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Hydraulic cylinder piston nut keeper

Ronray

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And so does the part of the O-ring with the smaller o-ring insert face towards the outside of the piston as pictured?20180826_235051.jpg
 

funwithfuel

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If it has a "cupped" side, you want those to the outside of the piston. So your finished piece would resemble an hourglass. If that makes sense.
 

Ronray

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Ok, two more questions. The cupped part of the piston seals protruded about a sixteenth of an inch above the piston edge and it was so tight pushing it back into the canister that I had to use a 12-ton press to push it in. My own weight of 160 lb was not enough to push it in. And I did disconnect the lines to the holding valve . Should it be that tight? I am also hoping that the cup seals were not damaged as they passed through the canister threaded end.
Second question, do I need to prime the cylinder to get the air out of the cylinder and lines? The cylinder pushes and pulls in both directions and also has a holding valve for both directions.
 

funwithfuel

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If at all possible, you want to get all the air out. What is usually recommended is to run the rod in and out several times with no load and not reaching end of travel in either direction. I find it easier to just fill both sides of the cylinder on the bench. Bumping end of travel with air in the cylinder will lead to dieseling which will destroy your shiny new packing you worked so hard on.
Should not have needed a press to reassemble. Packing must be hella tight. At least she won't bypass. Lol
 

John C.

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Did you lube it good before you installed in the cylinder?
 

Ronray

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No I did not pre lube the cylinder. Guess I should have. The packing was not from the OEM seal kit. It was just what my local hydraulic shop recommended after they measured the cylinder and piston with their micrometer. The old o-ring packing that came out of the cylinder was flat on both sides, but the packing from the hydraulic shop was raised up on one Edge where the second o ring was inserted.
 

Ronray

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I did not see little bits of black vinyl on the threads so that is good to hear! I read about dieseling on Google and will take your advice about filling the cylinder on the bench. What if there is a small amount of air in the several inch line between the holding valve and the cylinder? And what about air and the hose between the hydraulic pump and the holding valve? I think the factory service manual said that it was self priming, but now I'm nervous about that. And I also noticed when I took the cylinder apart that there was very little oil in the cylinder. Thanks so much for all of your help!
 

funwithfuel

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Just follow the recommended procedure stated earlier. Run the rod in n out at idle slowly going a little further in each direction each time. Eventually you'll run out of rod. Once you've exercised the rod in and out fully 4-5 times, you should be golden. I just didn't want you to put a dry cylinder in and run it to end of travel both ways. That would have maybe hurt something.
 

Ronray

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Okay so I hooked up the hydraulic lines and exercised the cylinder back and forth a few times and it was working good until two other lines at a different location on the machine blew out and spewed oil. So I am guessing that this reduced the available pump pressure to the basket level cylinder I was testing since it would no longer move in and out. So my question is are all of the hydraulic lines supposed to maintain a certain amount of pump pressure even when their cylinders are not activated? How much pressure? Thanks much!
 

John C.

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Displacing the air out of the cylinder moves it to the reservoir which applies some pressure to all the oil in all the components of the system. Usually there is a pressure vent or the cap is vented and will release any pressure over the manufacturer's setting. The pressure is usually one atmosphere or somewhere around 14 to 15 PSI. If you blew out hoses at that bit of pressure you have a whole lot of bad hoses.
 

funwithfuel

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Are these hoses by Chance the orange cloth reinforced no metal hoses . If they are and this machine has some age to it I don't think I would trust my life to them as John stated you have a lot of bad hoses more than likely it might be time to just re hose the machine.
At least those that are exposed to the sunlight
 

Ronray

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Yes it is the orange thermoplastic hoses that are exposed to the sunlight and the orange plastic coating was cracked up quite a bit. And I was planning to replace them with standard black steel-reinforced hosing. So if I just loosened up the vented filler cap of the hydraulic oil storage tank, theoretically, should I be able to exercise the basket level cylinder without oil being spewed out from other hoses that are disconnected at other components of the machine?
 

funwithfuel

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If your hoses are failing from tank pressure better to let them burst now and I would advise against replacing them with traditional braided hose you lose the insulation properties of the nylon bucket and the fiberglass boom sections. Any path to ground is a dangerous path for you when you're the one in the bucket. Additionally now that we know we're dealing with a man lift ,that uses a special oil it's a very light viscosity Aero oil if I'm not mistaken.
 

Ronray

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visalia
Thanks for that great advice. My 1980 marklift must be a little outdated since the boom sections are metal and the basket is also metal LOL. Anyway the orange thermoplastic lines inside the boom appear good as new. But it is 4 short 12 inch orange thermoplastic lines at the base of the boom that are exposed to sunlight that are cracked up, and those were the ones I was thinking of replacing with the steel braided hose.
 
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