Dump Trailer Reservoir Rupture

RickB · Dec 6, 2019

ovrszd said:
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 · Dec 6, 2019

Ford850 said:
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 · Dec 6, 2019

CobyRupert said:
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 · Dec 6, 2019

ovrszd said:
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 · Dec 6, 2019

Ford850 said:
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 · Dec 6, 2019

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 · Dec 6, 2019

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 · Dec 6, 2019

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 · Dec 7, 2019

ovrszd said:
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?