to the inlet. The check valve is to prevent the small gear set from going backwards and unloading to the inlet like the large gear set is doing. So it’s not a variable pump it just unloads the large gear set by the unloading valve and the check valve. Look for a hi-low unloading or two stage gear pump schematic on the web and it should be fairly easy to figure out if you’re familiar with schematics
 
werminghausen

werminghausen

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Thanks Kevin, I think I know what you are talking about. This is exactly what the diagram is telling me.
If the check valve would fail the 2 pumps would always work together under low pressure until it would entirely fail under higher pressures (under pressures higher than the set pressure of the relief valve/control valve (you called it unloading valve). I heard this relief pressure would be at about 900 psi).
This is obviously not the case and therefore if there is no massive restriction in oil flow (Post #2) then the problem must be the unloading valve.
However the pump will produce a fair amount of suction pressure if there was an obstruction and I doubt that this can happen with sufficient oil in the thank.
The only viable option is the relief/unloading valve failing. It must be stuck open or leaking badly.
Question is if I can remove this valve without draining much of the oil.... maybe best position is piston expanded in the down position, then open the unloading valve and check if it moves freely and how the cone seat looks.
Best, Martin
 
werminghausen

werminghausen

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From what I can tell in the pictures it looks like your splitter was built 11/2019. If so, have you contacted the manufacturer?
Yeah, their service is not great, they don't have any service around. There might be a chance that I 'll get some help but for the most part I am on my own unfortunately. Maybe it is something easy to fix. Martin
 
sundance

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Yeah, their service is not great, they don't have any service around. There might be a chance that I 'll get some help but for the most part I am on my own unfortunately. Maybe it is something easy to fix. Martin
Another thought......although it wouldn't seem likely as new as your machine is I've read of folks having suction lines fail internally and partially block flow even though they look fine outside.
Looking at the design of yours I doubt there is a strainer on the suction coming out of the tank. Looks too small to have one but if you pull the suction line it's worth checking.
 
werminghausen

werminghausen

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Hi Sundance, thanks.
If there was a restriction in the suction line how would you explain, that the piston still works in low gear and putting out pressure?
Also the failure happened all at once.
Best, Martin
 
sundance

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Hi Sundance, thanks.
If there was a restriction in the suction line how would you explain, that the piston still works in low gear and putting out pressure?
Also the failure happened all at once.
Best, Martin
At a guess...restriction allows some fluid but not enough for full flow. I'm only offering thoughts, not saying this is the problem.
 
werminghausen

werminghausen

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Thanks again Sundance, yes I know and I am thankful for your input!
I have no experience with these type of pumps. Information I could gather: Suction vacuum of a gear pump (generic) is about -0.5 bar.
It cannot create a perfect vacuum. So yes, you are absolutely right, there could be a restriction on the suction side that is restricting oil flow and therefore the piston movement is very limited (see also Post #2).
But how can that happen all of a sudden?
And yes I need to check the oil flow, disconnect the suction hose and check for free flow....in case the Chinese worker dropped something in the oil tank that now clogs the suction port.
Martin
 
sundance

sundance

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Thanks again Sundance, yes I know and I am thankful for your input!
I have no experience with these type of pumps. Information I could gather: Suction vacuum of a gear pump (generic) is about -0.5 bar.
It cannot create a perfect vacuum. So yes, you are absolutely right, there could be a restriction on the suction side that is restricting oil flow and therefore the piston movement is very limited (see also Post #2).
But how can that happen all of a sudden?
And yes I need to check the oil flow, disconnect the suction hose and check for free flow....in case the Chinese worker dropped something in the oil tank that now clogs the suction port.
Martin
werminghausen. it could happen all of a sudden if the suction hose de-laminated internally and is now blocking flow (while looking fine on the outside). Thinking about it with a fairly new unit, maybe a bad cut on one end leaving the internal lining exposed and subsequently failing so it partially blocks! Again, I'm just offering thoughts.
 
werminghausen

werminghausen

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I did update the technical drawings and diagram of the pump which I attached earlier in the thread. I had the rotation of the gear in reverse. I added the unloading path through the unloading valve and corrected the terms as good as possible.

Possible issues for failing spitter are
- failing unloading valve in gear pump
- restricted oil flow at suction side
I'll let you know what I'll find out.
Worst case I need to replace the pump. What do you guys think of the Haldex 16 GPM Two-Stage Hi Low Gear Log Splitter Pump Part#1300487.
It looks more old school and solid than the cheap Chinese pumps?
Martin
 

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Sandhill Crane

Sandhill Crane

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I recently replaced a pump on my conveyor as the shaft seal was weeping and small bits of oil making a mess of things.
The replacement pump from Built-Rite, the conveyor manufacture, was a new pump they have switched to.
The point being, the ten year old pump was cast, the new pump was aluminum, and the style of fittings are different, with o-rings.
Just saying, something to check when swapping out a new pump and hoses.
 
triptester

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I have noticed that the majority of 2-stage log splitter pumps with aluminum bodies are imports.
Another possible cause for fluid obstruction, although usually only during cold weather, the filter mounting base has a plastic by-pass valve that can break entering the system partially blocking fittings.

I would try adjusting the pressure shift at the pump first, if there is a broken spring the large section continuously by-pass.
 
werminghausen

werminghausen

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I am thinking of buying a pump from
1300487 Barnes Haldex interchange Hi/Lo 2 stage hydraulic gear pump
This is a cast iron pump.... feels more solid than a Chinese import... and it should fit straight in. It has the same shaft (1/2", keyed), 1" suction side and
1/2"NPT pressure port, same bores for the bracket 2" square.

Filters/Strainers: I hope there is no filter in the suction side. That would be wrong. A filter always should be in the output or return side. I think Yardmax has a filter in the return line where it meets the thank. That is correct in my opinion.

Unloading valve spring: I think you are correct here. If the spring is broken oil from the larger gear set (high gear0 would return straight to the suction side, making the large gear set idle at all times (not producing any pressure). However it would be very unexpected that a spring is failing?
Well you never know.
Martin Screenshot 2020-07-18 11.10.28.png_page-0001.jpg
 
sundance

sundance

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werminghausen

werminghausen

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Sundance, this rough strainer (150 micron) from wire mesh has a lot of surface and will be okay, not a big chance to clog.
Anyhow if the rubber hoses are in good working order (not falling apart internally) and you don't drop anything in the oil during refill there is not much big stuff that could get in there.
I am talking about a much finer filter and that one should definitely live on the pressure /return side.
 
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