Dump Trailer Reservoir Rupture

[KY Gun Geek]

A little excitement at the farm yesterday-

A dump trailer we use to haul muck was being lowered after dumping a load when the bed suddenly dropped about 3 feet. Nice bang, and oil all over the place! I wasn't there so I don't have first hand observation of the failure. Person who was there says there's no more to know than bang and splash.

Preliminary inspection is that the plastic reservoir is ruptured - large split all the way down one side, and, of course oil all over the place in the pump box. I think reservoir is vented, so the build must have been very fast.

The "obvious" resolution is that I need a new reservoir (and believe it or not, the first answer I got from the manufacturers parts department).

However, I got to thinking about this, and I think there's more going on - like something else failed, causing pressure to build to high levels quickly in the reservoir, causing it to rupture. Feels to me like a check valve/flow control in the pump gave way. Could we have lost a seal in a cylinder that back-fed pressure (pressure from gravity on the bed) to the lift side of the pump? If this is true, a new reservoir will fail in a similar way.

These trailers are a little strange to me - they are pressure up, gravity down. But the pump controls the down speed and has to move fluid to fill the back side of the cylinder - the reservoir is engineered so that it does not hold lots of fluid, only the difference between one side of the cylinder and the other (the rod).

Parts guy is doing some investigation, but I thought I would run this by the forum.

The trailer is a Gatormade, 16'. I can't find any manufacturers labels on the pump/reservoir. Best I have is a sticker that says WX-1788. This returns hits on hydraulic pumps when googled, but nothing clearly marked with a manufacturer, manual, etc. and no posts of videos about this being a known issue and what the fix is.

Thanks for your help!

 

[CobyRupert]

I don't know much about much....but...
I think you're definitely right to be concerned that the ruptured reservoir is a symptom, not the real problem.
If it's "gravity down" is there really fluid on the back side of the cylinder or just vented? How many hydraulics lines go to cylinder?

If just one, I'd guess cylinder is ok, but whatever restricts flow to reservoir or a valve that is suppose to block pump pressure to reservoir has failed.
If it is a double acting (2 hose connections) cylinder, (not strictly gravity down), then maybe losing a seal in cylinder could pressurize tank....but I don't fully understand how.
:2cents:

 

[jmc]

Long shot, but could someone have filled the reservoir while the cylinder was extended since "It was low on oil." ?

 

[Ford850]

If it's a power down trailer, an overflowing tank is usually caused by a low battery. The power down function partially fails due to low battery but the bed continues to lower by gravity, which forces fluid one way out of the cylinder and overflowing the tank. I could see that putting pressure on a tank if it can't vent fluid out fast enough.

 

[radios1]

that's a good lesson on why to never trust your life on hydraulics!. yes, something failed that let the fluid come rushing into the reservoir, that's why it came down so fast..

 

[ovrszd]

I struggle to see how the tank has anything to do with the bed dropping 3ft. That plastic reservoir tank isn't what holds the bed up.....

As Coby eluded to, the tank rupture is the effect, cause hasn't been determined yet.

 

[CobyRupert]

If it's a power down trailer, an overflowing tank is usually caused by a low battery. The power down function partially fails due to low battery but the bed continues to lower by gravity, which forces fluid one way out of the cylinder and overflowing the tank. I could see that putting pressure on a tank if it can't vent fluid out fast enough.

Seems reasonable.
So you’re saying pump doesn’t pump (and extract oil from tank giving room for incoming oil) yet the solenoid valve allowing oil to/from cylinder still functions? This lets gravity be the driving force that pressurizes the the loop at the lift side of the cylinder instead of the pump. And first thing pressure hits is reserve tank.
I’ll buy that for a nickel.

I’m curious, would a low pressure relief valve on the return line that’s piped to output of pump only opens in this scenario? Be a solution?
Also a bigger (working?) vent in reserve tank or being quicker on the buttons might of helped.

 

[ovrszd]

I contend the tank ruptured because it filled faster than it could vent. This was caused by cylinder or check valve failure that allowed the bed to instantly drop 3ft and overrun the tank.

 

[ruffdog]

Was the trailer overloaded so it struggled lifting, then the operator hit the down button? High pressure forced back to the reservoir?

 

[Ford850]

Seems reasonable.
So you’re saying pump doesn’t pump (and extract oil from tank giving room for incoming oil) yet the solenoid valve allowing oil to/from cylinder still functions? This lets gravity be the driving force that pressurizes the the loop at the lift side of the cylinder instead of the pump. And first thing pressure hits is reserve tank.
I’ll buy that for a nickel.

I’m curious, would a low pressure relief valve on the return line that’s piped to output of pump only opens in this scenario? Be a solution?
Also a bigger (working?) vent in reserve tank or being quicker on the buttons might of helped.

All I know is a low battery is the common cause. I've read it can be due to the pump not keeping and the free fall overloads the tank. I grabbed this from another site from someone who worked on them: "When the battery is low it will not open the solenoid valve to allow fluid back into the top of the cylinder. The cylinder has fluid on both sides of the ram. When you lift the dump bed up the pump moves fluid to the bottom of the ram, pushing fluid out the top side of the ram. When you lower the fluid is released by a valve on the bottom of the ram and pushes fluid out the bottom. What happens is the valve that allows fluid back to the top does not open and the fluid pushed out the bottom goes into the tank overfilling it."

 

[RickB]

I contend the tank ruptured because it filled faster than it could vent. This was caused by cylinder or check valve failure that allowed the bed to instantly drop 3ft and overrun the tank.

This needs to be investigated. ^^^^^

 

[CobyRupert]

All I know is a low battery is the common cause. I've read it can be due to the pump not keeping and the free fall overloads the tank. I grabbed this from another site from someone who worked on them: "When the battery is low it will not open the solenoid valve to allow fluid back into the top of the cylinder. The cylinder has fluid on both sides of the ram. When you lift the dump bed up the pump moves fluid to the bottom of the ram, pushing fluid out the top side of the ram. When you lower the fluid is released by a valve on the bottom of the ram and pushes fluid out the bottom. What happens is the valve that allows fluid back to the top does not open and the fluid pushed out the bottom goes into the tank overfilling it."

I buy the first and 2nd sentences.
I guess the rest could happen if:
There were separate valves to opposite sides of the cylinder, one opens the other does not, I don’t think that’s the case...but one path could still be blocked.
The weight (gravity) pushing the oil out of the cylinder can overcome the vacuum being created on the other side of the ram because no fluid can enter.

I don’t know OP’s unit, but my thinking is based on a typical like in the following. Unit goes up when path is though “YA1”, goes down when path switches direction through “YA2”, and hold when there’s no path like shown.

 

[ovrszd]

I buy the first and 2nd sentences.
I guess the rest could happen if:
There were separate valves to opposite sides of the cylinder, one opens the other does not, I don’t think that’s the case...but one path could still be blocked.
The weight (gravity) pushing the oil out of the cylinder can overcome the vacuum being created on the other side of the ram because no fluid can enter.

But none of that would cause a sudden drop and put fluid into the tank with such force that it explodes.

The statement Ford850 linked explaining this simply says "fluid pushed out the bottom goes into the tank overfilling it". Nothing said about sudden drop of bed.

 

[Ford850]

But none of that would cause a sudden drop and put fluid into the tank with such force that it explodes.

The statement Ford850 linked explaining this simply says "fluid pushed out the bottom goes into the tank overfilling it". Nothing said about sudden drop of bed.

I agree that's an issue with my suggested reason. Although, I've read that when that tank overflow happens, it can be blasting fluid out the vent. Does that mean the tank becomes pressurized? And if so, if it splits open would that allow the bed to free fall? I'm not so sure. But even with a normal 'down' speed on my trailer the bed slams pretty violently onto the frame.

 

[ovrszd]

I agree that's an issue with my suggested reason. Although, I've read that when that tank overflow happens, it can be blasting fluid out the vent. Does that mean the tank becomes pressurized? And if so, if it splits open would that allow the bed to free fall? I'm not so sure. But even with a normal 'down' speed on my trailer the bed slams pretty violently onto the frame.

The reservoir tank in no way ever carries the weight of the descending bed unless there is catastrophic failure somewhere in the system.

I'm very curious to hear the end result. Hopefully the OP will return with a verdict of his findings.

 

[Ford850]

Here's a note on a trailer site regarding a low battery causing the tank to crack under pressure:
How to Fix a Hydraulic Dump Trailer System - Felling Trailers
"Typically any leak is caused by a battery with a low charge. The weight of the box is putting pressure on the system so as the box is lowered, the pump can’t keep up with that pressure due to the low battery. Then it creates excessive pressure causing the oil to blow out of the breather on the tank. We have seen some cases that the breather is plugged with so much with dirt that it creates excessive pressure and cracks the tank. It is advised prior to use of the hydraulic system to look over the unit and ensure it is free of debris and dirt."

I forgot about another reason, the screen filter can be plugged causing the same issues.

 

[ovrszd]

Yep. The vent being plugged could certainly cause the plastic tank to rupture as it fills.

But we still haven't explained the bed dropping 3ft?

In this context would it be possible for the pressurizing plastic tank to have the structural strength to hold up the bed while the pressure side of the cylinder drained, then explode and drop the bed???

 

[flyerdan]

A lift system like this should only need a regular spool valve; when it's in the raise position it activates a switch that turns on the hydraulic pump, when it's in the lower position gravity does the work, just like a fel or forklift with the engine off. The top of the cylinder is usually vented with a sintered bronze fitting, or a vent hose.
If it has solenoid valves, like some kind of Bobcat hand control system, it would need some kind of electronic control to feather the inputs, and even so, a full scale downward deployment should be well within the engineered specs.
I would suspect operator error, and they've just dummied up to avoid a bolloxing for breaking the trailer.

 

[CobyRupert]

Yep. The vent being plugged could certainly cause the plastic tank to rupture as it fills.

But we still haven't explained the bed dropping 3ft?

In this context would it be possible for the pressurizing plastic tank to have the structural strength to hold up the bed while the pressure side of the cylinder drained, then explode and drop the bed???

Good questions.
I’m back to not understanding the basics: What normally prevents the bed from suddenly dropping when one lowers?
The weight is still going to be driving the oil into the tank under a lot of pressure (gravity).
Is it a case of: a working pump would be distributing some of that pressure around the loop so the tank doesn’t experience it all?
Or is there enough restriction (small diameter) in the lines to slow the flow (so no sudden drop) and create enough pressure drop in the line that the tank doesn’t experience the pressure caused by bed weight? Plus tank is vented. Wait, is tank vented?

 

[ovrszd]

Tank would have to be vented to at least release atmospheric changes due to heat/cold.