My first post to this forum so hello everybody. I recently acquired a Bobcat excavator from the late 90's, an X325. I finished installing a hydraulic thumb on this machine and need to reduce my auxiliary pressure relief. The service manual is not exactly helpful regarding this, it has some info on main relief valves and port relief valves and their corresponding pressure settings, while never strictly addressing how to adjust the Aux line relief pressure for something like a thumb attachment. - If anybody has experience with this particular Bobcat could you send me some knowledge? thanks!
Hi Hschmitt Welcome to the forum. I had a quick look at a 325 manual and I did not see any information regarding adjustment of the aux line port reliefs , also I did not see any port reliefs installed in the valve bank itself, only a auxillary spool option with a single acting/double acting 3 way change over valve. There appears to be a provision in the valve bank to accept auxiliary port reliefs but it may not be a standard factory set up and has to be purchased separately or as an add on option. Bobcat use a hand pump to set all other port reliefs with a cracking pressure reference so the same process would apply to the auxiliary port reliefs if you require these to be set higher than the main relief. Kind regards
Thanks for that info. Would it be possible to determine by looking at the valve body whether or not this machine has any aux port relief installed? I've been poring over the service manual and been able to determine which spool operates the auxiliary flow. I noticed the aux spool on the machine does not have any kind of pressure relief on it. TLDR: The service manual literature states that the boom and bucket valve sections have "work port" relief valves installed on them (I do not understand what the significance of a work port relief valve is, and is it possible the aux spool piggy backs off the bucket spool's work port relief? [the bucket and aux spool are next to each other]). While another section describes that when the "Bucket or auxiliary section spool of the body is activated, it sends fluid to bucket cylinder or aux couplers. return fluid flows back to the control valve. when a cylinder reaches the end of its stroke the pressure increases to 2550 psi and opens the main relief valve. Would'nt this mean that the aux lines relieve pressure at 2550 psi? Or am I misunderstanding that text? (Its hard to imagine not having any kind of relief pressure for the aux on a machine with built-in two way aux) I apologize for the miriad questions. Just trying to see if I can get to the bottom of this problem without having to take the machine in to the dealership. I'll include the most pertinent info i can find from the service manual regarding the machine's relief pressures and aux info. Thanks again to anyone willing to have a look at my issue.
The port relief protects the work port components from high load pressure that can occur when the function is not operating but gets a high shock loading force to its cylinder or hydraulic motor. When a control valve spool is in the neutral position the functions are no longer connected to the main relief so the port reliefs will open to protect the function from high pressure intensification. For example on some set ups the thumb can come into contact with the boom if the thumb is partially closed and the arm is retracted in towards the cab The port reliefs can also serve as means of having a lower operating pressure to a function that needs to have its maximum pressure set lower than the control valves main system relief setting. You have 2 main reliefs one set at 2550psi and the other at 3700 psi, with the auxiliary section operating on the 2550psi main relief but only when the aux function is in operation. The exploded diagram you posted of the 5-spool control valve shows the auxiliary section is cable controlled and does not appear to have a port relief cavity. If you have a hydraulic circuit diagram available, this may also confirm that there is no provision for a port relief. If this is the case then you will need to put a cartridge relief block assembly mounted in line with the thumb hose connections. Kind regards
I will post the hydro schematic, hope it is clear enough to decipher. If it is necessary to install the cartridge relief valve you mentioned, do you have a recommendation of where I can obtain the proper one? And is it a straightforward enough installation that I could plumb it in myself or is it something I ought leave to a hydraulic shop or the dealership? Thanks for the info thus far, cheers!
My aux valve does appear to have plugs in both the front and rear top section that look like they could potentially have a relief valve installed in them (like it's brother next door) Is this a possible provision for relief valve installation?
Here is a bobcat parts breakdown for the part number of the port reliefs you need, item 12 - part number 6674259. See bobcat attachment pdf If the genuine relief valves are not available from BC then you would want to look at mounting and plumbing a manifold assembly, see Eaton attachment pdf for description. Link to complete Eaton catalogue below: https://www.eaton.com/ecm/groups/public/@pub/@eaton/@japan/documents/content/pct_3451921.pdf It looks like bobcat also do a similar manifold option in one of there parts breakdowns and its mounted on the side of the boom with quick coupler connections and a drain line. They call it an Auxiliary relief kit Link to BC Parts catalogue below: Bobcat Parts Catalog - Find Diagrams for Your Equipment - Bobcat Company Locate all parts and component information about your Bobcat equipment with detailed visual diagrams and illustrations with parts numbers and add to your list. partscatalog.bobcat.com Best regards
Thanks Kobe, your help has been outstanding. It looks like bobcat does still sell the relief valve I would need to install in the aux valve. They are costly though at about $550 a piece. Can you tell me if installing reliefs in the ports on the aux valve would function properly at any psi lower than the main relief? For instance, the thumb I want to use recommends setting aux relief pressure to 1700. any more could potentially damage the ram or thumb cross members. But wouldn't the baseline fluid pressure in the open center control valve always be at least 2500 psi if that's the setting of the lowest main relief valve? rendering the port relief valves useless if set any lower than this. On a side note: Would installing port relief valves into the aux valve alleviate the issue of there being no relief unless the aux is activated? in other words, would the relief valves give the aux valve relief functionality even with the valve in the neutral position? Finally, would simply installing a hydraulic cushion valve/crossover valve out near the thumb ram and setting that to function at 1700 psi be a decent work-around? My understanding is that crossover valves aren't best suited for a single ram, but have seen some people use it this way succesfully.
No problem , happy to help If the thumb function requires 1700 psi max limit setting then you would set your port reliefs to this setting, then when using the aux valve, the max pressure will only go to your 1700 psi. You may also find when combining certain operations with the aux valve that the maximum system pressure will only reach the aux valve setting. The auxiliary will still function correctly with a lower pressure setting and when the aux is not in use it will protect the thumb from pressure spikes if the thumb gets a shock load from an impact like hitting into hard ground or a stump while extended out. cross port reliefs block will also work but as you pointed out, if you use a 4 port cross relief it has the potential to damage your cylinder and/or system. This is because when the aux function is not in use and a shock load occurs within the cylinder ,the oil is relieved from one side of the cylinder to the other via the cross port relief but due to the cylinders displacement/volume difference from the piston side to the rod side, only so much of the oil can be displaced before a hydrostatic lock occurs with no place for the oil to go resulting in buckling of the cylinder rod, cylinder bore expansion or blown seals and pipe work. If you choose a 5 port cross relief block with anti cavitation check valves, then a tank / drain line must be plumbed to the block. When either of the relief valves opens then all oil will be directed to tank for both normal operation and in a shock loading scenario. This is a better and safer option than the 4 port cross relief but it does require the plumbing of a tank line to the valve. Note that the bobcat aux reliefs only state what they are set too and not the range that they can be adjusted within. It may not have the ability to be adjusted down to your 1700 psi setting that you require so watch out for this. Kind regards
This is great. are the anti cavitation capabilities an absolute must? I would like to go the route of installing an external relief valve in my Aux lines with a return to tank. I can find plenty of aftermarket single line pressure relief valves for sale but would have to install two of them, one for each line and T the return lines together to return to tank. I cant find much in the way of a 5 port cross relief valves for external applications. Only this info page from sun hydraulic. https://www.sunhydraulics.com/model/YRFN/LANAM_S I am not sure this valve can be mounted externally though as it is only a drawn diagram with the spec sheet. Do you know of any suppliers or outlets where I might obtain a five port crossover with the anti cavitation protection that can be mounted externally on a machine? Otherwise I would be inclined to install one of something like this (below) on each line, and just connect both the tank ports into the same line returning back to my return line in the cab. (I know the rated gpm is lower than what my aux provides but since these relief valves will be installed on the boom specifically for thumb functionality I do not think the loss of flow will matter) Do you have a recommendation?
Sun cartridges and manifolds are an excellent made product out of the US. Not having anti-cavitation is not ideal but the main thing is that you can relieve to tank if the thumb gets an impact when not in use so if your only options are single reliefs plumbed together then that will be fine. Walvoil is a large hydraulic component manufacturing company that has a number of dealers across the globe, you may have a supplier in your area. If you speak with a hydraulic specialists they should be able to help or at least point you in the right direction. See link below for Walvoil products which can cater for different pressure and flow specification, just look at the catalogue pdf in the link. Walvoil link Walvoil - VMDACSV - Walvoil S.p.A. www.walvoil.com SUN link https://www.sunhydraulics.com/model/YRFM/LANCL Best regards