Chinese backhoe hydraulic pressure issue

[dfkrug]

I assume you mean the filler cap (vent cap). What havoc
can a blocked vent cap wreak, other than not allowing fluid expansion as it warms? Can
it affect PSI performance, too?

A clogged vent may increase the suction (low pressure) on the inlet side of the
pump. Any restrictions on the inlet of a hyd pump should be minimized to avoid
cavitation.

I would like to see what the inside of that pump looks like.

 

[brettski]

I would like to see what the inside of that pump looks like.

Me too. Tomorrow's project is just that; exploratory pump surgery with pics.

 

[brettski]

I removed the pump, disassembled on the bench, and inspected. This is my first exposure to the guts of a hydraulic pump, but it was pretty obvious to me that this would be categorized as a gear pump. I did find the Mfgr stamp on the pump exterior. It listed 20Mpa (I convert to 2900 PSI). The pump model is: CBF-F425. There are 2 one-piece rubber gaskets; one at each end of pump body. They were in very good condition. The machining on the plate sealing surfaces was good, but a bit scuffed. No gouging, just light marring. IMO, no issue for sealing against the rubber gaskets. The fits were all good; no slop. In summary, I could find nothing wrong. I cleaned, lubricated, and re-assembled and re-installed.







The best/only option I have for a flow/pressure test is to take it to the nearest JD dealer. Because of the the time/effort/cost to load it up, take it there, leave it for testing, pick up and return, I am holding back on that option. If it comes to that, the cost for a new pump would be the better investment in my mind. The Chinese factory will ship me the necessary repair parts at n/c, but I must provide evidence of the failed parts. I cannot, at this point, say that I am suspicious of the pump. Given all that, I took the tractor/backhoe out to the field and used it for an hour or so, digging a small trench, trying to identify performance indicators. I set the tractor rpm at 1800. This is what I know from use:
1) It struggles mightily to rip a single tree root that is about 1" diameter.
2) no 2 functions can be operated at the same time, or they both collapse during the struggle to fill 2 cylinders at the same time
3) I still hear the bypass of fluid at an early point, before any one cylinder can build up the power to dig (for instance, when I hook the uncurled bucket onto that 1" tree root, then start to curl the bucket to rip the root, the bucket stalls and I can hear the fluid by-passing. This happens with the same result when I try to pull in the dipper with the bucket teeth barely stuck into the soil)
4) Even at 1800 tractor rpms, the functions are slow to react to full opening of the valve. It may take 3 - 4 seconds to get the larger boom and dipper cylinders to react

I can't help but be suspicious of the controller, now.

 

[FredH]

My Brother bought a chinese import from a dealer north of Us , by Eugene Oregon , last fall . We used it real early this last spring to put in a complete irrigation system for Our Moms yards . His had a similar issue , Basically no " Real " power . Sure it would move around , but when it came to digging , bah , nothing . Tried adjusting pressure relief screw . Loosen lock nut and turn allen screw , nothing . Like You , I was perplexed . Upon closer examination , there was a 2'nd relief nut screw set up near first . Adjusting just one provided zilch . Adjusting other and Boom , had enough power to blow a pinched line that We did not see under the top link . Thing Dug like a Grape Ape after that adjustment . Not sure Why 2 on his , but I would look around , the 2'nd one on his was behind a hose fitting , thus easily missed .

We also installed the shim kit for the Hydraulics on His JD tractor . Wow , what a difference that made . I think everything is sold now days at minimum pressure settings , thus limiting liability or ???

Fred H.

 

[brettski]

Hey FredH,
Well, that is VERY interesting. Thank you for sharing that story. When you say "the 2nd one was behind a hose fitting", can you be a bit more specific? I have a threaded plug that covers a hole directly below the obvious pressure relief valve. In fact, I removed that plug to screw in a pressure gauge to see what the pressure was at the controller block. Is it possible that there is an adjustment screw beneath that plug? Is that the type of fitting you encountered with your brother's issue? It is a flat plug, about the size of a quarter, with a hex drive hole in the center.

 

[FredH]

That plug does not sound like what he had , His I believe was just like the first with a lock nut and a allen screw in the center ????? Memory sucks from that long ago , beyond yesterday , I only remember half of what I should . Going to email him and see if he can shoot me a picture of his . Hopefully I can get it before I hit the road for the week .

Found this , although crude drawings = http://www.pegasus-industries.com/manuals/Backhoe.pdf

But it did jog my memory , Seems like I remember that 1 was located by the line from the pump to the valve body , other was the out pressure from the valve body ?? Don't hold me to that , just seems I remember something wierd how it was set up ??

Fred H.

 

[brettski]

 

[FredH]

Yes , not the same as his . His adjustments were on the other side . When You look at the design of these type B.H. , It is pretty simple , kind of , So either pump is not pumping enough or there is a restriction some were and that would be the direction I would go . With that said though , a gauge would really help .

I know I was super frustrated with his , since I was use to My 757 N.H. , but once We figured out the issue , it was game on . Do you have a Hydraulic store of some kind around ? Like a Parker Store or ??? . They may be able to set you up with a cheap pressure gauge setup .

Fred H.

 

[brettski]

Dang. I am going to pull that plug again anyway to see if there is something hiding underneath. I also sent an email to my factory contact, asking her to reach out to the controller mfgr to ask about any/all PRV adjustment screws.

I do have a gauge and ran two tests. I put the gauge right on that plug on the block and got about 1100 PSI max. Then I moved the gauge to the end of the dipper hose and got about 1200 PSI max. I also followed that feed hose. It runs directly from the pump output side to the controller block inlet (the hose with the 90 degree bent tube on the far right in the pic above). That is why I am suspicious of that plug. It is located directly in line with that inlet feed hose and also directly below the obvious PRV.

 

[brettski]

Well, it's 5 months later and I have finally resolved the issue. Long story, short: it was the pump. The Chinese factory started by sending me a new controller since I had disassembled the pump and found zero obvious indicators that it was the problem. I installed the new controller; nothing changed. The pressure would go up to about 1200 psi, then quickly drop back to 800 and hover. After reading about filter location, I decided to move mine. The oil filter was between the tank and the intake side of the pump. Moreover, the hoses and filter were located at or just above the top oil level in the tank. I removed the filter and piped the tank output directly to the pump inlet, keeping the hoses well below the tank oil level. I moved the filter over to the return side. Hoping this might yield good results, I fired it up and got exactly the same thing, except this time the pressure would shoot up to 1600 PSI, then drop to 800. Well, assuming 2 controllers were highly unlikely to both be defective, I focused back onto the pump as the only remaining major piece in the puzzle. I went ahead and ordered another pump from a different Chinese vendor. It was the same pump manufacturer and same pump model family, but slightly higher in GPM volume (I moved from 6.6 GPM to 8). It was pretty cheap, too (pump = $60 and UPS = $58). I installed the pump onto the inlet hose and manually cranked the pump a turn or so until oil gushed out of the outlet hole (to verifiy prime inside the pump housing). Then, the outlet hose, then start the tractor on very low rpm and engage the PTO. OK, it's running nice and slow so I waited for about 3 minutes, then pulled one of the outrigger handles. It jumped into action. Tried the other outriger; same jump. I ran all the functions back and forth a number of times (staying short of full extension or retraction) to purge air. Everything ran like "right here, right now!". Then I bottomed out one of the cylinders to see how far the pressure gauge would go before by-pass. It hit 2400 PSI consistently. I took it out for field test digging and WOO-HOO....back in the game.