41b Hydraulic issues

[J_J]

Quote:

So, you are saying that there are no O-rings on the spool, what seals it?

The valves spools are made to such precision/tolerance, that the spool will slide without binding, and not leak. I believe the o-rings are there to keep out water/debris. Some valves have o-rings, most don't. Some manufactures measure the valves ability by the leakage rate, as to so many drops per minute, the less the better. You probably have heard of bucket/lift arm leak down, and that is caused primarily by the pressure on the cyl to push the fluid past the spools, in the neutral position.

 

[AKKAMAAN]

I tried taking those bottom caps off and one of them looked manageable, but the other had a bunch of ball bearings that tried to fall out and didnt look like it would come apart. So, you are saying that there are no O-rings on the spool, what seals it?

I was told that I needed to take the small hex head screws out (on the top and the two on the face) that are shown in this pic and check for debris in them. Was this advice corrrect? What I am starting to think is that maybe you guys think I shouldnt mess with the valves and the problem can be there..... Im at the point where im not going to mess with the valves for myself, but take them somewhere and have them re-built and just bolt them back on the machine, but I would hate to do that if its not the problem.

The spool is fitted in to the cast iron housing, about 1/1000 of an inch tolerance, which allows a very small amount of leakage to lube the spool.....on the out side en of the housing, outside the return core/gallery, which is low pressure, there is o-rings, the prevent external leakage....but these o-rings do not effect any of the port pressure....

I bet your pump is not receiving a pressure signal, and thats why we need a manual figure to logic of the system and to locate pressure check points....

About your bucket dropping/drifting down is a fault of a different matter....has nothing to do with the pump pressure....no hurry to fix that either.....and usually there is a failing piston seal or a leaking port relief valve that causes the drift.....

I read in some of your posts on other forums about this pump...and your previous pump was obviously so badly wrecked so metal scarp had traveled around in the system.....

There are some small orifices in the signal line system, also small shuttle valves if it is a Load Sensing system, that could be blocked by metal scrap...

You should not taking hydraulic hardware apart if you do not know what to expect coming out....no matter how much auto mobile experienced you are....

Very likely your problems could be solved just by reading and interpreting the hydraulic symbol diagram/drawing....300-700$ for a manual, start becoming cheaper and cheaper, the more you tear that cat 416B down.....

 

[wdchyd]

You should not taking hydraulic hardware apart if you do not know what to expect coming out....no matter how much auto mobile experienced you are....

Very likely your problems could be solved just by reading and interpreting the hydraulic symbol diagram/drawing....300-700$ for a manual, start becoming cheaper and cheaper, the more you tear that cat 416B down.....

Absolutely....100%.....this is not Auto School where you can keep changing stuff till it works.....:thumbsup:

 

[futuresweets10]

Absolutely....100%.....this is not Auto School where you can keep changing stuff till it works.....:thumbsup:

Im not the type to just start changing things untill I find the problem. I can usually figure anything out on my own, but like I posted before.... I think I am going to take the valves to someone and have them go through them. Anyone have any idea how much I might be looking at? Few hundred? In the thousands? Few thousand?

 

[futuresweets10]

I bet your pump is not receiving a pressure signal, and thats why we need a manual figure to logic of the system and to locate pressure check points....

About your bucket dropping/drifting down is a fault of a different matter....has nothing to do with the pump pressure....no hurry to fix that either.....and usually there is a failing piston seal or a leaking port relief valve that causes the drift.....

The retired cat mechanic that looked at it seemed pretty sure that the bucket leaking down so quickly and the pressure signal not getting to the pump were related. I.E. the valve for the bucket was the one with the problem keeping the pump from getting the signal. I am going to try to take the valves somewhere on tuesday and have them re-done, but only if I know for almost certain that the problem (or at least part of the problem) lies in the valves.

 

[wdchyd]

The retired cat mechanic that looked at it seemed pretty sure that the bucket leaking down so quickly and the pressure signal not getting to the pump were related. I.E. the valve for the bucket was the one with the problem keeping the pump from getting the signal. I am going to try to take the valves somewhere on tuesday and have them re-done, but only if I know for almost certain that the problem (or at least part of the problem) lies in the valves.

I've never seen valves not hold load because of a weak load sensing signal...but I suppose doesn't mean it could not be....the valves will hold pressure with spools in neutral whether the pump/engine is on or not....that's why when you shut off machine things stay up....Yes?....Like others have said it could be another problem (I E Cylinder packing blown ect)...

Bringing in somewhere for a good go thru is good advice....have them bench pressure test after strip out, clean and reseal.....also have them backfeed pressure to work ports on top for leakdown (this will rule out worn out valve not holding possiblity due to wear or work port relief stuck open or worn)....also check spools for proper spring centering....if they stick or hangup off center (from corrosion in spring housing and/or foreign metal particles)this will do funky things too....

 

[wdchyd]

also when going for the strip, clean and reseal every plug needs to be removed, cleaned, rinsed and blown out.......

I've seen some load sense porting has small set screws deep in valve housing with very little holes drilled in them( 1/16" or less) to supply pressure to pump.....these small orifices can be blocked with an old piece of oring or packing stuck in the hole....so don't overlook tiny stuff....

About 15 yrs ago we fixed a Portable Grinder Machine http://www.cbi-inc.com/ (the company that owned it spent 3 wks trying to fix it and gave up......Problem?....No Load Sense Signal.....
Small 3/8" set screw with .040 hole in it was plugged up.....VIOLA....after pulling all valves on a fishing expedition we found it!!!!!Plugged with old chunk of oring....Million Dollar Machine down cuz of something this small....:confused2:

Oh BTW....we found the basic problem cuz we had the Hyd Schem/test guages/flow meter on the machine....at least it gave us some insight on what to look for....

 

[futuresweets10]

I've never seen valves not hold load because of a weak load sensing signal...but I suppose doesn't mean it could not be....the valves will hold pressure with spools in neutral whether the pump/engine is on or not....that's why when you shut off machine things stay up....Yes?....Like others have said it could be another problem (I E Cylinder packing blown ect)...

Bringing in somewhere for a good go thru is good advice....have them bench pressure test after strip out, clean and reseal.....also have them backfeed pressure to work ports on top for leakdown (this will rule out worn out valve not holding possiblity due to wear or work port relief stuck open or worn)....also check spools for proper spring centering....if they stick or hangup off center (from corrosion in spring housing and/or foreign metal particles)this will do funky things too....

He wasnt saying that it would hold load because of a weak load sensing signal, but rather what was causeing it to not hold a load would be the same thing causeing the load senseing system to not work. Weather the bucket dropping is in the valve or weather the valve has a problem with the load senseing circuit its still worth my time to take the entire valve assembly in, am I right in this logic?

 

[AKKAMAAN]

The retired cat mechanic that looked at it seemed pretty sure that the bucket leaking down so quickly and the pressure signal not getting to the pump were related. I.E. the valve for the bucket was the one with the problem keeping the pump from getting the signal. I am going to try to take the valves somewhere on tuesday and have them re-done, but only if I know for almost certain that the problem (or at least part of the problem) lies in the valves.

Cleaning valve and reseal do not make a lot of sense if you do not make a TOTAL CLEANING of the entire system

Clean up valve 150-250$ at the most IMO. 2-3 hr labor for a trained tech in a proper shop...resetting pressure on RV's not included....

 

[oldnslo]

He wasnt saying that it would hold load because of a weak load sensing signal, but rather what was causeing it to not hold a load would be the same thing causeing the load senseing system to not work. Weather the bucket dropping is in the valve or weather the valve has a problem with the load senseing circuit its still worth my time to take the entire valve assembly in, am I right in this logic?

Depending on how CAT designed their load sense system there is a possibility that the load sense line could bleed flow off to tank if one or more load sense checks are stuck open. This could also cause the pump to not build pressure. Like others have said you need a complete hydraulic schematic to know for sure.

Roy