Hydraulic Lift Table Troubleshooting

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
Back in January I picked up an electrically powered hydraulic lift table at an auction. It raises and lowers with foot-pedals that control a motor and solenoid down valve. Below is the lift table. It has been very nice to put the work at any height I want. Prevents me from bending over in weird positions and good for when my daughter is working in the shop too since I can lower it down to her height.




I'm having an issue where the height of the table slowly drops, maybe 8-12 inches overnight. I had a much smaller and cheaper foot operated lift table that didn't hold it's height, so I knew this could be an issue. This is one of the first things I checked when I got the unit. For the first month or so it would hold it's height overnight (or at least it moved so little, I would never notice).

1. I have replaced the foot pedals (the ones in the pic are new) and the solenoid down valve. No improvement.
2. The table drops with the unit plugged in and unplugged, so I can rule out the possibility of the solenoid being slightly energized.
3. I don't see any hydraulic fluid on the floor or on the lift table, so I don't think anything is leaking out of the system.

I don't know anything about hydraulics and I don't know how to debug this thing. I had high hopes that replacing the down valve would do the trick, but it didn't. Any suggestions?
 

Skymaster

Jack
Senior User
is there a way to bleed the system? Really go thru every inch, we both know there is a leak somewhere,pressure loss, maybe a pin hole where so slow it dries on a hose OR the hydraulic cylinder itself might be the problem, check all connections.Also check the fluid level, might be low,
 

Michael Mathews

Michael
Corporate Member
Jeremy, I don't suppose you got a schematic with the system, did you? There might be a pilot operated check valve (often called a PO Check Valve) in the down circuit that might be leaking by. Does the motor only run when you step on the pedal? I'd have to look at the plumbing and the components to be able to troubleshoot. Or as I said, if you have a schematic, that would be a big help! Any idea how dirty the oil is? if there's a tiny bit of dirt in a valve, that would cause it to hang up and not fully close causing it to bleed through letting the table drop slowly.
 

badger fan

Bruce
User
+1 to Mathews comments. There has to be a check valve in the circuit if not you could have some by pass in the valve assembly itself where the tolerance between the valve body and the spool allows the table to drop.
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
Jack,
I'll take another look for signs that fluid is leaking out of the system. I suspect it isn't leaking to the external environment, but leaking and causing fluid to circulate within the closed system. I really don't know though.

Michael,
I do have schematics, pics below.

The motor only runs when I step on the pedal.

I'm not sure about the age of the oil. I did add some when I got the unit. A bunch leaked out when the unit was moved to the basement. I think I was supposed to replace the vented tank plug with a sealed tank plug when the unit is tipped/flipped.

Here are the schematic pics:
1588812812477.png




1588812883193.png



I have the LS4-36 model from Southworth. Full manual here: https://www.southworthproducts.com/images/documents/manuals/Lift-Tables/LS_Manual-new_1.pdf
 

badger fan

Bruce
User
I think given the one way check vale’s you have one that is hanging up ie not closing complete. This allows oil to by pass. Not sure which one to check first but taking one at a time out and cleaning the check and ball will be in order
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
Thanks for the input, I'll inspect the check valves. I was only looking at the down valve.

So here is a dumb question: I have to drain all the oil out to remove the check valves for cleaning right? (assuming I don't want oil dumping all over the floor)
 

Michael Mathews

Michael
Corporate Member
Jeremy, you shouldn't have to drain the oil from the system to clean the check valves. You may lose minimal oil, so just be prepared for that. There are actually two check valves you want to clean. One, the most obvious is the Load Check. The second, not so obvious, has the same symbol as the load check but it's inside the Down Solenoid valve. That valve is a single acting spring return type of valve. You actuate the down command and when you stop actuating it, the spring (symbol sticking out the left) presses the valve back into the check valve position. So within that valve there is a check valve when the down valve is NOT actuated. You want to clean that also. And check for scoring or wear. That could cause leakage as well.
 

chris_goris

Chris
Senior User
Is the circled item the load check valve or is that just a fitting?
View attachment 193715
That is a fitting. Most hydraulic check valves are nothing more than a ball bearing that sits in a cylindrical housing with a coil spring forcing the ball against a spherical seat at the bottom. the spring is on the opposite side of the fluid flow. The spring is light duty , just enough to allow the ball to be unseated and allow fluid to flow passed. I suspect this may be built into that pump housing. You said you replaced the down valve?.
 

chris_goris

Chris
Senior User
The "O" rings in the cylinders could also be leaking fluid past them. Look at you tube "floor jack rebuilding" for tips.
Bruce has a good point here. Check the "vent" line going back to tank from the cylinders at the top of them. Since the cylinders are single acting (pressure only on one side) there should be zero fluid in the vent line. If there is fluid, you have piston leakage. Im not sure why the vents dont simply go to atmosphere however... maybe it keeps it cleaner.
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
I checked the vent line, there isn't any fluid in the vent line.

Jeff, I did call Southworth Technical Service at one point, which was when I ordered a replacement down valve assembly. The load check valve was never discussed.


I believe I have located the check valve(s). I took much closer look at the manual and there was a picture.
1588880950612.png



It looks like it is these bolts circled in red. I know I can identify the down valve because I have already replaced it.
1588881172206.png




https://photos.google.com/photo/AF1QipOFZ4aVWp8K_gjxQmPjPiFcW7yP83BVoSnj1LSE
 

Jeremy Scuteri

Jeremy
Staff member
Corporate Member
I removed the check valve bolt and a spring and little steel ball came out. I wiped them off and reinstalled. I tried to remove the relief valve, but it didn't seem like there was quite enough room to remove it without removing the pump assembly from the motor (the tank was in the way). It was close, I may have been able to get it out, but I was concerned it would be a nightmare to get back in, so I figured I would see if cleaning the check valve fixed the problem before getting into deeper water. We will see if the height moves overnight.
 

medic

john
User
I have to agree with chris a check valve will lock a cylinder in place have you checked the pump with a pressure gauge might be a possibility the pump might be bypassing internally also I would suggest replacing the fluids if you do not know how long is has been inservice just my 2 cents worth
 

chris_goris

Chris
Senior User
I removed the check valve bolt and a spring and little steel ball came out. I wiped them off and reinstalled. I tried to remove the relief valve, but it didn't seem like there was quite enough room to remove it without removing the pump assembly from the motor (the tank was in the way). It was close, I may have been able to get it out, but I was concerned it would be a nightmare to get back in, so I figured I would see if cleaning the check valve fixed the problem before getting into deeper water. We will see if the height moves overnight.
were you able to check the ball seat?
 

Our Sponsors

LATEST FOR SALE LISTINGS

Top