Backhoe Building a thumb for a model 48 Backhoe

[texasranger556]

Yes there are two pumps, the smaller one feeds the steering and serves as the charge pump for the transmission if it's hydrostatic. The larger one feeds the loader, three point, backhoe. Pressure sounds right. You got the idea.

 

[texasranger556]

One thing to be aware is if your new valve has a relief valve make sure it is set to 2500. Mine came set to 2150 or so and I do notice less digging power with the backhoe, so I will either be shimming it or replacing it with a plug. You already have a relief upstream in the loader, and I suspect there is one in the backhoe as well.

 

[DanMc77]

This valve supports 30 gpm, power beyond, with adjustable relief valve factory set to 2000 PSI, max PSI 3000, spring center, $184. More pricey.
Prince One Spool Control Valve, Model# HC-V-R22 | Control Valves| Northern Tool + Equipment

 

[texasranger556]

30 is a bit big, I'd stick with 10-15 or maybe even 20 due to physical size of the valve, less need for adapters, and stiffness of the spool. The one I used is rated for 10 and my tractor flows around 8.

 

[DanMc77]

30 is a bit big, I'd stick with 10-15 or maybe even 20 due to physical size of the valve, less need for adapters, and stiffness of the spool. The one I used is rated for 10 and my tractor flows around 8.

Ok, so 30 gpm would mean larger ports, bigger fittings and having to adapt down to my smaller fittings. Do you have a link or info on the one you used? I'll keep looking for something smaller.

 

[DanMc77]

Now here's another novel idea: If I'm going to go through the effort to add another control valve to my backhoe, why not add a 2 or 3 spool valve so I'm already plumbed in if I want to add additional functions to my machine some day in the future? Here's a 2-spool, 10 gpm, power beyond capable, spring center, for $73.43. The image shows 3-spool. What is "European Style?".
CHIEF G Series: 1 GPM, SAE 1 Inlet/Outlet, 2 Spool, 3625 PSI, 15-3625 PSI Relief Setting, SAE 8 Work Ports, 2297

I could run that second spool to some quick connects so I can easily tie in a removable attachment.

 

[texasranger556]

Just depends how you want to control it. Mine is an extra stick between the two backhoe ones as you can see in the picture. Not as convenient as foot control, and I still may try to make it foot controlled with a cable or other custom linkage. I really considered a dual electronic spool valve so I could put thumb switches on the original valve handles but that got expensive pretty quickly and you're stuck with on/off versus the ability to modulate flow with a manual valve. Also keep in mind running all the hoses to what you want to run. I used 3/8" hoses to run the twist and 1/2" hoses to run the splitter cylinder. I could only fit one 3/8" hose through the boom and dipper along with the factory 1/4" hose routing. The 1/2" hoses and second 3/8" hose I tied to the outside of the boom and dipper, and have to watch when I swing all the way left that it doesn't crush the hose. Doing it again I'd go with 1/4" hoses for the twist (it will also feed a thumb...project for another day) and hopefully fit both of them inside the boom for protection. As it is I'll have to add an orifice to slow down the twist function since the cylinder is only 1.5" diameter. Live and learn.

Edit: That valve looks promising, and a good price. Just have to watch what "power beyond capable" means. Often there is a plug or sleeve you buy separately to enable power beyond, I've never heard of that brand so just make sure the part is available before you buy it. It is also sometimes called a closed center plug depending on the design of the valve body.

 

[DanMc77]

I see that MobileHydraulics lists a power beyond plug for this 3-spool valve.

Now on to the cylinder. The diameter of the model 48 bucket cylinder is 2.6". Would that mean this is a 2" bore? I would expect that the thumb cylinder would be selected to match the bucket cylinder, since they would be in the position to oppose each other. Additionally, it seems to me that the lever distance between the thumb pivot and the attachment point for the thumb cylinder should match the lever distance in the bucket so that one doesn't exceed the capability of the other. But then, I'm thinking that there still may need to be a relief valve in the line that feeds the thumb extension. When the thumb is partially retracted, the effective lever arm is reduced, so the bucket could push on it and blow a seal? I know that the valve has adjustable relief, but does that relief apply when the valve is in neutral?

And yet one more question: All the cylinders I can find would put the hydraulic lines coming out facing the boom, where they are most likely to be in the way. I want the lines to come out the side of the cylinder. Can the cylinder-end pivot tube be cut off and rewelded in a 90 degree rotation?

 

[texasranger556]

In the link you provided the picture shows a 3 spool but description says 2, just FYI. I wouldn't recommend cutting a welded cylinder just to re-clock the ports. You could use a tie rod cylinder and clock the ports as you wish, but a welded cylinder is generally going to be more compact and stronger. If you absolutely can't find a port configuration you like, it would be easier in my opinion to plug the existing port and drill a new one where you want it. A lot of times aftermarket cylinders will have two ports 90 degrees apart on the base end, and some will have it on the rod end too.

As far as a relief valve I wouldn't worry about it. You would likely bend the thumb or break your pivot pin long before blowing out cylinder seals.

 

[DanMc77]

In the link you provided the picture shows a 3 spool but description says 2, just FYI. I wouldn't recommend cutting a welded cylinder just to re-clock the ports. You could use a tie rod cylinder and clock the ports as you wish, but a welded cylinder is generally going to be more compact and stronger. If you absolutely can't find a port configuration you like, it would be easier in my opinion to plug the existing port and drill a new one where you want it. A lot of times aftermarket cylinders will have two ports 90 degrees apart on the base end, and some will have it on the rod end too.

As far as a relief valve I wouldn't worry about it. You would likely bend the thumb or break your pivot pin long before blowing out cylinder seals.

I'll continue looking at cylinders.

I need to think about the relief valve. I don't want to be bending or breaking anything. It should be fairly idiot proof, just in case an idiot is running the machine.:confused2: