Backhoe Pressure check on JW03 backhoe

[Johnny P]

Hello,
Is it possible to check the pressure on the hydraulic system of a JW03 backhoe by disconnecting a hose that goes to one of the cylinders and screwing a pressure gauge on to that hose? I have the connections to do this if it is possible and is there a particular procedure to follow?

Ta
Johnny P

 

[RonMar]

Yes, that would work, provided you have the metric adapter to screw into the Metric "O" ring face seal hose end. I have not been able to find any adapters compatible with this type fitting on this side of the ponds. An easier way to find adapters for is if you put the gauge onto a port at teh control valve body. On my HW-03 backhoe the outlet ports to the cylinder hoses use a straight metric adapter to a metric "O" ring face seal fitting. The hose end is ORFS and screws onto this adapter. I can get straight metric to NPT or AN type fittings at my local hydraulic shop.

As for procedure, pick a working port on the valve, or a cylnder end of a hose if you have the adapters. Figure out exactly which backhoe cylinder it feeds and make sure that backhoe structure is physically supported. IE: if you remove the boom up/down line and the boom is not supported, it may head for the ground pretty quickly and crush or maim anything in it's way It will also spray fluid from the fitting you just disconnected, so a good rule when working around hydraulics is to wear safety glasses. Once supported, work the control levers to make sure no pressure is present in that circuit. Once the pressure is off, remove the hose end(don't loose the "O" ring or fiber sealing washer) from the cylinder or from the valve body adapter. If working at teh valve body, then remove the adapter itself. The adapter should have a "O" ring and perhaps a washer at it's base, again, don't loose these Screw in your metric adapter that is compatible with your gauge, and the gauge into the adapter.

The hose end you removed, should go into a bucket in case you operate the lever for the circuit you are working with in the wrong direction. If this happens, the cylinder will move, and fluid will come out of that hose end(don't ask me how I know this). IF you are working at teh cylinder end, cover the port with a rag and put a bucket underneath the cylinder port. Start up the tractor, engage the backhoe pump drive and move the appropriate lever to send fluid to the port or hose end that the gauge is screwed into. Since the fluid has no where to flow, the pressure will quickly build to the point that the relief valve opens. The pressure read on the gauge will be the pressure that the relief is set to open at and maintain.

Another option which I did for my BH is to modify an adapter that will screw down into the plug that holds down the spring for the check valve ball. When seated at your backhoe, there should be a round slotted screw head plug to the left side of the valve. This plug is directly over the relief valve assembly which is on the bottom left end of the valve block. You can modift an adapter to the same dimensions as this plug and put it in place of hte plug, and screw the gauge down into the adapter. This worked well for me to check system/relief pressure. IF you like, I have some diagrams of the adapter I modified, but it requires a little machine work with a lathe to make one out of a standard metric adapter.

Good Luck

 

[Johnny P]

Ron,

Thanks for the reply, I have seen your photos/diagrams of the PRV setup. It is the machined part that is a problem for me at the moment. I was wondering if I could put a longer spring in the check valve which would fit inside the adapter but I didn't know whether this would effect the working of the check valve and cause me a problem there, hence looking for a "easier" way.
Whilst on the subject of the backhoe hydraulics, when you fill the reservoir to find you correct level of fluid should the boom, dipper and stabalizer legs be fully extended or not or doesn't it matter. I again wondered that if I filled the reservoir with the boom, dipper or stabilizer legs up and then extended them would the level of fluid fall to a dangerous level with possible damage to the pump. or vice versa. So many questions.

Thanks Johnny P

 

[RonMar]

The length of the spring for the check valve shouldn't matter much. In fact, the check ball would probably work without a spring as gravity naturally wants to pull it down into it's seat anyway. The only issue you might run into is screwing an unmodified fitting down into the plug hole over the check ball with enough thread engagement to withstand the pressure of the system.

As for resovoir filling, the difference between cylinders extended and cylinders retracted, is of course the volume of fluid displacd by the rods. The rods are about 1 5/8" in diameter with about a 12" stroke. This works out to about 24 CU/IN or 0.1 gallons per rod. So the difference between all 5 cylinders fully extended, or all 5 fully retracted is about 1/2 gallon of fluid. Since the normal stowed/travel position has 3 cylinders retracted and 2 extended, the maximum the resovoir volume will change from the stowed position is 3/10 of a gallon... My resovoir is 9.25" X 9.25" X 23", for a total volume of about 8.5 gallons. Because of the filler neck, it will only take about 6-7 gallons. 3/10 gallon is not going to make that much difference in the fluid level of that ammount of fluid, so I would say just check and or fill it in the same configuration all the time...

I am curious, are you using the pump that mounts to the rear of the tractor above the PTO, or are you using some other pump configuration? Does your pump make any noise at all when in operation?

Ron

 

[Johnny P]

Ron,

I am using the pump that came with the backhoe which connects to the tractor above the PTO. No, the pump does not make a noise at all. Brief history. My problems started with the hydraulics completely failing. Nothing at all in any cylinder, stabalizer legs and all. I had no experience of hydraulics but decided to have a look. Drained fluid checked filter which had none of the mesh on it at all. Thought I might find some in the system and that could be part of my problem. No, nothing. I wondered if it was there in the first place. Stripped valve block cleaned and rebuilt. Stripped PRV and rebuilt. This is where I think my problems are. Refilled with new oil ISO 32 and new filter. Still nothing. I had read on another forum that someone had replaced the spring on the check valve and this had sorted their similar problem. This I did and hey presto movement in the stabilizer leg. As the backhoe was only attached to the tractor by the pump and it was getting late in the day I did not proceed with any more tests. The next day I attached the backhoe and checked that the oil was circulating by seeing that it was flowing across the reservoir. Then I tried the boom and dipper, with success.
After running around the garden in an uncontrollable euphoria I returned to the tractor and performed a few movements of the cylinders. My joy was short lived as the boom and dipper went slow again and failed. It was at this point I decided to disengage the drive to the pump. I found on inspection that the shaft seal had blown on the pump. I replaced this and tried again. The same thing happened. Was the PRV set too high or could it be the spring on the check valve being too strong? I believe it could be the PRV. ISO 32 oil is expensive in France . They tend to use ISO 46 and all I was doing was filling the gearbox with this oil.
I decided to purchase a pressure gauge, but where should I insert it into the hydraulic system as easily as possible. Hence the original question. My check valve does not have a "ball" in it, unless the component (A) in mine is called a "ball". See attached photos In my PRV I have a component, either B1 or B2 that I cannot get out. B1 has an o ring on it so I imagine it should come out. So as not to cause any damage by forcing this part I decided to leave it be. I considered the fact if this part is removable has it moved and got stuck and is effecting the adjustment of the pressure in the valve. The reason for my thinking of this is that I have again rebuilt the PRV and when I insert the bottom pin (6b) it feels like I can only just insert it and I mean just, with the o ring just inside the valve and not as far as the red line in the photo. The o ring on my pin does appear to be slightly nearer the end of the pin than the one in the picture. I suppose that could explain that. It's past midnight here now so I will sign off. Thanks for your help so far.

Johnny P

 

[RonMar]

The term "Ball" is generic, and refers to the moving part of a ball type check valve. part "A" in your attached pics is the check valve ball and mine looks lust like the one in the pictures. I do not think the upper check valve portion of the control valve inlet would have anything to do with your described problems. The fluid enters the control valve body from the left side(when seated at the hoe controls). As it enters the valve body, it flows into the vertical cavity that houses the PRV and check valve. The fluid enters on the middle leg of this "T" shaped cavity, with the PRV on the bottom and the check valve on the top. The fluid has two paths it can possibly take. It's normal path is up past the check valve, pushing it easilly up and out of the way. The fluid flows past the valve ball and enters a gallery that runs all the way across the control valve body and enters into an exit gallery. As you operate any spool control valve, fluid is diverted from this cross gallery and sent to a cylinder. The return from the other side of the cylinder comes back and makes it's way to the exit gallery. As long as the commanded cylinder movement occurs, there is always fluid flowing out of the exit gallery. The other path the fluid can take is used when the comanded cylinder movement does not occur. As the pressure builds in the inlet "T" cavity from the stalled flow, this pressure forces open the PRV, and the flow is redirected thru the PRV to the exit. THE FLUID IS ALWAYS IN MOTION, either thru the valve unrestricted, performing work in a moving cylinder with flow comming back from the backside of the cylinder, or thru the PRV when it's limit has been reached. Fluid not flowing does bad things, like blow out seals in a hydro pump, or blow hoses, or bend/break structurs ect...

If you are seeing flow across the reservoir with the pump runing, then the pump is obviously moving fluid. If at this same time, you cannot perform any work with the hoe, then the fluid is bypassing the gallery that feeds the spool valves, and no pressure can be built to move the cylinders. This bypassing is most likley occuring in the PRV, that has most likley something stuck in it and holding something open, that should be pushed closed by a spring. As you surmised, the part with the "O" ring on it that you cannot remove, is probably the root of your problem. It could be that a piece of crud has worked it's way thru the system and wedged itself into this close tollerance part. The dealer I bought my hoe from said that crud in the valve was the only problem they had had with these units.

The only purpose of the check valve that I can see is to prevent fluid from exiting back from an open control valve on a heavilly loaded cylinder toward the pump, or the PRV. In my experience, most valves do not have a check at this location. Instead they have whats called a "load check" on the inlet to each spool of the control valve that prevents fluid from flowing back into the cross gallery and being fed to another open spool valve. This valve dosn't have individual load checks, which IMO is probably it's biggest weakness as far as smooth operation is concerned.

In your position, I would disassemble the PRV and check valve again and using some smooth faced rod stock or punch, see if I couldn't gently get that immovable part to move either up or down, and perhaps out of the valve body. Once out, a testube or bore brush and some kerosene or diesel could be used to scrub out the PRV cavity.

 

[erj]

Johnny,
I would sure like you to check the pressure with that gauge before you tear the PRV valve apart again.
RonJ

 

[Johnny P]

Thanks chaps. I will keep you posted.

 

[Johnny P]

Hello,

Well had time to look at the backhoe today. I connected the pressure gauge to one of the hoses that goes to a stabilizer leg. Engaged drive to pump, operated opposite stabilizer leg and got a response. Tried the other leg and the pressure gauge read 500 psi, then I released the pressure. Tried other leg, it worked tried the one with the pressure gauge on, 500psi. i checked the fluid in the reservoir and it was going down. That sinking feeling came over me again. Yes the shaft seal had blown again!!!!

I will try again after a visit to the U.K. where I can stock up on cheaper oil, as it is expensive trial and error at the moment. When I mean cheaper I don't mean on quality.

Johnny P

 

[erj]

I connected the pressure gauge to one of the hoses that goes to a stabilizer leg. Engaged drive to pump, operated opposite stabilizer leg and got a response. Tried the other leg and the pressure gauge read 500 psi, then I released the pressure. Tried other leg, it worked tried the one with the pressure gauge on, 500psi. i checked the fluid in the reservoir and it was going down.

Johnny,
Can you give us any sort of time-line for these activities. For example-
engaged drive pump and let it run for a couple of minutes; checked the hydraulic oil flow through the tank fill hole; etc.

What I'm wondering is if there is any way to tell whether you were getting the 500psi readings before the hydraulic pump seal blew.
RonJ