Hydraulic hookup for small backhoe

[metalguy]

I think this is the section I should post in. Guys, I have a tiny backhoe that came off the smallest excavator I have ever seen. (It was a SS16 by Kobelco) I have fabbed up all the mounts to put it on my 646, but the hydraulic feed from my PTO is way too much pressure, I think. It is super jerky, to the point it is useless. Is there a better place to tap into that maybe has less pressure? I am at a loss here. I have put reducers in, and no change. I'd really like to get this sorted out so I can start using it to plant some small trees I have, and other light work. Any suggestions for a less....robust source of hydraulic pressure?--------Metalguy

[metalguy]

Here is a pic of the tiny backhoe:

[Toolslinger]

Couple things to check...
Can you find out what the operating pressure, and pump flow was on the donor machine?

Is the valve stack you have on there able to handle the back pressure, or is it going straight back to the tank?

I run my 646 basically at idle, or just above for the D100. The cylinders on your hoe are a fraction of the size of that, so they're going to move FAST if you don't have flow limiters. As it is, the Case unit has flow limiters on the swing circuit, and it's still faster then you want most times.

That's a good looking setup, and will beat the hell out of a shovel any day if you can tame it...

[JSinMO]

@metalguy Unfortunately I don’t have the expertise to answer your question and I’m not sure if this will be helpful but I looked through my books and took some pictures of the plumbing for my D100 on my 648.

We’re having a rain storm at this moment but if you think it would be helpful to you I’d be glad to get some pictures of how my tractor is plumbed this weekend.

[Harry]

Couple things to check...
Can you find out what the operating pressure, and pump flow was on the donor machine?

Is the valve stack you have on there able to handle the back pressure, or is it going straight back to the tank?

I run my 646 basically at idle, or just above for the D100. The cylinders on your hoe are a fraction of the size of that, so they're going to move FAST if you don't have flow limiters. As it is, the Case unit has flow limiters on the swing circuit, and it's still faster then you want most times.

That's a good looking setup, and will beat the hell out of a shovel any day if you can tame it...

I agree with you Toolslinger. I run mine just above idle when I use the hoe. The swing circuit on mine is very touchy. If you move the lever to much it can hurt you. Harry

[metalguy]

I had thought of tapping into the three point circuit for mine, as I believe it has lower flow? I have tried flow limiters, but the difference is negligable at best. I'll have to see if I can find specs on the original pump, and such. Maybe I can run a hydraulic motor off the PTO for it's own pump? LOL. The valve stack has power beyond, so it ends up going back to the tank. -----Metalguy

[myerslawnandgarden]

I think this is the section I should post in. Guys, I have a tiny backhoe that came off the smallest excavator I have ever seen. (It was a SS16 by Kobelco) I have fabbed up all the mounts to put it on my 646, but the hydraulic feed from my PTO is way too much pressure, I think. It is super jerky, to the point it is useless. Is there a better place to tap into that maybe has less pressure? I am at a loss here. I have put reducers in, and no change. I'd really like to get this sorted out so I can start using it to plant some small trees I have, and other light work. Any suggestions for a less....robust source of hydraulic pressure?--------Metalguy

Metalguy,

I think you are confusing pressure with flow. The very first 644/646 loader/backhoes had no flow restrictors and the swing of the D100 was way too quick even at low rpms. The pressure should not be an issue as I would expect the stack valve on the hoe would have a relief. I would suggest a flow control (not just a restrictor) that will return excess oil to the tractor hydraulic system.

Bob

[RoamingGnome]

Howdy!

First off, that is a really nice looking setup for your loader / backhoe

I tried a quick Google for Kobelco SS16 and didn't get any hits for that specific model -

The Kobelco USA website shows an SK17SR Mini Excavator - but I don't know how that would compare with your donor machine... If it was similar, the specs for the SK17 show it has 2 variable displacement pumps (main circuits) + 2 additional gear pumps - 1 for pilot/servo the other - ? (possibly the brake circuit on the travel motors or a cooling fan circuit)

I mention it because if you are using the control valves from the donor machine it would make a difference what type of pumps it had and what type of pump you have in your loader. Systems with variable displacement pumps are usually set up differently than ones with gear pumps. (Closed Center vs Open Center systems) So it might be worth a little more investigation into the original hydraulic system.

Just my 2 cents...

[thebuildist]

I agree with what others have said. Your problem isn't pressure, it's flow: too much of it.

If you put in flow limiters and it didn't help, then your flow limiters are still too big. Get smaller flow limiters, and that'll tame this beast.

Bob

[Toolslinger]

I found an SK008 that looks like it's their smallest model, and seems about right (honestly, it looks a little bigger in the photos, but close). Cut sheet says it has gear pump for the main system, and variable displacement pumps for the travel. Pressure on that machine was 2600psi. Doesn't list the flow. Engine is nominally 10hp. Perhaps the SS16 is a gray market machine that we're not going to see cut sheets on easily.

That would lead me to believe it can handle the Case output just fine. I would ask again if you plumbed the valve stack outlet straight back to the tank? If you didn't, then the oil that should just be free flowing to 0 pressure is going to hit the reliefs down stream, and could cause issues. The early d100's were made to go back in series. When I had to replace my control valves the manufacturer was explicit that it couldn't handle that, and needed the tank line.

I believe the flow control may well be a good choice as well to control your speed issues.