Hydraulic Lift Table Troubleshooting

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
I would suggest replacing the fluids if you do not know how long is has been inservice just my 2 cents worth
I drained a bunch of fluid out when I removed the down valve and replaced it with new fluid last night.



were you able to check the ball seat?
I stuck my finger in the hole where the spring and ball were and tried to feel for burs or debris and didn't notice anything. I'm not sure that is the official inspection method. I then stuck a paper towel in there and twisted it around a bit before re-assembly.

About an hour after I put things back together it seemed like it moved a 1/4" or so. Didn't seem like a good sign. I just checked it now, about 15 hours later and it has moved about 1/2" total. If it just moved about a 1/2" per day, that would be fine by me. I am going to create a story stick to track it's movement over time.
 

Skymaster

Jack
Senior User
Now that we know check valves are in play, imho, dont even bother with those in machine, replace them. check valves are simple in concept,but are a living nightmare when they go bad. They have diabolical magic and go bad in ways that defies all rules of physics and logic :D :D :D :cool: :cool: :):):oops::oops::oops:.
 

Charles Lent

Charley
Corporate Member
More likely it's the seal rings on the piston. They wear from high use and then the oil leaks past them. If oil is showing at the cylinder vent, this is likely the problem.

Charley
 

junquecol

Bruce
User
[QUOTE="chris_goris, post: 649754, member: 8747 Im not sure why the vents dont simply go to atmosphere however... maybe it keeps it cleaner.
[/QUOTE]To keep hydraulic fluid off the table and surrounding areas. A atmosphere vented cyclinder that "pissing" fluid past the "O" rings is a nasty thing.
 

chris_goris

Chris
Senior User
[QUOTE="chris_goris, post: 649754, member: 8747 Im not sure why the vents dont simply go to atmosphere however... maybe it keeps it cleaner.
To keep hydraulic fluid off the table and surrounding areas. A atmosphere vented cyclinder that "pissing" fluid past the "O" rings is a nasty thing.
[/QUOTE]
Im pretty sure I said that Bruce, maybe a little more eloquently...
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
No luck with the lift table, it still isn't holding it's setting overnight. It doesn't seem to always seem to lose height at the same rate. Sometimes only 1/8" per hour, sometimes over 1/2" per hour.

Some history and a possible cause??:
The weird thing is that it didn't always do this (lower slowly over time). For the 1st month or so that I had it, it didn't seem to move at all overnight. I replaced the up/down pedals that came with the unit. They were old and didn't have a housing that held both pedals, just two loose pedals that I screwed to a board. At one point the UP pedal got stuck and to prevent the table from trying to go too high I pressed the DOWN pedal at the same time (it was a moment of panic, I probably should have just ran over and unplugged the unit). The motor was driving the pump and the down valve was open at the same time. The table did lower under this condition. It seems like this issue may have started after the pedal got stuck. I'm not really sure though. Does that make any sense for a root cause? I don't know why it would be a problem, but I keep wondering if that somehow caused issues.


Things that have been done:
1. The entire down valve assembly has been replaced already.

2. I took out the load check valve, cleaned it and replaced the o-ring.
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3. I have inspected visually for leaks. No fluid in the vent lines and no leaking fluid detected on the floor or cylinders.


To Do:
I'm not really sure how to bleed air out of the system. Does moving the table all the way up and down do that? Do I need to disconnect the vent lines?
 

Michael Mathews

Michael
Corporate Member
if the up valve got stuck once, I'll bet there's some dirt in the system. Just the tiniest spec of dirt can wreak havoc in a hydraulic system and cause the symptoms you're describing. If the dirt is floating, sometimes it sticks in the right position and holds a check valve just the slightest bit open, enough to allow a 1/8" per hour drift down. Other times it's a larger piece of dirt and now the drift is 1/2" per hour. Dirt is the worst thing in a hydraulic system. You might just be best off figuring out how much oil your system needs, then buy double the amount or even more. Drain, clean everything including the pipes, and flush with the first half, then fill with the last half. Hopefully that will clear it all out.
 

chris_goris

Chris
Senior User
The other option is you could install a ball valve in the cylinder feed line (labeled filter and suction line in your connections drawing) that you simply close off , acting like the obviously leaking check valve. If the fluid cant drain back, nothing can move, simple as that. There wouldnt be enough air in the system to cause leak down that youre describing. If there was, it would simply cause the cylinders to be "bouncy" , or allowing the air to compress. Hydraulic systems typically can easily tolerate air in the system without issue, the air simply compresses so much ( many hydraulic systems generate pressures easily exceeding 2000 PSI) the air becomes negligible.
 

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