Well, I am replacing about 5 hyd. lines on my 655D from the backhoe valve area and I was wondering if there is anything special I need to do to get any air out of the lines after I hook everything back up? As always any help is appreciated.
Nope, they'll purge as you cycle through the functions, work every function as far as it will go a few times, then you can let the machine set to let the air settle out in the tank. Not needed though, its good to go as soon as the last fitting is tight.
That is true for just about all hydraulic systems, one exception I came across a little over a year ago was on a Cat 988H, not sure if this applies to others for the last step after installing a lift cylinder manual says: Air Evacuation Procedure Air must be evacuated from hydraulic cylinders prior to use to prevent dieseling. Do not operate the implement functions until instructed to do so in this procedure. Start engine. Do not increase engine speed above low idle. While maintaining system pressure as low as possible, fully extend and fully retract the lift cylinders for ten cycles. Lower the implement to the ground and shut off the engine. Fill the hydraulic tank with fluid until the "FULL" level is reached in the sight glass.
Greta info...thank guys!!!
Wow, I'd never really gave dieseling a thought but yeah, high system pressures if you really slammed it home, it might well cause a big problem.
I had sort of thought about that in the past but figured I was over thinking it. That said when I read that while working on the 988H I did make it a point to work cylinders in and out nice and slow. Then again most of the time I put a new.rebuilt cylinder on a machine I would work it through the full range a few times to work out the air so it was a little smoother moving while hooking up pins. When they are half full of air they can jump several inches at a time making keeping all the fingers still attached to the hands a trick!
Today I put the new hyd. lines on and worked each of the controls several times and everything worked great. Thanks for all the input guys!
I used to leave the hydraulic tank cap loose while cycling the cylinders as described. I would also start just moving the cylinder out and in only part way going a little more each time until I got to full stroke. After that was done I tightened the cap and then cycled all the functions from end to end to charge the hydraulic tank.
A couple maybe minor problems with that, at least where I worked and the equipment we had. First in a stone quarry things can be very dirty and it is not always easy to clean them before working on them so running with cap off could allow dirt to get into the tank. Second thing some of the machines had the filler cap low enough or positioned so the return air/oil would overflow the tank. But yes moving slow in each direction to "prime" the system is a good idea. Also be sure to check oil level after it has worked and then sat over night to be sure all air is out.
I didn't say running with the cap off, just loose so the air can vent easy. As far as overflowing goes we didn't worry much about it as the oil was filling the cylinders during the venting process. Usually kept someone at the sight glass to make sure the level didn't go so low as to run the pump out of oil. Those are good things to consider though.
1. Open the air valve at the upper side or the hydraulic cylinder. 2. Make sure every hose or pipe is connected as it should be connected. 3. Set-up the hydraulic system and start it up. 4. Extend the piston rod slowly with no pressure built-up. Keep extending until there is oil / foam coming out of the air valve. (Hydraulic cylinders that go over-center, must be air-released before mounting in the construction!) 5. Shut down the system and close the air valve. 6. Depressurize the system before opening the air valve at the lower side of the hydraulic cylinder. 7. Start up the hydraulic system. 8. Retract the hydraulic cylinder slowly with no pressure built-up. Keep retracting until there is oil / foam coming out of the air valve. 9. Shut down the system and close the air valve. 10. Retest the hydraulic cylinder by extending and retracting the piston rod until it’s running smoothly.