Can this be air?

[jimmysisson]

I have a home-built wood splitter with a log lift. The splitter piston auto-return valve PB goes to the lift valve, then through a filter and back to the tank. The problem I have is if you pause the log lift part way up, when you resume lifting the platform goes down instead, by gravity. Pulling the lift lever quicker keeps this from happening, at the expense of being jerky.
In the pic there's a proportioning valve, which I have since removed for simplicity, and because it was too finicky to solve the jerky lift problem. Now the PB from the splitter valve supplies the lift valve directly. There's a speed-limiter washer/orifice in the hose from the valve to the lift. The problem is the same w or w/o the proportioning valve or orifice washer.
I've been assuming there was some air in the retract side of the lift cylinder (extends to lift), but it's been like this for tens of hours of use. So I guess it can't be air. Any ideas what makes the platform drop? If someone's near the lift platform when it drops it can be scary.
Thanks, Jim

 

[Leejohn]

If the top valve is for the lift, it does not have a load check valve in it and that well let it drop when shifting the spool.

 

[J_J]

If the hyd cyl moves due to weight, it is probably worn spools.

A load check valve will prevent a drop when shifting the lever.

Could also be weak springs in the valve spool.

 

[J_J]

If the hyd cyl moves due to weight, it is probably worn spools.

A load check valve will prevent a drop when shifting the lever.

Could also be weak springs in the valve spool.

I also see water pipe fittings in the valve. Not a good idea.

 

[jimmysisson]

JJ, thanks for the reminder on the fittings. It's been like that since I got it 15 yrs ago but I will change them out.
Cyl does not drop due to weight, just when I try to raise it higher from half-up.
Where does the load check valve go - I assume in the extend line somewhere? And it somehow permits reverse fluid flow when the cyl is retracted? Thanks, all. Jim

 

[Leejohn]

Here is a good picture of and where they are on most valves.

 

[J_J]

JJ, thanks for the reminder on the fittings. It's been like that since I got it 15 yrs ago but I will change them out.
Cyl does not drop due to weight, just when I try to raise it higher from half-up.
Where does the load check valve go - I assume in the extend line somewhere? And it somehow permits reverse fluid flow when the cyl is retracted? Thanks, all. Jim

Load check valves are on most valves as in Leejohns link.

It's purpose is to keep the load from shifting when the lever is moved, and also to prevent the fluid from going to the input of the valve.

 

[jimmysisson]

That makes sense. It looks like a load check feature can't be added to an existing valve? (Couldn't see Leejohn's link on my phone, it's very clear on the desktop.)
When I added the log lift I re-used the old splitter valve for the lift, and added a new identical one for the splitter cylinder. Probably the best solution is get a new two-spool valve w load checks, but that's maybe more $ than is worth it on this old beast.
Thanks for the help
Jim

 

[aircommuter]

You can add a holding valve in the line or mount it directly to the cylinder or the control valve. You can get one at Surplus Center in Nebraska. Then it won't go down until you push the lever down.