Third Function Cylinder not Holding Position

[irsmun]

I have had 3rd function hydraulics installed for sometime now. I don't usually use my machine as I have an employee who is an excellent operator. When operating today I noticed that when I open my grapple and let go of the switch (its electric) that the cylinder releases and starts going down. When I clamp it and let go it relaxes when I release the switch. Isn't it supposed to hold in the position it stopped in? Why is the fluid in the cylinder equalizing the pressure when the switch is not applied? Could I have a faulty solenoid. I think I have a 4 way 3 position solenoid valve with a spring to center.

Any help would be appreciated. It makes operation aggravating.

 

[ptsg]

Sounds like a bad cylinder seals

 

[irsmun]

Hmm. I will have to check that. I don't remember seeing any fluid leaking around the cylinder.

 

[ptsg]

Sorry, I meant the internal seals of the piston could be leaking from one side of the piston, to the other.

 

[irsmun]

Is there a way to check for that without opening up the cylinder?

 

[irsmun]

Ok, so I had the cylinder repaired. It now bites and stays down...but when I raise to full open it slowly goes down. I was under the impression that my electric solenoid valve would be closed when no power was applied. That means it should hold its position wherever it stops. Why is the fluid slowly returning to the tank? Do I have a problem with my valve?

 

[J_J]

Solenoid spools can leak also.

Install a needle valve in the cyl line and see if it still retracts.

 

[trktrman]

Solenoid spools can leak also.

Install a needle valve in the cyl line and see if it still retracts.

Agreed! I've learned a lot from your posts J_J

 

[Budweiser John]

To accomplish a third function circuit for my grapple I installed an electric diverter on the bucket curl circuit.
I initially had a similar problem with the grapple clamp mode not holding the load tightly but through trial and error figured out the diverter button must be held down for several seconds to allow the full hydrolac pressure to build up in the clamping cylinder. For compress able loads such as lose brush it's often necessary to activate the cylinder additional times as the load compresses in transit.

 

[irsmun]

Can you help me better understand your suggestion? Put a needle valve where? On the line to the open function?

 

[J_J]

Remove the base end of the cyl hose at the valve work port.

Raise the loader and shut off the needle valve.

If the loader drops, the cyl seals are leaking

If the cyl holds, then you know the valve spool is leaking.

 

[irsmun]

I'm game. Where do I get a hydraulic needle valve? and do I need one or two since there are two ports on the solenoid valve?

 

[J_J]

Hyd shop, or Surplus Hyd.

3/8 NPT 8 GPM PRINCE WNV-600 NEEDLE VALVE

 

[irsmun]

Ok. So here is what I don't understand. If I have an electric over hyrdaulic solenoid valve and it shuts off in the center position, then whether or not my seal is leaking in the cylinder it should still hold position. I mean, where else could the fluid go? That would indicate the solenoid valve is bad right?

 

[J_J]

These are my thoughts, and everybody might not agree, so take it for what it is worth.

Not if there is a load on the cyl.

Excerpt:

Exception involves a load hanging on a double-acting cylinder (Figure 2). In this arrangement, the volume of pressurized fluid on the rod side can easily be accommodated on the piston side. But as the cylinder drifts, a vacuum will develop on the piston side due to unequal volumes, and depending on the weight of the load, this vacuum may eventually result in equilibrium that arrests further drift.

Once the fluid pressure equalize on both side of the piston, then it will stop.

People have been arguing this forever.

If you have a load, and that means any load , even the weight of the bucket or whatever, that load represents pressure.

Install a needle valve in the base end of the cyl and raise a load and then shut off the needle valve. Shut off engine..

If the rod moves any at all, there is some bypass.

Are you also saying that your solenoid valve is not leaking. It can leak like anything else because of worn parts or damage seals, etc.

 

[irsmun]

The solenoid valve was leaking. It had to be. I installed a new one and it is now holding. What gets me is that I did not consider this at first before I had my cylinder seals rebuilt. Chances are there was nothing wrong with them. With the old valve I could push the cylinder down with my hand like there was an open circuit. Nothing in the series could be leaking that badly except the solenoid valve. It is the point where it all comes together. Of course when I say leaking I don't mean leaking out, just not sealing and allowing the fluid to return to the tank. Not sure why this happens or if I could repair this valve.