BH77 - has anyone considered converting mechanical thumb to hydraulic?

[jim_wilson]

This is what I've been wondering. And where do you put it?

How is it done on the B26? Do they come stock with the extra valve in the stack already and the option of the aux lines gives you the linkages to the valve and the boom lines?

I've been throwing around some ideas in my head about how the add a hydraulic grapple onto the BH77 too - and I think it just came to me how to add the valve in - put a foot pedal on - and not have to do any real big modifications to the hoe itself.

If you look at the online Kubota parts manual for the BT820 hoe on the B26 - what they do to add the hydraulic grapple is just add another valve into the existing stack. That's not really an option on the BH77 because the room just doesn't exist on the BH77 to do that. I've already sat there looking at that valve stack a lot trying to figure out how to do it - and I just don't see how to make it work - without major modification.

on the B26 the foot pedal goes on the side of the control tower - and then it just actuates that added on valve in the stack directly - because the valve appears to be the last (or first) - in the stack - and sits right below the pedal - so the linkage goes from the pedal right down the valve.

The easiest way to add a valve onto the BH77 - is to put it under the operators platform and plumb it into the existing valve stack with hoses. That means you have to actuate it somehow. I think I just figured out how to do it - I just need to think on it a little bit more - and see if there is an appropriate valve that would work for that position. I actually think the valve that Woods supplies with their BH80-X hydraulic grapple kit would work well - and if anybody knows what that valve is - I'd love to get the information.

If that Co. that bandit67 is dealing with doesn't come thru - I think this is coming together in my head how to make this complete system work. I've just got to do a little more research. I've got the number for the local Parker sales tech and I'm going to be making a phone call next week to see what the options are on hydraulic cylinders. I've got to do some measurements this weekend on the retract and extend dimensions on the thumb so I can give him something to work with. If I can track down that Woods valve - I think I'd have the full picture of the components needed for all of this.

 

[CDN Farm Boy]

Ok, you and I are both looking at the valve stack the same and there just isn't any room for an additional section but lots of room under the platform. How do you figure tying it in to the existing? Plumbing it in series seems like the only way but I thought that was bad for the valves

 

[CDN Farm Boy]

I'd guess that something as simple as this valve could be made to work:

https://www.surpluscenter.com/item.asp?item=9-7861&catname=hydraulic

 

[jim_wilson]

Ok, you and I are both looking at the valve stack the same and there just isn't any room for an additional section but lots of room under the platform. How do you figure tying it in to the existing? Plumbing it in series seems like the only way but I thought that was bad for the valves

Well the only way I can think of doing it is to use hoses - or maybe dedicated hard lines. Basically put the new valve inline with the existing stack somehow by just plumbing it in. I'm not completely familiar with hydraulics - why is that bad for the valves?

I'm doing some reading to try and get an education on hydraulics (more than my current basic understanding) - but from what I'm reading maybe the valve for the grapple needs to be plumbed in such a way that it's the first in the series - and it's setup for power beyond to feed the existing valve stack for the hoe?

 

[jim_wilson]

So - after doing a little reading - and from my cursory understanding of hydraulics - it looks like the way this additional valve for the grapple would need to be plumbed in would be like so (somebody please correct me if I'm wrong on this):

This is from my B3200 (may be different on other tractors)

- the existing BH77 valve stack has a pressure in from the power beyond coming from the FEL valve on the tractor. The "out" coming from the BH77 valve stack then feeds back to the 3 point hitch valve.

- from some of the stuff I just read - it sounds like putting an additional valve inline on that "out" line coming from the valve stack on the BH77 could be a bad idea because it might introduce back pressure into the BH77 valve stack. Which is actually warned against in the BH77 manual because it talks about NOT operating the 3pt while the BH77 is attached - because it can introduce backpressure and damage the valves in the hoe.

- So..... just adding another valve for the grapple on the OUT line would probably not work - maybe unless that added on valve had a dedicated tank return port and a pressure relief that was lower than that of the BH77 pressure relief. If I understand the way a valve with a pressure in, pressure out - and dedicated tank return port works - the pressure relief (if it goes off) - dumps directly to the tank. I think a setup like this would protect the BH77 valve stack. A setup like this would necessitate adding another line (tank return) - from the hoe. I'm actually thinking of modifying the hydraulics on my tractor for some added functionality and adding a connection for a dedicated tank return - but for the sake of this BH77 discussion I don't think that type of setup is likely the best way to go.

- so it seems as if that leave only one other option: the added grapple valve needs to be mounted "before" the BH77 valve stack and needs to have a power beyond function to supply pressure to the BH77 stack.

The problem is the diagrams of valves with power beyond that I have found - all still have a tank return line in the circuit. So it looks like maybe an added tank return line is going to be part of the picture no matter what.

If the added valve was part of the existing valve stack , from what I'm reading - none of this would be an issue because the integrated stack setups have internal passage designs that handle the fluid flow properly when the different valves are operating.

Adding a tank return line - if another valve is added in series - appears to me at the moment the way this has to be setup to avoid damage. I've got some plans to add one anyway like I said - but I don't know what you do if you don't add that return line.

 

[CDN Farm Boy]

I wonder if you could use a valve like the one I linked earlier mounted before the BH77 stack, use the PB port of the new valve to power the main stack as you suggest and T the 2 returns together?

No extra lines to mess with mounting/dismounting the hoe.

 

[CDN Farm Boy]

We need J_J and MtnViewRanch to chime in here.......I'm sure they'd have some valuable insight to the plumbing

 

[jim_wilson]

I wonder if you could use a valve like the one I linked earlier mounted before the BH77 stack, use the PB port of the new valve to power the main stack as you suggest and T the 2 returns together?

No extra lines to mess with mounting/dismounting the hoe.

Not sure if you can tee the return lines. My understanding is that the "Out" lines - are different from the tank return lines in that the "Out" lines may have higher pressure - whereas a dedicated tank return line is lower pressure. On the FEL valve on my B3200 for instance - the port that is marked as being the "return" line - is just plumbed back into the side of the resevoir with some low pressure rubber hose that is only held on with some simple hose clams.

Whereas - the "out" line coming from the backhoe is a full pressure line with crimped fittings - and it is feeding the 3pt valve on the tractor.

 

[CDN Farm Boy]

I know what you are saying, my B3300 is the same. However, I"m not sure there is a difference between "Out" and "Return". I think the "out" of the BH has full pressure fitting because it runs the 3pt. To me, that just means that when the new valve "out" is T'd into the existing "out", full pressure fittings need to be used.

I could be way off, it does seem a bit too simple.

 

[jim_wilson]

I know what you are saying, my B3300 is the same. However, I"m not sure there is a difference between "Out" and "Return". I think the "out" of the BH has full pressure fitting because it runs the 3pt. To me, that just means that when the new valve "out" is T'd into the existing "out", full pressure fittings need to be used.

I could be way off, it does seem a bit too simple.

There is a difference between a "return" and an "out" line. The terminology appears to be all over the place - but basically one is a pressurized return - and the other is a "drain" line which is not under pressure.

This document has some explanation on page 4:

http://www.greatplainsmfg.com/manuals/pdf/CDMR101209.pdf

The BH77 setup the way it comes from the factory - has a pressurized return and no case drain setup. My thought is that adding another valve in to feed the grapple - would necessitate adding a "drain" line - so that the added valve's pressure relief would have somewhere to dump. And the added valve needs a pressure relief because it cannot rely on the pressure relief in the factory valve stack - and also needs to pressure relief to avoid damage to the factory stack.

There's some explanations and diagrams here: Hydraulic valve power beyond or high pressure carry over

 

[jim_wilson]

I know what you are saying, my B3300 is the same. However, I"m not sure there is a difference between "Out" and "Return". I think the "out" of the BH has full pressure fitting because it runs the 3pt. To me, that just means that when the new valve "out" is T'd into the existing "out", full pressure fittings need to be used.

I could be way off, it does seem a bit too simple.

Here's another diagram that shows a similar setup to what would need to be done to add a grapple to the BH77:

http://www.princehyd.com/Portals/0/products/valves/SVInstS.pdf

see page 2 on the PDF

 

[CDN Farm Boy]

I think a case drain is only relevant to hyd motors, not valves and cylinders.

These are rather basic drawings, work ports have been omitted for clarity:



If I have to add an extra return line straight back to the tank for the new valve, I might as well just use longer hoses and plug them into one of my other sets of remotes. It would be much more simple (and cheaper) but I'd rather keep to only 2 hoses to have to mess with.

 

[jim_wilson]

I think a case drain is only relevant to hyd motors, not valves and cylinders.

These are rather basic drawings, work ports have been omitted for clarity:

View attachment 315345

If I have to add an extra return line straight back to the tank for the new valve, I might as well just use longer hoses and plug them into one of my other sets of remotes. It would be much more simple (and cheaper) but I'd rather keep to only 2 hoses to have to mess with.

If you look at the manual for the B3200 / B3300SU - there is a case drain coming from the FEL valve.

I believe a case drain is needed in some cases for valves controlling cylinders - so that the pressure relief can have somewhere to dump. In this case - where we would be adding another valve in series with the existing Kubota valve stack (and not adding a valve into that valve stack) - my current understanding is that a separate pressure relief is needed on this additional valve - to protect the Kubota valve stack - and that pressure relief will need somewhere to dump to.

I have the number of one of the sales engineers at the local hydraulics supply house - and I intend on calling him with some of these questions when I get a chance to see what he has to say - as well as see what kind of valve he would recommend using in this application.

 

[dfkrug]

I wonder if you could use a valve like the one I linked earlier mounted before the BH77 stack, use the PB port of the new valve to power the main stack as you suggest and T the 2 returns together?

No extra lines to mess with mounting/dismounting the hoe.

Yes, that is the only correct way to add a separate spool valve to the stack. If the BH77 had
a modular stack valve, then adding another stack section from the same maker would be ideal. In
that case the Return lines to the tank are all connected internally. No CUT backhoe attachment
that I have ever seen includes Power Beyond at the end of the stack; they are just 2-hose
setups that drain to the sump or thru the 3-pt valve. A separate valve before the stack would just use a
Tee for both return hoses as you say.

Of course, an electric spool valve can also be added, and it can be added to a work port instead
of the primary stack. That's what I did.

When I did my hydraulic thumb project, I found that the mechanical thumbs I had made before
that required complete re-designs rather than conversions. For one, the maximum forces needed
to be acommodated. That means the cylinder needed to be sized for stroke and diameter. Too
large a diameter, and excessive forces could require a relief valve. Pin sizes and rod sizes needed
to be at least 1 inch in my design, and pins needed to be fully greasable. Attachment brackets ended
up totally different from my mechanical thumbs.

 

[jim_wilson]

Yes, that is the only correct way to add a separate spool valve to the stack. If the BH77 had
a modular stack valve, then adding another stack section from the same maker would be ideal. In
that case the Return lines to the tank are all connected internally. No CUT backhoe attachment
that I have ever seen includes Power Beyond at the end of the stack; they are just 2-hose
setups that drain to the sump or thru the 3-pt valve. A separate valve before the stack would just use a
Tee for both return hoses as you say.

Of course, an electric spool valve can also be added, and it can be added to a work port instead
of the primary stack. That's what I did.

When I did my hydraulic thumb project, I found that the mechanical thumbs I had made before
that required complete re-designs rather than conversions. For one, the maximum forces needed
to be acommodated. That means the cylinder needed to be sized for stroke and diameter. Too
large a diameter, and excessive forces could require a relief valve. Pin sizes and rod sizes needed
to be at least 1 inch in my design, and pins needed to be fully greasable. Attachment brackets ended
up totally different from my mechanical thumbs.

I was under the impression that there is a difference between power beyond , "out" and " drain" . Power beyond is supplying full pressure. "Out" is or can be supplying either full pressure or something less - and "drain" would be at a much lower pressure.

The "drain" feed out of the FEL valve on my B3200 just uses a braided rubber hose (like you'd see on automotive cooling system) - with hose clamps. The "out" feed coming from the backhoe (and going back to the 3pt) - is a full high pressure hydraulic hose.

I suppose the way to really answer this question is to put a gauge on the backhoe "out" and see what kind of pressure it's running at.

From reading thru some of the earlier posts in this thread - as well as other posts here on TBN - my understanding is that any valve that is added for a hydraulic thumb should have a pressure relief of it's own anyway - and it should be set something lower than the backhoe control stack - to avoid damage to either the rod on the thumb cylinder - or to the backhoe stack itself.

 

[dfkrug]

I was under the impression that there is a difference between power beyond , "out" and " drain" . Power beyond is supplying full pressure. "Out" is or can be supplying either full pressure or something less - and "drain" would be at a much lower pressure.

The "drain" feed out of the FEL valve on my B3200 just uses a braided rubber hose (like you'd see on automotive cooling system) - with hose clamps. The "out" feed coming from the backhoe (and going back to the 3pt) - is a full high pressure hydraulic hose.

I suppose the way to really answer this question is to put a gauge on the backhoe "out" and see what kind of pressure it's running at.

From reading thru some of the earlier posts in this thread - as well as other posts here on TBN - my understanding is that any valve that is added for a hydraulic thumb should have a pressure relief of it's own anyway - and it should be set something lower than the backhoe control stack - to avoid damage to either the rod on the thumb cylinder - or to the backhoe stack itself.

Generally, an open-center (or tandem-center) valve will have an IN and an OUT, or an IN, OUT, and Power-Beyond. The
PB is the only pressurized out connection. The OUT is a low pressure return to tank, and is generally limited to 500psi max.

Hoe attachments often "cheat" the low pressure OUT thru the IN of the 3-pt valve because you can not use
the 3-point valve while the hoe is attached. If you did use the 3-pt valve and exceed 500 psi in that hookup, you would
blow out hoe valve(s).

If your hoe comes with 3 hoses, then you have PB. I have never seen a CUT hoe with 3 hoses. Not counting work
port hoses, of course.

My earlier point is that if you design a hyd thumb correctly, you do not need to have any additional relief valves.
Work port RVs on hoes are used as shock-reliefs in certain valves to limit forces in hi-momentum situations (usually
the boom).

 

[jim_wilson]

Not to poo-poo on anyones wishes to install one but realize I do cylinder rebuilding, and that includes damaged ones

Many bent rods (leading to scored barrels cuz the piston head cocked sideways internally) have been diagnosed back to the problem of induced load

Meaning a force pushing in to the thumb piston is greater than the hyd cylinder can survive from another source......the bucket curl.

The bucket curls larger displacement and leverage can put extreme forces while clamping down using the curl cyl, unless there is a relief setup to allow extra pressure to relax (ie:work port reliefs in the control valve) during curl cyl use

If the hyd thumb is properly installed, the thumb cyl should go back in when there is too much pressure.....not bend and self-destruct. Without the safety of the reliefs plumbed in to the base end of the thumb cyl, the pressure intensifies greater than the rated pressure of the cylinder (assuming the thumb cyl is smaller than the curl)

Ideally either work ports reliefs or sizing the cylinder large enough to match is my recommendation

I actually have no problem with hyd thumbs, just not on my machine, I don't make a living with it

So - in your opinion, what would be the "correct" way to set this up? Should a cylinder of equal bore size and rod diameter as the bucket curl cylinder be used for the grapple be used? - and then use a valve with work port reliefs built in - and set to a slightly lower pressure than the backhoe reliefs?

I'm doing the research on finding an appropriate cylinder. I took the measurements of the existing grapple last night so I think I know what will physically fit - I'm just trying to work out what size would actually be "correct"

 

[jim_wilson]

Generally, an open-center (or tandem-center) valve will have an IN and an OUT, or an IN, OUT, and Power-Beyond. The
PB is the only pressurized out connection. The OUT is a low pressure return to tank, and is generally limited to 500psi max.

Hoe attachments often "cheat" the low pressure OUT thru the IN of the 3-pt valve because you can not use
the 3-point valve while the hoe is attached. If you did use the 3-pt valve and exceed 500 psi in that hookup, you would
blow out hoe valve(s).

If your hoe comes with 3 hoses, then you have PB. I have never seen a CUT hoe with 3 hoses. Not counting work
port hoses, of course.

My earlier point is that if you design a hyd thumb correctly, you do not need to have any additional relief valves.
Work port RVs on hoes are used as shock-reliefs in certain valves to limit forces in hi-momentum situations (usually
the boom).

To your earlier point - my question is: What is "correctly"?

I can see how you could put a cylinder behind the thumb and not have to use a relief on the valve that controls that thumb - if that cylinder was large enough to hold pressure agains the force of the bucket curling against it. The valve stack for the hoe already has pressure relief - and when digging you will often run into situations where the bucket curl is stopped dead trying to dig an object out of the ground.

So is that the "correct" way to size out a cylinder - just make sure it's big enough to not be overcome by the force of the bucket curl cylinder?

 

[CDN Farm Boy]

So is that the "correct" way to size out a cylinder - just make sure it's big enough to not be overcome by the force of the bucket curl cylinder?

I'm guessing a whole bunch of complicated calculations depending on the geometry of the thumb & cyl & attaching points, also factoring in what angle the thumb/cyl is at while the bucket is pushing against it.

I'm planning on running a 2x8 cyl with 1.25" rod with 1" mounting pins. Mounting lengths of it fit quite well with the travel of the Kubota thumb

 

[wdchyd]

Jim,

the thumb work port relief can be set higher than the hoe relief....it's the induced load you need to worry about (from the larger cyl pushing against), not what the hoe PRV is set at

the work port relief can be set at the max of what that cyl can handle (it'll back off before it bends the rod)