Third Function Cylinder not Holding Position

[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.