Can anyone help figure this pressure gauge test? (video)

[Erik E]

Testing hydraulic pressure to track motor on a Magnatrac MH7000. Tracks are not getting enough power and engine start to choke on any strain beyond riding on level ground. It should have an operating pressure of 3200 PSI.
The machine might have a faulty pressure release gauge.

Here is a video of the test, and below is a written description.
Hydraulic pressure test: Magnatrac MH7 - YouTube

The track control is manipulated three times.
1. Slowly to about 1/4 open:
Engine struggles and pressure goes up to about 1000 PSI, then 1350 PSI as track control is released.

2. To about 1/2 open:
Engine struggles and almost dies as PSI reaches 1500. Pressure goes up to 2000 as track control is released.


3. Opened all the way:
Pressure goes up to 1500 PSI at which point the engine dies. Pressure kicks up to 2800 PSI for a second and then steadily goes down.


I would really appreciate if someone could give me an idea about what the problem is. The crawler has about 1k hours on it and is in good shape other than this issue. (Hydraulics to the front loader and backhoe runs on another pump. )

 

[AllDodge]

Don't know much about MT, but if this was happening on my dozer or tract loader I would be looking at the control valve. Its like the valve is blocking flow to the pump. The tract break wouldn't happen to be ON?

If unable to find an answer here, suggest posting on heavy equipment forum

 

[mike48130]

I don't know what your issue is that you are trying to fix on the machine. Where is the pressure gauge tied into the system? It is possible you are seeing pressure spikes due to the fluid dynamics of the oil. If you close the valve too quick and the fluid is in motion, it creates a pressure spike when the moving fluid has no where to go, force to stop the fluid. But, that all depends on the type of system and where the pressure gauge is.

My concern would be why the engine is stalling or struggling at 1000 - 1500 psi. That isn't much. Is the track motor turning when you do this?

 

[Erik E]

Don't know much about MT, but if this was happening on my dozer or tract loader I would be looking at the control valve. Its like the valve is blocking flow to the pump. The tract break wouldn't happen to be ON?

If unable to find an answer here, suggest posting on heavy equipment forum

Yes, the track break is off, but it's basically behaving as if they were on.

 

[Erik E]

I don't know what your issue is that you are trying to fix on the machine. Where is the pressure gauge tied into the system? It is possible you are seeing pressure spikes due to the fluid dynamics of the oil. If you close the valve too quick and the fluid is in motion, it creates a pressure spike when the moving fluid has no where to go, force to stop the fluid. But, that all depends on the type of system and where the pressure gauge is.

My concern would be why the engine is stalling or struggling at 1000 - 1500 psi. That isn't much. Is the track motor turning when you do this?

I apologize for not mentioning this in the original post. The tracks are not getting much power. Any strain beyond level ground will cause the engine to stall.
The track motor is not turning as the gauge is deadheaded between the control valve and the track motor.

One lead I have is that there is a pressure valve in the system that will dump back into the tank if pressure is too high, and this part will wear out. But I don't know if the results are consistent with valve dumping out at too low pressure.

 

[AllDodge]

Assuming it was working fine before and this is a new problem

I'm would still look at the track valves. might be something as simple as a linkage is not moving one of them open.

Don't see it being a dump valve right now, motor stats to stall before pressure gets to high

 

[oldnslo]

Erik
A couple of questions for you.

1) what style of pump feeds the track drive? Gear pump or variable volume piston. Do you have parts breakdown for the components?

2) Did this failure of travel drive happen suddenly?

My concern is the engine stalling. What changed to cause this. There should be some component to prevent engine stalling at those low pressures

 

[LouNY]

Fluid dynamics are a science all in them selves,
dead heading a line to look for pressure is not a good test of a system.
If you are looking for the pump preformance the test setup should be inline with the system and returning to the tank or component,
consisting of a flow meter and pressure gauge. The flow should be monitored and then restricted either by a valve or operating a component of the system,
Lots of flow at low pressure requires the same horsepower as lower flow at higher pressure, it takes flow and pressure to perform work.
On your system do you have two sticks to control forward and reverse with one stick for each side?
If you go full forward slowly with just one stick will you turn in a circle going faster the further forward you move the control?
do both sides perform the same?
Do those motors have case drains? If so how much are they flowing when you try to move?

 

[Erik E]

Fluid dynamics are a science all in them selves,
dead heading a line to look for pressure is not a good test of a system.
If you are looking for the pump preformance the test setup should be inline with the system and returning to the tank or component,
consisting of a flow meter and pressure gauge. The flow should be monitored and then restricted either by a valve or operating a component of the system,
Lots of flow at low pressure requires the same horsepower as lower flow at higher pressure, it takes flow and pressure to perform work.
On your system do you have two sticks to control forward and reverse with one stick for each side?
If you go full forward slowly with just one stick will you turn in a circle going faster the further forward you move the control?
do both sides perform the same?
Do those motors have case drains? If so how much are they flowing when you try to move?

Thanks LouNY,

What I was trying to test specifically, was to see if the pressure valve was dumping oil back in the tank at too low pressure.
Yes, two sticks to control forward and reverse with one stick for each side? They are obviously on the same pump, but as far as controlling the tracks, the controls are independent of each other.

The motors have case drains, but I don't know much they are flowing.