i have a hitachi ex165 to change main boom ram seals sounds straightforward but lifes never that simple the ram in question has been giving bother this last few months and has already been resealed twice before (by a reputable company) now i am stuck with the job of fixing it . before i go pulling it apart is there any reason this could be happening i looked over the rod still in place and it has no visible markings chips burrs or pitting my only other thought was has the wrong seals been fitted and every time the next man just matches up what comes out thanks for reading paul
Good day Paul I guess you have two rams have they both been resealed? Usually there is a straight forward explanation for seal failure often the bent rod can figure or the swollen jacket. Have you checked if both cylinders fully extend or retract together or is the a difference. We have some information on the subject at excatech.com you can obtain for free. Or you can get back to me at bucketsense@gmail. Kind regards Uffex
There are a couple of items that might not have been checked when the cylinder was repacked. If this is an older machine was the outside diameter of the rod checked? It is common to wear a couple of thousands of an inch over a long period of time. It doesn't take a lot of wear to let the rod settle to one side and put less compression on the top side to allow a leak. There is usually a composite or brass bushing inside the packing gland that needs to be replaced whenever the cylinder is repacked. Some manufacturers don't include those bushings in a kit. They have to be purchased separately. I have also seen the inside of the gland have some damage which presents a place for high pressure oil to leak through. Usually the seals will take up that space but depending on where the damage is and how bad it is the cylinder will begin leaking shortly after being returned to service. The last thought is where did the replacement packing come from. I used to use a lot of stuff from packing stores in years past but when the high pressure machines showed up it there wasn't enough savings in cost to warrant the risk of early failure. If I do a cylinder now, it gets factory parts put back in.
Key factor here is checking BOTH boom cylinders, if one has not been resealed, it may have excellent rod seals and bad piston seals. The effect of this is to create pressure multiplication in both cylinders and the weakest link will fail. If one cylinder develops a bypass at the piston and it is left untreated you may also see swelling of the cylinder tube and or twisting of the boom as one cylinder will be doing more than it's share of the lifting/holding.
sorry should have said its the gland seal leaking and its always been the same ram giving bother i have been thinking that the gland nut could be wore does anyone know what the clearances should be between the gland nut and the rod i see what your saying lantraxco if the piston seal was not good on one ram it would make the other work harder something i need to look into how would you go about checking it or do you just reseal both thanks for the replys
Good day Paul From observations of the comments it would appear this problem is limited to that of the rod seal, unequal pressures in each cylinder is extremely improbable since both the negative side of the cylinders are linked together. High pressure will only occur in this side of the cylinder when you raise the tracks from the ground of force the bucket into the dig. Replacing a piston rod seal today involves removing the rod from the jacket undoing the piston and totally dismantling the unit. In the ninty's a company know as Polypack made a split seal these did not involve dismantling but as far as I am aware these are no longer on the market. If you would like the manufactures instructions for seal replacement drop me a line. Kind regards Uffex
With two cylinders tandemed together, both extend ports teed together and both retract ports teed together, if either piston seal is bypassing when the boom is holding a load, then the cylinders effectively become "displacement" cylinders. In other words you lose the area of the piston and only have the area of the rod to hold the load. This can more than double the pressure in the cylinder above rated. The saving grace in excavators is that the port relief valves will normally open saving the cylinders, but still it induces a higher than normal pressure on all the rod seals. If your boom cylinders drift down quickly then I would suspect piston seals. If you don't have faster than spec boom drift down then it's just as John C stated, use OEM seals, make sure the rod is straight, smooth and the correct size, and that the bushing is not sloppy.
Good day folks As I understand the post it refers to piston rod seal and not that of piston seal. Kind regards Uffex
I have repacked alot of john deere and Hitachi cylinders and have found that if you dont use OEM seals they will leak i personally havent been satisfied with any after market kit also the bushings are another big deal alot of companys dont replace them and that causes issues to
Uffex, not trying to start an argument, but trying to explain that when holding a load if the piston seals bypass oil, then it creates a higher than normal pressure for those rod seals which MAY cause otherwise leakless rod seals to leak due to the fact that the effective piston area is reduced to the area of the rod itself.
And those leaking piston seals won't cause the boom to drop under it's own weight (because the rod has become the piston) but if the stick is extended with a full bucket, they'll either drop or leak out the gland, right?
Correct, if the pressure gets high enough the port relief will open and the boom will come down, or more likely kind of chatter as the piston bypass probably won't be huge, or if the gland seals are not up to spec they'll leak oil there. Again it's just a possibility to be aware of.
Final got the rams pulled apart today didn't see any thing out of place or damaged looking have to go get a set of genuine seals in the morning have it all striped now but what do you lot find the best way of loosening the main nut at the end of the piston I did get it loose in the end but can't say it went with out a fight Thanks again for your replies