Onboard Hydraulic Grenade

[chrisinnh]

Hello!

The onboard hydraulic pump on my B7100 died last night. You can see a long crack just below the pump's equator in the following picture:

Some circumstances of the failure:

1. This is the first time I've used the onboard hydraulics to power the loader.
2. The transmission was filled about 50/50 with gear oil and UDT substitute from TSC.
3. I was raising the empty bucket at the moment of failure.
4. The transmission may have been overfilled.

Any idea what could cause such a failure? The tractor has less than 800 hours on it.

Here's a sketch of how I plumbed my hydraulic system for the loader:


Any clues about what might have gone wrong?

Can somebody recommend a favorite salvage yard where I can source a used pump?

Thanks very much.

/chris

 

[irwin]

I'm no expert hydraulic or otherwise, but seems that gear oil would be to thick, maybe that had something to do with the failure?

I'm sure guys with more experience will give a more thorough answer

good luck...

 

[chrisinnh]

I'm no expert hydraulic or otherwise, but seems that gear oil would be to thick, maybe that had something to do with the failure?

Gear oil was the original spec for this application.

Later they changed it to UDT. This pump ran in 80wt all last winter with no problem, but I never asked it to do any work.

/chris

 

[claridon]

I'm not an expert by any means but two questions come to my mind:
Does the loader valve an allow flow back to tank when it's in neutral?
Do you have a relief valve in the loader system?

 

[chrisinnh]

Does the loader valve an allow flow back to tank when it's in neutral?

The loader valve causes fluid to flow back into the transmission at all times.
In neutral, it's just an open circuit.
When moving a cylinder, the drain from the other side of that cylinder goes back to the trans.

Do you have a relief valve in the loader system?

Yep, it's part of the loader valve.

/chris

 

[chrisinnh]

Something I didn't mention, but the question about a relief valve got me thinking about it:

The motor was at about 50% throttle at the time of the failure.

I would expect this pump to be able to stall the motor under a substantial hydraulic load.

...But nothing of the sort happened. The motor was not under load at the moment of failure.

I'm planning to take things further apart tonight. It looks like it will be a real challenge to get to the back mounting bolts. Hopefully I will have autopsy photos tomorrow.

/chris

 

[chrisinnh]

Autopsy Update:

Removing the pump turned out to be easier than I thought it would, once I got the hydraulic lines, throttle linkage, fuel fiter and brackets out of the way.

The filter screen on the intake side was intact and clean. I don't think anything nasty could have gotten into the pump.

...And the pump looks good inside too (except for the crack). There's no carnage on the pump housing or gears, and the pump turns easily by hand.

I'm disappointed that nobody has suggested what I might be doing wrong. I've sourced a used pump for $150, and sure would be bummed if I repeat some stupid mistake and wind up killing this this replacement unit too.

Ideas?

Here are some pictures of the housing:

/chris

 

[Wayne County Hose]

Autopsy Update:
I'm disappointed that nobody has suggested what I might be doing wrong. I've sourced a used pump for $150, and sure would be bummed if I repeat some stupid mistake and wind up killing this this replacement unit too.

Ideas?

/chris

Yo, chill lil' brother. We're here to help. Not everything is black and white. That pump could have failed for any number of reasons. You were the one operating it at the time. If you don't know what happened, how are we?

It's hard telling what happened to your pump. I don't see any scoring of the internal surfaces. Did it make a "Pop" noise when it blew? What were the exact circumstances from one second before it blew to one second after? Exactly how long did you have the lever pulled before you noticed a problem? All of this info is very important. The more details, the better. If there was a pop, I would bet on your pump dead-heading. Especially with no internal scoring. There is a company called Attica Hydraulics that specializes in this type of stuff. You may want to give them a call. Real nice pics by the way.

 

[rbargeron]

Can you tell us some info about the history of the control valve? Is it new? Is the relief valve visible and intact? The pump housing fracture looks like what happens when there is NO relief valve functioning in the system. This can happen when the in and out ports are reversed at the control valve so the relief valve is beyond the load instead of before it. Everything would seem ok until oil was directed to a circuit that was at the end of its travel and couldn't move (dead headed). Then something would have to give - usually a hose blows, or the pump seals extrude out around the shaft - leaking oil into the engine, or maybe the pump housing burst from the pressure spike. As always, prompt cheerful refund if info is bogus. Good luck.

 

[alchemysa]

I'm no expert but I'd have thought that bad or faulty plumbing would have blown a hose (or some other weak spot) before it would crack a casting. Are there any hoses between the pump and any obstructions?. If so, and the hoses are still intact, then it may be just a bad casting.

 

[ronjhall]

After installing the new pump. Put a gage on the system to check relief valve setting. I would guess that old pump cracked from over pressure.

 

[techman]

being a hydraulic "expert", there must be a relief valve in the circuit. The failure is clearly a result of overpressure. You should plumb a relief valve directly to the output of the pump. The statement that the pump should stall the motor before any failure is just dead wrong. Just the mechanical inertia of the engine/trans will be able to generate momentary pressures well beyond the rating of any component in there.

You're lucky nothing else failed.

paul

 

[chrisinnh]

Thanks everybody for the responses.

Larger versions of the pictures included can be found here.

Here is some more info around the issues you've all raised:

The loader control valve is not new. It's an ancient twin stick thing which was on the tractor when I bought it. I took it into a hydraulic shop to ask if it could be fitted for power beyond. The guy there told me that wouldn't be possible, and that the thing I was looking at was the relief valve. This is the best picture I've got of it, taken before I made any changes.

When I bought this tractor, the loader was plumbed to the hydraulic system on the PTO driven backhoe. The same selector valve I'm using now used to allow me to switch the backhoe PTO system between the backhoe and the loader. Here's a shot of that selector in its old home on the backhoe.

I'm beginning to become suspicious of the thing I belive is the relief valve. Prior to my re-plumbing efforts, when the loader reached the end of its travel I heard squealing from the backhoe. I presume that sound came from a relief valve on the backhoe. I don't know that I've ever heard the relief on the loader valve trip.

There's also the possibility that I've hooked the valve up backwards. I've got the right side of the valve (clearly visible in the picture above) receiving fluid from the pump via the selector. The other side of the valve is the one with the large hex thing sticking out of it, which I believe is the relief valve. Thinking about it now, I'm guessing that the relief valve (if that's indeed what it is) needs to be on the inlet side of the pump.

Okay, some more about what happened:

I did hear a sound when the pump failed. Not so much a "pop", more of a "clink" sound.

I'd just pushed a big pile of snow with the bucket, and was unable to back up due to lack of traction. I was simultaneously raising and tipping the bucket with the intention of lowering the fully tipped bucket to the ground, then curling it to push myself backward.

I'm pretty sure I was manipulating both sticks at the moment of failure.

The fluid flow at that point would have been:

• Fluid from the pump was extending the lift cylinders
• Fluid expelled from the the lift cylinders would have been extending my tip cylinders.
• Fluid expelled from the tip cylinders was getting returned to the transmission.

There's no way that the lift cylinders reached the end of their travel, but the tip cylinders may have. If that's the case, and the relief valve was at the wrong end of things (or non-functioning), then I can see that I may have dead-headed the pump: The tip cylinders stopped accepting fluid from the lift cylinders, which would have stopped accepting fluid from the pump.

Sound reasonable?

I'll take some pictures of the loader valve tonight. I'll be seeking opinions about whether I've really got a relief valve integrated, which side is in and out, and how to test that the relief operates correctly.

I'm still suprised at the engine not stalling out: My backhoe pump easily stalls the engine (even with the extra inertia that comes from having the transmission engaged) at the low-ish RPMs that I was turning at the time.

The backhoe pump is much larger, I guess.

Thank you all, very much.

/chris

 

[KubotainNH]

Chris, I can't believe you broke your tractor!!

Seems to me it cannot be connected backwards, I would think it wouldn't have worked properly but by the sounds of it you got some use before it cracked. I'd go with the dead heading on full curl.

BTW, how well did the little pump do with that loader while it worked?

One last comment, my loader barely makes the engine lose RPM when maxed out so I can't see it stalling if dead headed. Maybe this is because of the way it's attached to the engine and geared as opposed to running off the PTO.

 

[chrisinnh]

Chris, I can't believe you broke your tractor!!

Hi Mike. Me too :-(

Seems to me it cannot be connected backwards, I would think it wouldn't have worked properly but by the sounds of it you got some use before it cracked. I'd go with the dead heading on full curl.

If there's a relief valve in my loader control, then it probably matters which way I hook it up.

BTW, how well did the little pump do with that loader while it worked?

It was annoyingly slow, but maybe not much different than when running off the backhoe as before.

I just learned about the regenerative feature for the curl on joystick-style control valves. It would make a big improvement. There may be one of those in my future, but that's second priority to getting the tractor running. Right now I can't even start the engine.

One last comment, my loader barely makes the engine lose RPM when maxed out so I can't see it stalling if dead headed. Maybe this is because of the way it's attached to the engine and geared as opposed to running off the PTO.

Mine only stalled when running at low RPM. At high speed it wasn't really noticeable. I just happened to be at low-ish speed when I broke the pump. If I'd reached the end of travel on my backhoe at that speed, the motor would have stalled.

/chris

 

[rbargeron]

..........There's no way that the lift cylinders reached the end of their travel, but the tip cylinders may have. If that's the case, and the relief valve was at the wrong end of things (or non-functioning), then I can see that I may have dead-headed the pump: The tip cylinders stopped accepting fluid from the lift cylinders, which would have stopped accepting fluid from the pump......Sound reasonable?..............

Yes, it does. Ordinarily a hose would be expected to be the weakest link in the system. But sometimes small bore hoses have actual burst pressures much higher than their rating. Paul (techman) is right about engine inertia being able to cause a huge spike in pressure, it would come and go so fast that you wouldn't notice a change in speed - just a "knock" when the pressure pulse broke the pump.

 

[ccsial]

I'm still questioning the gear oil. That seems a bit heavy for hydraulic use but maybe that is OK. How cold was it?

 

[chrisinnh]

I'm still questioning the gear oil. That seems a bit heavy for hydraulic use but maybe that is OK. How cold was it?

Below freezing for sure, maybe around 15 farenheit.

Gear oil is definitely correct for this application:

/chris

 

[john_bud]

It sounds like you may have hooked the loader valve up backwards.

The relief valve is always (far as I know) on the inlet side. If you hooked it up with the "IN" hose going to the "OUT" of the valve, then when you operate the controls, you are isolating the relief from the fluid. Any over pressure can't be relieved and the weak spot is located with much fan fare and excitement.

A second thought, your selector valve. If you operate the selector valve while the tractor is running, it may dead head the pump. Instantly killing it. Don't know if that is the case or not here. Just something to beware of.

Your hyd diagram does not include the BH circuit. There may be a relationship there, don't know for sure.

Also, I got the impression that you put the pump on replacing the function of a PTO pump. Did I read that right? If so, the fluid may be too thick for the pump. Check with the pump mfg to be sure. Over pressure situations can occur even with an operable relief valve if the viscosity is too high. Basically, the fluid can't get out the relief port fast enough to drop the pressure. Again, may not have a bearing on the case. But good to know.

There was a guy on here a while back with a ford BH loader. He had some of the same issues with blowing a new pump when plumbing hydraulics. It's easy to do, happens in a heartbeat and expensive as all get out.

Do try and document the entire set up you have. Folks here will chip in to try and get you up and running.

jb

 

[SPYDERLK]

Yes, it does. Ordinarily a hose would be expected to be the weakest link in the system. But sometimes small bore hoses have actual burst pressures much higher than their rating. Paul (techman) is right about engine inertia being able to cause a huge spike in pressure, it would come and go so fast that you wouldn't notice a change in speed - just a "knock" when the pressure pulse broke the pump.

Yes, all hoses will have a burst pressure well beyond their rating. Rating is for continuous pressure. Burst has a time element involved. Waynecountyhose would know the specifics. Id guess a 4k hose would take 8 or 10k for a few seconds- and even more for an instant. Plenty of time and pressure to pop a cast aluminum pump.
larry