Cause of pump damage?

[hayden]

I'm cross posting this in the Hydraulics forum since it's now clearly a hydraulic problem. I'd love to get a read from experienced hydraulic repair people about what might have caused this damage.

This is a 3PH PTO driven hydraulic pump that is part of a power pack for powering a hydraulic snow blower. It's used and new to me, so I have no history on the machine. But it wasn't developing power as expected so I started looking into the system pressure which turned out to be 1000 psi rather than 3000 psi. I rearranged my test gear to test the pump, and here's what I found.

I hooked up my flow meter, gauge, and variable restrictor immediately at the outlet of the pump. With engine at idle, no load but the blower rotating, I get 10 gpm and barely detectable pressure. That's normal. But when I apply load to the pump by restricting flow, it couldn't develop more than 500 psi, even when completely dead headed. This is down from 1000 psi just yesterday.

So I pulled the pump apart and indeed it's trashed. Take a look at the attached pictures. I think the housing it too damaged to even attempt a rebuild, so I'll be getting a new pump. Now I just need to figure out what it is. I did finally find some numbers on it and an embossed "Eaton", so with that I suspect I can figure it out.

If anyone has any pump rebuild experience, I'd be real interested in a read on what might have caused this damage. Because this power pack has no active cooling, and relies solely on ambient temp and operator attention to duty cycle to prevent overheating, I think previous overheating is a distinct possibility. So I'm particularly interested in whether this could have been caused by overheating. I guess the other possibilities are cavitation or contamination.

Thanks in advance.

 

[ericm979]

It'd be interesting to see what's in the filter and the bottom of the tank. Just debris from the pump, or more?

 

[ruffdog]

Just thinking here....debris got into the bearing on one of the rotors and took out the bearing. Pieces from the bearing moved to the end of the rotor, then to the teeth of the rotor. Why didn't the filter get the debris in the first place? When cold, a filter may not handle the thick oil so it passes unfiltered oil through the bypass. Lots of equipment to clean out now because debris will be throughout the system.

 

[LouNY]

Is that a direct drive PTO pump or a gear box mounted pump?
Most of the direct PTO pumps are only rated to around 2000PSI.
That pump definitely had debris damage damage were the debris came from is an interesting
question was it contamination from and outside source?
Or did the pump cavitate and produce it's own debris?
It looks like an aluminum pump they will erode rapidly with cavitation.
Does the system have a suction filter and or a return filter?

 

[hayden]

The filter is on the return, and I will pull it out and inspect. I'll also get a light in there somehow to get a look at the tank bottom.

The pump mounts to a 1:3.75 step-up gear box, and the whole assembly slides over the PTO shaft.

The pump is an Eaton 25506, 2.85 CID. 46.7 CC gear pump, 3200 psi operational pressure, and 3650 max intermittent, 2500 rpm. At 540 PTO rpm, the pump is tuning at 2025 rpm. The system has a 3000 psi fixed relief valve, so that's the max operating pressure in this application.

Interestingly, I can't see any damage to the gears or teeth. The damage all seems to be in the idler gear rear shaft bearing, the end surfaces that the idler gear rides against (one of which is the wear plate), and the chamber edge.

It seems odd to me that the idler gear bearing and shaft, plus the idler gear side the wear plate are all torn up, but the drive gear side is mostly OK. If debris had entered in the oil stream I would expect both gears to be more or less equally damaged. Same if there was cavitation. Wouldn't that equally affect both gears and chambers?

So it makes me think that perhaps the idler bearing was starved for oil, started shedding, and that jammed it against the wear plate and trashed the wear plate. The bearing that is torn up is opposite the bad wear in the wear plate. That's the only way I can see one side being so trashed and the other being mostly OK. It makes me wonder if it ran dry in it's initial startup and caused the damage.

 

[oldnslo]

Hard to tell exactly but I larger brass side plate damage is not cavitation since I would expect that to be evident on Other areas of the pump as well.

My guess is something got between gear and bearings plate forcing it towards one side. This reduced the side clearance which limited the leakage flow to the shaft bearing. Once shaft bearing started to scour it just became self destructive.
On a gear pump highest leakage is between gear teeth tips and gear case. Gear case wear is usually a result of pressure pushing the gears sideways into the shaft bearings and gear teeth rubbing on inlet side of gear case.

 

[Dave M7040]

This is a question not a statement!
Could the control valve for the implement, in this case blower but previously who know, have been a spool valve for a cylinder and not a motor?
If this was indeed the case how would this "mistake" show itself in pump damage?

Dave M7040

 

[oldnslo]

This is a question not a statement!
Could the control valve for the implement, in this case blower but previously who know, have been a spool valve for a cylinder and not a motor?
If this was indeed the case how would this "mistake" show itself in pump damage?

Dave M7040

As long as the pump is unloaded and not being dead headed it shouldn’t make a difference what spool type is used. Using cylinder style spool on motor could cause excessive pressure in the motor but valve should isolate the pump from seeing the pressure

 

[hayden]

As long as the pump is unloaded and not being dead headed it shouldn’t make a difference what spool type is used. Using cylinder style spool on motor could cause excessive pressure in the motor but valve should isolate the pump from seeing the pressure

Agreed. And the relief valve which is immediately downstream of the pump would limit pressure to 3000 psi and prevent any damage.

 

[dstig1]

You said in your other thread that the PO had some odd additional connections to the system that you removed. Perhaps some other piece of equipment he was using is the source of the damage?