LW-6 pressure relief valve

[Bob Rooks]

This is how I did mine. The Prince pump has two common outlets. I used a 3,000 PSI No-Shock glycerine filled guage, a 10,000 PSI S.S. needle valve, and schedule 80 fittings. To do less would be asking for it. IMHO.

 

[dfkrug]

dfkrug- On the LW-6 I have, removing a hose from a cylinder to place in a pressure gauge is difficult. The cylinders have bajo fittings. At the control block the lower hose on a valve is a banjo fitting while the upper hose is a right angle face seal fitting. As I mentioned in an earier post in this thread, in order to get the motions going the correct way on some functions my only recourse was to make extentions on the control block so I could swap the hoses. Due to the right and fitting I had to use this adapter so the banjo fitting would clear the right angle fitting. To complicate matters, the thread on the banjo bolt is 17 mm x 1.5. A 1.50 metric thread is 16.9 threads per inch. American lathes do not cut 17 threads per inch. Since the banjo bolts only hold the parts together and don't act as a seal, I was able to cut loose 16 TPI and get away with the fit. I'll try and post some phots of these adapters and the control block. I would like someone to confirm what I think is the pressure relief valve.

Banjo fittings?! How strange. How do you have hoses made with those
kind of ends? Does each use copper seals, as in fuel systems?

Anyway, take photos of what you suspect is the relief valve.

 

[Soundguy]

I've got some banjo fittings on my old ford tractos from the 50's... seemed they liked them on the hyd valves.. The new valves come with ORB provisions. The screw on banjo fittings are still available.. though spendy ( and SAE.. not metric! )

Soundguy

 

[psj12]

Rather then changing the hoses on the valves to make the valves work in the proper direction I simply reversed them on the cylinders of my LW-7. They are right next to each other on the cylinder and are identical fittings. This negated the need to make new fittings for the valves. I also accomplished the reversal in about 5 minutes.
The banjo fittings on my BH are subject to leakage as they have completly rubber clad washers in them. The pressure exceeds the sealing power of the rubber and fluid cuts through the rubber. This may be the reason for the pressure relief valve being turned down. I am replacing them with bonded Dowty seals which are metalic with a small rubber o ring bonded to the internal diameter. I have used them to replace similar hydraulic seals on the tractor with great success.
Most American lathes are capable of cutting metric threads but require changing the feed gears to metric ones.

 

[jezorek]

Attached are images of my control block. These are looking at the control block from the bucket side. The first image shows the inlet to the block and what I believe to be the relief valve below it. The other images are views of the adapters I had to make in order to swap the hoses on a particular valve. The only hoses I was able to swap otherwise were for the bucket curl. They were not able to be swapped on the cyliners because of the different lengths but I was able to swap them where they terminate at the steel lines that run along inside the boom. I did not bother to get the stablizers moving in the correct direction. I don't think I'll hurt anyone if I move them in the wrong direction.
The banjo fitting are sealed by fiber washers with a rubber insert bonded to the ID. These are marginal in their ability to seal. As one post pointed out, it may be that when I increase the pressure, they will start to leak. One of the adapters I made uses an O ring face seal instead of the fiber washer. If I do get leaks, I will probably convert to O ring seals where I can.
I agree with one of the other posts that American lathes can cut metric threads with the appropriate change gears. Unfortunately, a used set of change gears for my lathe is about $800. I've learned to do without.
I installed a 3000 psi gauge in the line from my flow control valve last night. I haven't tried it yet becasue my Farmi winch is on the tractor When I learn how to adjust the pressure on the relief valve from one of you guys, I'll give it a shot.

Thanks for all of your help

 

[Soundguy]

I've seen those metalic washers with the oring bonded to the ID. I almost had to use those on my HYD valve if the ORB orings didn't work. Are the faces on your valve body undercut for ORB.. or flat for copper washers.

Soundguy

Rather then changing the hoses on the valves to make the valves work in the proper direction I simply reversed them on the cylinders of my LW-7. They are right next to each other on the cylinder and are identical fittings. This negated the need to make new fittings for the valves. I also accomplished the reversal in about 5 minutes.
The banjo fittings on my BH are subject to leakage as they have completly rubber clad washers in them. The pressure exceeds the sealing power of the rubber and fluid cuts through the rubber. This may be the reason for the pressure relief valve being turned down. I am replacing them with bonded Dowty seals which are metalic with a small rubber o ring bonded to the internal diameter. I have used them to replace similar hydraulic seals on the tractor with great success.
Most American lathes are capable of cutting metric threads but require changing the feed gears to metric ones.

 

[jezorek]

The faces on my valve body are flat. The banjo fittings seal on the flat faces with the sealing washer. An adapter screws into the valve body to accomodate the O ring face seal fittings. You can see these adapters in the photos.

 

[RonMar]

Attached are images of my control block. These are looking at the control block from the bucket side. The first image shows the inlet to the block and what I believe to be the relief valve below it.

Yes, I would also say that is the pressure relief valve located below the inlet. Remove one of the fittings on one of the working ports that leads out to a cylinder and drop that hose end into a bucket. Screw a hydraulic rated pressure gauge into the port. Activate the valve handle that sends pressure to that port. If you move the handle the wrong way, the associated cylinder will move and that hose end will squirt fluid into the bucket. With the handle moved the correct direction, the flow will have no where to go but the gauge, the pressure will quickly build untill the safety bypass opens. The pressure maintained by the relief valve will be displayed on the gauge.

 

[jezorek]

I hooked up my PTO pump on the backhoe last night. I am now confused. Prior to installing a pressure gauge in the system, I assumed that the squeeling I heard when a cylinder reached the end of its travel ie the bucket fully curled, was the pressure relief valve opening.
Now that I have the pressure gauge installed on a tee at the outlet of my pressure relieved flow control valve, I read the pressure of 1500 psi. Since this is the factory setting of the Prince flow control, it would seem that this was the valve relieving and not the valve on the control block. I cranked in the screw on the Prince valve and the pressure now read 2100 psi when I curled to bucket to its extreme. This indicated that the pressure was being controlled by the Prince valve. However, I hear the squeeling coming from the area of the control block and not the Prince valve. What is the origin of this squeeling?

 

[RonMar]

The squeeling from the valve block is most likley that relief valve bypassing when you fully extend/retract the curl cylinder(pictured below inlet line in first picture). If you didn't have the prince flow control(with relief), that relief valve on your valve block would be the only one in your system and would determine the maximum available working pressure for the system.

What is the maximum rated pressure for your backhoe? Don't exceed this as you might bend structures, cylinders, shear pins or blow cylinders, seals or hoses. Sorry, had to say it again, there is just so much potential power and potential for damage if incorrectly setup.

Take the flow control valve out of circuit temporarilly or as you have done, screw in(raise) the relief pressure setting on the prince valve to a point just above the rated working pressure for the system. now go to the vlave on the main block and set it's relief pressure to maintain whatever the manufacturer says the backhoe operating pressure should be(or less) with a spool valve holding a cylinder at it's max travel the way you have been testing pressure. Once the valve block relief is set to maintain operating pressure, go back to the Prince flow control and gradually unscrew/lower the point that that relief valve opens till you just start to note a drop in the system pressure(start to hear it squeel) below that pressure you set with the main valve relief.

If your pump has too high a flow, the available passages in a single relief valve may not be large enough to pass all the fluid it must to maintain pressure. You shoud probably do this setup at the lowest pump RPM that provides enough pressure to open the relief valve without excessive flow. The good thing about having that second prince valve with a relief is that once the set points are matched up near the working pressure, you have a lot more available relief flow to deal with more fluid from a larger pump.