Backhoe Jinma LW-6

   / Jinma LW-6 #31  
These hydraulic systems are considered an Open Circuit. The pressure gauge needs to measure the pressure of the fluid flowing through the system. Here is a picture of the gauge on my JW03 backhoe. It is placed on top of the pressure relief valve where it is measuring the pressure at the point it comes into the backhoe valve assembly. Whenever I move one of the controls, the gauge tells me what the pressure is in the system. If I run a control to its maximum movement, it tells me at what pressure the pressure relief valve cuts in to relieve the pressure.
RonJ
 
   / Jinma LW-6 #32  
Hope you have figured it out in last 2 months. I had same issue, valve was bypassing fluid causing lack of pressure. There is a 2 piece black Nut on the valve body that IF FLUID IS BYPASSING, you need to tighten up a very small amount at a time. Remember that if you tighten to much (as I did) you will pop lines like they are popcorn. You can tell if bypassing by the squeal sound.
 
   / Jinma LW-6 #33  
trelli said:
I'm trying to find out what sort of pressure it's putting out. I thought that if I connect it straight into the block and opening p the valve it would effectively be like a cylinder piston at maximum position?? I am a novice with hydraulics, how else can i find out what the pressure is?
Click to expand...

Sorry I missed this back in July. Trelli, that method(deadheading the flow into a gauge on a particular circuit) will work just fine for showing the pressure that the relief is opening at. I have used that method quite a few times to confirm proper safety relief valve operation on a system without a gauge installed. It will not however, as mentioned show you the system pressure while operating the various circuits, like the gauge that RonJ showed a pic of.

NuJinma, Please excuse me if I am a little blunt, but it has been a long day. Attempting to set a pressure relief valve without the use of a gauge is an accident waiting to happen! Hydraulic oil under pressure is one of the most dangerous things most people will ever work with. Oil injection injuries are simply awfull... Machines have been destroyed, and people crippled and killed by someone "just giving it a little tweek to make it work better" or "that sounds about right"...
 
   / Jinma LW-6 #34  
RonMar said:
NuJinma, Please excuse me if I am a little blunt, but it has been a long day. Attempting to set a pressure relief valve without the use of a gauge is an accident waiting to happen! Hydraulic oil under pressure is one of the most dangerous things most people will ever work with. Oil injection injuries are simply awfull... Machines have been destroyed, and people crippled and killed by someone "just giving it a little tweek to make it work better" or "that sounds about right"...
Click to expand...
Succinctly put; I believe it is called a "train-wreck" - something you know that is inevitable given it's present course and speed, and devastating with casualties.
 
   / Jinma LW-6
  • Thread Starter
#35  
Hi all,
Just an update on my situation regarding the woes of the backhoe. It's been a few months, but in the end I have got a new hydraulic pump for the backhoe. i am still not sure what the true problem is but the supplier in China has been helpful to the extent of sending me a new pump. When I drained the resevoir of the backhoe I found sand in it! about 200g of sand actually! Apparently there had been a terrible dust storm and the apprentice who put it together hadn't bothered to clean out the tank. Anyway upon discovering the sand I believed that perhaps the grit had worn out the hydraulic pump. I took it apart and i noticed that the bore was scoured. Perhaps it was within tolerance but I thought that a new pump should not have any sign of scouring. I then totally deadheaded the pump but blocking it's output with a bolt and running the tractor PTO, with tractor revs at 2000+ rpm, and even in the this totally deadheaded situation the pump didn't blow up it maxed out at about 1700psi, and stayed there. This leads me to a few questions. Firstly the pump must be capable of somekind of bypass itself becasue it's pressure did not build up with each revolution rather it maintained pressure itself at the given tractor rev. When revs were lowered to about 1000rpm on the tractor the pump gave a reading of a steady-ish 700psi.

I took the new pump apart that the supplier sent me and it has the same scoured marks in the bore, so perhaps it isn't the pump after all and it's an issue of revs. I re-read the calculations in an earlier post and realised this. The hydraulic pump has a rating of 16mpa at 2000RPM. producing 25ml per revolution.


This means that to get 2320psi to the hydraulics I've got to spin that blasted pump at the PTO at 2000RPM! My tractor has an option of 500/750 pto speed, however these pto speeds are achieved at approximately 2300 engine RPMS. So the problem is How the heck do I ge the backhoe pump to spin at close to 2000rpm to generate the necessary pressure when All I can get from the pto is 750+ rpm? The tractor would have to be going at well over 3000rpm to do this. What can I do?

Help.

Thanks
 
   / Jinma LW-6 #36  
Does this pump connect to the pto shaft or the optional output above the pto shaft? The reason I ask is the pto is the only thing controlled by the 540/750 speed selector. If it connects to the pto you were supplied the wrong pump. Sounds like you got a pump that was not meant to be ran on the PTO. The optional hookup above the pto shaft is direct drive and will be roughly the same speed as the engine itself. At least that is the way I understand it.

Chris
 
   / Jinma LW-6 #37  
Trelli
The very first picture you posted showed a flange mounted pump. You unbolt a 4 bolt cover plate and bolt the pump on using the same 4 bolt holes right? The pump shaft has a tab that fits into the slotted end of a shaft inside the tractor right? It dosn't matter what pto speed you have selected as the pump is connected ahead of the gearbox. That shaft is the INPUT to the 540/720 gearbox. It goes all the way thru the transmission to the pto clutch. That shaft spins at engine RPM. I use the same type pump and run my tractor at 1800 RPM when running the BH, and it works great. I just checked pressure on mine this weekend and I get rated relief pressure, 16MPA all the way down to 1000 RPM.

The fact that you deadheadded the pump with no safety valve in the circuit and the pump didn't spray fluid or the engine stall, says it is damaged internally. Please don't try this with the new pump:) you cannot compress the fluid. It is either performing work, flowing thru the relief valve or something breaks/goes pop... The pump shaft seal could also be bad and it is dumping hydraulic oil into the tractor gearbox instead of making rated pressure. Check hydro level for lost fluid or gearbox level for extra fluid...
 
   / Jinma LW-6
  • Thread Starter
#38  
Thanks Ron for the reply but I must admit that I'm getting confused, the pump that was supplied with the backhoe simply fits onto the PTO shaft at the back of the tractor, The four bolts and that bracket is simply to stop it from moving and twsiting with the PTO shaft. This shaft that I connect the backhoe's pump to is not ahead of the gear box becasue I can disengage it and change its speed from 540/750. It's the same shaft that I connect every thing to - flail mower slasher etc. There isn't two shafts , just the single one at the back of the tractor. Am I missing something?

I was under the understanding that the PTO shaft will acheive the speeds of 540 or 750 at a given RPM, I just checked my manual and it's 2200rpm on the JM354.

So that means that the pump from the backhoe that fits on the PTO shaft is supposed to be spinning at 2000rpm to acheive 16mpa, which means that currently It's jsut not spinning fast enough becasue at most I am giving it 750+rpm.

sorry for my ignorance if I am missing something.
 
   / Jinma LW-6 #40  
I put 'CBN-E325' into Google and got several exporters offering the same specs you quoted.

But the search returned some apparent manufacturers too.

Here's a Google translation to English of a page from one manufacturer. He clearly states that CBN-E325 is a 2000~3000 rpm pump.
 
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