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

[Mike1955]

Air makes things bounce when trapped but since he is lowering air would be less likely to cause bounce since load induced pressure should not be changing significantly. Yes it would bounce like a pogo stick if you stopped lowering.

 

[Mike1955]

Another thing to is maybe it isn’t a hydraulic problem. Maybe the metal is springy. At this point all options are open

 

[Sodo]

Thanks BCP that was a great compilation on cylinder chatter!

Searching the DB-1277-A returns only a "new model" that has the same partnumber. The new model is clearly a different pump.

I have never changed the hydr oil, I bet it's the original 1998 oil.
I don't think it had a hard life, I think it was used by a wood-floor company to dump tearout wood floors. It doesn't have any dents. But I will definitely change the hydr oil!

The cylinder is permantly tipped up with the seal head high. Do you think it's worthwhile to disconnect it and tip it fitting-end up and cycle it?

It does a lot of it's chatter at the bottom of its stroke so I doubt the cylinder is binding.
At the bottom of its stroke the forces are increasing and the chatter becomes more violent. Springy metal could be a contributor.

 

[oldnslo]

Fenner Fluid Power was purchased by SPX several years ago but might be worth trying to call there facility in Rockford, Illinois 815 874-5556 they might have some one still working there in product support from the Fenner division.

 

[Sodo]

If power down suspect there could be Pilot operated check in the load holding circuit. There is some load induced pressure so you need xx amount of pilot pressure to open the check. Then gravity takes over and load starts to run away so pilot pressure is lost and check slams closed. Then cycle repeats.

Putting a flow restrictor will help when loaded but could potentially slow down dropping an empty bed.

oldnslo this explanation makes sense.

I should probably call EZ-Dumper first before calling the pump mfr.
How likely would positioning the cylinder such that cycling it would eject an air..... be the easiest solution? I can go under the trailer and do that if the pins coooperate.

What about adding a bypass circuit that has a restrictor, with a valve.
In normal conditions the valve is open and it runs fast / normal.
So I'd never close the valve except if I know it's gonna chatter.
But on those few conditions while heavy I close the valve and it restricts and of course lowers slowly.

This would be placed in the pressure side of the power-down, right?

As simple as this is, "there's ALWAYS something" and it ends up taking half a day.
I really hope it's something simple, like getting air out or adjusting a pilot valve etc.

 

[JCoastie]

It worked well for a couple decades right?
I'd take it to a hydraulic shop, and pay an hours labor and get a pro's opinion on what's wrong before I went randomly putting a band-aid on something that needs stitches or a cast.

 

[Sodo]

It worked well for a couple decades right?
I'd take it to a hydraulic shop, and pay an hours labor and get a pro's opinion on what's wrong before I went randomly putting a band-aid on something that needs stitches or a cast.

Trade it in on a new one! I see comments on the F-150 forum like ".....you didn't even ask your Ford dealer?"

....not my style. I like to sniff out the problem, understand it, learn something, chat with other problem solvers. Lotta old fellers here with a lot of knowledge.
And possibly make it better than new for $50.
That's why I'm here.

Calling pros..... not my style either. They have a right to make their living from those who are too busy or unable to DIY. Plus anytime I've talked with pros I they say "we're currently booking about 8 weeks out....".

 

[Leejohn]

I have used Fenner Fluid Power on 3 trailers, all were double acting never had that happen. One was used on a trailer I made for 32' pontoon house boat for Woodward Governor. I Know a guy that worked there before they sold to SPX. If it comes down to it I can try and get his number, if he still with us. He had his hands in getting it off the ground for them. I well go alone with others that you have a air lead, check your hoses out real good.

 

[Sodo]

OK thanks. I've been watching the behavior. It pushes hard from down low. As the bed gets real high, the trailer unloads the ball on the hitch and pulls up on the truck a little. Shortly after, the cylinder starts to unload and now the bed is trying to tip - and the cylinder is actually holding it back from tipping, while still extending.

During this transition between pushing up, going over the top, and then holding back, the cylinder behaves like there's air at the top of the cylinder. I will try to think of a way to get that air out. The ports are on the sides of the cylinder, so I can see how air can get trapped. So do I have to take both pins out and tip the ports up vertical to get the air out?

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It's a loaded trailer, ~5,000# of dirt in it so it will take some thought to be safe. It has a safety-prop. I'm inclinded to set it on the safety then use chain & binders and bind it down onto the safety prop. If I dump the trailer then I can't test if it's fixed. But if I get squashed I can't test it either.

 

[oldnslo]

Cycle the cylinder full stroke a couple of times when empty should help remove any air.

 

[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?