Dump trailer bounces on the way down (if coming down heavy)

[Sodo]

The cylinder is topped out every time the trailer is used. Do you think air could remain? For years?

It seems possible there could be air below the piston. When the bed is down on the frame, the cylinder stops appx 4” before bottom so feasible there’s trapped air below the piston.

 

[Dave M7040]

View attachment 880844
The cylinder is topped out every time the trailer is used. Do you think air could remain? For years?

It seems possible there could be air below the piston. When the bed is down on the frame, the cylinder stops appx 4” before bottom so feasible there’s trapped air below the piston.

Sodo
I see you have a small excavator.
Could you disconnect the upper end of the hydraulic cylinder and with the cylinder lying horizontal and the dump bed held up with your excavator, cycle the hydraulics and watch for smooth movement in the cylinder.
Next, raise and lower the bed using the excavator to see if there is any tightness in a hinge joint which could be cause the jerky movement.

Is it practical for you to connect the cylinder to say a remote valve on a tractor or on your excavator for a test. This would narrow down where your problem is originating
Dave_eng

 

[sandman2234]

A cheap and easy thing to try would be to raise bed, block it, and spray a light coat of Pam cooking spray on the exposed rod. Sounds crazy, but I actually saw it work many years ago.
David from jax

 

[Sodo]

Sodo
I see you have a small excavator.
Could you disconnect the upper end of the hydraulic cylinder and with the cylinder lying horizontal and the dump bed held up with your excavator, cycle the hydraulics and watch for smooth movement in the cylinder.
Next, raise and lower the bed using the excavator to see if there is any tightness in a hinge joint which could be cause the jerky movement.

Is it practical for you to connect the cylinder to say a remote valve on a tractor or on your excavator for a test. This would narrow down where your problem is originating
Dave_eng

I blocked it up like this. It's heavy, full of dirt. I have the mfr-provided prop in, but since the bed is full, it's near the balance point.
I was feared it could tip up off the prop, and then maybe slam down. Probably not, the dirt would slide and it would stay up.

Even so.... I blocked it with a 4x6 on the other side, and chained it down onto the two props with a chain binder.

Watching the motion with the bed immobilized, I think it might be a problem with the valve.
Could it be a solenoid operated spool valve?
Could the hydraulic pressure be moving the valve against it's electrical solenoid force?
Closing the valve a little and thus setting the oscillation in motion?

 

[oldnslo]

Yes valves can be overcome by flow forces. I suspect there is also some form of speed control - flow restrictor in that unit to try and control - limit dump speed when loaded. If not the drop speed would change significantly between empty and loaded.

Is this a “sudden” new problem?
I should have asked that question on day one but hind sight is 20/20.

 

[Sodo]

I bought it used in 2018 (mfrd 1998). It has chattered since 2018 (only coming down heavy). It doesn’t appear to have much use, no dents in the bed etc.

Here’s a video of the behavior.

 

[oldnslo]

Sodo
I looked through my old catalogs and I have nothing from Fenner so no help there. Guess I would try a flow control and possibly pressure compensated to provide a constant down speed loaded or empty. Would suggest one with free reverse flow for raising.

This should allow ability to lower via gravity if the pump stops.

Sizing: what is desired down speed or time? You can then perform a little math to get flow.

 

[Sodo]

Do all power-down dump trailers start with a little "up" before they go down (under load)?
Is this behavior an intended feature to unload a check-valve or something?

 

[ning]

Having seen that video, and knowing next to nothing about hydraulics...

Strongest suspicion for me is the solenoid. It sounds like the pump has consistent power, so the "down" switch should be ok (I'd still double-check it by using wires to jump around it and actuate the "down" circuit; verify that there's no fizzing going across the switch).

You're certain that you only have the one solenoid? A trace of electric wires should verify.
How much for a new solenoid? Probably wouldn't hurt much to swap it just to be certain it's not the problem.

 

[oldnslo]

Sodo
Not sure on how your dump trailer is supposed to operate but can you get access to take pictures of power from different sides. Also would suspect valves are either bolted to or part of the housing between the motor and reservoir. At least that is how most of the ones I have seen are made. Would expect there to be a start solenoid for the motor and also at least one coil or solenoid operating a valve or valves. These pictures might help us trouble shoot this system with you.

Should also be a system relief in this block.

Does the load drift down if you leave it raised for any period of time?