I'm trying to figure out how to hookup a Showtime hydraulic thumb to my Kubota U17 mini excavator. There are two factory hydraulic lines running from the boom to a 2-way foot pedal on the floorboard. From there they run back to the control block. Unfortunately, there's no relief valve on the control block. However, there is a lever that switches the auxiliary circuit from one-way (for breaker) to two-way (for thumb). Nearest I can tell, what's left to figure out is how to install the relief valve (or valves) and the return line back to the tank. Do I need one relief valve for each auxiliary line, and if so, what type? Should I mount the valve(s) under the floor near the control block and then run a separate return line to the tank? Or should I put the valves on the boom and run the return line back to the tank from there? Any help will be greatly appreciated!
First, are you sure there is no port relief at the foot pedal valve? Sounds like you have pressure and return from the foot pedal valve back to the main valve stack. Second, you really only need a relief on the butt end line to the thumb cylinder, it's not likely anything will pull out on the thumb hard enough to create excess pressure. Could it happen? Sure. Will it happen? Not bloody likely. I would tee the relief in under the floor, tee it into the line on the output side of the foot pedal valve that goes out to the butt end of the thumb cylinder, run the outlet to a tank port or teed into any return line going to the return filter. Either of these should work well, they have through ports so you don't need a separate tee: http://www.surpluscenter.com/Hydrau...-16-GPM-1000-2500-PSI-RELIEF-VALVE-9-1556.axd http://www.surpluscenter.com/Hydrau...-16-GPM-1000-2500-PSI-RELIEF-VALVE-9-1556.axd
Nearest I can tell, there's no mention in the WSM of a separate adjustable relief valve for the service port circuit. Therefore, I'll rig the valve as you've indicated. Thanks for your help!
Use a cross port relief valve. No tank line needed 1/2 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE ITEM NUMBER: 9-4019-50-H Surpluss center also
A cross port relief won't work on a single cylinder, there isn't anywhere for the fluid to go.
NO! As Lumberjack stated, the rod end is smaller then the piston end, you can't put a quart of oil in a pint jar, something will give. The difference in effective areas also will create a situation called pressure intensification, when you push back on the thumb you can create pressures high enough to blow a hose or shatter the cylinder. I have seen it done. You must have a relief that goes to tank. They do make twin relief blocks with a common tank line though, those will work.
Look at the schematics. Any excess flow when the valve is deadheaded in one direction or the other goes to the work port connected to tank.
Is this the schematic for the aux valve on this machine?
No generic cross port relief valves
First one is generic cross port relief. The second one just shows two single relief valves plumbed to each work port and the tank ports plumbed before the directional valve. With the first valve plumbed on the work ports only you could get intensification if you used the thumb like a pry bar. In the secon pic if you used the thumb as a pry bar and the relief poped due to excess pressure the flow would go directly to tanl and the cylinder would retract with no damage.
Okay, I think I'm following you now. Yes, the drawing on the right is the correct setup, and technically you also need makeup checks to backfill the cylinder when the reliefs are opened up. Just on the rod end really, but typically both work ports.
When the machine's valve is in neutral, both work ports are blocked, neither is to tank. That means with a crossover relief, your relief oil is sent to the rod end, which means intensification happens.
If I'm reading you properly, you're saying, when the thumb-control valve is in neutral, and the bucket comes up against the thumb with enough pressure to exceed the crossover relief pressure, the oil has nowhere to flow, so it intensifies pressure within the line instead of allowing oil to flow back to the tank; thus, retracting the thumb? And this would could bend the thumb cylinder rod or burst the line?
In general, yes. It wouldn't retract the cylinder appreciably, but the pressure intensification would happen. I don't know if the bucket cylinder would have enough force to cause a mechanical failure or not, but that's more academic than anything.
Not having any relief can cause high induced pressures and possible rod, etc. failure, using crossport reliefs with a double acting cylinder can cause extreme high pressures. It's the difference between the piston area and the rod end piston minus the rod area, once the force acting on the back side of the piston produces enough pressure to open the relief up to the rod end with nowhere else for oil to go the pressure has to balance, and since the effective area of the piston on the rod end is reduced by the area of the rod, pressure keeps rising. Depending on the rod size, the bigger the rod the higher the intensification, you may see two or three times higher pressure than what would normally occur at the butt end if the relief simply weren't there at all. I went to work for an outfit years ago, had a crossport on a thumb cylinder on a Deere 690B. I politely informed them it was wrong and dangerous. They responded that though they had experienced lots of trouble with hoses, since they had installed CAT high pressure lines, all was well and to leave it alone. Several months later, they had the thumb cylinder grenade from the rod end port all the way to the butt end weld, luckily it was winter because it covered the cab in hot oil, the operator had the window closed up, so he only had to change underwear. Once again I politely informed them what the problem was, but again overruled, they merely had the cylinder retubed with a heavier wall tube. They finally split the crossport relief block flat in two pieces. I replaced it without asking with the proper valve, lol.
I'd be very surprised if a <2 ton mini requires running a return line back to the tank for a relief valve. I've never heard of anyone having to do that for a machine that size. I would investigate how the factory pressure relief functions on that circuit before spending any money on possibly redundant parts.
According to the WSM (which I could be mistakenly interpreting), the service port lines are relieved by piggybacking on other system relief valves of about 3400 lbs. The U17 bucket curls at 3400 lbs, which is greater than the max rating of the thumb cylinder. I've confirmed when the SP foot control is in the middle position, there is no return to the tank. So it seems to me, in this position, the bucket force could bend the thumb cylinder. This brings me to the following question. If there is no return to the tank when the SP foot pedal is in the middle position, and I only install the relief valve on the butt end of the thumb, are both lines protected when the bucket curls against them?
Here's a link to a youtube video of a machine smaller than mine where the dealer installed a thumb and needed to use a crossover relief valve: https://www.youtube.com/watch?v=w7mmUejH1tk I called this dealer and inquired about installing a thumb for me, and he suggested a werk brau thumb and said a crossover relief valve was necessary on the U17 due to not having a dedicated relief valve on the service ports. However, as stated in this thread, a crossover relief valve is not suitable for this application, which is one of the reasons why I want to install a thumb myself.
The rod end of the cylinder will only build pressure if force is applied in some manner to pull the thumb cylinder out which should be near impossible? The butt end is pressurized when you curl the bucket back against it or you push out with the stick and catch the thumb on something. There are crossport relief blocks with both reliefs vented to a tank port, but they're rare so we have to say the typical crossover or cushion valve doesn't work with a cylinder. The thumb on that machine in the video seems to be working the way it's supposed to. Here's a link to a SUN manifold that has two reliefs vented to a tank port, with makeup checks to backfill the cylinder so it doesn't cause a vacuum and try to suck air someplace: http://www.sunhydraulics.com/model/YRDK
That makes sense. Thanks!
I concur that tis SUN valve assembly would work just fine.
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 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.
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.
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
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..
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.
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
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.
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.
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.
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
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.
Could it be some air hasn't worked its way out, or is finding its way in somehow?
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?
^^ 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!!!
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
Put a gauge on both thumb lines, if you clamp down on something, let the thumb valve go to neutral and then see a pressure rise on the ROD end of the thumb cylinder, your problem is piston seals bypassing.
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.