Backhoe Jinma LW-6

[Rich Waugh]

Well, the first pic looks like a backhoe with a separate hydraulic pump - not a PTO pump, but one that bolts on above the PTO shaft.

Second pic: I dunno about those, sorry.

Third pic: Yes on the relief valve and the other one may be the power beyond port, (to power another downstream device), for which you'd have to have the PB sleeve installed. Not sure, but it might be.

Fourth pic: I dunno, again. Mine doesn't have that; just the banjo fitting for the line to the sump.

Fifth pic: Makes me think there might possibly be a strainer inside that cannister. Or not.

Rich

 

[Bob Rooks]

#1) Tang drive pump. Runs at engine speed (no choice).
#2) Valve on the right is the system relief. Valve on the left is something I didn't have on mine, but it appears to be (maybe) on the boom valve.
#3) I think Rich called it. That appears to be in the correct location on the valve block to be a power-beyond port (that valve may have many applications). The other valve is a relief.
#4 & 5) Is presumably a cleanable strainer because the inlet is opposite of the end opening. If it's a filter cartridge, then the inlet would be next to the end opening.

 

[Brad_Blazer]

Sounds like you have plenty of flow. If the boom valve has a separate relief it might be the culprit. Install a 3000psi (200 bar) or greater gauge between the pump outlet and valve inlet usint a T fitting. It will show relief pressure when you operate any circuit until it is against the stop. The reliefs should be set at about 140 - 170 bar or 2000 - 2500 psi.

 

[Bob Rooks]

Install a 3000psi (200 bar) or greater gauge between the pump outlet and valve inlet usint a T fitting.

And please make sure you use only hydraulic or schedule 80 pipe fittings - no hardware store stuff!

 

[RonMar]

Yep, that first pic is a flange mounted hydraulic pump. It dosn't slip onto the splined PTO shaft, but bolts to the back of the tractor case(have to remove 4 bolts and a cover plate to install it?). It basically connects to the shaft that runs right thru the gearbox and up to the PTO clutch. That is the shaft that inputs torque to the 540/720 PTO gearbox, and that shaft turns at engine RPM, so 1500-1800 engine RPM should be plenty to run this pump.

The second pic, I agree with Bob, that looks to be the BH relief valve on the far right side of the pic. That second valve is connected to the left-right axis of that joystick control lever. If that joystic lever is for boom up and down, then the side to side axis of that joystick is most likley boom swing. If so, that is either a safety relief valve for the boom swing circuit, to help keep you from damaging the swing structure(weakest on the BH), or help keep you from rolling the tractor over with too much boom side force. It could also possibly be a flow control valve for the boom swing. I know on mine, the swing cylinders are the smallest on the tractor. They also don't have a very long moment arm to the boom pivot point. What all this adds up to is cylinders that fill and move much faster than any other cylinder on the BH, and which a small ammount of cylinder travel = a lot of boom swing. This makes for a boom swing that is way faster than any other travel on the BH. It is also the weakest circuit/activity...

 

[trelli]

Hello all,
I finally had the opportunity to look further into the problem, I recieved a gauge and then had a great deal of trouble trying to find fittings to connect to the loader - none could be found, it's apparantly a new Chinese thread. So I did a very basic weld job with the spares in the tool kit. Here's the results. I did think that it was only a problem withthe boom up but it seems that it's an overall low pressure situation, jsut more apparant with the boom up movement as ther is more weight.

The first pic you see is the pressure relief valve I took apart. This looks nothing like the PRVs I have seen on the forum, it's like something is missing and the spring has very little available movement in it. The rest of the pics are the pressure readings.

I connected the gauge to the port that tucks in the front arm of the backhoe. With the PTO at 750rpm speed I firstly took a reading at idle -approx 800rpm with the control level push forward fully. It came out at about 400psi. I held the lever for about 15 seconds.

Then I upped the revs to 1000rpm and it went up to 800psi. At 1500rpm it spiked at about 1600psi for a second, then fell back gradually to around 1400psi within a few seconds when I continued to hold the lever forwad.

At about 1900rpm the needle spiked at about 1950psi, then did the same thing and fell back within a few seconds to around 1700psi.


I'm surprised at this, not sure what this means. It seems to me that the only reason the needle would show a reduction in pressure after spiking up is becasue the pump is unable to hold the pressure??? After the initial surge in engine rpm, the pump suddenly puts out a burst of pressure but then the fluid back pressure causes the pumps to slip internally. That's my thinking at the moment. I'd like you ideas on how these pumps work. Can they hold pressure irrespective of RPM or do they need high RPM to put out working pressure? This is a pump that attaches to the PTO shaft (see earlier pics) I think it's a pretty standard pump that comes with these backhoes.

I did screw the PRV all the way in after the first run revealed a pressure of 400psi. But as you can see I don't think the fluid is even getting to the relief pressure. Also could this be some kind of checkvalve issue? where is the checkvalve? I don't see that PRV unit having a checkvalve built in. I'm thinking it's either a crap pump, and this is just how the pump is, or the pump is stuffed, or somehow this all points to the PRV but I can't see how with the readings from the gauge.

I also tested for oil bypassing the cylinder seals. no bypass at all, seals are fine.

ANy thoughts and suggestions are greatly appreciated.

 

[erj]

Please give a description of how you have the pressure gauge connected or a picture. Is it on a T allowing pressure to flow through to the valve?
RonJ

 

[trelli]

The pressure gauge is as conected in the picture. It's not on a tee, just screwed straight into the outlet, are you able to see the thumbnails in the former post?

 

[Bob Rooks]

Trelli, that setup won't work for what you are trying to do. The gauge must be tee'd into the circuit as Ron said.

 

[trelli]

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?

 

[erj]

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

 

[NuJinma]

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.

 

[trelli]

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

 

[Diamondpilot]

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

 

[RonMar]

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...

 

[trelli]

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.

 

[trelli]

Here's the specs of the pump, it's the last one on the list.

CBN-E3XX Series Gear Pump - Hangzhou Jinding Hydraulic Product Manufacturing Co., Ltd.

I still don't get this, what is this nominal RPM of 2000 and max rpm 900 business all about? I took the pump apart and there is no gearing, it's a direct drive.

 

[California]

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.