Cause of pump damage?

[workinonit]

What if the relief valve was bad?

 

[rScotty]

The damage in the pump body and wear plate are what I would expect if the bearings began to get sloppy. Higher pressure at the outlet port always pushes on the gears and shafts and tries to causes them to interfere with the pump body and wear plate 180 degrees from the outlet. To resist that pressure is why pumps are built so rigid. With too much clearance between the shaft and bushing, the gears can touch the body of the pump exactly where the torn metal and wear pattern exists. It looks to me like that interference between the outer edges of the gear teeth and the pump body & wear plate tore metal loose and created what looks like an incoming suction side debris wear pattern in the pump body and end plate. It might have been outside debris - no way to know. If it is internal wear it would still technically be debris, but originating from interference within the pump rather than from without.

Summary:
My guess is that at some point this pump was run without oil and that is what wore the shaft-to-bushing clearance. The bushing wear allowed the high pressure to force the gears against the pump body 180 degrees away from the high pressure port. All the rest follows. Replace the pump. Be sure to pre-lube. Replace the oil and filter with new and do at least one additional filter change within the first hour of operation.

good luck,
rScotty

 

[hayden]

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?

Excellent point. I had forgotten about that and was similarly reminded looking back through some pictures last evening.

I believe the snow blower and power pack were originally purchased as a package because they have sequential serial numbers. But there was an extended filler neck on the tank, and a barbed hose fitting welded to it, presumably as a return for some other piece of equipment.

The snow blower itself clearly hadn't seen much use based on how little pant had been scraped off. Plus it came from Southern PA which isn't exactly snow country. But the power pack had a consistent layer of oil & dust all over it, suggesting more use. So this is piecing together to suggest it may have been used a bunch for other purposes, and perhaps abused. The package is 10 years old, after all. And use for other purposes, especially in weather above 40F, could have lead to overheating since there is no cooling system. If nothing else, this is wishful thinking that all the pump shreds contaminated some other piece of equipment and not the blower. Fingers crossed.

 

[Hay Dude]

The damage in the pump body and wear plate are what I would expect if the bearings began to get sloppy. Higher pressure at the outlet port always pushes on the gears and shafts and tries to causes them to interfere with the pump body and wear plate 180 degrees from the outlet. To resist that pressure is why pumps are built so rigid. With too much clearance between the shaft and bushing, the gears can touch the body of the pump exactly where the torn metal and wear pattern exists. It looks to me like that interference between the outer edges of the gear teeth and the pump body & wear plate tore metal loose and created what looks like an incoming suction side debris wear pattern in the pump body and end plate. It might have been outside debris - no way to know. If it is internal wear it would still technically be debris, but originating from interference within the pump rather than from without.

Summary:
My guess is that at some point this pump was run without oil and that is what wore the shaft-to-bushing clearance. The bushing wear allowed the high pressure to force the gears against the pump body 180 degrees away from the high pressure port. All the rest follows. Replace the pump. Be sure to pre-lube. Replace the oil and filter with new and do at least one additional filter change within the first hour of operation.

good luck,
rScotty

That’s what took out a $9,000 Rexroth aluminum pump in one of my tractors. Bushings began to move slightly in aluminum housing, releasing a glitter bomb in hydraulic system

 

[hayden]

The damage in the pump body and wear plate are what I would expect if the bearings began to get sloppy. Higher pressure at the outlet port always pushes on the gears and shafts and tries to causes them to interfere with the pump body and wear plate 180 degrees from the outlet. To resist that pressure is why pumps are built so rigid. With too much clearance between the shaft and bushing, the gears can touch the body of the pump exactly where the torn metal and wear pattern exists. It looks to me like that interference between the outer edges of the gear teeth and the pump body & wear plate tore metal loose and created what looks like an incoming suction side debris wear pattern in the pump body and end plate. It might have been outside debris - no way to know. If it is internal wear it would still technically be debris, but originating from interference within the pump rather than from without.

Summary:
My guess is that at some point this pump was run without oil and that is what wore the shaft-to-bushing clearance. The bushing wear allowed the high pressure to force the gears against the pump body 180 degrees away from the high pressure port. All the rest follows. Replace the pump. Be sure to pre-lube. Replace the oil and filter with new and do at least one additional filter change within the first hour of operation.

good luck,
rScotty

Many thanks. That's exactly the sort of analysis I has hoping for. I think your summary makes perfect sense given the damage, i.e. the origin was bearing failure, and subsequent movement of the gear tore everything else up. That explains why only one gear and mating surfaces is trashed. If the pump had ingested crap from the intake, I would expect damage to be uniform across both gears and mating surfaces. Same if it was cavitation. This could have been run dry right at its initial startup, and damage has been accumulating over it's use. It might even be why the thing was for sale in the first place, either because the owner knew there was a problem, or because performance was poor.

 

[hayden]

What if the relief valve was bad?

That was my hope, but I narrowed it down to the pump itself.

 

[Hay Dude]

Why are some pump housing built out of aluminum? Easy machining?
Cast would hold bushings longer. But I guess the bushings pressed in the housing could wear out and create same problem?

 

[rScotty]

Why are some pump housing built out of aluminum? Easy machining?
Cast would hold bushings longer. But I guess the bushings pressed in the housing could wear out and create same problem?

I think we are right on the reason for failure, but I also think it doesn't change things. The OP is going to have to replace the pump and clean out the system as best he can in any case. Changing filters makes sense over changing oil. The only thing better than filtering oil is to let it stand absolutely quietly for a month - like in glass containers - and then siphon the clean oil off the top without disturbing the sludge. That works, but who wants to do that?

Right. Cost of manufacture. It costs a LOT less to machine aluminum. The problem then becomes heat - just as you were wondering about.
Design can compensate for the way the different materials respond to stress, but not to heat. Aluminum expands twice what steel does. As things heat up, the pump wall ends up moving away from the gear teeth, and the bushing moves away from the shaft. This is compensated to some degree because the steel is surrounded by hot oil whereas the aluminum is surrounded by cool air.

For pumps made with both housing and the gears out of the same metal, radial expansion is the same, and the clearances stay constant. Much better for high temperatures.

Steel shafts in an aluminum case always get sloppy with heat unless you figure a way to cool the aluminum. Fins help a lot.
BTW, in case you were wondering..... To figure how much a hole expands, just pretend it is not a hole at all, but a solid metal plug the same diameter.

 

[hayden]

New pump ordered. $830. It was $1300 through Erskine.

 

[hayden]

Today I pulled the filter housing and removed and inspected the filter. There are flecks of crap caught in the filter, so it was doing it's job. That's good.

I also drained all the fluid out of the tank and it's a lot darker than I would expect, and I think thicker than the ISO 32 oil called for. I think it might even be motor oil, but am not sure. Regardless, I'm just going to replace it so I know it's the correct grade.

Once I got the tank drained, I can see flakes of copper on the tank bottom which would be from the thrust plate in the pump. Now I need to figure how to get it cleaned out. I have about a 4" access hole in teh tank top on one side where the filter fits in, so I have reasonable access there. But there is a baffle down the middle of the tank that blocks access the other side. But the other side also have a 1-1/2" fitting for the suction hose, and I can take that out to get some access, but not as good as the other side.

Anyone have any suggestions on how to best clean the tank out? I'm thinking that I need to get some solvent in there to clean out the oil, then I can probably get a vacuum hose in there at least on the side where the filter mounts, and maybe blast some compressed air in the other side with hopes of stirring things up enough so it ultimately gets sucked out by the vacuum.

Any other ideas?