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

[Sodo]

How do I prevent the dump bed from bouncing (on the hydraulics) when I have to lower a heavy bed?
It seems kind of violent, it can't be good.
I suppose there is an accumulator, but how do I size it?
The trailer is about 3 yds (6'x10'x1.5')

Thanks for the knowledge!

 

[oldnslo]

Does this gravity down or have power down option?

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.

If gravity down not sure could cause that problem

 

[Sodo]

Thx very much for the help oldnslo!
Power-down. Upon bottoming the pump motor strains.

Usually the bed is empty and I'd like it to come down as fast as possible most of the time, but a little slower wouldn't hurt. I could try a restrictor, it sounds cheap & easy. It would be nice if it could sense high pressure and come down slowly if the bed is real heavy.

What do you think of this one?

And where's the best location for it?
I'm thinking on the bottom of the cylinder.

 

[oldnslo]

A question is where is the check valve presuming that it has one? Is there a block on the cylinder where both the rod end and cap end cylinder hoses connect? I can’t tell in the picture you posted.

I believe it would work best to have the flow control between the cylinder and check valve.

2 nd option is to find the check valve and replace it with a counterbalance or over center valve. This would provide a pressure regulation to lower and typically eliminates the chatter when lowering. Then you would have same lower speed empty or loaded but would not allow gravity down.

 

[Mike1955]

That bounce sounds a lot like air is somewhere in there. That fluid would have to be compressing and that don’t happen. Just my two cents worth

 

[jmc]

That looks a lot like the underbelly of my EZ-Dumper. I bought it new from a serious hydraulic shop, not a "Trailers-R-Us" sales lot. Try calling the manufacturer or their competent distributor.

 

[Sodo]

Can't be any air. Wouldn't pumping both ways eject any air?
Yes jmc it's an EZ-Dump. I like it a lot. It's the same width as my truck, easy to reverse it straight in the mirrors. I bet it's 30 years old. I got it on craigslist. It's been great, I've worn out/replaced 2 good tires since. I cannot believe how much work this trailer has done.

I thought $4500 was a lot for a used trailer 20+ years old when new ones were costing $6000 & nice tractors could be had for $10k. But it's been a great $4500 purchase. I never could have got the work done renting. It's arguably worth more than $4500 today - which is no help cuz I can't do without it.

oldnslo here's pics of the pump.
There's a little box with a wire on the left side.
On the right jammed up against the battery is a hex-shaped item.
I don't see any other components or what might look like a check-valve.
The two hoses leave the pump and go directly to the cylinder ends.

My knowledge of hydraulics is simple and basic.....
I can't imagine what a check valve would do in a system that pumps both ways.
Doesn't the pump motor simply turn the direction you want the fluid to go?

Anyway if you can help me stop it from bouncing I will be happy.
It seems like it might pop a hose or wear out the pump or something bad will happen from the violent motion.

 

[oldnslo]

Is there a lever or switch you operate to lower? I suspect there is some type of valve in that pump housing to lower the load and it might have some type of flow control that is acting up.

Very, very unlikely pump runs in reverse to lower.

 

[Sodo]

It's the standard rectangular yellow switchbox with U and D buttons.

 

[oldnslo]

Then down is operating a valve to lower the bed. I believe you need to find a schematic for that power unit to determine what you have.

 

[nyone]

That bounce sounds a lot like air is somewhere in there. That fluid would have to be compressing and that don’t happen. Just my two cents worth

I think the same.

You may need to disconnect the cylinder and flip it upside down and cycle it to get all the air out.

 

[Sodo]

I don't know where to find a schematic but I will look.
The pump runs to power down, it seems appx the same speed up and down.
It mashes the bed hard onto the frame at bottom, and the pump stalls.

So is it feasible to add an accumulator (or some hydraulic device) on the down circuit to stop the bounce?

nyone.... you think there could be some air below the piston that cannot escape? I could perhaps reverse the trailer over a bank to tip the cylinder upward. I will look at the angles when it's "down".

 

[jmc]

I don't know where to find a schematic but I will look.
The pump runs to power down, it seems appx the same speed up and down.
It mashes the bed hard onto the frame at bottom, and the pump stalls.

So is it feasible to add an accumulator (or some hydraulic device) on the down circuit to stop the bounce?

nyone.... you think there could be some air below the piston that cannot escape? I could perhaps reverse the trailer over a bank to tip the cylinder upward. I will look at the angles when it's "down".

Low reservoir oil level might let it suck air. I've had that bounce and I've had low oil but don't remember if the two faults were related.

You don't have a schematic but do you have the manual?

Afterthought: my ez-dumper uses automatic transmisssion fluid. The reservoir level line is for when the bed is either up or down, IIRC.

 

[Mike1955]

I don't know where to find a schematic but I will look.
The pump runs to power down, it seems appx the same speed up and down.
It mashes the bed hard onto the frame at bottom, and the pump stalls.

So is it feasible to add an accumulator (or some hydraulic device) on the down circuit to stop the bounce?

nyone.... you think there could be some air below the piston that cannot escape? I could perhaps reverse the trailer over a bank to tip the cylinder upward. I will look at the angles when it's "down".

Sodo I do not think an accumulator would help your situation. That should be a simple hydraulic circuit. But it might be layed out so it’s difficult to follow. also gauges in some places would help. And don’t forget that you may be overloading that thing to. But if it isn’t air that oil is overcoming a spool valve somewhere

 

[oldnslo]

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.

 

[Sodo]

There's no "up&down". It stutters violently. "Stick-slip" might be a better description.

 

[bcp]

Maybe something useful here:

What Causes a Hydraulic Cylinder to Chatter? - Cylinders, Inc.

Discover the causes of hydraulic cylinder chatter and learn how to fix it. Explore solutions to prevent chattering and extend your cylinder's life.

cylindersinc.com

Bruce

 

[Dave M7040]

Is there a lever or switch you operate to lower? I suspect there is some type of valve in that pump housing to lower the load and it might have some type of flow control that is acting up.

Very, very unlikely pump runs in reverse to lower.

oldnslo
E-Z dumper's web site mentions a Monarch double acting pump.
Double Acting Monarch Hydraulic Pump With 1 Quart Reservoir

Dave M7040

 

[oldnslo]

oldnslo
E-Z dumper's web site mentions a Monarch double acting pump.
Double Acting Monarch Hydraulic Pump With 1 Quart Reservoir

Dave M7040

Dave,
I suspect the double acting monarch unit is implying will work with double acting cylinders.

How would you prevent over speeding the DC motor if Running pump opposite direction to pull oil out of the cylinder especially with load induced pressure?

I will first to admit that I could be wrong.

 

[MattB4]

When was the last time you replaced the hydraulic oil?