adding hydraulic thumb kubota B21

[joea99]

As I finally close in on finishing the Top and Tilt add, I think I want to convert my mechanical thumb to hydraulic. I found several threads here on exactly that, so I got the gist of it.

I ordered a single spool open center mono block valve, with power beyond, from Summit, thinking to use that. After some thought, planned on mounting it on backhoe, "in line" with the existing BH lines (before or after seems to be just a matter of my convenience), but, since this valve requires a Tank line, I paused realizing the BH itself has no Tank line. That seems to be done in conjunction with the 3pt hitch "maze o' stuff" where I see what appear to be two Tank lines. I guess to do with selector position. Not great at reading hydraulic schematics.

While can run a Tank line (gotta add one anyway for the TNT) and just use two smaller Quick Couplers for when I need to dismount it, it "would be nice" to find a valve that does not require a direct tank line.

Is there such a thing? I was gonna refresh myself on open center vs closed center but am having too much fun playing with fire in the form of plasma cutting and mig welding the valve mount. I'll hold off on the bulkhead until I figure out if I want to allow for a future coupler, based on what I hear back.

I even hear of people adding a section to the BH modular (?) valve, but that seems WAY beyond my skills and budget.

 

[joea99]

Does anyone know if there is such a spool valve, that does not need/have a return to tank and would work? I've no idea what it would be called.

 

[rScotty]

A hydraulic thumb requires fluic flowing from the control valve in order to open or to close.
So no matter which way the thumb is moving, one side of the hydraulic cylinder moving that thumb is getting fed pressurized fluid from the control valve to fill an increasing volume in one side of the cylinder, while the other side of that cylinder is having its volume reduced. The fluid in that other side of the cylinder getting smaller has to go somewhere - and it goes back to the control valve and from there it is returned to the tank. There isn't any other option.

OK. I take that back. Technically there is an option called a "regenerative" system that add a small portion of that return fluid back to the pressurized side of the cylinder, but you don't want to go there in a simple system..... and anyway even regenerative systems are not 100%; they still require a return to the tank.

However, the good news is that the return to the tank doesn't have to be a bundle of discrete lines. Several smaller return lines can "Y" into a single larger return line.

I'm a little bit concerned on just where in the circuit you are gong to put this valve in the first place....
My own preference for simplicity would be to put a manual selector valve somewhere in your T&T circuit. Turn the lever one way for T&T flow and the other way for Thumb flow.

rScotty

 

[joea99]

A hydraulic thumb requires fluic flowing from the control valve in order to open or to close.
So no matter which way the thumb is moving, one side of the hydraulic cylinder moving that thumb is getting fed pressurized fluid from the control valve to fill an increasing volume in one side of the cylinder, while the other side of that cylinder is having its volume reduced. The fluid in that other side of the cylinder getting smaller has to go somewhere - and it goes back to the control valve and from there it is returned to the tank. There isn't any other option.

OK. I take that back. Technically there is an option called a "regenerative" system that add a small portion of that return fluid back to the pressurized side of the cylinder, but you don't want to go there in a simple system..... and anyway even regenerative systems are not 100%; they still require a return to the tank.

However, the good news is that the return to the tank doesn't have to be a bundle of discrete lines. Several smaller return lines can "Y" into a single larger return line.

I'm a little bit concerned on just where in the circuit you are gong to put this valve in the first place....
My own preference for simplicity would be to put a manual selector valve somewhere in your T&T circuit. Turn the lever one way for T&T flow and the other way for Thumb flow.

rScotty

I've had a few different ideas on this. Right now, the idea is that I will never use the thumb and T&T at the same time. I may not be describing this properly, but, when the BH is disconnected, it's essentially bypassed by connecting the tractor supply that goes to the BH, into the "return" which feeds the 3PT circuits. So, I was simply going to add the T&T stuff right there. That is, a 2 spool valve and two appropriate quick connects and plug the tractor supply into that and have the PB from the valve plug into the QC going on to the 3PT circuits. And of course a third line back to tank, plus the lines to the T&T cylinders.

When putting the BH into use, I would just connect it normally, put the dust caps on the T&T QC's and tuck them out of the way. Obviously having removed the 3PT implement and hoses, etc.

I was thinking to put a single spool valve on the BH, with a PB adapter in it and plumb in into the supply or outlet of the existing BH controls as convenient. I guess I have to add another set of QC's and hoses for the tank line and T that into some convenient place, maybe the same place as the T&T tank return. I'd like to avoid adding the tank return line, but that seems impossible from what I am learning.

Make sense or am I lost?

 

[rScotty]

I've had a few different ideas on this. Right now, the idea is that I will never use the thumb and T&T at the same time. I may not be describing this properly, but, when the BH is disconnected, it's essentially bypassed by connecting the tractor supply that goes to the BH, into the "return" which feeds the 3PT circuits. So, I was simply going to add the T&T stuff right there. That is, a 2 spool valve and two appropriate quick connects and plug the tractor supply into that and have the PB from the valve plug into the QC going on to the 3PT circuits. And of course a third line back to tank, plus the lines to the T&T cylinders.

When putting the BH into use, I would just connect it normally, put the dust caps on the T&T QC's and tuck them out of the way. Obviously having removed the 3PT implement and hoses, etc.

I was thinking to put a single spool valve on the BH, with a PB adapter in it and plumb in into the supply or outlet of the existing BH controls as convenient. I guess I have to add another set of QC's and hoses for the tank line and T that into some convenient place, maybe the same place as the T&T tank return. I'd like to avoid adding the tank return line, but that seems impossible from what I am learning.

Make sense or am I lost?

No, I think that all makes sense. You seem to have thought it out well. It sounds like you already have hydraulic power & return to the rear and that makes the TnT or Backhoe easy. One is connected and the other removed and capped.

For those systems all that remains is to decide on some sort of pressure release gadget for the quick connectors - there are several on the market. Or you can use the old rag and soft hammer method.

Likewise adding the thumb to an existing BH line is just a matter of deciding which line to use. Then you can either interrupt that line with your control and use PB to continue the original flow. Or you can use a manual (or solenoid driven) diverter valve to chose one or the other.

rScotty

 

[joea99]

The "tank" line continues to cause me confusion. It seems the valves I have, for this and a Top&Tilt, from Summit Hydraulics, and most others from what I can see, have a Tank line even with the PB adapter installed. Still, reading some threads here and elsewhere seem to say this may not be the case. While I don't doubt Summit, it still leaves me confused.

In any event, I will go ahead and plan on installing a return to Tank line, hoping to find a convenient place to T in, but have questions. I've been told there is very little pressure on that line and it does not have to work line a plumbing drain, that is, working by gravity. So there must be "some" pressure, surely?

Also, no mention of what flow rate, hence what size line or hose should be used. I don't want to overspend or overbuild, but, since I have no clue, gotta ask.

Thanks.

 

[rScotty]

When a spool valve is activated to move the piston in a cylinder, the liquid on the other side of the piston is forced out and has to go somewhere.... so the valve simultaneously opens a return passage that allows that displaced fluid to go into the return line and from there it goes to a hydraulic sump tank - which is usually the hydro/transmission sump.

Yes, I agree with that. Gravity isn't quite enough by itself, and without a small amount of pressure there wouldn't be enough flow. But that sump is vented, so the return flow mainly has to overcome the resistance of its own movement through the return line. In this it is aided by the movement of the cylinder piston. The sump being vented, there is no high pressure possible in the return line. So the return does have flow but not much pressure. The return line pressure is farther minimized by the return line being larger diameter than the pressure lines. Approximently double the diameter is common and should be sufficient. . Also a "Y" is used when return lines are joined instead of a "T". It helps that having little pressure, the return line can simply be attached with hose clamps.

LATER EDIT added: Re: flow rate. The return line has to handle the full flow of the hydraulic system when the spool valve is not actuated. For a clue about sizing, think about your garden hose spigot for watering the lawn. Most household spigotsoperate in the 5 to 10 gallons/minute range at 40 to 60 psi. Measure your outside spigot into a 5 gallon bucket to develop a mental picture for a reference. Small tractors operating without restriction are in that same gallon/minute flow range. Garden hoses are typically 5/8 to 3/4" I.D. The return line on your tractor is much shorter than the garden hose, so the fluid friction due to length is proportionately less.

Does any of this help?

rScotty

 

[joea99]

When a spool valve is activated to move the piston in a cylinder, the liquid on the other side of the piston is forced out and has to go somewhere.... so the valve simultaneously opens a return passage that allows that displaced fluid to go into the return line and from there it goes to a hydraulic sump tank - which is usually the hydro/transmission sump.

Yes, I agree with that. Gravity isn't enough, and without a small amount of pressure there wouldn't be enough flow. But that sump is vented, so the return flow mainly has to overcome the resistance of its movement through the return line. In this it is aided by the movement of the cylinder piston. The sump being vented, there is no high pressure possible in the return line. So the return does have flow but not much pressure. The return line pressure is farther minimized by the return line being larger diameter than the pressure lines. Approximently double the diameter is common and should be sufficient. . Also a "Y" is used when return lines are joined instead of a "T". It helps that having little pressure, the return line can simply be attached with hose clamps.

Does any of this help?

rScotty

Yeah, I think so. Given what you said and taking another look at the spool valve "schematic" it makes sense to me now. Also now assured the over pressure relief goes to tank (where else could it?) so my thought of using small lines is not the way to go.

Thanks for helping clear it up.

joe a

 

[rScotty]

Yeah, I think so. Given what you said and taking another look at the spool valve "schematic" it makes sense to me now. Also now assured the over pressure relief goes to tank (where else could it?) so my thought of using small lines is not the way to go.

Thanks for helping clear it up.

joe a

Joe, I just added an edit on flow rate to my last message.
rScotty

 

[joea99]

LATER EDIT added: Re: flow rate. The return line has to handle the full flow of the hydraulic system when the spool valve is not actuated. For a clue about sizing, think about your garden hose spigot for watering the lawn. Most household spigotsoperate in the 5 to 10 gallons/minute range at 40 to 60 psi. Measure your outside spigot into a 5 gallon bucket to develop a mental picture for a reference. Small tractors operating without restriction are in that same gallon/minute flow range. Garden hoses are typically 5/8 to 3/4" I.D. The return line on your tractor is much shorter than the garden hose, so the fluid friction due to length is proportionately less.

Does any of this help?

rScotty

Thanks. I can see that being the case when the valve is the last one "in line", but these will each have a PB port in play so when not actuated most, hopefully all, of the flow should be directed to the next valve, right?

Regardless, if I just size them the same as existing tank lines it should be fine. I can see it would be foolish or false economy anyway, to size smaller.

joe a.

EDIT - Now that I think, such as I do, maybe the valve over pressure relief needs to "free dump" via the Tank port and that's the bottom line?