I concur that tis SUN valve assembly would work just fine.
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Kubota U17 Thumb Install
- Thread starter Jonness
- Start date
Jonness
Member
I talked to four pressure-relief-valve installers today about installing a pressure relief valve on the Kubota U17.
Installer 1 said I didn't need a valve because the thumb cylinder was rated at 3000 lbs. When I told him the bucket curl was rated at 3417 lbs, he wasn't sure if I needed the valve or not.
Installer 2 was the Kubota dealer responsible for installing the thumb in the link I linked above where the thumb appears to be working properly. He said he would install a crossflow valve with a return line to the tank.
Installer 3 said there are two ways to install it. The best is using the crossflow valve with a return to the tank. The other way is a single relief valve on the butt-end of the thumb. He said the problem with the single relief valve method is, when the bucket pushes the thumb back, and then you re-extend the bucket, the thumb will fall back to where it originally was. He said this occurs because the pressure is not equalized in the rod end of the cylinder.
Installer 4 said a relief valve on the butt-end with a return back to the tank was enough. When I asked him about the thumb falling back after having been pushed by the bucket, he back-pedaled a bit and said he wasn't sure if the Kubota U17 was set up in a manner to allow pressure equalization or not. If it was, he said it would prevent the problem. If not, then the bucket would fall back.
I thought I would report my findings here, because nobody brought up the thumb falling back issue that can occur with the single relief valve. Does anyone have any more information about this problem? I'm a bit confused by the different responses I got by the different installers.
Thanks
Installer 1 said I didn't need a valve because the thumb cylinder was rated at 3000 lbs. When I told him the bucket curl was rated at 3417 lbs, he wasn't sure if I needed the valve or not.
Installer 2 was the Kubota dealer responsible for installing the thumb in the link I linked above where the thumb appears to be working properly. He said he would install a crossflow valve with a return line to the tank.
Installer 3 said there are two ways to install it. The best is using the crossflow valve with a return to the tank. The other way is a single relief valve on the butt-end of the thumb. He said the problem with the single relief valve method is, when the bucket pushes the thumb back, and then you re-extend the bucket, the thumb will fall back to where it originally was. He said this occurs because the pressure is not equalized in the rod end of the cylinder.
Installer 4 said a relief valve on the butt-end with a return back to the tank was enough. When I asked him about the thumb falling back after having been pushed by the bucket, he back-pedaled a bit and said he wasn't sure if the Kubota U17 was set up in a manner to allow pressure equalization or not. If it was, he said it would prevent the problem. If not, then the bucket would fall back.
I thought I would report my findings here, because nobody brought up the thumb falling back issue that can occur with the single relief valve. Does anyone have any more information about this problem? I'm a bit confused by the different responses I got by the different installers.
Thanks
Jonness
Member
Installer 3 (a hydraulic shop) estimated between $500 and $600 dollars to install the crossflow valve with return to tank. Installer 2 (Kubota dealer) quoted between 6 and 7 hours labor at $100/hr. plus parts.
The crossflow valve linked above is $260. I'm thinking perhaps another $100 in hoses and fittings. So the hydraulic shop would install it for a max of $240 in labor, which seems pretty darn reasonable compared to the Kubota shop.
The crossflow valve linked above is $260. I'm thinking perhaps another $100 in hoses and fittings. So the hydraulic shop would install it for a max of $240 in labor, which seems pretty darn reasonable compared to the Kubota shop.
With the single relief valve, IF the machine's control valve has makeup checks when the relief opens, the makeup check on the opposite port will open and allow oil to fill the rod end. If there are no makeup checks what typically happens is the rod end of the cylinder will suck air around the rod gland seals so you have to push that out before it will operate smoothly again. You can always install a makeup check teed into the rod end line and the tank line. It's a matter of how thrifty people want to be, or how much work they want to do.
Jonness
Member
lantraxco: Interestingly, I grew up in Coos Bay and left in 1992. I still have friends there and visit sometimes.
At any rate, I decided to splurge and go for the between $500 and $600 dual crossflow relief valve quoted by a hydraulic shop in Tacoma, WA. Unfortunately, when I picked up the completed excavator, I was billed for $922. OK, so I'm walking a little bow-legged, but at least I have my thumb hooked up.
The installer set the pressure at 1850 psi citing it would put minimal wear on the thumb pin, cylinder rod, etc. Unfortunately, it doesn't have enough pinch pressure to lift the 2-man rocks I'm using to build my retaining wall. The thumb cylinder is rated at 3000 psi, the bucket cylinder is relieved at 3400 psi, and the thumb pin is made from 4140 steel. What do you recommend setting the relief pressure of the thumb cylinder at in order to get maximum pinch pressure without risking damage to the thumb pin and cylinder rod?
Thanks
At any rate, I decided to splurge and go for the between $500 and $600 dual crossflow relief valve quoted by a hydraulic shop in Tacoma, WA. Unfortunately, when I picked up the completed excavator, I was billed for $922. OK, so I'm walking a little bow-legged, but at least I have my thumb hooked up.
The installer set the pressure at 1850 psi citing it would put minimal wear on the thumb pin, cylinder rod, etc. Unfortunately, it doesn't have enough pinch pressure to lift the 2-man rocks I'm using to build my retaining wall. The thumb cylinder is rated at 3000 psi, the bucket cylinder is relieved at 3400 psi, and the thumb pin is made from 4140 steel. What do you recommend setting the relief pressure of the thumb cylinder at in order to get maximum pinch pressure without risking damage to the thumb pin and cylinder rod?
Thanks
Last edited:
movindirt
Senior Member
I've only ran 2 machines that had a thumb relief valve, and they were rentals, all of my own machines have aftermarket thumbs on them with no reliefs, they will actually push the bucket out if you close the thumb against them, that said, in a few thousand hours of operation we've not had one problem with them or broken a thumb cylinder, or any cylinders for that matter. :beatsme I didn't want them to be too weak to keep a good hold on whatever we are grabbing with them, and how they are now they will grab more than the machine can lift. And we've not broken any pins yet..
Jonness
Member
movindirt:
Yeah, I'm regretting my (expensive) decision to put reliefs on the thumb.
What doesn't make sense to me is, why is the thumb cylinder slightly retracting when set at 1850 psi? Given the force (Cylinder Effective Area * Hydraulic Pressure) of my 2.5" bore cylinder, it seems like picking up a 1000 lb rock should not create nearly enough force to retract the thumb enough for the rock to slip.
My cylinder has a 2.5" bore, so Pi(r)^2 * 1850 = 4.91 * 1850 = 9,081 lbs of pinch force between the thumb and the bucket. If I were to increase the hydraulic pressure by 400 psi (bringing it to 75% of max rated psi), it would raise the force of the pinch by about another 2000 lbs (about 20% more pinching power). The USA Attachments website says not to adjust the psi above 75% of rated value, so I'm guessing this is considered the "cover your ass" maximum save pressure and seems like a good place to start my experiments.
When I picked up the excavator, I asked them to show me how to adjust the hydraulic pressure in case I need to increase it. The reply was, "you don't do anything; we do." When I asked them to specifically point out every part and alteration that was installed, I got the run around. But the hydraulics seem understandable enough. I'll post some pictures and see if anyone can explain how the circuit works.
Yeah, I'm regretting my (expensive) decision to put reliefs on the thumb.
What doesn't make sense to me is, why is the thumb cylinder slightly retracting when set at 1850 psi? Given the force (Cylinder Effective Area * Hydraulic Pressure) of my 2.5" bore cylinder, it seems like picking up a 1000 lb rock should not create nearly enough force to retract the thumb enough for the rock to slip.
My cylinder has a 2.5" bore, so Pi(r)^2 * 1850 = 4.91 * 1850 = 9,081 lbs of pinch force between the thumb and the bucket. If I were to increase the hydraulic pressure by 400 psi (bringing it to 75% of max rated psi), it would raise the force of the pinch by about another 2000 lbs (about 20% more pinching power). The USA Attachments website says not to adjust the psi above 75% of rated value, so I'm guessing this is considered the "cover your ass" maximum save pressure and seems like a good place to start my experiments.
When I picked up the excavator, I asked them to show me how to adjust the hydraulic pressure in case I need to increase it. The reply was, "you don't do anything; we do." When I asked them to specifically point out every part and alteration that was installed, I got the run around. But the hydraulics seem understandable enough. I'll post some pictures and see if anyone can explain how the circuit works.
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Jonness
Member
Reflecting back, my posts are seeming way too grumpy here. Just to be clear, the installer said they would make the adjustment for free if I bring the machine to them. The owner even offered to come out and make the adjustment at my house (seemingly for free?). Also, the price I paid (that was above the original quote) included two short lines and quick couplers that were not on the original estimate (they asked if I wanted them before installing them).
That said, I prefer to make the adjustment myself so that I can fine tune the pressure (now and in the future) and learn something in the process that can increase my limited understanding of hydraulic work.
Here is a photo of the installed components:
Apparently, there's a crossflow relief valve with another relief valve plumbed into it that returns fluid to the tank. So there are three adjustments that can be made. Pressure on Auxiliary port 1, pressure on auxiliary port 2, and pressure at which the tank flow opens and keeps the crossflow valve from exploding. I'm sure others understand this system way better than I do. I'm thinking Aux 1 is set at a pressure for the thumb close (currently 1850 psi). Aux 2 is set at a pressure for the thumb open that's less than Aux 1. And if pressure builds too high between Aux 1 and Aux 2, the tank relief opens and keeps the valve from exploding. So it's probably set somewhere close to Aux 1.
If my thinking is correct, and I want to set the hydraulic pressure on the thumb close cylinder to 2250 lbs, what should I set the other adjustments to? Or should I measure the current pressures and keep the same ratio between the lines?
Thanks
That said, I prefer to make the adjustment myself so that I can fine tune the pressure (now and in the future) and learn something in the process that can increase my limited understanding of hydraulic work.
Here is a photo of the installed components:
Apparently, there's a crossflow relief valve with another relief valve plumbed into it that returns fluid to the tank. So there are three adjustments that can be made. Pressure on Auxiliary port 1, pressure on auxiliary port 2, and pressure at which the tank flow opens and keeps the crossflow valve from exploding. I'm sure others understand this system way better than I do. I'm thinking Aux 1 is set at a pressure for the thumb close (currently 1850 psi). Aux 2 is set at a pressure for the thumb open that's less than Aux 1. And if pressure builds too high between Aux 1 and Aux 2, the tank relief opens and keeps the valve from exploding. So it's probably set somewhere close to Aux 1.
If my thinking is correct, and I want to set the hydraulic pressure on the thumb close cylinder to 2250 lbs, what should I set the other adjustments to? Or should I measure the current pressures and keep the same ratio between the lines?
Thanks
Jonness
Member
I've been experimenting with the thumb. At this point, I'm not sure the hydraulic pressure is too low. Maybe it's that the rocks are too large for the design of the pin-mounted thumb on such a small excavator. It's possible having a stick-mounted thumb would provide a wider clamp. What are your guys' opinions of whether this excavator should be able to pick up these rocks? The excavator easily picks up the rocks when chained, but I'm having problems getting the thumb to grip and lift them.
Ronsii
Senior Member
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I find that I also always want to grab things that are to big for the arrangement of the thumb... you could add some thumb tooth extensions to give a bit more length towards the bucket teeth at the end of the thumb... but this can get in the way when digging in certain situations.
tawilson1152
Member
I got a U25 with a thumb in May and spent a lot of the summer tossing rocks and logs around and I seemed to be limited more by the lifting capacity of the machine than the gripping capacity of the thumb.
Jonness
Member
It seems to me like when I keep the thumb pedal pressed (opening the relief valve) the thumb pressure on the rock is maxed out, but when I first let off the pedal, the thumb backs off just slightly. It's strong enough to still clamp the rock, but not enough to lift it unless I have a really good angle on it. When I look at the following video (at 4 seconds in), it seems like the thumb clamps on the rock and never backs off after letting off the thumb pedal. I'm not sure if that's because the operator is not clamping until the relief valve opens, or whether allowing the relief valve to open should have no bearing on the final clamp pressure between the bucket and thumb.
https://www.youtube.com/watch?v=S6_vAKeVF7s
https://www.youtube.com/watch?v=S6_vAKeVF7s
Ronsii
Senior Member
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Depends on the vales you have but usually when you let off a control it stays right where you stop it... minus any slop in the pins and such. So when I grab rocks and what not I usually bring the thumb in and stop it before it makes contact then use the bucket to apply the final clamping force... this give me control of just how much pressure I exert on the items I am picking up whether it be rocks that like to break or thin wall pipe.
tawilson1152
Member
Could it be some air hasn't worked its way out, or is finding its way in somehow?
Jonness
Member
Thanks for your suggestions.
I ordered a pressure gauge, fittings, hoses, and quick disconnects that I can temporarily plumb into the thumb line in order to test the pressure as it clamps the rock. Will I need to bleed the air pressure in these lines when first hooking them up in order to get an accurate reading on the gauge?
I ordered a pressure gauge, fittings, hoses, and quick disconnects that I can temporarily plumb into the thumb line in order to test the pressure as it clamps the rock. Will I need to bleed the air pressure in these lines when first hooking them up in order to get an accurate reading on the gauge?
Ronsii
Senior Member
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- Western Washington
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^^ Air should work it's way out with a few minutes of use, Be ** very careful ** bleeding air out with loosening lines as the spraying fluid can easily pierce the skin on your body parts resulting in blood poisoning!!!
Jonness
Member
The owner of the hydraulic company that installed the relief valve came to my house (about an hour each way and didn't charge me). He gave me a bunch of excavator operating tips and taught me about the different pressures that occur at different bucket and thumb positions. This was away above my expectations.
We discovered the hydraulic pressure in the thumb line is initially fine, but it leaks off pretty fast after the thumb pedal is put in the neutral position. He offered to isolate and fix the problem if I bring the excavator to his shop. Before I do, I'm going to test the pressure with new thumb cylinder taken out of the circuit. That way, if it turns out to be the problem, I can deal directly with the thumb builder without further bothering the hydraulic shop owner. I can also test the pressure with the relief valve out of the circuit just to ensure the problem is not in my control block.
Here's a video that shows the pressure bleeding down until the rock is dropped. This explains why I was having such a difficult time trying to pick up and move the rocks around.
https://www.youtube.com/watch?v=xGeZ1wrA9i0&feature=youtu.be
We discovered the hydraulic pressure in the thumb line is initially fine, but it leaks off pretty fast after the thumb pedal is put in the neutral position. He offered to isolate and fix the problem if I bring the excavator to his shop. Before I do, I'm going to test the pressure with new thumb cylinder taken out of the circuit. That way, if it turns out to be the problem, I can deal directly with the thumb builder without further bothering the hydraulic shop owner. I can also test the pressure with the relief valve out of the circuit just to ensure the problem is not in my control block.
Here's a video that shows the pressure bleeding down until the rock is dropped. This explains why I was having such a difficult time trying to pick up and move the rocks around.
https://www.youtube.com/watch?v=xGeZ1wrA9i0&feature=youtu.be
TimT
Well-Known Member
I have a question... "I posted about my thumbs installed on the two E27B New Holland's I owned/own on this page. because of this post. Check it out" Is it because that this Kubota does not have auxillary valves installed or because it has no adjustment???
I just lowered the relief pressure on m older machine using the adjustment screw on the Auxiliary valve spool. On the second machine with the variable flow valve, I just left it alone at 3335 PSI "that is the master relief setting on the machine." With the "toggle" switch on the new machine I have control over the speed of the thumb. On the old one it was either opening or closing full flow. I had several guys tell me that with a good thumb matched to the machine "small mini'" you should never have to worry about it wrecking the thumb it self or the machine. So I just left the pressures alone on the new one. Have not had an issue at all with it. The thumb will push the bucket back if I let it. But I don't see how it could hurt the machine as long as I don't make a habit of it. Any ideas? Lowering the pressures on my old machine relay made the thumb less useful. The new one will pinch nicely.
I just lowered the relief pressure on m older machine using the adjustment screw on the Auxiliary valve spool. On the second machine with the variable flow valve, I just left it alone at 3335 PSI "that is the master relief setting on the machine." With the "toggle" switch on the new machine I have control over the speed of the thumb. On the old one it was either opening or closing full flow. I had several guys tell me that with a good thumb matched to the machine "small mini'" you should never have to worry about it wrecking the thumb it self or the machine. So I just left the pressures alone on the new one. Have not had an issue at all with it. The thumb will push the bucket back if I let it. But I don't see how it could hurt the machine as long as I don't make a habit of it. Any ideas? Lowering the pressures on my old machine relay made the thumb less useful. The new one will pinch nicely.