The local hydraulic expert in response to my question about a weak thumb on an excavator said that I could remove the pressure relief valve. Well I did so, had the ram extended, overextended, was bleeding and pushed thumb back with the bucket and bent the cylinder rod. So if I had the advice from the expert and I told him I really didn't know hydraulics (Now I know the pressure relief sends oil back to the tank in case of pressure situations) what is his responsibility for repair?
Main relief Or circuit relief?
Ouch. Morally it's my opinion he owes you the repair. Legally may be another subject.
Um, is he on retainer? do you have a service contract with him? how much did you pay for the fine advice? I'm thinking the answer is no, nada, zero... Only advice I can give is don't retract that cylinder, take it off and fix it before it ruins the rest of the cylinder. It MIGHT be straightenable. But don't ask me to pay for it if you drop it on your toe cause you don't know how gravity works
Would have to side with Delmer on this one. He may have made a mistake saying what he did but also might have thought he was telling you how to test something to isolate a problem, not how to set it up to actually be used. Kind of like if you had asked someone how to get a small riding lawn mower to start and the told you to disconnect the safety switches. You do that and it starts up just fine. Then you went ahead and let someone borrow it to mow their lawn and they end up getting hurt when it takes off in gear and runs over their foot. You then expect the guy to pay the hospital bills for the other guys injuries.
I fail to see how removing a relief valve can, presumably, dead head a cylinder. Further I can't see how you can bend the rod by pushing it in unless there's something strange about the geometry of the setup. I would be curious to see a bigger picture of the machine.
None Zero zip no responsibility at all Morally or otherwise
I'd like to see a picture of the whole thumb before I comment any further
From a moral standpoint the hydro thumb arrangement on the hoe wasn't built tough enough for the application Somebody failed in the design or mounting of the thumb , like mentioned bad geometry or simply not enough metal where it needs to be ( bigger cylinder) to match curling cylinder power from the bucket . Good news is the cylinder can be repaired .
When a thumb is extended all the way out and you curl the bucket back in against it i can see them bending like this. The thumb cylinder is parallel with the stick and the bucket when it curls is pushing perpendicular to the stick so I can see this happening no problem when the reliefs are removed. Thumb cylinder rods are long and usually not a big diameter
Relief valves are installed for a reason, ANYBODY that tells you to remove a relief valve from a circuit, if that's what actually transpired, is most likely criminally negligent in doing so. Telling you to adjust up or replace with a higher pressure relief may be acceptable.
It all depends on what's meant by "removing a relief valve". I had in mind a cartridge valve unscrewed from a valve block in which case the cylinder wouldn't work at all. Could it have been an independent in line valve that's been removed? I've never seen an excavator without cartridge line relief valves on the auxiliary circuit.
Thumb cylinders are generally not the strongest thing in the world and that's why they have relief valves in the circuit so that when the bucket curls round it doesn't bend the thumb cylinder rod or worse still break the thumb cylinder mount clean off the stick. If the OP removed the pressure relief function to the thumb cylinder he should not be surprised if the cylinder rod turns into a banana IMHO.
While he's not legally responsible I would think he should repair it at a heavy discount.
Did the one you received the advice from install the thumb?
The thing is there a many "Experts" around some truly know there stuff some we just assume must know the answer to every question because they work at the hydraulic repair shop Sometimes we ask different experts until we find the answer that we like. One thing is for sure the manufacture of the machine was not contacted and told you to remove or bypass a circuit protection devise that they designed One has to sort all the advice given and use your own judgement even on the internet full of experts as you are the one putting the wrench to it as some would say if you have to ask you shouldn't be messing with it Even given the poor advise followed the operator bent the cylinder pushing back on it with the bucket
I did that with the pressure relief working properly. Pressure relief prevents the pump from supplying too much oil (or oil pressure) to the cylinder. It is not designed to receive a large volume of oil back to the reservoir. A thumb needs a bypass valve. It moves pressure from one side of the piston to the other. Mine is a small block of steel with four ports for hoses, and an adjuster. It is incumbent on you to sort advice. Does this make sense. Did he fully understand my question. I will counter that turning up the relief valve likely didn't cause your problem. The lack of a bypass valve did. If I told you to solve a tripping circuit breaker by bypassing the breaker, I hope you'd wonder if it'll work better without, why is it there in the first place. Willie
Circuit relief I guess. Understood that I am just learning about hydraulics
No retainer no service contract free advice just helping me with hoses and why the thumb was weak. There was a question about the pressure relief valve working that he answered and suggested it could be the problem and remove it from the circuit as it was not doing anything possibly Took your advice and removed the cylinder the service guy says that he knows someone with a press that can straighten possibly most likely good cheap fast pick two good and cheap
Op: pictures to come
the guy who installed the thumb is dead killed by the doctors who tried to cure him of cancer. The guy who was operating the previous machine thumb was installed in died in an accident with the machine the thumb was salvaged. The thumb came from a bigger machine than this one Thumb cylinder and bucket cylinder are the same size but thumb was fully extended bucket was fully retracted pressure too Great from the bucket to the thumb no pressure relief valve
Is this a geometry problem, instead of a hydraulic problem? Did the thumb get side pressure on it from the thumb or mount?
The guy that gave you the advice free of charge has no moral or legal obligation to repair or pay for repairs. If the one that installed it told you to do it then yes I would say he should help pay for repairs but he's dead.
I ruined two thumb cylinders. The first, a hydraulic expert told me was because when the bucket cylinder crushes it, it can't eject fluid fast enough to the tank. He sold me a valve to move it from a high pressure side of the cylinder to the side with lower pressure. The other was when a pivot pin tube I had relocated failed. I was concerned about too much heat on the cylinder. I had under welded it reasoning it was pushing, not pulling. The weld failed, and before I noticed, it bent the rod. I couldn't find a cylinder with the bore, stroke, pin center distance I needed. The choice was a compromise. I settled for an anemic cylinder with small rod. They will take a pounding. Stop blaming someone else. Either buy with warrantee, paying the price, or accept some fault yourself. I get it, everything is somebody's fault. My perception is the expert wasn't. Your taking his advice wasn't good judgement. Willie
Valves plumbed to move oil from the butt end to the rod end of a cylinder will create pressure intensification. I worked at a place with a Deere 690B had a thumb plumbed that way. Before I got there they had blown hose after hose, finally replacing them with CAT XT5 hoses.... I warned them but they said it was fine now with the new hoses. Couple months later the cylinder fractured from butt to gland, they said it sounded like an explosion. If it hadn't been a cold day with the front window down the operator may well have been badly burned, it covered most of the machine in hot hydraulic oil. Thumb reliefs need to go to tank. If it won't handle the flow, use a bigger valve and lines. Motors can use crossport reliefs, not cylinders. YMWNV.
Thanks for the advice. A mechanic for the local hydraulic rebuilder has just opened his own business. I'll take it up with him. Willie
The reason you get pressure intensification is because of the size difference in the two ends of the cylinder. The old Ford backhoe service manuals had a good explanation of this, and even took advantage of it to test the circuit reliefs that had higher settings than the main relief, by switching some hoses around.
OP: Yep, I agree! OP: My 'removed' pressure relief was located before the thumb piping and was piped to the tank return. Is that a bypass valve? See, I don't even really know, lol. I think what I have is actually a bypass valve. I will need to get it back from the shop where it is being tested and post pictures. Definitely, I need to sort advice...I just thought it would be OK to bleed the system and then I could see that it was all working. So I guess the thumb is strong and does work. I wil straighten the rod, inspect and test the relief and reinstall a known good valve. He doesn't owe me. He was trying to help me troubleshoot; He tested the thumb cylinder for 'internal leakage'.The thumb cylinder was taken to him for inspection. There was no internal leak. I had told him the thumb was weak and the valve was capped off. He sold me a cap saying that the valve wasn't doing anything, so it could be removed (removed! instead of hey you need a safety) He's a good guy that will likely not give advice like what he gave me.
Usually, it feels like the thumb cyl has a crossover relief valve where the hoses leave the boom, the bucket can always shove the thumb back on every machine I've rented. Altering a relief valve without a pressure gauge verification to back it up can be a recipe for disaster. Often a slow thumb or any other cyl I've run across has already been bent, internal drag in the bore makes it move really slow. Its possible it had some bend already. Agree though, pull it off, pin it back and that rod might be a candidate for straightening.
Not sure I'm following "valve was capped off" what was capped off prior to your removing it?
The valve had a hose coming out of it there was a cap on that. Without the cap it was supposed to go back to the piping tank return
Free advice is worth what you paid for it. You can't expect any recourse except in certain situations which require very expensive lawyers. The thumb cylinder rod is bent because the base of the cylinder is welded too far forward on the stick letting the thumb go past parallel with the stick. Removing the circuit relief for the base end of the thumb and leaving the control valve for the spool controlling the thumb in the hold position meant the bucket had the mechanical advantage of putting down pressure in the middle of the extended cylinder. The weak link was the cylinder rod which bent. You are actually very lucky the cylinder was in the position it was in. I've seen cylinder barrels split from a dead head and it is much more expensive. From the description we don't know if the circuit relief was actually removed and the passages capped off as it sounds like the Mr. Grenier doesn't know where it would be or even what it looks like. When I was installing thumbs I used a cross over relief setup that was an aluminum or stainless steel block drilled for two relief valve cartridges and a return to tank. In latter years the manufacturers came out with provision for low pressure circuit reliefs to be installed in the auxiliary valve blocks operating the thumbs and we didn't need the cross over relief blocks anymore. At any rate you need to have a circuit relief for each side of the thumb cylinder. The common setting was 2,100 PSI on the piston side and up to 2,400 PSI on the open side. You also need to check the thumb for being past parallel when fully open. If it does so you should cut out the welding on the thumb cylinder base bracket and move it back to the point of the thumb only reaches parallel with the stick. Expensive lesson in hydraulics but good you allowed all of us the reminder of the possibilities.
Well, that would have had the same effect, so what he said was true, the relief could not have done you any good. What he should have said was you needed to connect it to tank and adjust the valve properly. My opinion only.
OP: The Vickers Valve was located on circuit #23 #36 and controlled by the foot valve
What is your make and model of machine? The parts break down shows a typical gray market machine pilot controlled auxiliary circuit. The photo is usually associated with an articulated boom machine. Item number 23 and 36 are hoses going to some kind of block which appears to be some kind of shuttle valve. Item number 31 may be a hose or a wire going to the block that has a component identified as a pressure switch but has no number. Those hoses are pilot control hoses and have nothing to do with the pressure in the lines going to the thumb. They are to shift the control valve spool that controls the implement function.
It is a Hitachi EX100-3 and purchased from Assetline, JP back when the Yen was 136/$ It had a breaker once, aftermarket, and the piping was used to hook up the thumb. The piping comes from the valve:control, has a Vickers Valve on the positive and there is a hose from that Vickers to the hydraulic return Great advice... I am unsure if there is pressure adjustment, would it be both in the Vickers and the Valve:Control Vickers is getting tested
You are right...additionally, the foot pedal is 10 in the right sheet and has hose 8 to a valve:lock. (Vickers valve) This is the one removed, if I am not mistaken.
The valve:lock is your safety shutoff, it stops pilot pressure from going to all the controllers so all functions are dead. The hose 8 is the beginning of a daisy chain to all the pilot controls.
damn
You sure about hose 8 going to a daisy chain?...The one side of the Valve:Lock is what I am asking about as the other side of hose 8 is the foot pedal control (see right side of diagram) for AUX thumb/breaker/crusher. It looks like the Valve:Lock is the 'safety' pls correct me if I'm wrong, just askin and tryin to learn. I realize I was wrong about hose #23 and #36... All the best, b
I could be wrong, I should have said "I think". Hard to be sure from a parts picture, sorry.