Hello, first post here but I've been following along for a while. Very helpful forum! I recently installed a hydraulic thumb on our 2000 Cat 302.5 (4AZ01260) and have been reluctant to use it yet because I think we need to incorporate some form of relief into the system to avoid having the bucket overpower the thumb and damage the thumb equipment. I've read through various threads on similar topics, but a lot of them seem unresolved and I want to try and get some additional input. Here are the options I'm looking at: 1. Purchase two Cat p/n's 140-5605, VALVE AS, which I believe are overload/relief valves, per our parts manual. I read through Cat Special Instruction GEBI0248-02 ( http://64.22.192.186/CWT/groups/public/documents/special_instructions/cwt009971~2.pdf ) and as part of the installation procedure for mounting hydraulic thumbs on Cat mini's, it says to install relief cartridges with the p/n's above. This machine already has (5) of these same cartridges used in the main valve block, but did not come with any for the aux. hydraulic circuit unfortunately. Even worse, to buy these cartridges new, it looks like they're nearly 700$ a piece from the local Cat dealership. This is a little steeper than I was hoping since our machine is just used for home/farm purposes, so I'm interested in other options as well (including finding those parts used). 2. Purchase one generic relief valve ( https://www.surpluscenter.com/Hydra...0-3000-PSI-Relief-Valve-RV-H4-9-6135-50-H.axd ) and plumb this into the hydraulic line that acts to close the thumb against the bucket, with the relief plumbed into a hose/line that returns back to the hydraulic tank. With this valve only costing $50, this is clearly a lot more affordable, so I'm very interested in determining whether or not this configuration achieve the results I'm looking for. I haven't determined exactly where I would place this valve or how I'd manage the plumbing, but I've seen other threads on here that determined it was likely doable. I think it would certainly cost less than the 1400$ required for the two relief cartridges above. The only thing I'm trying to do is protect the thumb cylinder so when you curl the bucket in against it, the thumb would retract by the pressure of the bucket rather than bending the thumb cylinder or causing other damage. I find it unlikely that damage would occur in the other direction, so I don't think I need relief on both sides of the thumb. With that being said, I have only a basic understanding of hydraulic systems but am very mechanical. This is something I'm more than capable of doing myself, with the right input from knowledgeable individuals to make sure I don't get myself into trouble. Please let me know if you have any recommendations or experience doing this same thing. I would greatly appreciate other perspectives on this. Thank you!
Thanks for the given information on the hydraulic thumb. If you need relief on both sides of the thumb, then I have some recommendations on demolition hire .
Are you sure you have no aux section on the main control valve?
There is an aux section (I believe they call it power take off), however there's no relief valves installed that I can see. I have the parts manual for the machine and it matches up with what we actually have, and there's nothing to adjust. There are at least 5 other relief valves in use on the main control valve for other circuits, but nothing that covers the aux. Ohio Cat confirmed this to be the case.
You need relief valves on both sides of the thumb and you will need two manifolds to install them on and then add two hoses to plumb them back to tank. How is the aux valve activated? Is it pilot or mechanical spool? If you don't want to mess with the aux valves then you will need a treadle valve to tap off the main pump and then you will need some way to put the pump into stroke when you use the thumb.I hate to be a Debbie Downer here but I have done this before and by the time you finish you might end up paying( for all the extra plumbing you need)as much as the dealer wanted for those 2 reliefs or more.Then you have to find someplace to put all this extra stuff and on a mini excavator space is very limited. Let me know what you already have and I can walk you through it.
Hi. Just a question for any Cat guys out there. I'm working on a 308ccr. I'm adding a double acting control valve and double crossover relief valves to run a thumb. Got it all figured out except for a location to plumb in a return to the tank. I have a block on the side of the tank near the top with a -20 and a -04 line connected to it. Could my return be plumbed in here? I have a schematic, but not being familiar with the Cat's, I do not recognize any obvious returns other than mentioned above. Thanks for any help.
Did you resolve this. I read that the bucket should over power the thumb. Relief cartridges for pa5 and pb5 are needed. I just installed thumb on 301.5 and thumb overpowering bucket. Says I need to install cartridges and set Relief to just allow bucket to move thumb. Please respond with your experience. Thank you
Good day JHead To be correct providing relief is only part of the issue you must refill the opposing chamber to prevent cavitation, attaching the file with the information is to large for the site, however if you go excatech.org - library - adapted applications - thumb ? & answers. I hope you will find the information helpful there is much more of the web site, any questions please drop me a line. Kind regards Uffex
Thanks for that awesome link, uffex ! I just installed a thumb on my own machine and I have been looking on the specific information in regards to the pressure relief. It addressed all of my concerns about the pressure relief in the thumb cylinder. This page addresses the pressure issues directly.
Hi JHead, Did you get this figured out? I am adding a thumb and hammer to my Cat 304 CR. Both the thumb and the hammer require 1750 - 1800PSI. When I checked the pressure on the hydraulic lines at the attachment quick connects with a gauge I had 3700PSI. I adjusted the pressure at, what I think are the relief valves, and now have 1750 PSI. We have the correct flow to the hammer of 40L/min. Only problem I am having is the thumb falls off on its own. So, now I am wondering if I have relief valves or just control valves. Attached is a photo of he valve body. The valve just below and to the left of the cable tie is the valve I have been adjusting. I have the same valve on the rear of the circuit. Is this a relief valve? If so, how do I adjust it to prevent the thumb from falling under its own weight? Any help would be really appreciated. regards, Don
Good day Don It may be worth giving a thought to the port relief valve as a rule these are installed to take care of spike pressures coming from the attachment. In most case's these valves are high pressure low flow, if the thumb cylinder is taking into consideration the flow it can generate may well exceed the port relief specifications offering only minimal protection. It may be of help such valves are often named as "Port relief valve" always connected directly to the appropriate line port, maybe you have chosen the wrong side. By following the line from the thumb’s positive side (Piston not rod) you can be sure you are on the correct valve. Kind regards Uffex
You need to check with the hammer manufacturer, but as far as I know, that pressure spec is a minimum requirement, there should be no need to lower the port relief settings for the hammer. Set the port relief for the butt end of the thumb cylinder so that you can overpower the thumb somewhat by curling the bucket into it.
Thanks Uffex. I am told by the cat tech that the port valves I have are just control or shut off valves. He is saying I need line relief valves to be able to adjust properly. I adjusted the pressure on both the inside and the outside port control valves to 1750 PSI and the thumbs falls. Adjust the pressure back to 3700PSI and the thumb stays where is supposed to - only issue is it wants to beat itself to death. I have ordered the line relief valves. Hopefully this fixes my issues. Cat wants $3000 Canadian (including taxes) for the two line relief valves! I managed to find 2 brand new, OEM Cat line relief valves on ebay for $380 Canadian. 2 Thumbs up for Ebay! Don
Thanks Lantraxco. I have the hammer manual and it states 120 bar (1750 PSI) operating pressure. I also have have the thumb installation instructions and they state 1800PSI maximum operating pressure. Therefore, I want to set the pressure for this circuit at 1750 PSI. The line pressure from the machine is 3700PSI. At 3700PSI, the thumb moves like greased lightening and wants to beat itself to death. At 1750 PSI it moves at, what I would call, the proper speed and sets itself correctly. I may be a bit cautious, but I don't want to put 3700PSI to the hammer and possibly blow seals. This is only a small 460lb hammer on a 4 ton mini excavator. The hammer is a HM200 by Mustang and I have tried numerous times to get information from them but nobody returns any of my emails. Very poor custom service.
My next door neighbour who has been operating excavators for some 40+ years (from a mini to the Alberta Oil Sands monster) and who is mentoring me (this is my first excavator) has preached to me "NEVER bring the bucket to the thumb, ALWAYS bring the thumb to the bucket, that way you NEVER break anything". I have spent many a hour watching him work his machines like it is a part of him - Fast, Smooth, and VERY effecient! I'm willing to bet he could pick your nose with an excavator!
well did you work it out?
CapnDean, The new relief valves did the job. The thumb is still a little fast but it stays in the posistion that I put it in without falling off when I release the switch. The bucket and the thumb work well together. The hammer works like it should as well.
Hi don I know this is an older post but I thought I’d reach out anyway.. I’m dealing with the exact same thing. trying to get the thumb working on my 303.5.you wouldn’t happen to know the part numbers of the line relief valves you purchased would you? Any help would be greatly appreciated